WO2003087898A1

WO2003087898A1 - Wavelength filter and wavelength monitoring apparatus

Info

Publication number: WO2003087898A1
Application number: PCT/JP2002/009173
Authority: WO
Inventors: Masao Imaki; Yoshihito Hirano; Yohei Mikami; Makoto Satoh; Akihiro Adachi; Yasunori Nisimura
Original assignee: Mitsubishi Denki Kabushiki Kaisha
Priority date: 2002-04-15
Filing date: 2002-09-09
Publication date: 2003-10-23
Also published as: WO2003088436A1

Abstract

A light-transmissive solid material, planes formed in the solid material and facing substantially parallel to each other, and a wavelength filter for periodically selecting the wavelength determined by the optical path length between the planes facing each other by performing resonance between the planes facing substantially parallel to each other. The solid material is a doubly refracting material and the optical axis thereof has a predetermined angle with respect to the normal to the planes facing substantially parallel to each other. Thus, the temperature characteristic of the wavelength filter can be freely set, and an arbitrary wavelength characteristic can be selected by changing the temperature of the wavelength filter.

Description

Specification

Wavelength filter and wavelength monitor

Technical field

The present invention relates to a wavelength finolator for selecting a wavelength of a laser beam used in a wavelength division multiplexing transmission (WDM) system and the like, and a wavelength monitor device for measuring an oscillation wavelength of the laser beam using the wavelength filter.

Background art

FIG. 1 is a configuration diagram showing a conventional wavelength monitor device disclosed in Japanese Patent Application Laid-Open No. H03-160774. In FIG. 1, a semiconductor laser 101 can control the wavelength of an emitted optical signal. Light emitted from the semiconductor laser 101 is converted into parallel light by an optical lens 1.05, and the parallel light is further condensed on a photodetector 108, for example, a photodiode. The other light is incident on the Fabry-Perot resonator. The Fabry-Perot resonator 111 is branched in two directions by a reflection film 109 and a beam splitter 106. One of the branched lights passes through a lens 107, has 110, and is formed of two types of optical materials. The light transmitted through the Fabry-Perot resonator 111 is focused on the photodetector 113 via the lens 112.

FIG. 2 is a configuration diagram of the Fabry-Perot resonator 111 in FIG. The temperature coefficient γ of a Fabry-Perot resonator made of one type of optical material is expressed by equation (1). Here, η is the refractive index of the optical material, and α is the net tension coefficient in the optical axis direction.

_1, dn. _/ 1

γ = α +-(-) (l)

n dt A generally known Fabry-Perot resonator uses a glass material. In that case, the temperature coefficient (thermo-optical coefficient) of the linear expansion coefficient α and the refractive index n was fixed. Therefore, the temperature coefficient γ is uniquely determined.

If this temperature coefficient _{に becomes} zero, the cavity length of the Fabry-Perot resonator 111 does not change in accordance with the temperature, but is emitted from the semiconductor laser 101 and transmitted through the Fabry-Perot resonator 111. Since the wavelength dependence of the light intensity does not change, the wavelength can be accurately monitored irrespective of the temperature of the resonator 111. In order to make the temperature coefficient γ zero, the Fabry-Perot resonator 111 is composed of two types of optical materials having different signs of the temperature coefficient γ. Equation (2) must be satisfied in order to make the temperature coefficient of the entire Fabry-Perot resonator 1 1 1 zero.

^Γ ι ^η _οι 1 ₀ ι + r ₂ n ₀₂ l ₀₂ = 0 (2) where n 0 and ₁₀₁ are the refractive index and physical length of the first optical material, respectively, and r _x is the first optical material. This is the temperature coefficient according to equation (1). Also n. _2, 1 ₀₂ the refractive index and physical length of the second optical material, respectively it, r ₂ is Ru temperature coefficient der of the second optical material. In actual construction of the Fabry-Perot resonator 111, quartz was used as the optical material with a positive temperature coefficient, and rutile was used as the optical material with a negative temperature coefficient. When the C-axis (optical axis) and are oriented in the same direction as the optical axis, since the absolute value of the temperature coefficient of the rutile is 2.7 times the absolute value of the coefficient of quartz, I n _₀₁ 1 ₀₁ | : | n. ₂ 1. ₂ | = 2. 7: 1

Here, η ₀₁ , ₁₀₁ are the refractive index and physical length of quartz, η. _Two , one. ₂ is the refractive index and physical length of Lutheran. By adjusting the respective physical lengths to satisfy equation (2), it is possible to configure the Fuaburipero co oscillator unchanged in the resonator length _{_{L = n 01 1 01 + n}} 02 1 02. In addition, I n ₀₁ 1 ₀₁ |: | n ₀₂ 1. _The temperature coefficient can be arbitrarily changed by changing the ratio of ₂ | from 2.7: 1.

In the above-mentioned conventional technology, a Fabry-Perot resonator in which the resonator length does not change with temperature is configured by using two optical materials having different signs of the temperature coefficient. There is a need. When bonding two optical materials It is necessary to take into account the reflection at the bonding surface due to the difference in the refractive index of each material and the reflection at the bonding surface due to the difference in the refractive index between the adhesive and the optical material.Consider the optical material or the combination of the adhesive It is necessary to carry out various troublesome adjustment work.

Conventionally, it has been difficult to select an arbitrary temperature coefficient using a Fabry-Perot resonator composed of one type of optical material.

The present invention has been made in view of the above, and comprises a Fabry-Perot resonator (wavelength filter) whose resonator length does not change in response to a temperature change using a birefringent crystal, whereby the configuration is simplified, It is an object of the present invention to obtain a wavelength filter capable of realizing mass production and a wavelength monitor provided with the wavelength filter.

In addition, the present invention includes a wavelength filter capable of freely setting a temperature characteristic of a wavelength filter, and selecting an arbitrary wavelength characteristic by changing a temperature of the wavelength filter, and the wavelength filter. The purpose is to obtain a wavelength monitor.

Disclosure of the invention

A wavelength filter according to the present invention resonates light between a solid material that transmits light, a substantially parallel opposing plane formed on the solid material, and the substantially parallel opposing plane. In a wavelength filter for periodically selecting a wavelength determined by an optical path length, the solid material is a birefringent material, and an optical axis thereof has a predetermined angle with a normal to a plane substantially parallel to the birefringent material. I do.

According to the present invention, a birefringent material having a predetermined angle with respect to a normal to a plane whose optical axes are substantially parallel to each other is used, and by changing the angle, the temperature characteristic of the wavelength filter is changed. Can be set freely, and by changing the temperature of the wavelength filter, an arbitrary wavelength characteristic can be selected.

In the above invention, the temperature coefficient of the optical path length between the planes has a predetermined value, wherein the predetermined angle between the normal line of the substantially parallel opposing plane and the optical axis has a predetermined value. Is set as follows.

According to the present invention, since the temperature coefficient of the optical path length between the planes is set to have a predetermined value, it is possible to easily and accurately adjust the wavelength characteristics by changing the temperature, Adjustment to the grid is also facilitated.

In the following invention, in the above invention, the birefringent materials face each other substantially in parallel so that the absolute value of the sum of the product of the refractive index and the linear expansion coefficient in the optical axis direction and the thermo-optic coefficient is minimized. The angle between the optical axis and the normal to the plane to be set is set.

According to the present invention, the temperature characteristic can be suppressed to a sufficiently low value, and a wavelength filter having a temperature compensation function can be provided. Therefore, the configuration of the wavelength filter is simplified, the reliability of the wavelength filter is improved, and a troublesome adjustment operation is not required at the time of production, so that mass production can be realized.

In the following invention, in the above invention, the birefringent material comprises a product of a product of a linear expansion coefficient in a direction parallel to the optical axis and a refractive index of light propagating parallel to the optical axis, and light propagating parallel to the optical axis. And the product of the linear expansion coefficient in the direction perpendicular to the optical axis and the refractive index of light propagating in the direction perpendicular to the optical axis, and the thermo-optics of light propagating in the direction perpendicular to the optical axis. The sum of the coefficients is different from each other.

According to the present invention, while the angle formed by the optical axis with the normal to the plane is changed by 0 to 90 degrees, there is a predetermined angle at which the temperature characteristic becomes zero, and the angle has a characteristic of zero. By setting the angle to be a predetermined angle, a wavelength filter having a temperature compensation function can be provided. Therefore, the configuration of the wavelength filter is simplified, the reliability as the wavelength filter is improved, and troublesome adjustment work is not required at the time of production, so that mass production can be realized.

The following invention, in the above invention, the birefringent material is alpha-BBO crystal,] 3 - wherein beta beta Omicron crystal, L i I 0 ₃ crystals, that is either C a C 0 ₃ crystals And

According to the present invention, as the birefringent crystal, c one Β Β Ο, - BBO, L i I 0 3, C a CO in the case of using any of _3, a wavelength having a temperature compensation function of the precision A filter can be realized.

In the following invention, in the above invention, light incident on the birefringent material uses polarized light aligned with the extraordinary optical axis, and when the birefringent material is an α-BBO crystal, an angle of the optical axis with respect to the optical axis. When the birefringent material is a 3-3 crystal, the angle of the optic axis to the optical axis is about 65 degrees, and when the birefringent material is L i IO ₃ , the angle to the optical axis is The angle is about 23 degrees.

According to the present invention, the polarization of light incident on the extraordinary optical axis is made uniform, and when any of α-ΒΒΟ,] 3-BBO, and Li IO ₃ is used as a birefringent material, high accuracy is achieved. A wavelength filter having a temperature compensation function can be realized.

In the following invention, in the above invention, the light incident on the birefringent material uses polarized light aligned with the ordinary optical axis, and when the birefringent material is an α-BBO crystal, the angle of the optical axis with respect to the optical axis is changed. When the birefringent material is a 3 / 3-ΒΒΟ crystal, the angle of the optic axis to the optical axis is about 57 degrees. When the birefringent material is a Li IO ₃ crystal, the optical axis is the optic axis. angle of about 19 degrees with respect to the birefringent material in the case of C a C0 ₃ crystal, characterized by an angle of about 66 degrees with respect to the optical axis of the optical axes.

According to the present invention, aligning the polarization of light incident on the ordinary axis and the birefringent material, Te odor when using a-BBO, j3- BBO, one of _{L i IO 3, C a CO} 3, A wavelength filter having a highly accurate temperature compensation function can be realized.

A wavelength monitoring device according to the next invention is a wavelength monitoring device that monitors the wavelength of laser light output from a semiconductor laser, comprising: a solid material that transmits laser light; and a substantially parallel opposed flat surface formed on the solid material. A wavelength filter that resonates laser light between the substantially parallel opposing planes, and periodically selects a wavelength determined by an optical path length between the opposing planes; and The solid-state material is a birefringent material, and an optical axis thereof has a predetermined angle with a normal line of the substantially parallel opposing plane. According to the present invention, the wavelength filter is formed using a birefringent material having a predetermined angle with respect to a normal to a plane whose optical axes are substantially parallel to each other. By changing the temperature, the temperature characteristics of the wavelength filter can be set freely, and further, by changing the temperature of the wavelength filter, it is possible to select an arbitrary wavelength characteristic.

In the following invention, in the above invention, the laser light output from the semiconductor laser is polarized in one direction, and the birefringent material forming the wavelength filter is: The optical axis is in a plane parallel to a plane formed by the directions, and the optical axis is inclined at a predetermined angle with respect to the optical axis of the laser beam.

According to the present invention, it is possible to realize a wavelength monitor having a wavelength filter in which the polarization of light incident on the extraordinary optical axis is uniform and which can select an arbitrary wavelength characteristic by changing the temperature. it can.

In the following invention, in the above invention, the laser light output from the semiconductor laser is polarized in one direction, and the birefringent material forming the wavelength filter is: The optical axis lies in a plane perpendicular to the plane formed by the directions, and the optical axis is inclined at a predetermined angle with respect to the optical axis of the laser beam.

According to the present invention, it is possible to realize a wavelength monitor having a wavelength filter capable of selecting an arbitrary wavelength characteristic by changing the temperature by aligning the polarization of light incident on the ordinary optical axis. it can.

In the following invention, in the above invention, the birefringent material constituting the wavelength filter is configured such that an angle of the optical axis with respect to the optical axis is set based on a refractive index of a crystal, a linear expansion coefficient in an optical axis direction, and a thermo-optic coefficient. It is characterized by having.

According to the present invention, since the birefringent crystal in which the angle of the optical axis with respect to the optical axis is set based on the refractive index, the coefficient of linear expansion in the optical axis direction, and the thermo-optic coefficient, the birefringent crystal is used. Thus, a highly reliable wavelength monitor having a wavelength filter having a temperature compensation function can be realized.

The next invention is the above-mentioned invention, wherein the normal and the optical axis of the plane substantially parallel The predetermined angle with the axis is set such that the temperature coefficient of the optical path length between the planes has a predetermined value.

According to the present invention, since the temperature coefficient of the optical path length between the planes is set to have a predetermined value, it is possible to easily and accurately adjust the wavelength characteristics by changing the temperature, Adjustment to the grid is also easy.

According to the present invention, the temperature characteristic of the wavelength filter can be suppressed to a sufficiently low value, so that the configuration is simplified, the reliability as a wavelength monitor is improved, and a troublesome adjustment operation is not performed during production. And mass production can be realized.

In the following invention, in the above invention, the birefringent material comprises a product of a product of a linear expansion coefficient in a direction parallel to the optical axis and a refractive index of light propagating parallel to the optical axis, and light propagating parallel to the optical axis. Of the light propagating in the direction perpendicular to the optical axis and the product of the tension coefficient in the direction perpendicular to the optical axis and the refractive index of the light propagating in the direction perpendicular to the optical axis. The sum of the coefficients is different from each other.

According to the present invention, while the angle formed by the optical axis with the normal to the plane is changed by 0 to 90 degrees, there is a predetermined angle at which the temperature characteristic becomes zero. By setting the angle between the line and the specified angle at which the temperature characteristic becomes zero, the wavelength filter has a temperature compensation function, which simplifies the configuration and improves the reliability as a wavelength monitor. At the same time, there is no need for troublesome adjustment work during production, and mass production can be realized.

The following invention, in the above invention, the birefringent material, and wherein the alpha-BBO crystal, beta one beta beta Omicron crystal, L i I 0 ₃ crystals are either C a C 0 ₃ crystals I do.

According to the present invention, as a birefringent crystal, Hiichi BBO, 3—BBO, L i I 0 ₃ , In the case of using the C a C_〇 ₃ either, it is possible to realize a wavelength monitor device provided with a wavelength filter having a temperature compensation function of high accuracy.

In the following invention, in the above invention, the light incident on the birefringent material uses polarized light aligned with the extraordinary optical axis, and when the birefringent material is a BBO crystal, the angle of the optical axis with respect to the optical axis is about and 64 degrees, in the case of the birefringent material is 3-ΒΒΟ crystals, and an angle of about 65 degrees with respect to the optical axis of the optical axis, if the birefringent material is a L i I 0 _3, the angle with respect to the optical axis of the optical axis It is characterized by about 23 degrees.

According to the present invention, the polarization of light incident on the extraordinary optical axis is made uniform, and when any of a-BBO,] 3-BBO, and Li IO ₃ is used as a birefringent material, high-precision A wavelength monitor having a wavelength filter having a temperature compensation function can be realized.

In the following invention, in the above invention, the light incident on the birefringent material uses polarized light aligned with the ordinary optical axis, and when the birefringent material is an α-BBO crystal, the angle of the optical axis with respect to the optical axis is changed. and about 77 degrees, in the case of the birefringent material is / 3- BBO crystal, and the angle of about 57 degrees against the optical axis of the optical axis, if the birefringent material is a L i I 0 ₃ crystal, the light of the optical axis an angle relative to the axis of about 19 degrees, the birefringent material in the case of C a C0 ₃ crystal, characterized by an angle of about 66 degrees with respect to the optical axis of the optical axes.

According to the present invention, aligning the polarization of light incident on the ordinary axis and the birefringent material, a -B BO] 3- BBO, when using any of _{L i I 0 3, C a} CO 3 In addition, it is possible to realize a wavelength monitor including a wavelength filter having a high-precision temperature compensation function.

In the following invention, in the above invention, the birefringent material constituting the wavelength filter is optically controlled so that a sum of a product of a refractive index and a linear expansion coefficient in an optical axis direction and a thermo-optic coefficient are equal to zero. The angle of the axis with respect to the optical axis is set.

According to the present invention, when the polarization of the laser beam is aligned with the extraordinary optical axis, the optical product is set so that the sum of the product of the refractive index and the linear expansion coefficient in the direction of the optical axis and the thermo-optic coefficient is equal to zero. Since a uniaxial birefringent crystal whose angle is set with respect to the optical axis is used, high-precision temperature A wavelength monitor having a wavelength filter having a degree compensation function can be realized.

In the following invention, in the above invention, the birefringent material constituting the wavelength filter is any one of α-ΒΒΟ,] 3—BBO and L i IO _{3. If} the birefringent material is α—BBO, The angle of the optical axis with respect to the optical axis is 63.35 degrees, and the birefringent material is] 3—In the case of BBO, the angle of the optical axis with respect to the optical axis is 64.75 degrees, and the birefringent material is L i I 0 ₃ In this case, the angle of the optical axis with respect to the optical axis is 22.70 degrees.

According to the present invention, aligning the polarization of the incident, single laser light to extraordinary optical axis, and as a birefringent crystal, a- BBO,] 3- ΒΒΟ, in the case of using any of L i I 0 _3, It is possible to realize a wavelength monitor with a wavelength filter that has a high-precision temperature compensation function.

The following invention, in the above invention, the birefringent material forming the wavelength filter, alpha-BBO, one BBO, either as _{L i L0 3, C a C0} 3, the birefringent material is alpha-BBO of In this case, the angle of the optical axis with respect to the optical axis is 76.95 degrees, and when the birefringent material is 0— 、, the angle of the optical axis with respect to the optical axis is 57.05 degrees, and the birefringent material is L i L0 ₃ for the angle with respect to the optical axis of the optical axis is 18.65 degrees, the birefringent material in the case of C a C0 _3, and Toku徵that the angle 67.05 degrees with respect to the optical axis of the optical axis .

According to the present invention, aligning the polarization of the incident laser light into ordinary light axis, also as a birefringent crystal, using α- BBO, 3 -BBO, one of _{L i I 0 3, C a} CO 3 In this case, a wavelength monitor having a wavelength filter having a high-precision temperature compensation function can be realized.

In the following invention, the birefringent material constituting the wavelength filter in the above invention satisfies the temperature compensation condition by changing the thickness in the optical axis direction while maintaining the set angle with respect to the optical axis. And the wavelength discrimination region can be adjusted.

According to the present invention, the temperature compensation condition does not depend on the thickness of the birefringent crystal. It is possible to obtain a wavelength filter having an arbitrary wavelength discrimination region satisfying the adjustment condition.

The next invention is characterized in that, in the above invention, there is provided a lens for adjusting a beam size of laser light emitted from the semiconductor laser, and outputting the adjusted laser light to the wavelength filter.

According to the present invention, it is possible to adjust the beam size of the laser light and make it incident on the wavelength filter.

In the following invention, in the above invention, the wavelength detecting means comprises: a first photodetector for detecting light transmitted through the wavelength filter; and a second light for directly detecting laser light output from the semiconductor laser. It is characterized by comprising a detector and a wavelength detector for detecting the oscillation wavelength of the laser light using the ratio of the detection signals of the first and second photodetectors.

According to the present invention, since the oscillation wavelength of the laser light is detected using the ratio of the detection signals of the first and second photodetectors, the laser light is not affected by a change in the output intensity of the semiconductor laser. The oscillation wavelength can be accurately detected.

In the following invention, in the above invention, the semiconductor laser and the wavelength filter are mounted, and the first and second optical detectors are arranged such that the second photodetector is located above the first photodetector. A base scanner for installing a photodetector is further provided, wherein the height of the wavelength filter is adjusted so that the laser light transmitted through the wavelength filter mounted on the base carrier is not received by the second photodetector. It is characterized by

According to the present invention, the laser light transmitted through the wavelength filter is not received by the second photodetector, and the oscillation wavelength can be accurately detected.

In the following invention, in the above invention, the semiconductor laser and the wavelength filter are mounted, and the first and second optical detectors are arranged such that the second photodetector is located above the first photodetector. A base carrier on which a photodetector is installed, wherein the laser light transmitted through the wavelength filter mounted on the base carrier is the second light; The second photodetector is arranged closer to the wavelength filter side than the first photodetector so as not to be received by the detector.

The following invention is the wavelength monitoring device for monitoring the wavelength of the laser light output from the semiconductor laser in the above invention, wherein the first solid material transmitting the laser light; and the first solid material formed on the first solid material. A laser beam is resonated between a substantially parallel opposing plane and the substantially parallel opposing plane to periodically select a wavelength determined by an optical path length between the opposing planes, and the solid material is a birefringent material. A first wavelength filter for a narrow band having a predetermined angle with a normal to a plane whose optical axis is substantially parallel to the first surface; a second solid material that transmits laser light; and a first solid material. The laser light is resonated between a substantially parallel opposed plane formed on the substrate and the substantially parallel opposed plane, and a wavelength determined by an optical path length between the opposed planes is periodically selected, and the solid material is birefringent. Material and A second wavelength filter for a wide band, the optical axis of which has a predetermined angle with the normal of the plane substantially parallel to each other, and an oscillation wavelength of the laser light based on light transmitted through the first and second wavelength filters. And a wavelength detecting means for measuring.

According to the present invention, the configuration is simplified, the reliability as a wavelength monitor is improved, and troublesome adjustment work does not have to be performed during production, and mass production can be realized. Furthermore, according to the present invention, the oscillation wavelength of the laser beam is monitored using two wavelength filters for the narrow band and the broad band, so that the oscillation wavelength can be detected very accurately.

In the following invention, in the above invention, the laser light output from the semiconductor laser is polarized in one direction, and the birefringent material constituting the first and second wavelength filters is An optical axis is in a plane parallel to a plane formed by the optical axis and the polarization direction of the laser light, and the optical axis is inclined at a predetermined angle with respect to the optical axis of the laser light. I do. According to the present invention, it is possible to realize a wavelength monitor having two wavelength filters having a temperature compensation function by using a birefringent crystal by aligning the polarization of the laser light with the extraordinary optical axis.

According to the present invention, it is possible to realize a wavelength monitor having two wavelength filters having a temperature compensation function by using a birefringent crystal in which the polarization of laser light is aligned with the ordinary optical axis.

In the above invention, the wavelength discrimination region of the second wavelength filter for the wide band is larger than the wavelength variable region of the semiconductor laser, and the wavelength discrimination region of the first wavelength filter for the narrow band is the second wavelength filter. The thickness of the birefringent material constituting the first and second wavelength filters in the optical axis direction is set so as to be sufficiently smaller than the wavelength variable region of the first wavelength filter.

According to the present invention, the two wavelength filters for the narrow band and the wide band are configured by setting the thickness of the birefringent crystal in the optical axis direction, and the two wavelength filters for the narrow band and the wide band are simply provided. Can be realized.

In the following invention, in the above invention, the wavelength detecting means directly detects laser light output from the semiconductor laser, and a first photodetector for detecting transmitted light of the first wavelength filter. A second photodetector; a third photodetector for detecting light transmitted through the second wavelength filter; a ratio of detection signals of the first and second photodetectors; A wavelength detector that detects the oscillation wavelength of the laser light using the ratio of the detection signal of the second photodetector.

According to the present invention, the oscillation wavelength of the laser light is detected using the ratio of the detection signals of the first and second photodetectors and the ratio of the detection signals of the third and second photodetectors. As a result, the oscillation wavelength can be extremely accurately detected without being affected by a change in the output intensity of the semiconductor laser.

In the following invention, in the above invention, the semiconductor laser and the wavelength filter are mounted, and the first to third light detectors are arranged such that the second and third photodetectors are located above the first photodetector. A base carrier on which a third photodetector is provided, wherein the second and third photodetectors do not receive the laser light transmitted through the wavelength filter mounted on the base carrier. The third photodetector is disposed closer to the wavelength filter than the first photodetector. According to the present invention, the laser light transmitted through the wavelength filter is not received by the second and third optical detectors, and the oscillation wavelength can be accurately detected.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a configuration diagram of a conventional wavelength monitoring device, FIG. 2 is a perspective view showing a conventional Fabry-Perot resonator, and FIG. 3 is a configuration diagram of a wavelength monitoring device in the first embodiment. Fig. 4 is a graph showing the change in the transmittance of a Fabry-Perot resonator (wavelength filter) with respect to the wavelength. Fig. 5 shows a Fabry-Perot resonator (wavelength filter) using a uniaxial birefringent crystal. FIG. 6 is a diagram showing the physical property values of the -ΒΒΟ crystal, and FIG. 7 is a graph showing the dependence of the dn / d α + αη of the 3-3-ΒΒΟ crystal on the temperature Τ. Fig. 8 is a graph showing the dependence of the linear expansion coefficient α of the / 3-Β Β Ο crystal on the C-axis-to-optical axis angle <i> c. FIG. 10 is a graph showing the dependence of the extraordinary refractive index n on the angle φ between the C axis and the optical axis. FIG. 10 shows the temperature of the extraordinary refractive index of the] 3-BBO crystal. C-axis of Heni匕 dn / dT against - between the optical axis angle [Phi. FIG. 11 is a graph showing temperature characteristics of i3-— crystal with respect to φ c, and FIG. 12 is a graph showing temperature characteristics of C a〇〇 ₃ crystal with respect to ^ c , and the FIG. 13 is a diagram showing a temperature characteristic with respect to phi c of L i I 0 ₃ crystal, Fig. 14 shed - is a view to view the temperature characteristics for phi c of the BBO crystal, the first 5 Figure dependence on L i I 0 ₃ temperature T of dn / dT + αη crystals FIG. 16 is a configuration diagram illustrating a wavelength control device according to the first embodiment, and FIG. 17 is a configuration diagram illustrating a modification of the wavelength monitor device according to the first embodiment. FIG. 18 is a configuration diagram of a wavelength monitor device according to the second embodiment, FIG. 19 is a configuration diagram of a wavelength control device according to the second embodiment, and FIG. 20 is a Fabry-Perot for a narrow band. FIG. 21 is a graph showing the wavelength transmission characteristics of a resonator (wavelength filter) and a Fabry-Perot resonator (wavelength filter) for a wide band. FIG. 21 is a configuration diagram showing a modification of the wavelength monitor device according to the second embodiment. It is. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of a wavelength monitor device according to the present invention will be described in detail with reference to the accompanying drawings.

Embodiment 1

FIG. 3 is a configuration diagram showing a wavelength monitoring device (a certain wavelength is a wavelength stabilized light source) according to Embodiment 1 of the present invention. The semiconductor laser 1 emits laser light (hereinafter referred to as an optical signal) polarized in one direction. Examples of the semiconductor laser 1 include a distributed feedback (DFB) laser having a diffraction grating in an active layer, a tunable laser diode whose wavelength can be changed by injection current or temperature, or an electroabsorption element and a laser diode. And a compound type (EA / LD) module in which the components are arranged in series. In addition, the injection current or the temperature of the semiconductor laser 1 is controlled by the control signal T1 input from the wavelength control device shown in FIG. 16 to control the wavelength.

An optical signal emitted from the semiconductor laser 1 is condensed by the lens 2 and output as parallel light. The beam size of the optical signal is adjusted by the lens 2 and the light signal is incident on a Fabry-Perot resonator 3 as a wavelength filter. The axis connecting the center of the emitting surface of the semiconductor laser 1 and the center of the lens 2 is the optical axis. In Embodiment 1 and Embodiment 2 to be described later, the traveling direction (optical axis direction) of an optical signal is defined as the Z-axis direction in space coordinates, and the upward direction in space is defined as the Y-axis direction. The direction perpendicular to the Y-axis (the direction perpendicular to the page in Fig. 3 and facing the front) is defined as the X-axis. Semiconduct The optical signal emitted from the body laser 1 has a polarization component that vibrates in the X-axis direction.

The Fabry-Perot resonator (wavelength filter) 3 has reflection films 7 and 8 that reflect light on an incident surface on which an optical signal from the semiconductor laser 1 is incident and an exit surface on which the optical signal is emitted, and one kind of material is used. only uniaxial birefringent crystal (first material) (e.g., / 3 - BBO crystal, alpha - BBO crystal, L i IO ₃ crystal, any such C a CO ₃ crystals) are formed by. The crystal cut surface of the uniaxial birefringent crystal used as the material of the Fabry-Perot resonator 3 is arranged so as to be parallel to the XY plane orthogonal to the optical axis, and the optical axis of the uniaxial birefringent crystal (hereinafter referred to as the C axis) ) Is inclined at a predetermined angle with respect to the XY plane perpendicular to the optical axis of the laser beam.

The first photodiode (main photodetector) 4 receives the optical signal transmitted through the Fabry-Perot resonator 3, detects its intensity (photocurrent value), and outputs a light intensity monitor signal S1.

The second photodiode (sub-photodetector) 5 is disposed above the first photodiode 4 and directly receives an optical signal emitted from the semiconductor laser 1 without passing through the Fabry-Perot cavity 3 and receiving the light signal. Detects light intensity (photocurrent value) and outputs light intensity monitor signal S2.

These semiconductor laser 1, lens 2, Fabry-Perot cavity 3, first photodiode 4, and second photodiode 5 are mounted on base carrier 6. The height of the Fabry-Perot resonator 3 or the height of the second photodiode 5 is set so that the optical signal transmitted through the Fabry-Perot resonator 3 is not received by the second photodiode 5. Has been adjusted.

Here, the transmission characteristics with respect to the wavelength of the optical signal transmitted through the Fabry-Perot resonator 3 are kept constant irrespective of the temperature change. That is, the Fabry-Perot resonator 3 has a temperature compensation function. Next, the temperature compensation condition of the Fabry-Perot resonator 3 will be described. In the wavelength monitoring device shown in FIG. 3, an optical signal is vertically incident on the incident surface of the rectangular Fabry-Perot resonator 3. The Fabry-Bore-One resonator 3 Assuming that the emission surfaces have reflection films 7 and 8 and their intensity reflectivity is R, the dependence of the intensity of the optical signal transmitted through the Fabry-Bore-One resonator 3 on the wavelength is expressed by Equation (3) and FIG. Is done. TR (E) is the transmittance.

In this case, the intensity of the optical signal transmitted through the Fabry-Perot resonator 3 changes periodically with respect to the frequency of the optical signal. The frequency interval corresponding to one cycle is called a free spectrum range (hereinafter, referred to as FSR, free spectral interval) with respect to the wavelength of the optical signal transmitted through the Fabry-Perot resonator 3. The FSR depends on the resonator length in the direction of the optical axis, in the case of FIG. 3, the length L in the Z-axis direction of the uniaxial birefringent crystal 3 and the refractive index n, and is expressed by the following equation (4). . c is the speed of light.

FSR = (4)

The compensation condition for the Fabry-Perot single resonator is that the dependence of the intensity of the optical signal transmitted through the 2nL Fabry-Perot resonator 3 on the wavelength does not change with temperature. Therefore, in order to enable temperature compensation, it is necessary that F SR represented by equation (4) does not depend on temperature. In order for F SR to be constant with respect to temperature T, it is necessary that the resonator length n L has a constant value with respect to temperature T in equation (4). Equation (5) expresses this relationship.

d, _τ , dn _τ oL ...

— (NL) = —— L + n— = 0 · · · (5)

5T ar θτ The linear expansion coefficient in the optical axis direction (Ζ direction in Fig. 3) of Fabry Then, the physical length L of the Fabry-Perot resonator 3 is expressed by equation (6).

L = L ₀ (l + aT)..-(6) where L. Is the physical length of the Fabry-Perot cavity at 0 ° C in the Z-axis direction. By substituting equation (5) into equation (6), the temperature compensation condition of Fabry-Perot resonator 3 becomes equation (7).

— + Na = 0 (7)

When a uniaxial birefringent crystal having one C-axis is used as the material of the cT Fabry-Perot resonator 3, the positional relationship between the optical axis of the incident optical signal and the C-axis, and the linear expansion of the Fabry-Perot resonator 3 The coefficient and the refractive index will be described.

Note that the temperature compensation condition can be satisfied even when the polarization direction of the laser beam (in this case, the X direction) is aligned with the extraordinary optical axis or the ordinary optical axis of the uniaxial birefringent crystal. The case where the polarization direction of the light is aligned with the extraordinary optical axis of the uniaxial birefringent crystal will be described.

In Fig. 5, the C axis of the uniaxial birefringent crystal, which is the material of the Fabry-Perot resonator, is in the XZ plane, the optical axis is parallel to the Z axis, and the C axis is at a constant angle to the optical axis. Φ c is inclined. The polarization of the optical signal incident on the Fabry-Perot resonator 3 is p-polarized with respect to the Fabry-Perot resonator 3, and corresponds to the X direction in FIG. Since the extraordinary ray has the same vibration plane as the plane created by the C axis and the optical axis direction, in this case, the incident optical signal propagates inside the Fabry-Perot resonator 3 as an extraordinary ray. The refractive index n for an extraordinary ray depends on the angle between the optical axis and the C axis. Since ne and no depend on the temperature T, they can be expressed as n (0c, T), as shown in equation (8). .

Here, ne is the refractive index for the polarized light component in the direction parallel to the C axis (the extraordinary light refractive index), and no is the refractive index for the polarized light component in the direction perpendicular to the C axis (the ordinary light refractive index). Η (φΤ) is the refractive index for an optical signal incident on a Fabry-Bore-single resonator made of a uniaxial birefringent crystal.

The linear expansion coefficient α in the optical axis direction of a uniaxial birefringent crystal is expressed as in equation (9). ac is the coefficient of linear expansion in the direction parallel to the C axis, and aa is the coefficient of linear expansion in the direction perpendicular to the C axis.

a = cos φ. + sin φ— (9) Using the dn / d T and a, the temperature characteristic of the wavelength characteristic shown in FIG. 4 can be expressed by the formula (1) for the extraordinary optical axis direction and the ordinary optical axis direction. 0), and is expressed by equation (11).

(Abnormal optical axis direction)

(Ordinary light axis direction)

_{άλ άη η / άΤ + α (} φ α) · η 0

λ

(1 1)

The inventors of the present application have made it possible for the uniaxial birefringent crystal studied as a material of the Fabry-Perot resonator to change the value of the inclination φ c of the C axis with respect to the optical axis. According to the above, the uniaxial birefringent crystal satisfying the equation (7) and the value of φ c in that case were examined. As a result, 13-B BO (B a B 2 0 4) crystals, such as alpha-BBO _{crystal, L i I 0 3, C} a C0 3 was found to satisfy the equation (7). These crystals are used as wavelength conversion elements for laser light.

Fig. 6 shows the characteristics of] 3-BBO crystal. That is,]] — BBO has an extraordinary refractive index ne of 1.53 11 1, an ordinary refractive index no of 1.6467, and a thermo-optic coefficient d no / dT of — 16.8 X 10 0 6 / in K, thermo-optical coefficient d ne / d T - 8. 8 X 1 0 one ⁶ / a, coefficient of linear expansion etc is 3 3. 3 X 1 0- K, the linear expansion coefficient ca is 0. 5 X 1

0-1 ⁶ / K.

In addition, Fig. 7 shows that 3 η / 3 shown in equation (7) when a uniaxial birefringent crystal composed of BBO is used as the Fabry-Perot resonator 3 and the polarization direction of the laser beam is aligned with the extraordinary optical axis. and T + eta _alpha, a graph showing the relationship between the optical axis and the C axis and the angle phi c. Fig. 8 is a graph showing the dependence of the coefficient of linear expansion α on the angle φ c in a ΒΒΟ crystal, and Fig. 9 is a graph showing the dependence of the refractive index η on the angle φ c in a ΒΒΟ crystal. Yes, FIG. 10 is a graph showing the dependence of dn / dT on the angle ^ c in a / 3--3 crystal. That is, the relationship between the linear expansion coefficient α and the angle <f> c in FIG. 8, the relationship between the refractive index n and the angle ψ c in FIG. 9, and the relationship between dn / dT and the angle (ί> Using the relationship with c, the relationship between 3 η / 3 Τ + η α and the angle φ c shown in FIG. 7 is obtained.

Fig. 11 shows the relationship between Φ c and temperature characteristics in the direction of the extraordinary optical axis and the direction of the ordinary optical axis when / 3-BBO is used as the uniaxial birefringent crystal. 1 This is a graph using 1). According to Fig. 11, by changing the C-axis angle <i) c, the extraordinary optical axis direction is from 18 pmZ ° C to +36 pm / ° C, and the ordinary optical axis direction is from 15 pmZ ° C by changing c. Temperature characteristics can be freely set up to +36 pmZ ° C. In addition, the temperature characteristic becomes zero when φ c is between 0 and 90 degrees because of the relationship of (1 11/3 cho + hi ₍ : 11) 0 bracket (111 01 cho + « _{! 1} 11 <0 ψ For example, if the temperature characteristic is to be 1 pmZ ° C or less using the direction of the ordinary optical axis, φ c should be about 63 It may be set to any value between ~ 67 degrees. If the temperature characteristic is to be set to ± 1 pm or less using the direction of the extraordinary optical axis, c may be set to any value of about 55 to 59 degrees. The wavelength characteristics can be adjusted using the temperature characteristics. When it is desired to match the ITU grid wavelength to a desired wavelength control point, the wavelength characteristics are usually changed by tilting the filter, but the temperature of the filter (uniaxial birefringent crystal) is changed using the above characteristics. By doing so, it is possible to match the wavelength control point. For example, FSR = 25 GHz (= 0.2 nm), temperature characteristic is 10 pm. When using 3—BBO set to C, any lock point can be used with a maximum filter temperature change of 20 ° C. It should be noted that the ITU grid is a set of closely spaced wavelengths in a specific wavelength region specified by the International Telecommunication Union, for example, a window of 1550 nm. Corresponds to a wavelength interval of about 0.8 nm. The first 2 figures when using the C a C0 ₃ as uniaxial birefringent crystal, (0 1) wherein the relationship <ί> c and the temperature characteristics of the extraordinary optical axis direction and the ordinary axis direction and the formula (1 Graphed using 1). The property constants used were: extraordinary refractive index ne was 1.4.771, ordinary refractive index no was 1.63.37, and temperature coefficient of refractive index dno / d T in the ordinary optical axis direction was 2.1. 0 X 1 0- in ⁶ ZK, abnormal temperature coefficient of the optical axis of the refractive index dne ZdTH l 1 9 X 1 0- 5 / K, the linear expansion coefficient aa -. 5. 7 0 X 1 0 ~ 6 / At K, the coefficient of linear expansion c is 2.44 X 10-6 / Κ. According to Fig. 12, by changing φ c, the extraordinary optical axis direction is from +4 pm / ° C to +40 pmZ ° C, and the ordinary optical axis direction is from 17 pm / ° C to +40 pmZ ° C. Temperature characteristics can be freely set up to this point. With respect to the ordinary axis direction, d nZd T + acn> 0 and _{dn / d T + a a n} < because there is the relationship 0 0-9 0 degrees phi c temperature characteristics ing and zero opening between the Exists. For example, if it is desired to set the temperature characteristic to 1 pm / ° C or less using the direction of the ordinary optical axis, φ c may be set to any value of about 65 to 70 degrees. To obtain the minimum temperature characteristics in the direction of the extraordinary optical axis, ψ c = 90 degrees may be set. The wavelength characteristics can be adjusted using the temperature characteristics. I TU grid wave When it is desired to adjust the length to a desired wavelength control point, the wavelength characteristic is usually changed by tilting the filter. However, the wavelength is adjusted to the wavelength control point by changing the temperature of the filter using the above characteristics. For example, FSR = 25GHz (= 0. 2 nm), when the temperature characteristics using the C a C0 ₃ was set to 10 pmZ ° C, the use of any locking point filter temperature variation of up to 20 ° C Can be done.

The first 3 figures, in the case of using L i I 0 ₃ as a uniaxial birefringent crystal, the formula (10) the relation <ί> c and the temperature characteristics of the extraordinary optical axis direction and the ordinary axis direction and the formula (1 Graphed using 1). Physical constants used were extraordinary refractive index ne is 1.71 03, in the ordinary refractive index no is 1.8474, the temperature coefficient dn OZdT refractive index of ordinary light axial - 8. 49 X 1 0- ⁵ ZK The temperature coefficient d η eZdT of the refractive index in the direction of the extraordinary optical axis is — 6.92 X 10 — 5 / K, the linear expansion coefficient aa is 2.80 X 10 — ⁵ Z, and the linear expansion coefficient ac Is 4.80 X 10-1 ⁵ ZK. According to Fig. 13, by changing φ c, the direction of the extraordinary optical axis is from 20 pmZ ° C to +3 pmZ ° C, and the direction of the ordinary optical axis is −28 pmZ ° C to +3 pm, °. Temperature characteristics can be freely set up to C. Also, in both the normal optical axis and the extraordinary optical axis, there is a relationship of dn / dT + a _e n> 0 and d nZdT + _a n a 0, so that the temperature characteristic becomes zero when 0 c is between 0 and 90 degrees. c exists. For example, if you want the temperature characteristics to be less than 1 pm_ ° C in soil using the direction of the ordinary optical axis, you can set φ c to any value from about 15 to 22 degrees. If the temperature characteristic is to be 1 pm / ° C or less using the direction of the abnormal optical axis, φ c should be set to any value of about 18 to 27 degrees. The wavelength characteristics can be adjusted using the temperature characteristics. When it is desired to adjust the ITU grid wavelength to a desired wavelength control point, the wavelength characteristic is usually changed by tilting the filter, but by changing the temperature of the filter using the above characteristics, the wavelength control point can be adjusted. Match. For example, FSR = 25GHz (= 0. 2 nm), when the temperature characteristics using L i I 0 ₃ set to 10 pm Z ° C, the mouth Kkupointo arbitrary filter temperature change of up to 20 ° C Can be used. Fig. 14 shows the relationship between Φ c and temperature characteristics in the extraordinary optical axis direction and the ordinary optical axis direction when α-BBO is used as the uniaxial birefringent crystal, using equations (10) and (11). It is graphed using. The physical constants used were: extraordinary refractive index ne was 1.530, ordinary refractive index no was 1.6502, and temperature coefficient of refractive index in the ordinary optical axis direction was dn oZd T was 9.30 x in 1 0- 5 / K, abnormal temperature coefficient of the optical axis of the refractive index dne / d T one ^{1 6. 6 X 1 0- 5 /} K, the linear expansion coefficient aa 4. 0 X 1 0- ⁵ / in K, the linear expansion coefficient ac is 3 6. 0 X 1 0 one ^5. According to FIG. 14, by changing φ c, the direction of the extraordinary optical axis is from 11 pmZ ° C to +47 pmZC, and the direction of the ordinary optical axis is −3 pmZ ° C to +47 pm / Temperature characteristics can be freely set up to ° C. D nZd T + _{a for} both the normal optical axis and the extraordinary optical axis. Since there is a relation of n> 0 and dn / d T + a _a n <0, there exists c whose temperature characteristic becomes zero when φ c is between 0 and 90 degrees. For example, if it is desired to set the temperature characteristic to ± 1 pmZ ° C or less using the direction of the ordinary optical axis, φc may be set to any value of about 74 to 80 degrees. When it is desired to set the temperature characteristic to 1 pm_ ° C or less using the direction of the abnormal optical axis, ψc may be set to any value of about 63 to 66 degrees. The wavelength characteristics can be adjusted using the temperature characteristics. When it is desired to adjust the ITU grid wavelength to a desired wavelength control point, the wavelength characteristics are usually changed by tilting the filter.However, the temperature is adjusted to the wavelength control point by changing the temperature of the filter using the above characteristics. . For example, when FSR = 25 GHz (= 0.2 nm) and the temperature characteristic is set to 10 pm Z ° C, use a c-BBO with a filter temperature change of up to 20 ° C. Lock points can be used.

In addition to the above] 3—BBO, C a C〇 ₃ , Lil〇 ₃ , and α—B BO crystals, dn / ^/ d T + a _c n> C ^^^ dn no d T + a _a Any crystal that satisfies the relationship of n <0 or the relationship of dn / d T + a _c n 0 and dn / d T + a _a n> 0 may be used. In this case, a temperature characteristic in which φc always indicates zero is obtained in the range of 0 to 90 degrees. By selecting φc in the vicinity of this temperature filter, a wavelength filter having zero or very little characteristic can be obtained. In addition, the above-mentioned 011 ^/ (1 chore + £ ^ 11> 0 parentheses (111 _£ 1 chore + _£ ^ 11 <0, or (Ι

Ku 0 and _{dn / d T + a a n} > 0 dn / dT + α n is minimized by adjusting the even [psi c a relationship that does not satisfy the relation, i.e. formula (10), formula (1 1) Is obtained under the condition that the temperature characteristic is minimized.

As shown in Fig. 7, when the uniaxial birefringent crystal — BBO is used, if the angle φ c between the optical axis and the C axis is 64.75 degrees, d η / 3 Τ + η α = 0 Thus, the temperature compensation condition equation (7) is satisfied. For example, in the wavelength monitor for a narrow band used in the first embodiment, it is desired to set the FSR to 100 GHz (1.0 X 10 ^{X 1} Hz) corresponding to a wavelength fluctuation width of 0.8 nm of laser light. Sometimes, using Equations (4) and (8), a thickness L = 970 m of the uniaxial birefringent crystal] 3-BBO in the Z-axis direction is obtained. This thickness L = 970 / im is a sufficiently practical size.

That is, from the relationship with 3n / 3T + n one angle ψc shown in Fig. 7, an angle 0c that satisfies Equation (7) is obtained, and the obtained angle c is used to calculate The refractive index η is obtained, and the length L of the uniaxial birefringent crystal 3 in the Ζ-axis direction is adjusted based on the equation (4) using the obtained angle ψc and the refractive index η to obtain a desired FSR. Get it.

Note that the temperature compensation condition equation (7) does not depend on the length L of the uniaxial birefringent crystal in the 方向 -axis direction when the uniaxial birefringent crystal is used as the Fabry-Perot resonator 3, so that from equation (4) A Fabry-Perot resonator with any FSR that satisfies the temperature compensation conditions can be made.

Next, the operation of the wavelength monitor of FIG. 3 will be described. An optical signal emitted from the semiconductor laser 1 is collected by the lens 2. The upper part of the collected optical signal is directly received by the second photodiode 5. The second photodiode 5 detects and monitors the intensity of the received optical signal. An output control circuit (not shown) controls the optical output of the semiconductor laser 1 to be constant based on the difference between the intensity monitor signal S2 and a preset optical signal intensity.

The lower part of the optical signal collected by the lens 2 has a ρ polarization component, that is, This is an optical signal oscillating in the X-axis direction, and the optical signal passes through a Fabry-Low resonator 3 composed of / 3-BBO at an angle ψc = 64.75 degrees with respect to the C-axis. Since the polarization direction of the optical signal transmitted through the Fabry-Bore-single resonator 3 made of a uniaxial birefringent crystal such as / 3-BBO is parallel to the extraordinary optical axis of the uniaxial birefringent crystal, Fabry-Perot resonance When passing through the optical device 3, the polarization of the optical signal remains unchanged and remains p-polarized. The intensity of the optical signal emitted from the Fabry-Perot resonator 3 has a wavelength discrimination characteristic as shown in equation (3), and the characteristic is kept constant regardless of the crystal temperature change. Has temperature compensation function.

In this case, φο = 64.75 is set, but the temperature characteristics can be sufficiently suppressed if the angle is around this. For example, in the range of about 55 to 59 degrees, the temperature characteristic is 1 pm / ° C for soil, which is sufficiently smaller than the temperature characteristic of a conventional solid ethanol port (up to 10 pm / ° C). Furthermore, at other angles ψ c, the temperature coefficient can be arbitrarily set as long as the extraordinary optical axis direction is between 18 pmZ ° C and +36 pmZ ° C, and the normal optical axis direction is between 15 pmZ ° C and +36 pm. You can choose. This makes it possible to adjust the wavelength characteristics by changing the temperature, which facilitates adjustment to the ITU grid. For example, the thickness of uniaxial birefringent crystal 3 is set to about 3.6 mm so that FSR = 25 GHz, and φc is set so that the temperature characteristic is 8 pmZ ° C. In this case, it is possible to shift the 1 GHz wavelength characteristic by changing the temperature of the uniaxial birefringent crystal 3 by 1 ° C. Therefore, when trying to match the ITU grid with 25 GHz spacing to the wavelength control point specified in advance, the temperature of the base carrier 6 on which the semiconductor laser 1 is mounted is changed by up to 25 degrees and the semiconductor laser is changed. By changing the oscillation wavelength by adjusting the injection current to 1, it is possible to adjust to the desired wavelength control point.

The first photodiode 4 detects the intensity of an optical signal that has passed through the Fabry-Perot resonator 3, and outputs an optical intensity monitor signal S1. On the other hand, the second photodiode 5 directly detects the optical signal intensity emitted from the semiconductor laser 1 and outputs the optical intensity monitor signal S2, as described above. These light intensity monitor signals S 1 and S 2 are It is sent to the wavelength controller 50 shown in the figure. The wavelength controller 50 detects the wavelength of the optical signal, and controls the semiconductor laser 1 so that the detected wavelength matches a preset wavelength (for example, the reference wavelength; I 0 in FIG. 4).

The wavelength controller 50 will be described. FIG. 16 is a configuration diagram of the wavelength control device 50. The wavelength controller 50 includes a wavelength detector 51 and a laser controller 52. The wavelength detector 51 receives the light intensity monitor signals S1, S2 from the first and second photodiodes and a preset reference wavelength 0. The wavelength detector 51 obtains the oscillation wavelength of the optical signal emitted from the semiconductor laser 1 based on the light intensity monitor signals S1 and S2, and obtains the difference between the oscillation wavelength and the reference wavelength I0. The difference between the reference wavelength λ 0 from the wavelength detector 51 and the oscillation wavelength emitted from the semiconductor laser 1 is input to the laser controller 52. The laser control unit 52 obtains a control signal Τ1 for controlling the temperature, injection current, and the like of the semiconductor laser 1 so that the oscillation wavelength coincides with the reference wavelength 0 according to the difference. 1 is output to the semiconductor laser 1.

Next, the operation of the wavelength detector 51 will be described in detail. The relationship between the wavelength and the transmittance of the Fabry-Perot resonator 3 is shown in FIG. A case where the oscillation wavelength is adjusted to the reference wavelength λ 0 in FIG. 4 will be described. According to FIG. 4, when viewed in a wavelength region near the reference wavelength L 0, the value of the light intensity monitor signal S 1 detected by the first photodiode 4 is such that the wavelength of the optical signal is longer than the wavelength. It can be seen that it becomes smaller when it shifts to, and increases when it shifts to the shorter wavelength side. The change in the light intensity monitor signal S1 accompanying the change in the wavelength is monitored, and the deviation from the reference wavelength; L0 is calculated.

Next, a method of calculating the deviation from the reference wavelength λ 0 will be described. The light intensity monitor signal S 2 that directly detects the optical signal emitted from the semiconductor laser 1 and the light intensity monitor signal S 1 that detects the optical signal transmitted through the Fabry-Perot resonator 3 are the semiconductor laser 1 It changes in proportion to the intensity of the emitted optical signal. To detect the deviation from the reference wavelength 0, calculate the signal intensity ratio S1 / S2. Since the light intensity monitor signals S l and S 2 depend on the magnitude of the light intensity signal emitted from the semiconductor laser 1, these signal intensity ratios S 1 / S 2 are the ratios of the transmittance of the Fabry-Perot resonator 3. It depends on the value.

Since the transmittance of the Fabry-Cavity resonator 3 is uniquely determined with respect to the wavelength in the aperture including the reference wavelength 0, the wavelength of the optical signal emitted from the semiconductor laser 1 includes λ 0 If it is within the slope, the value of the signal intensity ratio S1 / S2 will represent the wavelength of the optical signal. In particular, if the FSR is one-half larger than the tunable region of the semiconductor laser 1 by + minute and the tunable region is included in one slope including L 0, the absolute wavelength monitor Can be used as The signal intensity ratio S 1 / S 2 at the reference wavelength 0 is obtained in advance, and the signal intensity ratio S 1 / S 2 at the reference wavelength 0 is stored in the wavelength detector 51. In the wavelength detector 51, the stored signal intensity ratio S 1 / S 2 at the reference wavelength λ 0 and the light intensity monitor signals S 1, S 2 from the first and second photodiodes 4 and 5 are output. The difference (deviation) between the oscillation wavelength and the reference wavelength; L0 is calculated by calculating the difference between the signal intensity ratio S1 / S2 obtained based on the above. The calculated deviation signal is input to the laser control unit 52.

Next, the operation of the laser control unit 52 will be described. The laser controller 52 uses the deviation signal input from the wavelength detector 51 to output a control signal Τ 1 for changing the value of the temperature or the injection current to the semiconductor laser 1. The wavelength of light.

When the wavelength is controlled by changing the injection current of the semiconductor laser 1, generally, when the injection current is increased and the output of the semiconductor laser 1 is increased, the oscillation wavelength of the semiconductor laser 1 becomes longer. In this case, when the laser control unit 52 receives the deviation signal from the wavelength detection unit 51 and the oscillation wavelength is shifted to a longer wavelength side than the reference wavelength, the injection current into the semiconductor laser 1 is increased. If the oscillation wavelength is shifted to a shorter wavelength side than the reference wavelength, a control signal Τ 1 for increasing the injection current to the semiconductor laser 1 is sent to the semiconductor laser 1.

When controlling the wavelength by changing the temperature of the semiconductor laser 1, generally, when the temperature is increased, the oscillation wavelength of the semiconductor laser 1 becomes longer. In this case, when the laser controller 52 receives the deviation signal from the wavelength detector 51, the oscillation wavelength becomes the reference wavelength. If the oscillation wavelength is shifted to a longer wavelength side, the temperature of the semiconductor laser 1 is increased. If the oscillation wavelength is shifted to a shorter wavelength side than the reference wavelength, the control signal T is set to lower the temperature of the semiconductor laser 1. Send 1 to semiconductor laser 1.

In the above description, the polarization direction of the laser light is p-polarization. However, s-polarization laser light, that is, laser light having a polarization direction perpendicular to the plane formed by the C axis and the optical axis Is incident on the uniaxial birefringent crystal, the temperature compensation condition of Equation (7) can be satisfied. That is, the above equation (7) is satisfied for both the ordinary optical axis and the extraordinary optical axis. In this way, when the polarization direction of the laser light is aligned with the ordinary optical axis, in other words, the C axis is set in a plane perpendicular to the plane formed by the optical axis and the polarization direction of the laser light. In this case, the angle ψc between the optical axis and the C axis is 57.05 degrees. Note that the refractive index n and d n / d t when the ordinary optical axis is used do not depend on the angle φ c and always take a constant value. In this case, only the linear expansion coefficient α in the equation (7) changes depending on the angle Φ c.

As can be seen from the above description, according to the first embodiment, uniaxial birefringent crystal constituting the Fuaburipero resonator 3 (such as _{0- BBO (B a Β 2 0} 4)), C -axis of the laser beam Since the C-axis of the parenthesis is located in a plane formed by the optical axis and the polarization direction or in a plane perpendicular to the plane, and the C-axis of the parenthesis is arranged to have a constant inclination with respect to the optical axis, This Fabry-Perot resonator 3 can have a temperature compensation function (a function in which the intensity of the signal light emitted from the Fabry-Perot resonator 3 does not depend on its temperature), and the light intensity monitor signal S 1 depends only on the wavelength of the optical signal. Can be detected and monitored. Also, the wavelength of the optical signal emitted from the semiconductor laser 1 can be controlled to a desired reference wavelength based on the detected light intensity monitor signal S1. Further, since only a uniaxial birefringent crystal of one material is used, the configuration of the semiconductor laser device can be simplified.Since the configuration is simplified, the reliability as a wavelength monitor can be improved. .

In the first embodiment described above, the material of the Fabry-Bore-single resonator 3 is a 3—Β Β Ο crystal. However, when a—BBO (BaB ₂ OJ crystal is used as the material), Thus, the temperature compensation condition (7) can be satisfied.

That is, in the case of α-BBO crystal, when the polarization of the laser beam is aligned with the extraordinary optical axis, <f) C = 64.35 degrees, and when the laser beam is aligned with the ordinary optical axis, φ c = 76. 95 degrees.

At this time, the physical constants of α-BBO are as follows: extraordinary refractive index ne is 1.53003, ordinary refractive index no is 1.6502, and thermo-optic coefficient d no / d T is -9.3 X 1 0 one ⁶ / K, a thermal optical coefficient d ne / dT is ^{1 6. 6 X 10- 6 / K} , in the linear expansion coefficient ratio c is 36. 0 X 10- ⁶ / K, the linear expansion coefficient aa 4 . is a 0X 10- ⁶ / K.

In this case, Ψ c = 64.35 degrees when the polarization of the laser beam was aligned with the extraordinary optical axis, and <ί> c = 76.95 degrees when the polarization of the laser beam was aligned with the ordinary optical axis. However, if the angle is in the vicinity of this, the temperature characteristics can be sufficiently suppressed. For example, in the normal light axis direction, the temperature characteristic is about 1 pm / ° C in the range of about 74 to 80 degrees, which is sufficiently smaller than the temperature characteristic of a conventional solid ethanol port (up to 10 pm / 'C). In addition, for other ψc, if the extraordinary optical axis direction is from 11 pm, ° C to +47 pm / ° C, and the ordinary optical axis direction is from −3 pmZ ° C to +47 pmZ ° C. Any temperature coefficient can be selected. This makes it possible to adjust the wavelength characteristics by changing the temperature, and it is easy to adjust to the ITU grid. For example, the thickness of uniaxial birefringent crystal 3 is set to about 3.6 mm so that FSR = 25 GHz, and Ψc is set so that the temperature characteristic is 8 pm / ° C. In this case, the 1 GHz wavelength characteristic can be shifted by changing the temperature of the uniaxial birefringent crystal 3 by 1 ° C. Therefore, when trying to match the ITU grid with a spacing of 25 GHz to the wavelength control point specified in advance, the temperature of the base carrier 6 on which the semiconductor laser 1 is mounted is changed by up to 25 degrees and the semiconductor laser 1 By changing the oscillation wavelength by adjusting the injection current into the device, it is possible to match the desired wavelength control point. Further, it is possible to satisfy the temperature compensation condition (7) even when had use crystals of L i I 0 ₃ on the material of Fuaburipero resonator 3 in Figure 3. Figure 15 shows the equation (7) for L i IO and the crystal when the polarization of the laser beam is aligned with the extraordinary optical axis. 9 is a graph showing the dependence of n / dT + αη on angle <ί> c. According to FIG. 15, when the L i I 0 ₃ crystal is used and the polarization of the laser beam is aligned with the extraordinary optical axis, the angle ψc satisfying the temperature compensation condition dn / dT + _an = 0 is set to 22. 70 degrees can be determined. Incidentally, using L i I 0 ₃ crystal, when aligned in polarization of the laser beam to the ordinary axis is the angle phi c satisfying the temperature compensation condition dn / dT + αη-Ο is 18.65 degrees. In this case, ψ c = 22.70 degrees when the polarization of the laser light is aligned with the extraordinary optical axis, and Φ c = 18.65 degrees when the polarization of the laser light is aligned with the ordinary optical axis. If the angle is in the vicinity of this, the temperature characteristics can be sufficiently suppressed. For example, in the normal optical axis direction, the temperature characteristic is 1 pmZ ° C in the range of about 15 to 22 degrees, which is much smaller than the temperature characteristic of a conventional solid etalon (up to 10 pmZ ° C). In addition, at other φc, the direction of the extraordinary optical axis is from -20 pmZ ° C to +3 pm / ° C, and the direction of the ordinary optical axis is any temperature from −28 pm, ° C to +3 pmZ ° C. Coefficient can be selected. This makes it possible to adjust the wavelength characteristics by changing the temperature, and it is easy to adjust to the ITU grid. For example, the thickness of the uniaxial birefringent crystal 3 is set to about 3.6 mm so that FSR = 25 GHz, and <i> c is set so that the temperature characteristic is 8 ρπιΖ ^. In this case, by changing the temperature of the uniaxial birefringent crystal 3 by 1 ° C., the 1 GHz wavelength characteristic can be shifted. Therefore, when trying to match the ITU grid with a spacing of 25 GHz to the wavelength control point specified in advance, the temperature of the base carrier 6 on which the semiconductor laser 1 is mounted is changed by up to 25 degrees and the semiconductor laser 1 By changing the oscillation wavelength by adjusting the injection current into the device, it is possible to match the desired wavelength control point. Further, a C a C O ₃ crystal may be used as the uniaxial birefringent crystal. For C a C0 ₃ crystal satisfies the ordinary axial only temperature compensation condition, becomes 67.5 degrees angle phi c satisfying dn / dT + at that time.

In this case, when the polarization of the laser light is aligned with the ordinary optical axis, c is set to 67.5 degrees. However, if the angle is around this, the temperature characteristics can be sufficiently suppressed. For example, in the ordinary optical axis direction, the temperature characteristic is 1 pmZ ° C in the range of about 65 to 70 degrees. This is sufficiently smaller than the temperature characteristics (~ 10 pm / ° C) of the conventional solid nozzle. Furthermore, for other <ί> c, the extraordinary optical axis direction is from +4 pmZT: to +40 pm /, and the ordinary optical axis direction is from -7 pmZ ° C to +40 pmZ ° C. The temperature coefficient can be selected arbitrarily. This makes it possible to adjust the wavelength characteristics by changing the temperature, and it is easy to adjust to the ITU grid. For example, the thickness of the uniaxial birefringent crystal 3 is set to about 3.6 mm so that FSR = 25 GHz, and c is set so that the temperature characteristic is 8 pm / ° C. In this case, it is possible to shift the 1 GHz wavelength characteristic by changing the temperature of the uniaxial birefringent crystal 3 by 1 ° C. Therefore, if an attempt is made to match the wavelength control point specified in advance with the ITU grid of 25 GHz spacing, the temperature of the base carrier 6 on which the semiconductor laser 1 is mounted is changed by a maximum of 25 degrees and the semiconductor laser is changed. By changing the oscillation wavelength by adjusting the injection current to 1, it is possible to match the desired wavelength control point.

In addition, any other uniaxial birefringent crystal may be used as long as the material satisfies the temperature compensation conditional expression (7) for the Fabry-Perot resonator. Also, by combining the wavelength monitoring device shown in FIG. 3 with the wavelength monitoring device shown in FIG. 16, it is possible to construct a wavelength stable light source.

FIG. 17 is a configuration diagram showing a wavelength monitor according to a modification of the first embodiment of the present invention. In the wavelength monitoring device shown in FIG. 17, the second photodiode 5 located above the Fabry-Perot resonator 3 is arranged forward of the first photodiode 4 so as to reduce the distance from the lens 2. . That is, in this case, the location where the second photodiode 5 of the base carrier 6 is installed is protruded toward the semiconductor laser 1, and the location where the first photodiode 4 of the base carrier 6 is installed A step is formed between the base carrier 6 and the position where the second photodiode 5 is provided.

As described above, according to the configuration of FIG. 17, since the second photodiode 5 is arranged ahead of the first photodiode 4, even if the optical signal is Even if the light is scattered on the bottom surface of the base carrier 6 after being incident on the Perot resonator 3, the scattered light is not received by the second photodiode 5 after passing through the Fabry-Perot resonator 3.

Embodiment 2

In the first embodiment, two photodiodes for receiving an optical signal are provided, and each photodiode monitors the wavelength and intensity of the optical signal. On the other hand, in the second embodiment, three photodiodes are arranged, and two Fabry-Perot resonators (wavelength filters) are vertically arranged in parallel, so that the three photodiodes are arranged. The two photodiodes are used to monitor the wavelength of an optical signal in a wide band and a narrow band, and the optical intensity signal is monitored using a single photodiode.

FIG. 18 is a configuration diagram showing a wavelength monitoring apparatus according to Embodiment 2 of the present invention. Note that, of the components of the second embodiment, the same components as those of the wavelength monitoring device of the first embodiment are denoted by the same reference numerals, and the description of those portions is omitted. The temperature and the injection current of the semiconductor laser 1 are controlled by the control signal T1 sent from the wavelength control device 60 shown in FIG. 19 to control the wavelength. The Fabry-Perot resonator (wavelength filter) 21 is the same as the Fabry-Perot resonator (wavelength filter) 3, and is cut out so as to have the temperature compensation function shown in the first embodiment. BBO), and has reflection films 23 and 24 on its entrance and exit surfaces.

In this case, the thickness of the Fabry-Perot resonator 3 arranged on the lower side in the Z direction is made larger than the thickness of the Fabry-Perot resonator 21 arranged on the upper side. The Fabry-Perot resonator 21 is used for broadband monitoring. The third photodiode 22 detects the intensity of an optical signal transmitted through the Fabry-Perot resonator 21, and is arranged between the first photodiode 4 and the second photodiode 5.

Next, the operation of the wavelength monitor shown in FIG. 18 will be described. Semiconductor laser 1 The light signal is condensed by the lens 2 and converted into parallel light. In the first photodiode 4, the intensity of the optical signal transmitted through the Fabry-Perot resonator (for narrow band) 3 is detected, and in the third photodiode 22, the optical signal transmitted through the Fabry-Perot resonator (for wide band) 21 The intensity is detected. The light intensity monitor signal detected by the first photodiode 4 is S1, the light intensity monitor signal detected by the third photodiode 22 is S3, and the light intensity monitor signal is detected by the second photodiode 5. The light intensity monitor signal is S2. The light intensity monitor signals S1, S2 and S3 are sent to the wavelength control device 60 shown in FIG. The wavelength control device 60 detects the oscillation wavelength using these signals S1, S2, and S3, and controls the control signal T for controlling the wavelength of the optical signal emitted from the semiconductor laser 1 based on the detected wavelength. The control signal T 1 is output to the semiconductor laser 1.

FIG. 20 shows the wavelength transmission characteristics of the Fabry-Perot resonator 3 for the narrow band and the Fabry-Perot resonator 21 for the wide band.

As shown in Fig. 20, the FSR of the Fabry-Perot resonator 3 for the narrow band is set to be very small compared to the FSR of the Fabry-Perot resonator 21 for the wide band. I do. Further, half of the FSR of the Fabry-Perot resonator 21 for a wide band, that is, the wavelength discrimination region is larger than the wavelength variable range of the semiconductor laser 1, and the wavelength variable range of the semiconductor laser 1 is 1 in the FSR of the Fabry-Perot resonator 21. Suppose it is within one slope. For example, the Fabry-Perot resonator 3 for narrow band has an FSR of 20 THz, the intensity reflectance of the reflective film is 30%, the FSR of the Fabry-Perot resonator 21 for broadband is 10 OGHz, and the intensity reflectance of the reflective film is Assume 30%.

Next, the configuration of the wavelength control device 60 shown in FIG. 19 will be described. The wavelength control device 60 includes a wavelength detection unit 61 and a laser control unit 52. The light intensity monitor signals S 1, S 2, S 3 from the first to third photodiodes 4, 5, and 22 and the reference wavelength; 0 are input to the wavelength detector 61. The wavelength detecting section 61 outputs an optical signal emitted from the semiconductor laser 1 by the light intensity monitor signals S1, S2, and S3. The difference between this oscillation wavelength and the reference wavelength; 0 is found. The difference between the reference wavelength λ 0 from the wavelength detection unit 61 and the oscillation wavelength emitted from the semiconductor laser 1 is input to the laser control unit 52, and the laser control unit 52 determines the oscillation wavelength according to the difference. A control signal Τ1 for controlling the temperature, injection current, and the like of the semiconductor laser 1 is determined so that the control signal に coincides with the reference wavelength λ 0, and the control signal Τ1 is output to the semiconductor laser 1.

The operation of the wavelength detector 61 will be described in detail. First, the wavelength detection unit 61 detects a shift from the reference wavelength; 0 using the light intensity monitor signal S3 transmitted through the Fabry-Perot resonator 21 for a wide band. That is, as described above, the wavelength detector 61 has a signal intensity ratio S 1 / S 2 at the reference wavelength λ 0, which is obtained in advance using the wavelength transmission characteristics of the Fabry-Perot resonator 21 for a wide band. By obtaining the difference between the signal intensity ratio S 3 / S 2 obtained based on the light intensity monitor signals S 2 and S 3 from the second and third photodiodes 5 and 22, the oscillation wavelength and the reference wavelength are obtained. Calculate the deviation (deviation) from λ 0.

If this deviation amount is larger than the slope width of the narrow-band fabric resonator 3, this value is sent to the laser control unit 52 as it is. However, if the deviation from the reference wavelength calculated from the light intensity monitor signals S 3 and S 2; I 0 is smaller than the slope width of the narrow-band Fabry-Perot resonator 3, the narrow-band Fabry-Perot resonance By using the slope characteristics of the detector 3 again to calculate the amount of deviation from the reference wavelength 0, the oscillation wavelength is detected with higher accuracy. That is, a reference wavelength previously calculated using the wavelength transmission characteristics of the Fabry-Perot resonator 3 for a narrow band; a signal intensity ratio S 1 / S 2 at 0; and light from the first and second photodiodes 4 and 5. The difference (deviation) between the oscillation wavelength and the reference wavelength λ 0 is calculated by calculating the difference between the signal intensity ratio S 3 / S 2 obtained based on the intensity monitor signals S 1 and S 2. The deviation amount (deviation signal) thus obtained is sent to the laser control unit 52.

Laser control unit 52 operates in the same manner as in the first embodiment. That is, the laser control unit 52 uses the deviation signal input from the wavelength detection unit 61 to output a control signal Τ1 for changing the value of the temperature or the injection current to the semiconductor laser 1. Thus, the wavelength of the semiconductor laser 1 is controlled.

Since one slope in the FSR 內 of the Fabry-Perot resonator 21 for a wide band is larger than the wavelength tunable region of the semiconductor laser 1, the absolute wavelength can be monitored over a wide band. However, as shown in FIG. 20, the wavelength transmission characteristic of the Fabry-Perot resonator 21 for a wide band is more dependent on the wavelength change than the wavelength transmission characteristic of the resonator element 3 for a narrow band. Is small. That is, the light intensity monitor signal S3 has a smaller signal intensity change with respect to the wavelength change than the light intensity monitor signal S1.

Therefore, when the value of S 3 / S 2 is deviated from the set value, the wavelength is largely deviated as compared with the case where the value of S 1 / S 2 is deviated by the same value. Therefore, the wavelength of the optical signal emitted from the semiconductor laser 1 can be fixed more accurately by using the optical signal intensity S1 transmitted through the Fabry-Perot resonator 3, which is a wavelength monitor for a narrow band.

The resonators of the resonators 3 and 21 are arranged such that the lower Fabry-Perot resonator 3 is used as a wavelength monitor for a wide band and the upper Fabry-Perot resonator 21 is used as a wavelength monitor for a narrow band. The length may be adjusted.

As described above, according to the second embodiment, the absolute wavelength of the optical signal emitted from the semiconductor laser 1 can be controlled with high accuracy over a wide band. Note that a wavelength stabilized light source can be configured by combining the wavelength monitoring device shown in FIG. 18 with the wavelength control device shown in FIG.

FIG. 21 is a configuration diagram showing a wavelength monitor according to a modification of the second embodiment of the present invention. In the wavelength monitor shown in FIG. 21, the second and third photodiodes 5, 22 located above the Fabry-Perot resonator 3 are connected to the first photodiode 4 so that the distance from the lens 2 is reduced. To the front. In this case, the location where the second and third photodiodes 5, 22 of the base carrier 6 are installed is configured to protrude toward the semiconductor laser 1, and the first photodiode 4 of the base carrier 6 is mounted. Location and location of base carrier 6 A step is formed between the third photodiode 5 and the place where the third photodiodes 22 are installed.

As described above, according to the configuration shown in FIG. 21, the second and third photodiodes 5, 22 are arranged in front of the first photodiode 4, so that the optical signal is Fabry. Even if the scattered light is transmitted through the Fabry-Perot resonator 3 and then scattered on the bottom surface of the base carrier 6 after being incident on the mouth resonator 3, it is received by the second and third photodiodes 5 and 22. Disappears. Industrial applicability

INDUSTRIAL APPLICABILITY The present invention is suitable for use as a wavelength filter or a wavelength monitor of a semiconductor laser as a light source used in wavelength division multiplexing (WDM) communication and high-density wavelength division multiplexing (DWDM) communication using an optical fiber. . In addition, it is required to select or monitor the wavelength of laser light with high accuracy without being affected by temperature fluctuations, and it is suitable for systems that require simplification of structure and assembly.

Claims

The scope of the claims

1. Light transmitting solid material,

A substantially parallel opposing plane formed on the solid material,

A wavelength filter that resonates light between substantially parallel opposing planes and periodically selects a wavelength determined by an optical path length between the opposing planes,

A wavelength filter, wherein the solid material is a birefringent material, and an optical axis of the birefringent material has a predetermined angle with respect to a normal line of the substantially parallel opposed plane.

2. The predetermined angle between the normal of the substantially parallel opposing plane and the optical axis is set so that the temperature coefficient of the optical path length between the planes has a predetermined value. The wavelength according to claim 1 that:

3. The birefringent material has a normal and an optical axis which are substantially parallel to each other so that the absolute ^! Of the sum of the product of the refractive index and the linear expansion coefficient in the optical axis direction and the thermo-optic coefficient is minimized. 3. The wavelength filter according to claim 2, wherein an angle with an axis is set.

4. The birefringent material is the sum of the product of the linear expansion coefficient in the direction parallel to the optical axis and the refractive index of light propagating parallel to the optical axis, and the thermo-optic coefficient of light propagating parallel to the optical axis. And the sum of the product of the linear expansion coefficient in the direction perpendicular to the optical axis and the refractive index of light propagating in the direction perpendicular to the optical axis and the thermo-optic coefficient of light propagating in the direction perpendicular to the optical axis are mutually The wavelength according to claim 2, wherein the wavelengths are different from each other.

. 5 the birefringent material, alpha-BBO crystal, - beta beta Omicron crystal, L i I 0 ₃ crystals, according to C a C_〇 ₃ claim 4, characterized in that either crystalline Wavelength filter.

6. The light incident on the birefringent material uses polarized light aligned with the extraordinary optical axis,

If the birefringent material is α-B B Ο crystal, the angle of the optical axis to the optical axis should be about 64 degrees,

If the birefringent material is a 0-Β Β Ο crystal, the angle of the optical axis to the optical axis should be about 65 degrees,

If the birefringent material is a L i I 0 _3, the wavelength filter according to claim 5, wherein approximately 2 3 degrees and to Rukoto an angle with respect to the optical axis of the optical axes.

7. The light incident on the birefringent material uses polarized light aligned with the ordinary optical axis.

If the birefringent material is α-B B Ο crystal, the angle of the optical axis to the optical axis should be about 77 degrees,

If the birefringent material is a 33 Β Ο Ο crystal, the angle of the optical axis to the optical axis should be about 57 degrees,

If the birefringent material is a L i I 0 ₃ crystal, the angle with respect to the optical axis of the optical axis is about 1 9 degrees,

If the birefringent material is a C a C_〇 ₃ crystal, the wavelength filter according to claim 5, characterized in that an angle of about 6 6 degrees with respect to the optical axis of the optical axes.

8. In a wavelength monitoring device for monitoring the wavelength of laser light output from a semiconductor laser,

A solid material that transmits laser light;

A substantially parallel opposing plane formed on the solid material,

A wavelength filter that resonates the laser light between the substantially parallel opposed planes and periodically selects a wavelength determined by an optical path length between the opposed planes;

A wavelength detecting means for measuring an oscillation wavelength of the laser light based on the transmitted light of the wavelength filter,

The solid material is a birefringent material, and the optical axes of the solid materials oppose substantially in parallel. A wavelength monitor having a predetermined angle with respect to a normal to a plane.

9. The laser light output from the semiconductor laser is polarized in one direction,

The birefringent material forming the wavelength filter has an optical axis in a plane parallel to a plane formed by the optical axis and the polarization direction of the laser light, and the optical axis is a predetermined optical axis with respect to the optical axis of the laser light. 9. The wavelength monitoring device according to claim 8, wherein the wavelength monitoring device is inclined at an angle.

10. The laser light output from the semiconductor laser is polarized in one direction, and the birefringent material forming the wavelength filter is a plane formed by the optical axis and the polarization direction of the laser light. 9. The wavelength monitor according to claim 8, wherein an optical axis is in a plane perpendicular to the optical axis, and the optical axis is inclined at a predetermined angle with respect to an optical axis of the laser beam.

11. The birefringent material constituting the wavelength filter is characterized in that the angle of the optical axis with respect to the optical axis is set based on the refractive index of the crystal, the coefficient of linear expansion in the optical axis direction, and the thermo-optic coefficient. 9. The wavelength monitor according to claim 8.

12. The predetermined angle between the normal to the substantially parallel opposing plane and the optical axis is set so that the temperature coefficient of the optical path length between the planes has a predetermined value. 9. The wavelength monitor according to claim 8.

1 3. The birefringent material should have a normal to a plane substantially parallel to the plane so as to minimize the absolute ^: of the sum of the product of the refractive index and the coefficient of linear expansion in the optical axis direction and the thermo-optic coefficient. The wavelength monitor according to claim 12, wherein an angle with respect to an optical axis is set. Data device.

1 4. The birefringent material is the sum of the product of the linear expansion coefficient in the direction parallel to the optical axis and the refractive index of light propagating parallel to the optical axis, and the thermo-optic coefficient of light propagating parallel to the optical axis. And the sum of the product of the linear expansion coefficient in the direction perpendicular to the optical axis and the refractive index of light propagating in the direction perpendicular to the optical axis and the thermo-optic coefficient of light propagating in the direction perpendicular to the optical axis are different from each other. 13. The wavelength monitor according to claim 12, wherein the wavelength monitor is a code.

1 5. the birefringent material, alpha-BB Omicron crystal, / 3- Β Β Ο crystals, L i I 0 ₃ crystal, C a CO ₃ ranging first claim, characterized in that either crystalline The wavelength monitor according to item 4.

1 6. Light incident on the birefringent material uses polarized light aligned with the extraordinary optical axis.

If the birefringent material is a ct-B BO crystal, the angle of the optical axis to the optical axis should be about 64 degrees,

If the birefringent material is / 3—BBO crystal, the angle of the optical axis to the optical axis should be about 65 degrees,

16. The wavelength monitor according to claim 15, wherein when the birefringent material is Li IO ₃ , the angle of the optical axis with respect to the optical axis is about 23 degrees.

1 7. Light incident on the birefringent material uses polarized light aligned with the ordinary optical axis.

When the birefringent material is a single BBO crystal, the angle of the optical axis to the optical axis is about 77 degrees,

If the birefringent material is a J3-BBO crystal, the angle of the optical axis to the optical axis should be about 57 degrees,

If the birefringent material is a L i I 0 ₃ crystal, the angle with respect to the optical axis of the optical axis is about 1 9 degrees, If the birefringent material is a C a C_〇 ₃ crystal, wavelength monitor device according to claim Section 15 claims, characterized in that an angle of about 66 degrees with respect to the optical axis of the optical axes.

18. The birefringent material constituting the wavelength filter has an angle of the optical axis with respect to the optical axis such that the sum of the product of the refractive index and the linear expansion coefficient in the optical axis direction and the thermo-optic coefficient are zero. 10. The wavelength monitor according to claim 9, wherein the wavelength monitor is set.

19. The angle of the optical axis with respect to the optical axis is set so that the sum of the product of the refractive index and the coefficient of linear expansion in the optical axis direction and the thermo-optical coefficient is zero. The wavelength monitor device according to claim 10, wherein the wavelength monitor device is set.

20. birefringent material forming the wavelength filter, _alpha - and BBO,] 3- BBO, either as L i I 0 _3,

If the birefringent material is α-BBO, the angle of the optical axis to the optical axis is 63.35 degrees,

If the birefringent material is i3—BBO, the angle of the optical axis to the optical axis is 64.75 degrees,

If the birefringent material is a L i I 0 _3, wavelength monitor device according to claim 18, wherein claims, characterized in that the angle 22.70 degrees with respect to the optical axis of the optical axes.

21. birefringent material forming the wavelength filter, alpha-and ΒΒΟ, β-ΒΒΟ, either as _{L i L0 3, C a CO} 3,

If the birefringent material is α—B Β 角度, the angle of the optical axis to the optical axis is 76.95 degrees,

If the birefringent material is J3—BBO, the angle of the optical axis to the optical axis is 57.05 degrees, If the birefringent material is a L i L 0 _3, the angle with respect to the optical axis of the optical axis is 1 8.6 5 degrees,

10. The wavelength monitor according to claim 19, wherein when the birefringent material is CaCO ₃ , the angle of the optical axis with respect to the optical axis is set to 67.05 degrees.

2 2. The birefringent material that constitutes the above wavelength filter can maintain the set angle to the optical axis and change the thickness in the optical axis direction to satisfy the temperature compensation condition and adjust the wavelength discrimination area. 9. The wavelength monitor according to claim 8, wherein:

23. The method according to claim 8, further comprising a lens that adjusts a beam size of laser light emitted from the semiconductor laser and outputs the adjusted laser light to the wavelength filter. Wavelength monitor.

24. The wavelength detecting means,

A first photodetector that detects light transmitted through the wavelength filter;

A second photodetector for directly detecting laser light output from the semiconductor laser, and a wavelength for detecting an oscillation wavelength of the laser light using a ratio of detection signals of the first and second photodetectors. A detection unit;

9. The wavelength monitoring device according to claim 8, comprising:

25. The semiconductor laser and the wavelength filter are mounted, and the first and second photodetectors are installed so that the second photodetector is located above the first photodetector. Further equipped with a base carrier,

25. The apparatus according to claim 24, wherein the height of the wavelength filter is adjusted so that the laser light transmitted through the wavelength filter mounted on the base carrier is not received by the second photodetector. The wavelength monitor according to the item.

26. The semiconductor laser and the wavelength filter are mounted, and the first and second photodetectors are installed so that the second photodetector is located above the first photodetector. Further equipped with a base carrier,

The second photodetector is more wavelength-filtered than the first photodetector so that the laser light transmitted through the wavelength filter mounted on the base carrier is not received by the second photodetector. 25. The wavelength monitor according to claim 24, wherein the wavelength monitor is arranged close to the side.

27. In a wavelength monitor that monitors the wavelength of laser light output from a semiconductor laser,

Resonating the laser light between a first solid material that transmits the laser light, a plane formed on the first solid material that faces substantially parallel, and a plane that faces substantially parallel to each other; A wavelength determined by an optical path length is periodically selected, and the solid-state material is a birefringent material, and the optical axis of the solid-state material has a predetermined angle with the normal of the substantially parallel opposed flat surface. A first wavelength filter;

Causing the laser light to resonate between a second solid material that transmits the laser light, a plane formed on the first solid material that faces substantially parallel, and a plane that faces substantially parallel to each other; The wavelength for which the optical path length is determined is periodically selected, and the solid material is a birefringent material, and the optical axis thereof has a predetermined angle with the normal of the plane substantially parallel to each other. 2 wavelength filters,

Wavelength detecting means for measuring the oscillation wavelength of the laser light based on the transmitted light of the first and second wavelength filters;

A wavelength monitor device comprising:

28. The laser light output from the semiconductor laser is polarized in one direction, The birefringent material forming the first and second wavelength filters has an optical axis in a plane parallel to a plane formed by the optical axis and the polarization direction of the laser light, and this optical axis is 28. The wavelength monitor according to claim 27, wherein the wavelength monitor is inclined at a predetermined angle with respect to the optical axis.

29. The laser light output from the semiconductor laser is polarized in one direction,

The birefringent material forming the wavelength filter has an optical axis in a plane perpendicular to a plane formed by the optical axis and the polarization direction of the laser light, and the optical axis is a predetermined angle with respect to the optical axis of the laser light. 28. The wavelength monitoring device according to claim 27, wherein the device is inclined at an angle.

30. The wavelength discriminating region of the second wavelength filter for the wide band is larger than the wavelength variable region of the semiconductor laser, and the wavelength discriminating region of the first wavelength filter for the narrow band is the wavelength variable region of the first wavelength filter. 28. The wavelength monitor according to claim 27, wherein the thickness in the optical axis direction of the birefringent material constituting the first and second wavelength filters is set so as to be sufficiently smaller than the wavelength monitor. .

3 1. The wavelength detecting means,

A first photodetector that detects transmitted light of the first wavelength filter,

A second photodetector that directly detects a laser beam output from the semiconductor laser; and a third photodetector that detects transmitted light of the second wavelength filter.

A wavelength detector that detects the oscillation wavelength of the laser light using the ratio of the detection signals of the first and second photodetectors and the ratio of the detection signals of the third and second photodetectors. 28. The wavelength monitor according to claim 27, wherein:

32. While mounting the semiconductor laser and the wavelength filter, And a base carrier for installing the first to third photodetectors such that the third photodetector is located above the first photodetector,

The second and third photodetectors are set to a higher position than the first photodetector so that the laser light transmitted through the wavelength filter mounted on the base carrier is not received by the second and third photodetectors. 28. The wavelength monitor according to claim 27, wherein the wavelength monitor is arranged close to the wavelength filter.