WO2004070468A1

WO2004070468A1 - Optical switch device

Info

Publication number: WO2004070468A1
Application number: PCT/JP2003/001373
Authority: WO
Inventors: Takashi Yamane; Toshiya Kishida; Manabu Komiyama
Original assignee: Fujitsu Limited
Priority date: 2003-02-10
Filing date: 2003-02-10
Publication date: 2004-08-19
Also published as: JP4282606B2; JPWO2004070468A1

Abstract

Incoming light from an input optical fiber (10) is split into a P polarized light and an S polarized light in a doubly refracting crystal plate (16). By controlling the voltage on an liquid crystal element (26) having an electrode corresponding to each axis of polarization, the P polarized light is converted into the S polarized light to obtain only S polarized light, or the S polarized light is converted into the P polarized light to obtain only P polarized light. A polarization separating film (30) provided on a back of the liquid crystal element (26) transmits the P polarized light and reflects the S polarized light. If only the S polarized light is present in the liquid crystal element (26), the light reflected by the polarization separating film (30) is reflected by a total reflection film (32), again reflected by the polarization separating film (30), again incident on the doubly refracting crystal plate (16) via the liquid crystal element (26), returned to the non-polarized light in the doubly refracting crystal plate (16), and incident on a first output optical fiber (12). If only the P polarized light is present in the liquid crystal element (26), the light is transmitted through the polarization separating film (30) to be incident on a doubly refracting crystal plate (18) via a liquid crystal element (28), returned to the non-polarized light, and incident on a second output optical fiber (14).

Description

Technical Information Hikari Switch

The present invention relates to an optical switch device. Background art

In recent years, the increase in optical communication capacity is urgently required due to the increase in Internet traffic. Measures to increase communication capacity include increasing bit rates and wavelength multiplexing (WDM), and the realization of optical devices that make up these systems is urgent.

WDM transmission is a technique for transmitting a large number of wavelengths through one optical fiber, and increases the capacity by transmitting information to each wavelength. In these WDM transmission systems, for example, an optical switch with a small channel is almost always used, for example, a redundant configuration is established by switching ports, and monitoring is performed by switching ports.

Also, when transmitting in an optical fiber, the propagation loss at each wavelength is different, and the light level after long-distance transmission changes at each wavelength. This phenomenon becomes more pronounced when a branching device or EDF amplifier is used in the transmission path.

For this reason, it is necessary to keep the optical level at each wavelength constant before transmitting or receiving light. As a solution to this, a variable attenuator device that controls the level of each wavelength and an optical switch are used to control the optical output during transmission and the optical output during reception to be constant. The device is being devised.

However, when assuming WDM transmission, light is transmitted for each wavelength (channel). In order to set the level, it is necessary to provide an attenuator-optical switch that can change the light for each channel. At present, the actual situation is that individual devices are mounted in the equipment, which leads to an increase in the size and cost of the equipment. Techniques using waveguides (PLCs) have been developed as measures for miniaturization, but the configuration is inadequate in terms of cost and size.

Patent Document 1

JP-A-5-113582 (Fig. 3 (a))

Patent Document 2

Patent No. 3008964

Patent Document 3

Japanese Patent Laid-Open No. 5-204000 Disclosure of the Invention

The present invention proposes, as one of means for solving the above-described problems, a device that achieves both optical path switching and variable optical output while using a small channel.

According to the present invention, unpolarized light incident from the first surface is converted into polarized light in the first direction, and polarized light in the first direction incident from the second surface opposite to the first surface is converted to unpolarized light. A polarization control unit that can be switched according to a control signal between a first state for conversion, and a second state for converting unpolarized light incident from the first surface to polarized light in the second direction, and a polarization control unit. A polarization separating unit that reflects polarized light in the first direction and transmits polarized light in the second direction; and a reflecting unit that reflects light reflected by the polarized light separating unit and reenters the polarized light into the polarized light separating unit. An optical switch device arranged so that the polarized light in the first direction reflected by the reflecting portion and reflected again by the polarized light separating portion is incident on the second surface of the polarization controlling portion. Is provided. It is preferable that the optical switch device further includes a polarization state recovery unit that returns the polarized light in the second direction transmitted through the polarization separation unit to non-polarized light.

The polarization controller includes, for example, a first birefringent crystal that separates non-polarized light into polarized light in a first direction and polarized light in a second direction, and a polarization direction of polarized light in a second direction from the birefringent crystal. And a second state in which the polarization direction of the polarized light in the first direction from the birefringent crystal is rotated into a polarized light in the second direction. And a first liquid crystal element that can be switched between according to a control signal.

The polarization separation unit includes, for example, a polarization separation film provided on a first surface of the prism, and the reflection unit includes a reflection film provided on a second surface of the prism.

The polarization state recovery unit is, for example, a part of the second-direction polarized light transmitted through the polarization separation unit, and a part originating from the second-direction polarized light in the first birefringent crystal. A second liquid crystal element that converts the light into polarized light in the first direction, the remaining part of the polarized light in the second direction that has passed through the polarization splitter, and the polarized light in the first direction that has been converted by the liquid crystal element. The second birefringent crystal to be non-polarized.

As another example, the polarization state recovery unit is a part of the polarization in the second direction transmitted through the polarization separation unit, and originates from the polarization in the second direction in the first birefringent crystal. A half-wave plate for converting a portion to be polarized into a first direction of polarized light, a remaining portion of the polarized light in the second direction transmitted through the polarization splitter, and a first half-wave plate converted by the half-wave plate. Includes a second birefringent crystal that combines polarized light in different directions to make it unpolarized. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a side view of one embodiment of the optical switch device of the present invention; Figure 2 is a plan view of the device of Figure 1;

Figure 3 is a diagram of the prism 34;

'Figure 4 is a graph showing the characteristics of the polarization separation membrane 30;

Figure 5 is a plan view schematically showing the light path when 0UT1 is selected as the output light;

Figure 6 is a side view of Figure 5;

Figure 7 is a plan view schematically showing the optical path when 0UT2 is selected as the output light;

Figure 8 is a side view of Figure 7;

FIG. 9 is a graph illustrating the light output variation by voltage control of the liquid crystal element 28; and

FIG. 10 is a side view of an optical switch device having a level monitor function. BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 (side view) and FIG. 2 (plan view) show an optical output variable switch device according to an embodiment of the present invention. This device consists of optical fibers 10, 12, 14, birefringent crystal plates 16, 18, lenses 20, 22, 24, liquid crystals 26, 28, and a prism 34 provided with a polarization separation film 30 and a reflection film 32. It realizes a very small device configuration. Reference numerals 36 and 38 denote fiber blocks that hold the optical fibers, and reference numeral 40 denotes a transparent medium such as glass that is the same size as the prism 34. The overall configuration is a 1X2 switch with one of the two fibers 10, 12 as input, the other as 0UT1, and the port on the opposite side of the transmission direction as 0UT2. The port of 0UT1 or 0UT2 can be selected by controlling the voltage of the liquid crystal 26, and the light output of 0UT2 can be changed by controlling the voltage of the liquid crystal 28.

The basic principle will be described below. Incident from 10 on one side of 2-core fiber The incident light enters the birefringent crystal plate 16 via the lens 20. The light incident on the birefringent crystal plate 16 is separated into ordinary light (P-polarized light) and extraordinary light (S-polarized light) and travels inside the crystal. Here, a liquid crystal 26 having electrodes corresponding to the P polarization axis and the S polarization axis at the exit of the birefringent crystal 16 is formed. In addition, a cube-shaped prism 34 (see Fig. 3) with a polarization splitting film 30 and a total reflection film 32 provided behind the liquid crystal element 26, reflects and transmits the liquid crystal 26 by turning it on and off. It is configured so that can be selected. Here, the characteristics of the polarization separation film 30 have the characteristics shown in FIG. 4, and the reflection film 32 is a normal total reflection film characteristic. The input light is split into ordinary light (P-polarized light) and extraordinary light (S-polarized light) by the birefringent crystal plate 16, and enters the liquid crystal element 26 immediately after passing through the birefringent plate 16. The light whose polarization direction is controlled by the liquid crystal element 26 is incident on the polarization splitting film 30, and if it is S-polarized light, it is reflected upward and is turned back by the total reflection film 32 formed on the top to return to the original. It will return to the optical axis. If it is P-polarized light, it will pass through the polarization separation film 30. Here, by turning ON / OFF the voltage of the electrode corresponding to the P-polarized light of the liquid crystal element 26, the polarization direction of the ordinary light (P-polarized light) from the birefringent crystal plate 16 is rotated by 90 ° or passed as it is. By doing so, reflection or transmission of the polarization separation film 30 can be selected. Further, by providing the liquid crystal element 28 ahead of the prism 34 and controlling the direction of polarization incident on the next birefringent crystal plate 18, output in the 0UT2 direction becomes possible. On the other hand, the same applies to the extraordinary light (S-polarized light). The 0N / 0FF control of the electrodes of the liquid crystal element 26 corresponding to the S-polarized light changes the light incident on the polarization separation film 30, whereby Transmission and reflection are selected, and in the case of transmission, output to the 0UT2 port is enabled by the liquid crystal 28 provided at the back of the prism.

Specifically, when 0UT1 is selected as the output destination, as shown schematically in FIG. 5 (plan view) and FIG. 6 (side view), the P-polarized light from the birefringent crystal 16 in the liquid crystal 26 Electrode (A electrode) corresponding to the polarization axis (solid line) Pole) is turned ON, and the electrode (B electrode) corresponding to the polarization axis of S-polarized light (broken line) is turned OFF. As a result, when the P-polarized light from the birefringent crystal 16 passes through the liquid crystal, it changes to S-polarized light and becomes all S-polarized light, and is reflected by the polarization separation film 30. The S-polarized light reflected by the polarization separation film 30 is reflected by the total reflection film 32, reflected again by the polarization separation film 30, and enters the liquid crystal 26 again. In the liquid crystal 26, at the A electrode portion, the S-polarized light reflected by the polarization separation film 30 and returned (the P-polarized light from the birefringent crystal 16 is converted to the S-polarized light) passes through the liquid crystal 26 when The other S-polarized light (S-polarized light from the birefringent crystal 16) is changed to polarized light, enters the B electrode (OFF state), enters the birefringent crystal 16 as S-polarized light, is synthesized, and is output from 0UT1. .

When 0UT2 is selected as the output destination, the A electrode is turned off and the B electrode is turned on, contrary to the above, as schematically shown in Figure 7 (plan view) and Figure 8 (side view). . As a result, the S-polarized light is changed to the P-polarized light, and is transmitted through the polarization separation film 30. By turning the A electrode of liquid crystal 28 to 0N and the B electrode to OFF, a part of the transmitted P-polarized light (P-polarized light from birefringent crystal 16) is changed to S-polarized light, and the remaining birefringent crystal 18 Combined with P-polarized light (S-polarized light from birefringent crystal 16 converted to P-polarized light) and output from 0UT2.

Here, by minutely controlling the voltage applied to the liquid crystal element 28, the optical output output to the 0UT2 can be varied. Specifically, by having a light component different from the light component that can be coupled to the 0UT2 port via the birefringent crystal plate provided behind the liquid crystal 28, it becomes 0U

Loss due to failure to couple to T2 port. That is, fine light output variation can be realized by minute control of the voltage of the liquid crystal element 28 (see FIG. 9).

As described above, a small and inexpensive optical output variable switch device can be realized.

Optical fibers 10 and 12 include, for example, a two-core fiber assembly. Alternatively, two single-core fiber assemblies are used, and the interval between the optical fibers 10 and 12 is, for example, about 300 m. The lenses 20, 22, and 24 are collimating lenses, and are arranged near the center of the lens so as to form a folded reflection optical system such that light incident from the optical fiber 10 and reflected by the films 30 and 32 enters the optical fiber 12. The optical axis is formed at a position off the outer periphery. The turning point of the reflection type optical axis is the rear part of the prism 34 (the interface with the liquid crystal plate 28), as shown in FIGS. As the birefringent crystal plate 16, for example, rutile (1 mm d X 3 min length, separation pitch: 300 μπι) is used, and the lens 20 and the liquid crystal 26 are fixed with an optical adhesive. Each component may be configured so that an optical system can be established on a base member. On the liquid crystal element 26, for example, electrodes of about 250 μm square are formed in the P polarization port and the S polarization port, respectively. The prism 34 provided with the polarization separation film 30 and the total reflection film 32 is made of, for example, quartz or glass, and each film is formed of a dielectric multilayer film or a metal film. The prism size is about 2 mm square. The liquid crystal 28 formed on the side of the 0UT2 port may be the same as the liquid crystal 26 described above, and the birefringent crystal plate 18 formed at the rear thereof also has the above-described rutile (1 mm square X 3 mm length, separation pitch: 300 μm). m) is used. The OUT fiber 14 has one core and one lens 24. For example, an integrated lens and fiber may be used.

Each of these elements is fixed with an optical adhesive, and the whole is stored and fixed in a pre-mold package. As a result, an optical switch (1 X 2) capable of varying the optical output with a width of about 5 mm, a length of 20 mm, and a height of 3 mm can be configured.

A level monitor for monitoring the light level after changing the light output can be provided. A PD (photodiode) element is used for the level monitor, and the voltage applied to the liquid crystal is controlled by a feed-pack circuit using the PD current output outside the device. As shown in Figure 10, As a monitoring method, a force blur film 50 is formed in front of the 0UT2 port to guide light to the PD element 52. As the PD element 52 used here, a back-illuminated PD is used to make the entire device compact, and the PD element 52 is directly adhered and fixed to the coupler prism with an optical adhesive below the force-blown film 50. FIG. 10 further shows a power plastic film 54 and a PD element 56 for monitoring the light level on the 0UT1 side.

If the optical output of 0UT2 is not variable, a half-wave plate may be provided only in the area corresponding to the A port instead of the liquid crystal 28.

Claims

The scope of the claims

1. The first type that converts non-polarized light incident from the first surface into polarized light in the first direction and converts polarized light in the first direction incident from the second surface opposite to the first surface into non-polarized light. A polarization control unit that can be switched according to a control signal between a non-polarized state incident from the first surface and a second state that converts the non-polarized state incident to the polarized light in the second direction;

A polarization separation unit that reflects polarized light in the first direction from the polarization control unit and transmits polarized light in the second direction;

A reflection unit for reflecting the light reflected by the polarization separation unit and re-entering the polarization separation unit;

The polarization switching unit and the reflection unit are optical switch devices arranged so that the polarized light in the first direction reflected by the reflection unit and reflected again by the polarization separation unit is incident on the second surface of the polarization control unit. .

2. The optical switch device according to claim 1, further comprising a polarization state recovery unit for returning polarized light in the second direction transmitted through the polarization separation unit to non-polarized light.

3. The polarization control unit includes: a first birefringent crystal that separates unpolarized light into polarized light in a first direction and polarized light in a second direction;

The first state in which the polarization direction of the polarization in the second direction from the birefringent crystal is rotated to the polarization in the first direction, and the polarization direction of the polarization in the first direction from the birefringent crystal is rotated. 3. The optical switch according to claim 2, further comprising a first liquid crystal element that can be switched between a second state and a second state of polarization in accordance with a control signal.

4. The polarization separation unit includes a polarization separation film provided on the first surface of the prism,

The reflection unit includes a reflection film provided on a second surface of the prism The optical switch device according to claim 2 or 3.

5. The polarization state recovery unit is a part of the polarized light in the second direction that has passed through the polarization splitting unit, and a part of the first birefringent crystal originating from the polarized light in the second direction is the first. A second liquid crystal element that converts the polarized light into

4. A second birefringent crystal, which combines the remaining part of the polarized light in the second direction transmitted through the polarized light separating portion and the polarized light in the first direction converted by the liquid crystal element to make the polarized light non-polarized. An optical switch device as described.

6. The polarization state recovery section is a part of the polarized light in the second direction transmitted through the polarization splitting section, and is a part of the first birefringent crystal. A half-wave plate that converts the portion originating from the polarized light in the direction to the polarized light in the first direction;

A second birefringent crystal that combines the remaining part of the polarized light in the second direction transmitted through the polarized light separating portion and the polarized light in the first direction converted by the half-wave plate to make it unpolarized. Item 3. An optical switch device according to item 3.