CA2163630C - Frequency-selective optical switch using polarization rotation - Google Patents
Frequency-selective optical switch using polarization rotationInfo
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- CA2163630C CA2163630C CA002163630A CA2163630A CA2163630C CA 2163630 C CA2163630 C CA 2163630C CA 002163630 A CA002163630 A CA 002163630A CA 2163630 A CA2163630 A CA 2163630A CA 2163630 C CA2163630 C CA 2163630C
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- dispersive element
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2706—Optical coupling means with polarisation selective and adjusting means as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters
- G02B6/2713—Optical coupling means with polarisation selective and adjusting means as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters cascade of polarisation selective or adjusting operations
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
- G02B6/2773—Polarisation splitting or combining
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
- G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
- G02B6/2931—Diffractive element operating in reflection
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1347—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
- G02F1/13471—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
- G02F1/31—Digital deflection, i.e. optical switching
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
- H04Q11/0003—Details
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
- G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
- G02F1/141—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent using ferroelectric liquid crystals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
- H04Q11/0005—Switch and router aspects
- H04Q2011/0007—Construction
- H04Q2011/0022—Construction using fibre gratings
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
- H04Q11/0005—Switch and router aspects
- H04Q2011/0007—Construction
- H04Q2011/0024—Construction using space switching
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
- H04Q11/0005—Switch and router aspects
- H04Q2011/0007—Construction
- H04Q2011/0035—Construction using miscellaneous components, e.g. circulator, polarisation, acousto/thermo optical
Abstract
A frequency-selective optical switch capable of switching separate optical signals in a physical input channel to a selected output channel. A diffraction grating (12) spatially divides the input channel (10) into its frequency components, which pass through different segments of a liquid-crystal modulator (24). The liquid-crystal modulator segments (20, 22) are separately controlled to rotate the polarization of the frequency channel passing therethrough or to leave it intact. The channels then pass through a polarization-dispersive element (28) which spatially separates the beams (14, 16) in the transverse direction according to their polarization. A second diffraction grating (40) recombines the frequency components of the same polarization into multiple output beams (42, 44).
Description
FREQUENCY-SELECTIVE OPTICAL SWITCH USING POLARIZATION ROTATION
Field oir the Invention The invention relates generally to liquid-crystal devices. In particular, the invention relates to liquid-crystal and similar devices useful for switching in a multi-frequency communication system.
Background Art Communication networks increasingly rely upon optical fiber for high-speed, low-cost transmission. Optical fibers were originally envisioned as an optical replacement for electronic transmission media, such as high-speed coaxial cable and lower-speed twisted-pair cable. However, even high-speed optical fibers are limited by the electronics at the transmitting and receiving ends, generally rated at a few gigabits per second, although 40 Gbls systems have been prototyped. Such high-speed electronic systems are expensive and still do not fully exploit the inherent bandwidth of fiber-optic systems, measured in many terabits per second.
1 S All-optical transmission systems offer many intrinsic advantages over systems that use electronics within any part of the principal transmission path. Wavelength-division multiplexing (WDM) electronically impresses different data signals upon different carrier frequencies, all of which are carried by a single optical fiber. The earliest WDM systems did not provide optical switching but only point-to-point WDM.
Recent research and development have suggested that an all-optical network can be constructed having switching nodes that can switch the separate WDM channels (carrier frequencies) in different directions without the necessity of converting the optical signals to electronic signals. If such optical switching can be accomplished with simple optical components, a sophisticated optical network can be constructed at relatively low cost with the high-speed electronics being confined to end terminals that require speeds of only the individual channels and not of the total throughput of the system.
However) such optical switching needs to effectively separate the switched channels. A cross-talk requirement of 20 dB is a minimum, 35 dB would be a reasonable s design requirement, 40 dB would be better: Also, the switching bands should be relatively wide to accommodate significant frequency fluctuations in the optical transmitters) particularly due to frequency chirping in directly modulated laser sources.
That is, the switch must have its frequency bands registered with the transmitter even when the transmitting frequency is varying somewhat. The combination of a wide ~o switching band and low cross talk requires a flat-top switch spectrum.
Furthermore, a somewhat minimal WDM switch has a size of 2'X2', that is) two physical input fibers and two output fibers, each bearing four WDM channels freely switched from either input to either output.
Cheung et al. in U.S. Patent 5,002,349 have suggested that an acousto-optical ~s tunable filter (AOTF) be used in such a WDM network) either at the switching node or at the terminal end. However) AOTFs have many intrinsic problems) such as cross-talk between adjacent-frequency signal. To date) these problems have prevented ATOFs from being adopted into communication networks. The physical mechanisms of AOTFs seem to preclude a good flat-top response.
zo Patel) sometimes in conjunction with co-inventors, has suggested that liquid-crystal filters be used in such WDM communication networks; see, for example) U.S.
Patents 5,111,321 and 5,150,236. Indeed, Patel has suggested in U.S. Patent 5,111,321 that a liquid-crystal system could be used as a drop-add circuit. However, such a system appears difficult to implement.
2s Weiner and collaborators have disclosed how an optical signal can have its frequenry-divided components separately phase-modulated or amplitude-modulated by using a diFfraction grating to divide the input signal into spatially separated frequency components which are separately operated upon by a segmented modulator. See) for example) U.S. Patent 4,685,547 to Heritage et al. Patel et al. have applied this concept to 3o a system incorporating liquid-crystal modulators, as disclosed in U. S.
Patent 5) 13 2,824.
The use of diffraction gratings for multiplexing in a WDM system has been described by Nishi et al. in "Broad-passband-width optical filter for multi/demultiplexer using a diffraction grating and a retroreflector prism," Electronics Letters) vol. 21, 1985, pp. 423-424 and by Shirasaki et al. in "Broadening of bandwidths in grating multiplexer by original dispersion-dividing prism," Electronics Letters, vol. 22, 1986, pp. 764-765.
Nonetheless, the prior art fails to disclose an effective, economical optical switch for a WDM telecommunication system.
Summary of the Invention The invention may be summarized as an optical switch, preferably using a segmented liquid-crystal modulator. The switch divides an input signal into multiple outputs according to the frequency components of the input signal. In particular, the input signal is spatially divided into its frequency components, which pass through different segments of a liquid-crystal polarization modulator. The different frequency components, depending upon their polarization impressed by the polarization modulator, are separated by a polarization divider. The frequency-divided components are then separately I S recombined according to their polarization, thereby producing two or more output signals that have been selectively separated according to optical frequency.
In accordance with one aspect of the present invention there is provided an optical switch, comprising: a frequency-dispersive element receiving an input beam and dispersing it into a plurality of first beams according to frequency; a polarization-dispersive element receiving said first beams and outputting corresponding second beams;
a segmented liquid-crystal polarization modulator receiving said second beams on respective segments thereof and selectively rotating polarizations thereof to form third beams; and a reflector reflecting said third beams back through said polarization modulator, said polarization-dispersive element, and said frequency-dispersive element.
In accordance with another aspect of the present invention there is provided an optical switch comprising: an entrance frequency dispersive element for receiving first and second input optical signals and dispersing them into dispersed beams according to the frequencies thereof, a focusing lens receiving said dispersed optical beams, a segmented polarization modulator having multiple individually controlled segments and positioned essentially at the focal length of said focusing lens for selectively controlling polarization characteristics of individual elements of said dispersed optical beams, a first polarization-dispersive element positioned between said focusing lens and said segmented polarization modulator, a second polarization-dispersive element positioned to the other side of said segmented polarization modulator than said first polarization-dispersive element for receiving the dispersed outputs of said segmented polarization modulator and for spatially displacing individual elements of said dispersed outputs dependent on the polarization thereof, an exit lens for receiving the outputs of said second polarization dispersive element, said exit lens being essentially its focal distance away from said segmented polarization modulator, and an exit frequency dispersive element receiving the dispersed outputs form the second focusing lens and combining frequency components thereof into separate output optical signals.
In accordance with yet another aspect of the present invention there is provided an optical switch comprising, in sequence: a frequency dispersive element for receiving an input optical signal and dispersing it into a dispersed optical beam according to the frequencies thereof, a focusing lens receiving said dispersed optical beam, a polarization-dispersive element, a segmented polarization modulator having multiple individually controlled segments and positioned essentially at the focal length of said focusing lens for selectively controlling the polarization characteristics of individual elements of said dispersed optical beam, and means for recombining said dispersed optical beam after passage through said segmented polarization modulator into an output beam.
Brief Description of the Drawings FIGS. 1, 2, and 3 illustrate respective horizontal, vertical, and isometric views of a polarization-sensitive 1 x2 switch of the invention.
FIGS. 4, 5, and 6 illustrate respective horizontal, vertical, and isometric views of a polarization-sensitive 2x2 switch of the invention.
FIGS. 7, 8, 9, and 10 are graphs of experimental data of an embodiment of the invention.
FIG. 11 is a vertical view of a polarization-insensitive embodiment of the invention.
FIG. 12 is a vertical view of an alterative polarization-sensitive embodiment of the invention using Wollaston prisms.
FIG. 13 is a vertical view of an extension of the embodiment of FIG. 11 that has been made polarization insensitive.
-3 a-a WO 94/28456 ~ ~ ~ PCT/US94/05976 y~
FIG. 14 is a vertical view of a reflective embodiment of the switch of the invention.
Detailed Description of the Preferred Embodiments The invention achieves all-optical switching of the frequency-multiplexed multi-channel optical signals by frequency-dividing an optical input signal into spatially separated channels, selectively changing the polarization characteristics of the frequency-separated channels, further spatially dividing the channels according to polarization characteristics, and the recombining the channels of similar polarization characteristics.
~o Preferably) a segmented liquid-crystal modulator selectively changes the polarization of the physically separated channels.
A first, polarization-sensitive embodiment is shown in cross-section in FIG. 1 in which a relatively broad-band input beam 10 strikes an entrance frequency-dispersive medium) such as a diffraction grating 12. It is assumed that the input beam 10 is polarized along the x-direction. Other active or passive dispersive media are possible, such as prisms. The frequency-dispersive medium 12 divides the broad-band input beam into multiple frequency-separated input beams 14 and 16 which are spatially separated in the illustrated x-direction. An entrance lens 18 focuses the frequency-divided components upon separate segments 20 and 22 of a segmented liquid-crystal polarization zo modulator 24. An entrance polarization-dispersive element 26, such as a birefringent crystal, such as calcite) is disposed on the entrance side to spatially separate the different polarization components of the input beam, but its effects are not evident for the firn embodiment from FIG. 1 because the input beam 10 is assumed to be linearly polarized along the x-axis.
zs The number of frequency-divided input beams 14 and 16 and the number of liquid-crystal segments 20 and 22 depend on the number of WDM components on the optical medium (optical fiber) which require switching. Four frequency sub-bands provide a meaningful telecommunication system. The segments 20 and 22 of the segmented liquid-crystal modulator 24 are separately controllable to chaage the polarization direction or 30 other polarization characteristic of the physically separated frequency-divided input beams 14 and 16. In the simplest case, each segment 20 or 22 either linearly rotates the ~'O 94/28456 ~ ~ PCT/US94/05976 polarization of the properly polarized frequency-separated input beam 14 or 16 by 90° or does not rotate the polarization. A twisted nematic liquid-crystal modulator provides such performance.
After traversing the liquid-crystal modulator 24, the frequency-separated beams 14 s and 16 traverse the exit polarization-dispersive element 28, which, as additionally illustrated in FIG. 2, further separates the beams 14 and 16 into their respective polarization components 32) 34 and 36, 38. An exit lens 30 recollimates the beams. An exit frequency-dispersive medium 40) such as another grating, acts reciprocally to the entrance frequency-dispersive medium 123 and recombines frequency- and polarization-~o separated beams into only polarization-separated beams 42, 44, which, as will be shown later) are spatially separated as well.
Turning more completely now to the perpendicular illustration of FIG. 2, the two frequency beams 14 and 16 are congruent along the x-direction. It is assumed that the two input beams 14 and 16 are polarized along the x-direction and thus not affected by the ~s entrance polarization-dispersive element 26. This assumption manifests that the system of FIGS. 1 and 2 is polarization sensitive. As a result, the entrance polarization-dispersive element 26 is not required for this polarization-sensitive, single-input embodiment.
Referring simultaneously to FIGS. 1 and 2 and to an isometric view, illustrated in FIG. 3, of the central portion of these figures, when the first segment 20 of the segmented liquid-Zo crystal modulator 24 is not actively biased) it rotates by 90° the polarization of the incident beam 14 of the first frequency such that, when it traverses the output polarization-dispersive element 28, it is displaced downwardly along the y-axis into displaced output beam 34 of the first frequency. On the other hand, when the first segment 20 is actively biased, it does not rotate the polarization of the entrance beam 14 of the first frequency.
is As a result, it traverses the output polarization-dispersive element 28 without spatial displacement into undisplaced output beam 32 of the first frequency.
Similarly) active biasing of the second segment 22 rotates by 90° the polarization of the entrance beam 16 of the second frequency, and thus the output polarization-dispersive element 28 converts it into displaced output beam 38 of the second frequency; while inactive biasing leaves its so polarization unaffected, and thus the dispersive element 28 converts it into undisplaced output beam 36 of the second frequency. The output frequency-dispersive element 40 then PCT/US94/0597v recombines the undisplaced output beams 32 and 36 of both frequencies into a combined undisplaced output beam 42 and the displaced output beams 34 and 38 of both frequencies into a combined displaced output beam 44.
Therefore, the biasing of both of the segments 20 and 22 of the liquid-crystal s modulator 24 determines into which output beam 42 and 44 either or both of the entrance beams 14 and 16 are directed. That is, a polarization-sensitive 1 x 2 switch has been described.
Referring now to FIGS. 4) 5, and 6, a second input fiber outputs a second entrance beam 46, which strikes the entrance frequency-dispersive element 12 at a vertically ~o oblique angle so as to produce from the second input fiber multiple angularly separated) frequency-separated beams 48 and 50. The second entrance beam is assumed to be polarized along the y-axis so that the entrance polarization-dispersive element 26 deflects it along the y-axis. The angular resolution of the input frequency-dispersive element 12 and birefringent length of the first polarization-dispersive element 26 are such that the ~s components of the same frequency from the two input beams 10 and 46 are focused upon the same segment 20 or 22 of the segmented liquid-crystal modulator 24. As a result, the respective segmented polarization rotator of the liquid-crystal modulator 24 either rotates both the WDM components of the same frequency by the same polarization angle or does not. Preferably) the liquid-crystal modulator 24 rotates the polarization by 90° or does not so rotate it. That is, either the linear polarization directions of either beam pair 14, 48 or 16) 50 are reversed or left intact (within an angular factor of 180°).
The second polarization-dispersive element 28 is oriented so as to act conversely to the first polarization-dispersive element 26. The beams 32 and 36 polarized along the x-axis remain undeflected, while the beams 34 and 38 polarized along the y-axis are 2s deflected by the second polarization-dispersive element 28 back toward normal propagation path. The exit lens 30) however, angularly separates the resultant output beam 44 from the output beam 42.
In the parlance of a drop-add circuit, the input beam 10 is the IN channel) the input beam 46 is the ADD channel) the output beam 42 is the OUT channel, and the output 3o beam 44 is the DROP channel.
By the means of the illustrated circuitry) the frequency-dedicated segment 20 or 22 .s-~'~'O 94/28456 2 ~ 6 ~ ~ 3 p PCT/US94/05976 of the liquid-crystal modulator 24 determines whether a pair of channels of the same frequency on the two multi-frequency input fibers are to be switched to different output fibers. Of course) the two segments 20 and 22 can be separately controlled for the two frequency channels.
s Although only two frequency channels have been described, it is understood that more frequency channels can be accommodated by a liquid-crystal modulator 20 having additional separately controlled segments along the x-direction.
The above embodiments are sensitive to polarization of their input signals.
But, in many cases, the input light polarization cannot be controlled. Merely using an input ~o polarizer is unsatisfactory because possibly all the light may be lost and because the polarization state tends to be randomly vary in time, therefore leading to polarization-caused intensity fluctuations. However, the invention can be made to be polarization insensitive.
As illustrated in FIG. 11) a first polarization-dispersive element 60, such as a ~s calcite crystal, divides an input beam 62 into two polarization-separated beams 64 and 66, one the ordinary beam 64 and the other the extraordinary beam 66. One of the beams) in the illustrated case) the extraordinary beam 66) passes through a polarization converter 68, such as a half wave plate which rotates the polarization by 90°) so that both beams 64 and 66 have the same well-defined polarization characteristic) here a linear polarization along 2o the x-axis. The entrance lens 18 focuses both beams 64 and 66 upon the same segment 20 or 22 of the liquid-crystal modulator 24) which simultaneously acts on both beams 64 and 66, either leaving their polarization intact or rotating them or producing a combination between beams. The exit polarization-dispersive element Z8 then spatially separates them zs according to polarization; if unrotated, into beams 80 and 82; if rotated, into beams 84 and 86. Two more polarization rotators 88 and 90 are disposed in two of the beams 82 and 84. The exit lens 30 recollimates the beams 80-86, and a second polarization-dispersive element 92 acts coaverseiy to the first one 60 to recombine the beams 80 aad 82 into a combined OUT beam 44 and to recombine the beams 84 and 86 into a combined DROP
so beam 96.
The frequency-dispersed beams are not illustrated but are arranged similarly to WO 94/28456 PCT/C1S9410597f those of FIG. 4. The embodiment can be easily extended to a 2 X 2 drop-add circuit have an additional ADD input beam 98 by including a polarization rotator 100 for the added input on the entrance side.
The above embodiments have been described in somewhat theoretical terms. The s following discussion involves some of the design considerations. Let J
represent the focal lengths of the two lenses 18 and 30; d,, the lateral shift of the inner polarization-dispersive elements 26 and 28; dZ, the lateral shift of the outer polarization-dispersive elements 60 and 92; and L the distance between the input polarization-dispersive element 60 and its associated lens 18. The switched (extraordinary beams) have a virtual focus shifted by d, ~o from the ordinary focus. The extraordinary and ordinary beams therefore form an angle of d~ lJ with respect to the input and output ordinary beams. If J= 100 mm and d = 100 mm, the angle is 0.02 rad or about 1°. The main ordinary input beam is assumed to define x = 0 for each frequency. The ordinary beam is then at x = -dZ. The ordinary and extraordinary beams of the ADD (or DROP) channel at the lens 18 or 30 are located at x = d, and x = d= - d, , respectively. At the external crystals, these beams are at x = ld,lJ
d, and x = ld,lJ- d, - s.
For the beams to overlie at that point, it is required that L =,f The preceding embodiments have used a calcite crystal or similar uniaxial medium for the polarization-dispersive element. Wollaston prisms offer an advantageous 2o alternative design. Such prisms have two prisms of calcite, for example, separated by a thin layer of material having a refractive index intermediate between the refractive indices of the ordinary and extraordinary refractive indices of the calcite. The two component prisms are oriented such that one of the rays is totally internally reflected by the -intermediate thin layer. The result is that the ordinary and extraordinary rays are angularly 2s separated A polarization-sensitive embodiment utilizing Wollaston prisms is illustrated in FIG. 12. The perpendicular construction is very similar to that of FIG. 4. The entrance and exit calcite crystals 26 and 28 of FIGS. 1, 2, and 3 are replaced by entrance and exit Wollaston prisms 110 and 112. Their birefringent thicknesses and the focal lengths of the 3o two lenses 18 and 30 are arranged such that the two optical input beams 14 and 16, the IN
and ADD beams, are focused to the interface of the entrance Wollaston prism 110 having ~'O 94/28456 PCT/L1S94/05976 such a length that both beams 14 and 16 (of differing polarizations) then are congruent as they pass the liquid-crystal modulator 24. Preferably, the input beams 14 and 16 can be made parallel. Similar design factors on the output side allow the two output beams 42 and 44) the OUT and DROP beams, to be parallel.
Example I
We have constructed and tested a switch according to the above embodiment. It was designed to switch one or more of six channels having 4 nm spacing between the channels and to have a wavelength resolution of 2 nm. 'The liquid-crystal modulator was filled with commercially available E7 nematic liquid crystal and was twisted by 90°. The ,o polarization-dispersive element was a Wollaston prism. Many of the details of fabrication are found in the parent patent application and the various cited patents to Patel. The design of the switch was optimized for 1.5 pm. In an experimental prototype) we have shown an extinction ratio of at least 35 dB between the switched and unswitched states of the polarizers. In FIGS. 7 and 8 are shown the optical power spectra on the unswitched ~s output channel and the switched output channel respectively when no switching is performed. That is, FIG. 8 shows the residual power in the four unswitched channels.
The power levels indicated on the vertical scale are somewhat arbitrary and reflect an 8 dB
system loss. In FIGS. 9 and 10 are shown the optical spectra of the unswitched and switched outputs respectively when the first and third charnels are switched.
It is thus so seen that the inventive system effectively switches the WDM channels.
The embodiment of Wollaston prisms can be made insensitive to polarization) as illustrated in FIG. 13, by including the first and second polarization-dispersive elements 60 and 92) preferably calcite crystals or similar material, on the input and output ends. Half wave plates 120) 122, and 124 are placed in the path of the laterally displaced beams and zs in the path of both of the input ADD beams. The wide half wave plate 124 causes the IN
and ADD beams to have differing polarizations as they congruently pass through a segment of the liquid-crystal modulator 24. Similarly, half wave plates 126, 128, and 130 are placed in the oo-be-displaced output beams and both of the DROP beams.
The number of parts can be significantly reduced by using a reflector and operating in the retro-reflector mode. As illustrated in FIG. 14) the input beam 14, after diffracting WO 94/28456 2 ~ 6 3 6 3 PCT/US94/0597f from the grating (not shown)) strikes the lens 18 off-center and is refracted obliquely to the principal optical axis. Because it is polarized along the x-direction) it passes undeflected through the polarization-dispersive element 26, which may be calcite or a Wollaston prism.
It then passes through one segment of the segmented liquid-crystal polarization modulator s system 140, which differs from the previously described liquid-crystal polarization modulators in that it selectively rotates the light polarization by 90°
only after a double, back-and-forth pass. The light is then reflected from a mirror 142 and again traverses the polarization modulator 140. The polarization of light traversing actively biased segments of the modulator 140 is not rotated while that of light traversing inactively biased ~o segments is rotated by a total of 90°. The light with rotated polarization is displaced by the polarization-dispersive element 26 and) after diffraction, is output as a first output beam 144 while the light with unrotated polarization is output as a second output beam 146. The two output beams 144 and 146 are angularly displaced so as to be easily separated physically.
~s The second input beam 46, assumed to be polarized along the y-direction strikes the lens 18 obliquely with respect to the first input beam 14 but in the same general off axis location. Because of their assumed different polarizations, the polarization-dispersive element 26 affects them conversely, but the segmented polarization modulator simultaneously rotates (or does not rotate) both of their polarization states.
In the so backward propagation) the diffraction grating recombines the optical frequency carriers into the desired ADD and DROP channels, as determined by the segmented polarization modulator 140.
The optical switch of FIG. 14 can be made frequency insensitive suing techniques described for the other embodiments.
~s The frequency dispersion at the liquid-crystal modulator of the invention allows the modulator to simultaneously change the phase and/or amplitude of the different frequency components of the signals. Such adjustment is particularly advantageous to additionally compensate for the frequency dispersion of the optical fiber or to equalize amplitudes between different channels.
3o Although the described embodiments have placed the frequency-dispersive elements on the outside of the polarization-dispersive elements, it is recognized that the two -~o-"'~ 94/28456 dispersions can be performed in the opposite order and even simultaneously.
The invention can thus be used in a number of related configurations, all of which are useful for providing an economical, all-optical multi-frequency switch.
When the polarization modulator is a segmented liquid-crystal modulator, tfie system is both easy to s construct, and the modulator has transfer characteristics consistent with a relaxed system design.
Field oir the Invention The invention relates generally to liquid-crystal devices. In particular, the invention relates to liquid-crystal and similar devices useful for switching in a multi-frequency communication system.
Background Art Communication networks increasingly rely upon optical fiber for high-speed, low-cost transmission. Optical fibers were originally envisioned as an optical replacement for electronic transmission media, such as high-speed coaxial cable and lower-speed twisted-pair cable. However, even high-speed optical fibers are limited by the electronics at the transmitting and receiving ends, generally rated at a few gigabits per second, although 40 Gbls systems have been prototyped. Such high-speed electronic systems are expensive and still do not fully exploit the inherent bandwidth of fiber-optic systems, measured in many terabits per second.
1 S All-optical transmission systems offer many intrinsic advantages over systems that use electronics within any part of the principal transmission path. Wavelength-division multiplexing (WDM) electronically impresses different data signals upon different carrier frequencies, all of which are carried by a single optical fiber. The earliest WDM systems did not provide optical switching but only point-to-point WDM.
Recent research and development have suggested that an all-optical network can be constructed having switching nodes that can switch the separate WDM channels (carrier frequencies) in different directions without the necessity of converting the optical signals to electronic signals. If such optical switching can be accomplished with simple optical components, a sophisticated optical network can be constructed at relatively low cost with the high-speed electronics being confined to end terminals that require speeds of only the individual channels and not of the total throughput of the system.
However) such optical switching needs to effectively separate the switched channels. A cross-talk requirement of 20 dB is a minimum, 35 dB would be a reasonable s design requirement, 40 dB would be better: Also, the switching bands should be relatively wide to accommodate significant frequency fluctuations in the optical transmitters) particularly due to frequency chirping in directly modulated laser sources.
That is, the switch must have its frequency bands registered with the transmitter even when the transmitting frequency is varying somewhat. The combination of a wide ~o switching band and low cross talk requires a flat-top switch spectrum.
Furthermore, a somewhat minimal WDM switch has a size of 2'X2', that is) two physical input fibers and two output fibers, each bearing four WDM channels freely switched from either input to either output.
Cheung et al. in U.S. Patent 5,002,349 have suggested that an acousto-optical ~s tunable filter (AOTF) be used in such a WDM network) either at the switching node or at the terminal end. However) AOTFs have many intrinsic problems) such as cross-talk between adjacent-frequency signal. To date) these problems have prevented ATOFs from being adopted into communication networks. The physical mechanisms of AOTFs seem to preclude a good flat-top response.
zo Patel) sometimes in conjunction with co-inventors, has suggested that liquid-crystal filters be used in such WDM communication networks; see, for example) U.S.
Patents 5,111,321 and 5,150,236. Indeed, Patel has suggested in U.S. Patent 5,111,321 that a liquid-crystal system could be used as a drop-add circuit. However, such a system appears difficult to implement.
2s Weiner and collaborators have disclosed how an optical signal can have its frequenry-divided components separately phase-modulated or amplitude-modulated by using a diFfraction grating to divide the input signal into spatially separated frequency components which are separately operated upon by a segmented modulator. See) for example) U.S. Patent 4,685,547 to Heritage et al. Patel et al. have applied this concept to 3o a system incorporating liquid-crystal modulators, as disclosed in U. S.
Patent 5) 13 2,824.
The use of diffraction gratings for multiplexing in a WDM system has been described by Nishi et al. in "Broad-passband-width optical filter for multi/demultiplexer using a diffraction grating and a retroreflector prism," Electronics Letters) vol. 21, 1985, pp. 423-424 and by Shirasaki et al. in "Broadening of bandwidths in grating multiplexer by original dispersion-dividing prism," Electronics Letters, vol. 22, 1986, pp. 764-765.
Nonetheless, the prior art fails to disclose an effective, economical optical switch for a WDM telecommunication system.
Summary of the Invention The invention may be summarized as an optical switch, preferably using a segmented liquid-crystal modulator. The switch divides an input signal into multiple outputs according to the frequency components of the input signal. In particular, the input signal is spatially divided into its frequency components, which pass through different segments of a liquid-crystal polarization modulator. The different frequency components, depending upon their polarization impressed by the polarization modulator, are separated by a polarization divider. The frequency-divided components are then separately I S recombined according to their polarization, thereby producing two or more output signals that have been selectively separated according to optical frequency.
In accordance with one aspect of the present invention there is provided an optical switch, comprising: a frequency-dispersive element receiving an input beam and dispersing it into a plurality of first beams according to frequency; a polarization-dispersive element receiving said first beams and outputting corresponding second beams;
a segmented liquid-crystal polarization modulator receiving said second beams on respective segments thereof and selectively rotating polarizations thereof to form third beams; and a reflector reflecting said third beams back through said polarization modulator, said polarization-dispersive element, and said frequency-dispersive element.
In accordance with another aspect of the present invention there is provided an optical switch comprising: an entrance frequency dispersive element for receiving first and second input optical signals and dispersing them into dispersed beams according to the frequencies thereof, a focusing lens receiving said dispersed optical beams, a segmented polarization modulator having multiple individually controlled segments and positioned essentially at the focal length of said focusing lens for selectively controlling polarization characteristics of individual elements of said dispersed optical beams, a first polarization-dispersive element positioned between said focusing lens and said segmented polarization modulator, a second polarization-dispersive element positioned to the other side of said segmented polarization modulator than said first polarization-dispersive element for receiving the dispersed outputs of said segmented polarization modulator and for spatially displacing individual elements of said dispersed outputs dependent on the polarization thereof, an exit lens for receiving the outputs of said second polarization dispersive element, said exit lens being essentially its focal distance away from said segmented polarization modulator, and an exit frequency dispersive element receiving the dispersed outputs form the second focusing lens and combining frequency components thereof into separate output optical signals.
In accordance with yet another aspect of the present invention there is provided an optical switch comprising, in sequence: a frequency dispersive element for receiving an input optical signal and dispersing it into a dispersed optical beam according to the frequencies thereof, a focusing lens receiving said dispersed optical beam, a polarization-dispersive element, a segmented polarization modulator having multiple individually controlled segments and positioned essentially at the focal length of said focusing lens for selectively controlling the polarization characteristics of individual elements of said dispersed optical beam, and means for recombining said dispersed optical beam after passage through said segmented polarization modulator into an output beam.
Brief Description of the Drawings FIGS. 1, 2, and 3 illustrate respective horizontal, vertical, and isometric views of a polarization-sensitive 1 x2 switch of the invention.
FIGS. 4, 5, and 6 illustrate respective horizontal, vertical, and isometric views of a polarization-sensitive 2x2 switch of the invention.
FIGS. 7, 8, 9, and 10 are graphs of experimental data of an embodiment of the invention.
FIG. 11 is a vertical view of a polarization-insensitive embodiment of the invention.
FIG. 12 is a vertical view of an alterative polarization-sensitive embodiment of the invention using Wollaston prisms.
FIG. 13 is a vertical view of an extension of the embodiment of FIG. 11 that has been made polarization insensitive.
-3 a-a WO 94/28456 ~ ~ ~ PCT/US94/05976 y~
FIG. 14 is a vertical view of a reflective embodiment of the switch of the invention.
Detailed Description of the Preferred Embodiments The invention achieves all-optical switching of the frequency-multiplexed multi-channel optical signals by frequency-dividing an optical input signal into spatially separated channels, selectively changing the polarization characteristics of the frequency-separated channels, further spatially dividing the channels according to polarization characteristics, and the recombining the channels of similar polarization characteristics.
~o Preferably) a segmented liquid-crystal modulator selectively changes the polarization of the physically separated channels.
A first, polarization-sensitive embodiment is shown in cross-section in FIG. 1 in which a relatively broad-band input beam 10 strikes an entrance frequency-dispersive medium) such as a diffraction grating 12. It is assumed that the input beam 10 is polarized along the x-direction. Other active or passive dispersive media are possible, such as prisms. The frequency-dispersive medium 12 divides the broad-band input beam into multiple frequency-separated input beams 14 and 16 which are spatially separated in the illustrated x-direction. An entrance lens 18 focuses the frequency-divided components upon separate segments 20 and 22 of a segmented liquid-crystal polarization zo modulator 24. An entrance polarization-dispersive element 26, such as a birefringent crystal, such as calcite) is disposed on the entrance side to spatially separate the different polarization components of the input beam, but its effects are not evident for the firn embodiment from FIG. 1 because the input beam 10 is assumed to be linearly polarized along the x-axis.
zs The number of frequency-divided input beams 14 and 16 and the number of liquid-crystal segments 20 and 22 depend on the number of WDM components on the optical medium (optical fiber) which require switching. Four frequency sub-bands provide a meaningful telecommunication system. The segments 20 and 22 of the segmented liquid-crystal modulator 24 are separately controllable to chaage the polarization direction or 30 other polarization characteristic of the physically separated frequency-divided input beams 14 and 16. In the simplest case, each segment 20 or 22 either linearly rotates the ~'O 94/28456 ~ ~ PCT/US94/05976 polarization of the properly polarized frequency-separated input beam 14 or 16 by 90° or does not rotate the polarization. A twisted nematic liquid-crystal modulator provides such performance.
After traversing the liquid-crystal modulator 24, the frequency-separated beams 14 s and 16 traverse the exit polarization-dispersive element 28, which, as additionally illustrated in FIG. 2, further separates the beams 14 and 16 into their respective polarization components 32) 34 and 36, 38. An exit lens 30 recollimates the beams. An exit frequency-dispersive medium 40) such as another grating, acts reciprocally to the entrance frequency-dispersive medium 123 and recombines frequency- and polarization-~o separated beams into only polarization-separated beams 42, 44, which, as will be shown later) are spatially separated as well.
Turning more completely now to the perpendicular illustration of FIG. 2, the two frequency beams 14 and 16 are congruent along the x-direction. It is assumed that the two input beams 14 and 16 are polarized along the x-direction and thus not affected by the ~s entrance polarization-dispersive element 26. This assumption manifests that the system of FIGS. 1 and 2 is polarization sensitive. As a result, the entrance polarization-dispersive element 26 is not required for this polarization-sensitive, single-input embodiment.
Referring simultaneously to FIGS. 1 and 2 and to an isometric view, illustrated in FIG. 3, of the central portion of these figures, when the first segment 20 of the segmented liquid-Zo crystal modulator 24 is not actively biased) it rotates by 90° the polarization of the incident beam 14 of the first frequency such that, when it traverses the output polarization-dispersive element 28, it is displaced downwardly along the y-axis into displaced output beam 34 of the first frequency. On the other hand, when the first segment 20 is actively biased, it does not rotate the polarization of the entrance beam 14 of the first frequency.
is As a result, it traverses the output polarization-dispersive element 28 without spatial displacement into undisplaced output beam 32 of the first frequency.
Similarly) active biasing of the second segment 22 rotates by 90° the polarization of the entrance beam 16 of the second frequency, and thus the output polarization-dispersive element 28 converts it into displaced output beam 38 of the second frequency; while inactive biasing leaves its so polarization unaffected, and thus the dispersive element 28 converts it into undisplaced output beam 36 of the second frequency. The output frequency-dispersive element 40 then PCT/US94/0597v recombines the undisplaced output beams 32 and 36 of both frequencies into a combined undisplaced output beam 42 and the displaced output beams 34 and 38 of both frequencies into a combined displaced output beam 44.
Therefore, the biasing of both of the segments 20 and 22 of the liquid-crystal s modulator 24 determines into which output beam 42 and 44 either or both of the entrance beams 14 and 16 are directed. That is, a polarization-sensitive 1 x 2 switch has been described.
Referring now to FIGS. 4) 5, and 6, a second input fiber outputs a second entrance beam 46, which strikes the entrance frequency-dispersive element 12 at a vertically ~o oblique angle so as to produce from the second input fiber multiple angularly separated) frequency-separated beams 48 and 50. The second entrance beam is assumed to be polarized along the y-axis so that the entrance polarization-dispersive element 26 deflects it along the y-axis. The angular resolution of the input frequency-dispersive element 12 and birefringent length of the first polarization-dispersive element 26 are such that the ~s components of the same frequency from the two input beams 10 and 46 are focused upon the same segment 20 or 22 of the segmented liquid-crystal modulator 24. As a result, the respective segmented polarization rotator of the liquid-crystal modulator 24 either rotates both the WDM components of the same frequency by the same polarization angle or does not. Preferably) the liquid-crystal modulator 24 rotates the polarization by 90° or does not so rotate it. That is, either the linear polarization directions of either beam pair 14, 48 or 16) 50 are reversed or left intact (within an angular factor of 180°).
The second polarization-dispersive element 28 is oriented so as to act conversely to the first polarization-dispersive element 26. The beams 32 and 36 polarized along the x-axis remain undeflected, while the beams 34 and 38 polarized along the y-axis are 2s deflected by the second polarization-dispersive element 28 back toward normal propagation path. The exit lens 30) however, angularly separates the resultant output beam 44 from the output beam 42.
In the parlance of a drop-add circuit, the input beam 10 is the IN channel) the input beam 46 is the ADD channel) the output beam 42 is the OUT channel, and the output 3o beam 44 is the DROP channel.
By the means of the illustrated circuitry) the frequency-dedicated segment 20 or 22 .s-~'~'O 94/28456 2 ~ 6 ~ ~ 3 p PCT/US94/05976 of the liquid-crystal modulator 24 determines whether a pair of channels of the same frequency on the two multi-frequency input fibers are to be switched to different output fibers. Of course) the two segments 20 and 22 can be separately controlled for the two frequency channels.
s Although only two frequency channels have been described, it is understood that more frequency channels can be accommodated by a liquid-crystal modulator 20 having additional separately controlled segments along the x-direction.
The above embodiments are sensitive to polarization of their input signals.
But, in many cases, the input light polarization cannot be controlled. Merely using an input ~o polarizer is unsatisfactory because possibly all the light may be lost and because the polarization state tends to be randomly vary in time, therefore leading to polarization-caused intensity fluctuations. However, the invention can be made to be polarization insensitive.
As illustrated in FIG. 11) a first polarization-dispersive element 60, such as a ~s calcite crystal, divides an input beam 62 into two polarization-separated beams 64 and 66, one the ordinary beam 64 and the other the extraordinary beam 66. One of the beams) in the illustrated case) the extraordinary beam 66) passes through a polarization converter 68, such as a half wave plate which rotates the polarization by 90°) so that both beams 64 and 66 have the same well-defined polarization characteristic) here a linear polarization along 2o the x-axis. The entrance lens 18 focuses both beams 64 and 66 upon the same segment 20 or 22 of the liquid-crystal modulator 24) which simultaneously acts on both beams 64 and 66, either leaving their polarization intact or rotating them or producing a combination between beams. The exit polarization-dispersive element Z8 then spatially separates them zs according to polarization; if unrotated, into beams 80 and 82; if rotated, into beams 84 and 86. Two more polarization rotators 88 and 90 are disposed in two of the beams 82 and 84. The exit lens 30 recollimates the beams 80-86, and a second polarization-dispersive element 92 acts coaverseiy to the first one 60 to recombine the beams 80 aad 82 into a combined OUT beam 44 and to recombine the beams 84 and 86 into a combined DROP
so beam 96.
The frequency-dispersed beams are not illustrated but are arranged similarly to WO 94/28456 PCT/C1S9410597f those of FIG. 4. The embodiment can be easily extended to a 2 X 2 drop-add circuit have an additional ADD input beam 98 by including a polarization rotator 100 for the added input on the entrance side.
The above embodiments have been described in somewhat theoretical terms. The s following discussion involves some of the design considerations. Let J
represent the focal lengths of the two lenses 18 and 30; d,, the lateral shift of the inner polarization-dispersive elements 26 and 28; dZ, the lateral shift of the outer polarization-dispersive elements 60 and 92; and L the distance between the input polarization-dispersive element 60 and its associated lens 18. The switched (extraordinary beams) have a virtual focus shifted by d, ~o from the ordinary focus. The extraordinary and ordinary beams therefore form an angle of d~ lJ with respect to the input and output ordinary beams. If J= 100 mm and d = 100 mm, the angle is 0.02 rad or about 1°. The main ordinary input beam is assumed to define x = 0 for each frequency. The ordinary beam is then at x = -dZ. The ordinary and extraordinary beams of the ADD (or DROP) channel at the lens 18 or 30 are located at x = d, and x = d= - d, , respectively. At the external crystals, these beams are at x = ld,lJ
d, and x = ld,lJ- d, - s.
For the beams to overlie at that point, it is required that L =,f The preceding embodiments have used a calcite crystal or similar uniaxial medium for the polarization-dispersive element. Wollaston prisms offer an advantageous 2o alternative design. Such prisms have two prisms of calcite, for example, separated by a thin layer of material having a refractive index intermediate between the refractive indices of the ordinary and extraordinary refractive indices of the calcite. The two component prisms are oriented such that one of the rays is totally internally reflected by the -intermediate thin layer. The result is that the ordinary and extraordinary rays are angularly 2s separated A polarization-sensitive embodiment utilizing Wollaston prisms is illustrated in FIG. 12. The perpendicular construction is very similar to that of FIG. 4. The entrance and exit calcite crystals 26 and 28 of FIGS. 1, 2, and 3 are replaced by entrance and exit Wollaston prisms 110 and 112. Their birefringent thicknesses and the focal lengths of the 3o two lenses 18 and 30 are arranged such that the two optical input beams 14 and 16, the IN
and ADD beams, are focused to the interface of the entrance Wollaston prism 110 having ~'O 94/28456 PCT/L1S94/05976 such a length that both beams 14 and 16 (of differing polarizations) then are congruent as they pass the liquid-crystal modulator 24. Preferably, the input beams 14 and 16 can be made parallel. Similar design factors on the output side allow the two output beams 42 and 44) the OUT and DROP beams, to be parallel.
Example I
We have constructed and tested a switch according to the above embodiment. It was designed to switch one or more of six channels having 4 nm spacing between the channels and to have a wavelength resolution of 2 nm. 'The liquid-crystal modulator was filled with commercially available E7 nematic liquid crystal and was twisted by 90°. The ,o polarization-dispersive element was a Wollaston prism. Many of the details of fabrication are found in the parent patent application and the various cited patents to Patel. The design of the switch was optimized for 1.5 pm. In an experimental prototype) we have shown an extinction ratio of at least 35 dB between the switched and unswitched states of the polarizers. In FIGS. 7 and 8 are shown the optical power spectra on the unswitched ~s output channel and the switched output channel respectively when no switching is performed. That is, FIG. 8 shows the residual power in the four unswitched channels.
The power levels indicated on the vertical scale are somewhat arbitrary and reflect an 8 dB
system loss. In FIGS. 9 and 10 are shown the optical spectra of the unswitched and switched outputs respectively when the first and third charnels are switched.
It is thus so seen that the inventive system effectively switches the WDM channels.
The embodiment of Wollaston prisms can be made insensitive to polarization) as illustrated in FIG. 13, by including the first and second polarization-dispersive elements 60 and 92) preferably calcite crystals or similar material, on the input and output ends. Half wave plates 120) 122, and 124 are placed in the path of the laterally displaced beams and zs in the path of both of the input ADD beams. The wide half wave plate 124 causes the IN
and ADD beams to have differing polarizations as they congruently pass through a segment of the liquid-crystal modulator 24. Similarly, half wave plates 126, 128, and 130 are placed in the oo-be-displaced output beams and both of the DROP beams.
The number of parts can be significantly reduced by using a reflector and operating in the retro-reflector mode. As illustrated in FIG. 14) the input beam 14, after diffracting WO 94/28456 2 ~ 6 3 6 3 PCT/US94/0597f from the grating (not shown)) strikes the lens 18 off-center and is refracted obliquely to the principal optical axis. Because it is polarized along the x-direction) it passes undeflected through the polarization-dispersive element 26, which may be calcite or a Wollaston prism.
It then passes through one segment of the segmented liquid-crystal polarization modulator s system 140, which differs from the previously described liquid-crystal polarization modulators in that it selectively rotates the light polarization by 90°
only after a double, back-and-forth pass. The light is then reflected from a mirror 142 and again traverses the polarization modulator 140. The polarization of light traversing actively biased segments of the modulator 140 is not rotated while that of light traversing inactively biased ~o segments is rotated by a total of 90°. The light with rotated polarization is displaced by the polarization-dispersive element 26 and) after diffraction, is output as a first output beam 144 while the light with unrotated polarization is output as a second output beam 146. The two output beams 144 and 146 are angularly displaced so as to be easily separated physically.
~s The second input beam 46, assumed to be polarized along the y-direction strikes the lens 18 obliquely with respect to the first input beam 14 but in the same general off axis location. Because of their assumed different polarizations, the polarization-dispersive element 26 affects them conversely, but the segmented polarization modulator simultaneously rotates (or does not rotate) both of their polarization states.
In the so backward propagation) the diffraction grating recombines the optical frequency carriers into the desired ADD and DROP channels, as determined by the segmented polarization modulator 140.
The optical switch of FIG. 14 can be made frequency insensitive suing techniques described for the other embodiments.
~s The frequency dispersion at the liquid-crystal modulator of the invention allows the modulator to simultaneously change the phase and/or amplitude of the different frequency components of the signals. Such adjustment is particularly advantageous to additionally compensate for the frequency dispersion of the optical fiber or to equalize amplitudes between different channels.
3o Although the described embodiments have placed the frequency-dispersive elements on the outside of the polarization-dispersive elements, it is recognized that the two -~o-"'~ 94/28456 dispersions can be performed in the opposite order and even simultaneously.
The invention can thus be used in a number of related configurations, all of which are useful for providing an economical, all-optical multi-frequency switch.
When the polarization modulator is a segmented liquid-crystal modulator, tfie system is both easy to s construct, and the modulator has transfer characteristics consistent with a relaxed system design.
Claims (16)
1. An optical switch, comprising:
a frequency-dispersive element receiving an input beam and dispersing it into a plurality of first beams according to frequency;
a polarization-dispersive element receiving said first beams and outputting corresponding second beams;
a segmented liquid-crystal polarization modulator receiving said second beams on respective segments thereof and selectively rotating polarizations thereof to form third beams; and a reflector reflecting said third beams back through said polarization modulator, said polarization-dispersive element, and said frequency-dispersive element.
a frequency-dispersive element receiving an input beam and dispersing it into a plurality of first beams according to frequency;
a polarization-dispersive element receiving said first beams and outputting corresponding second beams;
a segmented liquid-crystal polarization modulator receiving said second beams on respective segments thereof and selectively rotating polarizations thereof to form third beams; and a reflector reflecting said third beams back through said polarization modulator, said polarization-dispersive element, and said frequency-dispersive element.
2. An optical switch comprising an entrance frequency dispersive element for receiving first and second input optical signals and dispersing them into dispersed beams according to the frequencies thereof, a focusing lens receiving said dispersed optical beams, a segmented polarization modulator having multiple individually controlled segments and positioned essentially at the focal length of said focusing lens for selectively controlling polarization characteristics of individual elements of said dispersed optical beams, a first polarization-dispersive element positioned between said focusing lens and said segmented polarization modulator, a second polarization-dispersive element positioned to the other side of said segmented polarization modulator than said first polarization-dispersive element for receiving the dispersed outputs of said segmented polarization modulator and forspatially displacing individual elements of said dispersed outputs dependent on the polarization thereof, an exit lens for receiving the outputs of said second polarization dispersive element, said exit lens being essentially its focal distance away from said segmented polarization modulator, and an exit frequency dispersive element receiving the dispersed outputs from the second focusing lens and combining frequency components thereof into separate output optical signals.
3. An optical switch in accordance with claim 2 wherein said segmented polarization modulator is a liquid-crystal modulator.
4. An optical switch in accordance with claim 3 wherein said entrance and exit dispersive elements are gratings.
5. An optical switch in accordance with claim 2 wherein said first and second polarization-dispersive elements are birefringent crystals.
6. An optical switch in accordance with claim 2 wherein said first and second polarization-dispersive elements are Wollaston prisms, the focal length of said focusing lens being at the interface of said first polarization-dispersive Wollaston prism.
7. An optical switch in accordance with claim 6 further comprising a third polarization-dispersive element in front of said entrance frequency dispersive element and a fourth polarization-dispersive element behind said exit frequency dispersive element, the input to said third polarization-dispersive element being said first and second input signals and the output from said third polarization-dispersive element being a pair of beams for each of said first and second input signals, one beam of each pair being laterally displaced dependent on polarization, and a half-wave plate positioned in the path of only one of each pair of beams.
8. An optical switch in accordance with claim 7 wherein said third and fourth polarization-dispersive elements are birefringent crystals.
9. An optical switch in accordance with claim 7 wherein said half-wave plates are positioned in the path of each of said laterally displaced beams only.
10. An optical switch in accordance with claim 7 further comprising a further half-wave plate adjacent the side of said focusing lens receiving said dispersed optical beams but in the path of only one of said pair of beams.
11. An optical switch in accordance with claim 10 further comprising a half-wave plate adjacent the input side of said fourth polarization dispersive element in the path of each of said laterally displaced beams only.
12. An optical switch comprising in sequence a frequency dispersive element for receiving an input optical signal and dispersing it into a dispersed optical beam according to the frequencies thereof, a focusing lens receiving said dispersed optical beam, a polarization-dispersive element, a segmented polarization modulator having multiple individually controlled segments and positioned essentially at the focal length of said focusing lens for selectively controlling the polarization characteristics of individual elements of said dispersed optical beam, and means for recombining said dispersed optical beam after passage through said segmented polarization modulator into an output beam.
13. An optical switch in accordance with claim 12 wherein said means for recombining comprises reflector means for reflecting said dispersed optical beam back through said segmented polarization modulator, said polarization-dispersive element. and said frequency dispersive element.
14. An optical switch in accordance with claim 12 wherein said means for recombining includes a second polarization-dispersive element for spatially displacing individual elements of said dispersed beam received from said segmented polarization modulator dependent on the polarization thereof, a second lens, and a second frequency dispersive element.
15. An optical switch in accordance with claim 12 wherein said frequency dispersive element is a grating and said segmented polarization modulator comprises a liquid-crystal modulator.
16. An optical switch in accordance with claim 12 further comprising a second polarization-dispersive element in front of said frequency dispersive element, said second polarization-dispersive element including half-wave plates positioned in the path of laterally displaced beams only from said second polarization-dispersive element.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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US070,591 | 1993-06-01 | ||
US08/070,591 US5414541A (en) | 1993-06-01 | 1993-06-01 | Optical switch employing first and second ferroelectric cells with alignment layers having alignment directions offset by 45° |
US125,607 | 1993-09-22 | ||
US08/125,607 US5414540A (en) | 1993-06-01 | 1993-09-22 | Frequency-selective optical switch employing a frequency dispersive element, polarization dispersive element and polarization modulating elements |
PCT/US1994/005976 WO1994028456A1 (en) | 1993-06-01 | 1994-05-26 | Frequency-selective optical switch using polarization rotation |
Publications (2)
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CA2163630A1 CA2163630A1 (en) | 1994-12-08 |
CA2163630C true CA2163630C (en) | 1999-08-24 |
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CA002163630A Expired - Fee Related CA2163630C (en) | 1993-06-01 | 1994-05-26 | Frequency-selective optical switch using polarization rotation |
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EP (1) | EP0701710B1 (en) |
JP (1) | JP2757563B2 (en) |
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Families Citing this family (185)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5570180A (en) * | 1993-08-27 | 1996-10-29 | Minolta Co., Ltd. | Spectrometer provided with an optical shutter |
US5537252A (en) * | 1993-12-23 | 1996-07-16 | Xerox Corporation | Double blazed binary diffraction optical element beam splitter |
US6322220B1 (en) | 1994-02-14 | 2001-11-27 | Canon Kabushiki Kaisha | Exposure apparatus and device manufacturing method using the same |
US5526171A (en) * | 1995-01-18 | 1996-06-11 | The Trustees Of Princeton University | Laser pulse shaper |
IL115075A (en) * | 1995-08-25 | 1999-08-17 | Univ Ramot | All optical switch |
US5825517A (en) * | 1995-12-06 | 1998-10-20 | Tellium, Inc. | Parametric wavelength interchanging cross-connect |
US5606439A (en) * | 1996-04-10 | 1997-02-25 | Macro-Vision Technology , Inc. | Tunable add/drop optical filter |
US5847831A (en) * | 1996-05-29 | 1998-12-08 | Bell Communcations Research, Inc. | Apparatus for monitoring the state of a liquid-crystal polarization |
US6005697A (en) * | 1996-07-23 | 1999-12-21 | Macro-Vision Communications, L.L.C. | Multi-wavelength cross-connect optical network |
US6175436B1 (en) | 1996-07-30 | 2001-01-16 | Tellium, Inc. | Automatic feedback gain control for multiple channels in a doped optical fiber amplifier |
US6097518A (en) * | 1996-10-29 | 2000-08-01 | Chorum Technologies Inc. | N x M optical wavelength routing switch |
US6166838A (en) * | 1997-03-24 | 2000-12-26 | Chorum Technologies, Inc. | Optical add/drop wavelength switch |
US6115155A (en) | 1996-10-29 | 2000-09-05 | Chorum Technologies Inc. | System for dealing with faults in an optical link |
US6243200B1 (en) | 2000-03-02 | 2001-06-05 | Chorum Technologies, Inc. | Optical wavelength router based on polarization interferometer |
US6545783B1 (en) | 1996-10-29 | 2003-04-08 | Chorum Technologies Lp | Optical wavelength add/drop multiplexer |
US6847786B2 (en) * | 1996-10-29 | 2005-01-25 | Ec-Optics Technology, Inc. | Compact wavelength filter using optical birefringence and reflective elements |
US6163393A (en) | 1996-10-29 | 2000-12-19 | Chorum Technologies Inc. | Method and apparatus for wavelength multipexing/demultiplexing |
US6285478B1 (en) | 1998-03-26 | 2001-09-04 | Chorum Technologies Lp | Programmable optical add/drop device |
EP0963677A1 (en) | 1997-01-07 | 1999-12-15 | Tellium, Inc. | Hybrid wavelength-interchanging cross-connect |
US5841500A (en) * | 1997-01-09 | 1998-11-24 | Tellium, Inc. | Wedge-shaped liquid crystal cell |
EP0958518A1 (en) * | 1997-02-07 | 1999-11-24 | Tellium, Inc. | Dual liquid-crystal wavelength-selective optical switch |
US6097859A (en) * | 1998-02-12 | 2000-08-01 | The Regents Of The University Of California | Multi-wavelength cross-connect optical switch |
US6275312B1 (en) | 1997-04-02 | 2001-08-14 | Chorum Technologies Lp | Optical routing switch |
US6049404A (en) | 1997-04-02 | 2000-04-11 | Macro-Vision Communications Inc. | N+M digitally programmable optical routing switch |
US6519022B1 (en) * | 1997-04-02 | 2003-02-11 | Chorum Technologies Lp | Optical routing switch using symmetric liquid crystal cells |
EP0883255A3 (en) * | 1997-06-05 | 2002-01-09 | Nortel Networks Limited | Optically amplified WDM transmission system |
AU8666898A (en) * | 1997-08-08 | 1999-03-01 | Chorum Technologies, Inc. | Multi-wavelength cross-connect optical network |
US6631018B1 (en) | 1997-08-27 | 2003-10-07 | Nortel Networks Limited | WDM optical network with passive pass-through at each node |
US6075631A (en) * | 1997-09-05 | 2000-06-13 | Bell Communications Research, Inc. | Hitless reconfiguration of a wavelength division multiplexed optical communication network |
US7248626B2 (en) | 1997-12-05 | 2007-07-24 | Paradyne Corporation | System and method of communication via embedded modulation |
US9432172B2 (en) | 1997-12-05 | 2016-08-30 | Rembrandt Wireless Technologies, Lp | System and method of communication using at least two modulation methods |
US6134358A (en) | 1998-08-27 | 2000-10-17 | Chorum Technologies Inc. | N x N switch array with reduced components |
US6567202B2 (en) * | 1999-04-16 | 2003-05-20 | Corning Incorporated | Wavelength compensation in a WSXC using off-voltage control |
US7127172B1 (en) * | 1999-06-02 | 2006-10-24 | Massachusetts Institute Of Technology | Optical frequency filter |
US6519060B1 (en) | 1999-06-04 | 2003-02-11 | Chorum Technologies Lp | Synchronous optical network in frequency domain |
US6360037B1 (en) | 1999-06-16 | 2002-03-19 | Nuonics, Inc. | Polarization-based fiber-optic switch |
US6285500B1 (en) * | 1999-06-29 | 2001-09-04 | Corning Incorporated | Wavelength selective switch |
DE19930532C2 (en) * | 1999-06-30 | 2002-03-28 | Zeiss Carl Jena Gmbh | Arrangement for optimizing the pulse shape in a laser scanning microscope |
US6389044B1 (en) * | 1999-07-02 | 2002-05-14 | Corning Incorporated | Multi-wavelength laser usable for WDM applications and interferometric sensors |
US6275623B1 (en) * | 1999-07-12 | 2001-08-14 | Corning Incorporated | Dynamically configurable spectral filter |
US6826330B1 (en) * | 1999-08-11 | 2004-11-30 | Lightconnect, Inc. | Dynamic spectral shaping for fiber-optic application |
EP1083457A1 (en) * | 1999-09-07 | 2001-03-14 | Corning Incorporated | Liquid crystal matrix add/drop system |
US6560015B1 (en) * | 1999-09-23 | 2003-05-06 | Avanex Corporation | High-isolation dense wavelength division multiplexer utilizing birefringent plates and a non-linear interferometer |
US6501877B1 (en) * | 1999-11-16 | 2002-12-31 | Network Photonics, Inc. | Wavelength router |
US6535311B1 (en) | 1999-12-09 | 2003-03-18 | Corning Incorporated | Wavelength selective cross-connect switch using a MEMS shutter array |
US6335830B1 (en) * | 1999-12-31 | 2002-01-01 | Jds Uniphase Corporation | Double-pass folded interleaver/deinterleavers |
US6301046B1 (en) * | 1999-12-31 | 2001-10-09 | Jds Uniphase Corporation | Interleaver/deinterleavers causing little or no dispersion of optical signals |
US6335992B1 (en) | 2000-02-15 | 2002-01-01 | Tellium, Inc. | Scalable optical cross-connect system and method transmitter/receiver protection |
US6498872B2 (en) * | 2000-02-17 | 2002-12-24 | Jds Uniphase Inc. | Optical configuration for a dynamic gain equalizer and a configurable add/drop multiplexer |
EP1126650A3 (en) * | 2000-02-18 | 2007-01-03 | Ericsson AB | Optical communication system |
US6606197B2 (en) * | 2000-03-28 | 2003-08-12 | Corning Incorporated | Dual grating filtering system |
US6707550B1 (en) * | 2000-04-18 | 2004-03-16 | Pts Corporation | Wavelength monitor for WDM systems |
GB2362525B (en) | 2000-05-18 | 2002-07-24 | Marconi Comm Ltd | Radiation power equalization in wavelength division multiplexing (WDM) optical communication system |
US6594082B1 (en) | 2000-06-05 | 2003-07-15 | Avanex Corporation | Optical wavelength router using reflective surfaces to direct output signals |
WO2002001773A2 (en) * | 2000-06-23 | 2002-01-03 | Cirvine Corporation | Channel multiplexer and demultiplexer for optical communications |
US6517734B1 (en) | 2000-07-13 | 2003-02-11 | Network Photonics, Inc. | Grating fabrication process using combined crystalline-dependent and crystalline-independent etching |
US6449096B1 (en) | 2000-07-13 | 2002-09-10 | Network Photonics, Inc. | Diffraction grating with reduced polarization-dependent loss |
US6381387B1 (en) | 2000-08-02 | 2002-04-30 | Networks Photonics, Inc. | Athermalization of a wavelength routing element |
US6845187B1 (en) | 2000-09-08 | 2005-01-18 | Pts Corporation | Linear optical beam translator for optical routing |
WO2002025358A2 (en) * | 2000-09-22 | 2002-03-28 | Movaz Networks, Inc. | Variable transmission multi-channel optical switch |
US6532318B1 (en) | 2000-10-18 | 2003-03-11 | Corning Incorporated | Symmetric wavelength selective switch for interconnecting two WDM rings |
US6658212B1 (en) * | 2000-10-31 | 2003-12-02 | Agilent Technologies, Inc. | Polarization-independent, configurable optical multiplexer |
US6781736B2 (en) * | 2000-11-02 | 2004-08-24 | Cambridge Research And Instrumentation, Inc. | Folded liquid-crystal variable optical attenuator |
US8457501B2 (en) * | 2000-11-03 | 2013-06-04 | Altera Corporation | Reduction of polarization-dependent loss in double-pass grating configurations |
US6751415B1 (en) | 2000-11-03 | 2004-06-15 | Pts Corporation | Reduction of polarization-dependent loss from grating used in double-pass configuration |
US6792175B2 (en) * | 2000-11-30 | 2004-09-14 | Board Of Supervisors Of Louisiana State University And Agricultural And Mechanical College | Optical crossbar switch |
US6678445B2 (en) | 2000-12-04 | 2004-01-13 | Jds Uniphase Corporation | Dynamic gain flattening filter |
US6873755B2 (en) | 2000-12-20 | 2005-03-29 | Pts Corporation | Wavelength router with staggered input/output fibers |
US6542657B2 (en) | 2000-12-20 | 2003-04-01 | Network Photonics, Inc. | Binary switch for an optical wavelength router |
US6535664B1 (en) | 2000-12-20 | 2003-03-18 | Network Photonics, Inc. | 1×2 optical wavelength router |
AU2002245345A1 (en) * | 2001-01-30 | 2002-08-12 | Board Of Trustees Operating Michigan State University | Control system and apparatus for use with laser excitation or ionization |
US7973936B2 (en) * | 2001-01-30 | 2011-07-05 | Board Of Trustees Of Michigan State University | Control system and apparatus for use with ultra-fast laser |
US7450618B2 (en) * | 2001-01-30 | 2008-11-11 | Board Of Trustees Operating Michigan State University | Laser system using ultrashort laser pulses |
US7567596B2 (en) * | 2001-01-30 | 2009-07-28 | Board Of Trustees Of Michigan State University | Control system and apparatus for use with ultra-fast laser |
US7583710B2 (en) * | 2001-01-30 | 2009-09-01 | Board Of Trustees Operating Michigan State University | Laser and environmental monitoring system |
US8208505B2 (en) * | 2001-01-30 | 2012-06-26 | Board Of Trustees Of Michigan State University | Laser system employing harmonic generation |
US7609731B2 (en) * | 2001-01-30 | 2009-10-27 | Board Of Trustees Operating Michigan State University | Laser system using ultra-short laser pulses |
US6766081B2 (en) * | 2001-02-13 | 2004-07-20 | Pts Corporation | Focal length dispersion compensation for field curvature |
IL142773A (en) * | 2001-03-08 | 2007-10-31 | Xtellus Inc | Fiber optical attenuator |
US6625346B2 (en) | 2001-03-19 | 2003-09-23 | Capella Photonics, Inc. | Reconfigurable optical add-drop multiplexers with servo control and dynamic spectral power management capabilities |
US6760511B2 (en) | 2001-03-19 | 2004-07-06 | Capella Photonics, Inc. | Reconfigurable optical add-drop multiplexers employing polarization diversity |
US6636654B2 (en) * | 2001-03-30 | 2003-10-21 | Optical Research Associates | Programmable optical switching add/drop multiplexer |
US6813300B2 (en) * | 2001-03-30 | 2004-11-02 | Santur Corporation | Alignment of an on chip modulator |
WO2002084742A1 (en) * | 2001-03-30 | 2002-10-24 | Santur Corporation | Switched laser array modulation with integral electroabsorption modulator |
WO2002084372A2 (en) * | 2001-04-13 | 2002-10-24 | Movaz Networks, Inc. | Reconfigurable free space wavelength cross connect |
US6608712B2 (en) | 2001-05-15 | 2003-08-19 | Network Photonics, Inc. | Hidden flexure ultra planar optical routing element |
US6809863B2 (en) | 2001-06-07 | 2004-10-26 | Cirvine Corporation | Low dispersion filters |
US6600591B2 (en) | 2001-06-12 | 2003-07-29 | Network Photonics, Inc. | Micromirror array having adjustable mirror angles |
ATE285639T1 (en) * | 2001-06-21 | 2005-01-15 | Cit Alcatel | METHOD AND DEVICE FOR Amplifying WDM SIGNALS USING THE STIMULATED BRILLOUIN SCATTERING PROCESS |
US6639707B2 (en) | 2001-06-25 | 2003-10-28 | Cirvine Corporation | Tandem interleaver |
US6900938B2 (en) | 2001-06-25 | 2005-05-31 | Bin Zhao | Low dispersion interleaver |
US7042609B2 (en) * | 2001-07-03 | 2006-05-09 | Pts Corporation | Two-dimensional stepwise-controlled microstructure |
US6674584B2 (en) | 2001-07-03 | 2004-01-06 | Pts Corporation | Optical surface-mount lens cell |
US6701037B2 (en) | 2001-07-03 | 2004-03-02 | Pts Corporation | MEMS-based noncontacting free-space optical switch |
US6535319B2 (en) | 2001-07-03 | 2003-03-18 | Network Photonics, Inc. | Free-space optical wavelength routing element based on stepwise controlled tilting mirrors |
US6625342B2 (en) * | 2001-07-03 | 2003-09-23 | Network Photonics, Inc. | Systems and methods for overcoming stiction using a lever |
US6657759B2 (en) | 2001-07-03 | 2003-12-02 | Pts Corporation | Bistable micromirror with contactless stops |
US6873447B2 (en) * | 2001-07-03 | 2005-03-29 | Pts Corporation | Two-dimensional free-space optical wavelength routing element based on stepwise controlled tilting mirrors |
US6614581B2 (en) | 2001-07-03 | 2003-09-02 | Network Photonics, Inc. | Methods and apparatus for providing a multi-stop micromirror |
US6795182B2 (en) * | 2001-07-06 | 2004-09-21 | Arroyo Optics, Inc. | Diffractive fourier optics for optical communications |
US6515786B1 (en) | 2001-08-03 | 2003-02-04 | Chorum Technologies Lp | Bandwidth variable wavelength router and method of operation |
US6439728B1 (en) | 2001-08-28 | 2002-08-27 | Network Photonics, Inc. | Multimirror stack for vertical integration of MEMS devices in two-position retroreflectors |
US6947628B1 (en) * | 2001-08-30 | 2005-09-20 | Avanex Corporation | Dynamic wavelength-selective optical add-drop switches |
GB0121308D0 (en) | 2001-09-03 | 2001-10-24 | Thomas Swan & Company Ltd | Optical processing |
JP4786841B2 (en) * | 2001-09-21 | 2011-10-05 | シチズンホールディングス株式会社 | Liquid crystal optical switch and driving method thereof |
US7203421B2 (en) * | 2001-09-28 | 2007-04-10 | Optical Research Associates | Littrow grating based OADM |
JP4365680B2 (en) * | 2001-10-09 | 2009-11-18 | エクステルス インコーポレイテッド | Wavelength selective optical switch |
EP1438616A1 (en) * | 2001-10-17 | 2004-07-21 | Riso National Laboratory | A system for electromagnetic field conversion |
US6747799B2 (en) | 2001-11-12 | 2004-06-08 | Pts Corporation | High-efficiency low-polarization-dependent-loss lamellar diffraction-grating profile and production process |
US6798951B2 (en) * | 2001-11-12 | 2004-09-28 | Pts Corporation | Wavelength router with a transmissive dispersive element |
US6879749B2 (en) * | 2001-11-27 | 2005-04-12 | Ec-Optics Technology Inc. | System and method for multiplexing and demultiplexing optical signals using diffraction gratings |
JP2003198485A (en) * | 2001-12-28 | 2003-07-11 | Nec Corp | Cross connect device and optical communication system |
US6856068B2 (en) | 2002-02-28 | 2005-02-15 | Pts Corporation | Systems and methods for overcoming stiction |
US6901175B2 (en) * | 2002-02-28 | 2005-05-31 | Engana Ltd. | Tunable wavelength multiplexer |
US6990268B2 (en) * | 2002-03-08 | 2006-01-24 | Pts Corporation | Optical wavelength cross connect architectures using wavelength routing elements |
US8086101B2 (en) * | 2002-03-08 | 2011-12-27 | Altera Corporation | Multi-city DWDM wavelength link architectures and methods for upgrading |
US6813408B2 (en) * | 2002-03-08 | 2004-11-02 | Pts Corporation | Methods for performing in-service upgrades of optical wavelength cross connects |
US7079723B2 (en) * | 2002-03-08 | 2006-07-18 | Pts Corporation | Optical wavelength cross connect architectures using wavelength routing elements |
US6781730B2 (en) * | 2002-03-11 | 2004-08-24 | Pts Corporation | Variable wavelength attenuator for spectral grooming and dynamic channel equalization using micromirror routing |
US6690853B1 (en) | 2002-03-11 | 2004-02-10 | Pts Corporation | Tunable DWDM demultiplexer |
US7177498B2 (en) * | 2002-03-13 | 2007-02-13 | Altera Corporation | Two-by-two optical routing element using two-position MEMS mirrors |
US6959132B2 (en) * | 2002-03-13 | 2005-10-25 | Pts Corporation | One-to-M wavelength routing element |
GB2382246A (en) * | 2002-04-09 | 2003-05-21 | Bookham Technology Plc | Add-drop multiplexing through selective polarization control |
US20030215177A1 (en) * | 2002-05-14 | 2003-11-20 | Yiqiang Li | Highly stable compact configurable optical add/drop module |
US7194206B2 (en) * | 2002-05-15 | 2007-03-20 | Altera Corporation | Variable-density optical cross-connect architectures and upgrades |
JP4367684B2 (en) * | 2002-05-15 | 2009-11-18 | シチズンホールディングス株式会社 | Dynamic gain equalizer |
CN1656721B (en) * | 2002-05-20 | 2010-09-01 | Jds尤尼菲斯公司 | Reconfigurable optical add-drop module device |
US6785039B2 (en) | 2002-06-03 | 2004-08-31 | Pts Corporation | Optical routing elements |
AU2003236545A1 (en) * | 2002-06-12 | 2003-12-31 | Optical Research Associates | Wavelength selective optical switch |
US6941073B2 (en) * | 2002-07-23 | 2005-09-06 | Optical Research Associates | East-west separable ROADM |
DE10241472B4 (en) * | 2002-09-04 | 2019-04-11 | Carl Zeiss Microscopy Gmbh | Method and arrangement for the adjustable change of illumination light and / or sample light with respect to its spectral composition and / or intensity |
JP3852409B2 (en) * | 2003-02-04 | 2006-11-29 | 富士通株式会社 | Optical functional device |
US7050230B2 (en) * | 2003-02-10 | 2006-05-23 | Fujitsu Limited | Optical switch device |
WO2004070468A1 (en) * | 2003-02-10 | 2004-08-19 | Fujitsu Limited | Optical switch device |
US6954563B2 (en) * | 2003-03-28 | 2005-10-11 | Pts Corporation | Optical routing mechanism with integral fiber input/output arrangement on MEMS die |
JP4544828B2 (en) * | 2003-03-31 | 2010-09-15 | 富士通株式会社 | Wavelength selective switch |
US7092594B2 (en) * | 2003-03-31 | 2006-08-15 | Fujitsu Limited | Wavelength selector switch |
US7130505B2 (en) * | 2003-07-23 | 2006-10-31 | Jds Uniphase Corporation | Optical performance monitor |
US7035505B2 (en) * | 2003-07-23 | 2006-04-25 | Jds Uniphase Corporation | Optical performance monitor |
US7072113B2 (en) * | 2003-10-07 | 2006-07-04 | Rene Helbing | Wavelength selective switching device and method for selectively transmitting optical signals based on wavelength |
US7092599B2 (en) * | 2003-11-12 | 2006-08-15 | Engana Pty Ltd | Wavelength manipulation system and method |
US7142751B2 (en) * | 2003-11-18 | 2006-11-28 | Avago Technologies Fiber Ip (Singapore) Pte. Ltd. | Methods and systems for chromatic dispersion compensation in switched grating WDM devices |
JP4448721B2 (en) * | 2004-03-29 | 2010-04-14 | 富士通株式会社 | Wavelength demultiplexing unit |
WO2005121876A1 (en) * | 2004-05-28 | 2005-12-22 | Trimatiz Limited | Optical device using polarized variable element |
US7787720B2 (en) * | 2004-09-27 | 2010-08-31 | Optium Australia Pty Limited | Wavelength selective reconfigurable optical cross-connect |
CN101065979A (en) * | 2004-10-12 | 2007-10-31 | Jds尤尼弗思公司 | Systems and methods for optical switching to colourless ports and coloured ports |
WO2006088841A1 (en) * | 2005-02-14 | 2006-08-24 | Board Of Trustees Of Michigan State University | Ultra-fast laser system |
US7454100B2 (en) * | 2005-05-19 | 2008-11-18 | Xtellus, Inc. | Single-pole optical wavelength selector |
US7822303B2 (en) | 2005-09-08 | 2010-10-26 | Oclaro (New Jersey), Inc. | Optical wavelength selective router |
US9103991B2 (en) | 2005-09-08 | 2015-08-11 | Finisar Corporation | Multi-pole optical signal switch |
WO2007064703A2 (en) | 2005-11-30 | 2007-06-07 | Board Of Trustees Of Michigan State University | Laser based identification of molecular characteristics |
WO2007145702A2 (en) * | 2006-04-10 | 2007-12-21 | Board Of Trustees Of Michigan State University | Laser material processing systems and methods with, in particular, use of a hollow waveguide for broadening the bandwidth of the pulse above 20 nm |
US7702194B2 (en) * | 2006-11-07 | 2010-04-20 | Olympus Corporation | Beam steering element and associated methods for manifold fiberoptic switches |
US7873246B2 (en) * | 2006-11-07 | 2011-01-18 | Olympus Corporation | Beam steering element and associated methods for manifold fiberoptic switches and monitoring |
US8000568B2 (en) * | 2006-11-07 | 2011-08-16 | Olympus Corporation | Beam steering element and associated methods for mixed manifold fiberoptic switches |
US8131123B2 (en) | 2006-11-07 | 2012-03-06 | Olympus Corporation | Beam steering element and associated methods for manifold fiberoptic switches and monitoring |
US7720329B2 (en) * | 2006-11-07 | 2010-05-18 | Olympus Corporation | Segmented prism element and associated methods for manifold fiberoptic switches |
US7769255B2 (en) * | 2006-11-07 | 2010-08-03 | Olympus Corporation | High port count instantiated wavelength selective switch |
JP5023707B2 (en) * | 2007-01-15 | 2012-09-12 | 株式会社ニコン | Tunable filter, light source device, and spectrum distribution measuring device |
JP4787188B2 (en) * | 2007-02-22 | 2011-10-05 | 日本電信電話株式会社 | Wavelength selective switch |
US20080219668A1 (en) * | 2007-03-08 | 2008-09-11 | Giovanni Barbarossa | Liquid crystal optical device with arrayed waveguide grating |
US20080219663A1 (en) * | 2007-03-08 | 2008-09-11 | Haijun Yuan | Optical device with cascaded steering devices |
US20080260390A1 (en) * | 2007-04-18 | 2008-10-23 | Giovanni Barbarossa | Bistable liquid crystal optical device |
JP5333215B2 (en) | 2007-05-31 | 2013-11-06 | 株式会社ニコン | Tunable filter, light source device and spectrum distribution measuring device |
US8311069B2 (en) | 2007-12-21 | 2012-11-13 | Board Of Trustees Of Michigan State University | Direct ultrashort laser system |
US7929108B2 (en) * | 2008-02-15 | 2011-04-19 | Oclaro (North America), Inc. | Optical switching device with reconfigurable channel spacing |
US8190025B2 (en) * | 2008-02-28 | 2012-05-29 | Olympus Corporation | Wavelength selective switch having distinct planes of operation |
WO2009121003A1 (en) * | 2008-03-27 | 2009-10-01 | Cubic Corporation | Modulating retro-reflector optical communication using polarization differential signaling |
FR2930089B1 (en) | 2008-04-11 | 2010-06-04 | Univ Limoges | ELECTRICAL IMPULSE GENERATOR OF HIGH POWER WITH EVOLVING SPECTRUM, INSTALLATION AND EQUIPMENT IMPLEMENTING SUCH A GENERATOR. |
JP5071294B2 (en) * | 2008-07-29 | 2012-11-14 | 株式会社ニコン | Tunable filter, light source device and spectrum distribution measuring device |
DE102008050797A1 (en) * | 2008-10-08 | 2010-04-15 | Diehl Bgt Defence Gmbh & Co. Kg | Optical arrangement for imaging object scene on detector unit, has lens which consists of two optical units, and optical filter, where lens is telecentric and filter is arranged in intermediate level between optical units |
US20100129076A1 (en) * | 2008-11-24 | 2010-05-27 | Giovanni Barbarossa | Method and apparatus for spectral band management |
US8675699B2 (en) | 2009-01-23 | 2014-03-18 | Board Of Trustees Of Michigan State University | Laser pulse synthesis system |
US8861075B2 (en) | 2009-03-05 | 2014-10-14 | Board Of Trustees Of Michigan State University | Laser amplification system |
WO2010146590A1 (en) * | 2009-06-18 | 2010-12-23 | Xtellus Ltd. | Liquid crystal wavelength selective router |
DE102009059280A1 (en) | 2009-12-22 | 2011-06-30 | Leibniz-Institut für Analytische Wissenschaften-ISAS-e.V., 44139 | spectrometer arrangement |
US8630322B2 (en) * | 2010-03-01 | 2014-01-14 | Board Of Trustees Of Michigan State University | Laser system for output manipulation |
JP5718016B2 (en) * | 2010-10-26 | 2015-05-13 | 古河電気工業株式会社 | Optical operation device |
US8854597B2 (en) | 2011-03-16 | 2014-10-07 | Finisar Corporation | Wavelength selective switch |
US8867016B2 (en) * | 2012-03-12 | 2014-10-21 | Oplink Communications, Inc. | Wavelength selective switch |
GB2504970A (en) | 2012-08-15 | 2014-02-19 | Swan Thomas & Co Ltd | Optical device and methods to reduce cross-talk |
US9432750B1 (en) * | 2013-04-19 | 2016-08-30 | Wavexing, Inc. | Contentionless N×M wavelength cross connect |
US9588299B2 (en) | 2014-01-29 | 2017-03-07 | Oplink Communications, Inc. | 2×2 wavelength selective switch array |
JP2019039940A (en) * | 2016-01-07 | 2019-03-14 | 国立研究開発法人産業技術総合研究所 | Circularly polarized light input-output device |
CN112432904B (en) * | 2021-01-27 | 2021-04-23 | 中国工程物理研究院流体物理研究所 | Novel liquid crystal polarization modulator and detection method thereof |
Family Cites Families (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1168161A (en) * | 1967-01-30 | 1969-10-22 | Mullard Ltd | Improvements in or relating to Light Beam Deflector Systems |
US3506834A (en) * | 1967-04-17 | 1970-04-14 | Bell Telephone Labor Inc | Time-division multiplex optical transmission system |
US4655547A (en) * | 1985-04-09 | 1987-04-07 | Bell Communications Research, Inc. | Shaping optical pulses by amplitude and phase masking |
DE3514815A1 (en) * | 1985-04-24 | 1986-11-06 | Bayerische Motoren Werke AG, 8000 München | INDEPENDENT VEHICLE WHEEL SUSPENSION |
DE3853935T2 (en) * | 1987-09-30 | 1995-10-12 | Nec Corp | Time and wavelength division multiplexed switching system. |
JPH0634534B2 (en) * | 1987-12-01 | 1994-05-02 | 日本電気株式会社 | Wavelength / time division optical switch |
US5002349A (en) * | 1989-11-29 | 1991-03-26 | Bell Communications Research, Inc. | Integrated acousto-optic filters and switches |
US5111321A (en) * | 1990-10-16 | 1992-05-05 | Bell Communications Research, Inc. | Dual-polarization liquid-crystal etalon filter |
US5132824A (en) * | 1990-08-31 | 1992-07-21 | Bell Communications Research, Inc. | Liquid-crystal modulator array |
US5150236A (en) * | 1990-08-31 | 1992-09-22 | Bell Communications Research, Inc. | Tunable liquid crystal etalon filter |
FR2672173B1 (en) * | 1991-01-29 | 1993-09-03 | Cit Alcatel | TEMPORAL PHOTONIC MULTIPLEXER, AND PHOTONIC TEMPORAL DEMULTIPLEXER. |
-
1993
- 1993-09-22 US US08/125,607 patent/US5414540A/en not_active Expired - Lifetime
-
1994
- 1994-05-26 WO PCT/US1994/005976 patent/WO1994028456A1/en active IP Right Grant
- 1994-05-26 CA CA002163630A patent/CA2163630C/en not_active Expired - Fee Related
- 1994-05-26 DE DE69427975T patent/DE69427975T2/en not_active Expired - Fee Related
- 1994-05-26 EP EP94918143A patent/EP0701710B1/en not_active Expired - Lifetime
- 1994-05-26 JP JP7500975A patent/JP2757563B2/en not_active Expired - Fee Related
Also Published As
Publication number | Publication date |
---|---|
EP0701710B1 (en) | 2001-08-16 |
JP2757563B2 (en) | 1998-05-25 |
DE69427975D1 (en) | 2001-09-20 |
CA2163630A1 (en) | 1994-12-08 |
DE69427975T2 (en) | 2002-04-11 |
EP0701710A1 (en) | 1996-03-20 |
JPH08510564A (en) | 1996-11-05 |
WO1994028456A1 (en) | 1994-12-08 |
EP0701710A4 (en) | 1997-07-23 |
US5414540A (en) | 1995-05-09 |
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