JP2009175751A - Liquid crystal variable-wavelength filter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal variable-wavelength filter device, using liquid crystal, which is applicable to an optically configured network of wavelength multiplex (WDM) communication system using optical fibers. <P>SOLUTION: The liquid crystal variable-wavelength filter device has a liquid crystal beam deflector 101 having a liquid crystal layer between a first substrate and a second substrate, and a band-pass filter 111 disposed on a projection light side of the liquid crystal beam deflector 101, and the band-pass filter 111 is fixed to a surface of the liquid crystal beam deflector 101 obliquely at a predetermined angle (α) to a vertical direction. The first substrate and second substrate are provided with electrodes, respectively, and a voltage is applied to the electrodes to produce a striped electric field in a horizontal direction, so that projection light from the liquid crystal beam deflector 101 changes in angle (θ) to a direction perpendicular to the surface of the liquid crystal beam deflector 101 to be incident on the band-pass filter. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a variable wavelength filter device using a liquid crystal, and more particularly to a variable wavelength filter device using a liquid crystal used in a wavelength division multiplexing (WDM) communication method / optical network using an optical fiber and a driving method thereof.

  Today's wavelength division multiplexing (WDM) communication systems using optical fibers are electro-optical hybrid systems, and the technology has advanced toward an all-optical network that processes signals as they are. The variable wavelength filter that enables wavelength selection is considered to play an important role in this optical network. Examples of the use of the variable wavelength filter include a dynamic add / drop multiplexer and a wavelength router.

Conventionally, various methods have been proposed as a variable wavelength filter, such as a method that mechanically controls the optical path length (including MEMS), a Mach-Zehnder type that combines an optical waveguide and a thermo-optic effect, or a filter that uses an acoustooptic effect. (See, for example, Non-Patent Document 1 and Non-Patent Document 2.)

Among such various systems, a tunable filter using liquid crystal is expected as a tunable filter applicable to an optical network because it does not have a mechanical movable part and consumes less power. As a representative example, a Fabry-Perot filter using a liquid crystal layer as a cavity will be described (for example, see Non-Patent Document 3).

  FIG. 21 shows a sectional view of the basic liquid crystal Fabry-Perot filter. The liquid crystal Fabry-Perot filter 1000 includes a cavity layer 1003 filled with a nematic liquid crystal material 1001 sandwiched between a first dielectric multilayer mirror 1017 and a second dielectric multilayer mirror 1019. The nematic liquid crystal material 1001 is aligned by the first alignment film 1013 and the second alignment film 1015 so as to be aligned in parallel with the cross-sectional view of FIG. At this time, the surfaces of the first alignment film 1013 and the second alignment film 1015 are provided with anisotropy by rubbing treatment. Further, the first filter substrate 1005 and the second filter substrate 1007 are fixed by a spacer 1021 so that the cavity layer 1003 maintains a predetermined gap. Then, a first transparent conductive film 1009 and a second transparent conductive film 1011 are formed so as to apply an electric field to the nematic liquid crystal material 1001.

This liquid crystal Fabry-Perot filter 1000 changes the resonance wavelength by changing the refractive index of the cavity layer 1003 forming the resonator and changing the product of the refractive index to be the optical path length and the cavity layer. . The resonance wavelength λm of the liquid crystal Fabry-Perot filter 1000 is
λm = 2neff (V) · d / m (1)
Given in. Here, neff (V) is an effective extraordinary refractive index of the cavity layer 1003 and indicates a function of the applied voltage V. d is a cavity gap, and m is an integer. In FIG. 21, only light having a wavelength corresponding to the resonance wavelength λm of the equation (1) among the light of the incident linearly polarized light 1031 parallel to the cross-sectional view perpendicularly incident from above becomes the output linearly polarized light 1033 and is a liquid crystal Fabry-Perot filter. 1000 passes through. The effective extraordinary refractive index neff (0) when no electric field is applied to the nematic liquid crystal material 1001 takes a constant value in the cavity layer 1003 when the pretilt angle of the liquid crystal director 1041 is θ0.
neff (0) = (sin ² θ0 / n0 ² + cos ² θ0 / ne ² ) ^−1/2 (2)
It becomes. n0 represents an ordinary light refractive index, and ne represents an extraordinary light refractive index.

  When an electric field is applied to the nematic liquid crystal material 1001, the pretilt angle θp becomes a large value at the central portion in the thickness direction of the cavity layer 1003 according to the applied voltage, and approaches the first alignment film 1013 and the second alignment film 1015. Accordingly, θp approaches θ0. Therefore, when the electric field V is applied to the nematic liquid crystal material 1001, the average value in the thickness direction of the effective extraordinary refractive index neff (V) of the cavity layer 1003 is smaller than that when no electric field is applied, and is the same. When compared at the resonance wavelength λm of the order m, the value of the resonance wavelength λm shifts to the short wavelength side as can be seen from the equation (1). Thus, the liquid crystal Fabry-Perot filter 1000 that can selectively transmit a predetermined wavelength can be used as a tunable filter.

V. M. Bright “Selected Papers On Optical MEMS”, Vol. MS153, SPIE, 1999. H. T. Mouftah and J. M. H. Elmirghani, “Photonic Switching Technology”, IEEE, 1999. K. Hirabayashi, H. Tsuda, and T. Kurokawa, J. Lightwave Technol., Vol. 11, No. 12, pp.2033-2043, 1993.

  However, in the case of the liquid crystal Fabry-Perot filter 1000 represented by FIG. 21, the cavity layer 1003 is configured as a liquid crystal cell, so that the cavity layer is structurally a single layer. Therefore, the relationship between the transmittance and the wavelength of the liquid crystal Fabry-Perot filter is the characteristic 2201 in FIG. 22, and the isolation characteristic of the stop band close to the transmission band is low, and the transmission band characteristic has a sharp peak. End up. On the other hand, ideal characteristics 2203 (an example of filter characteristics with a 1.6 nm interval (200 GHz)) in the case of using a tunable filter realizes a high isolation characteristic of a stop band close to the transmission band. It can be seen that the filter has a band characteristic (flat top). As described above, the characteristic 2201 is only a characteristic far from the ideal characteristic 2203, and this is not applicable to a tunable filter using a liquid crystal Fabry-Perot filter in a high-density wavelength division multiplexing (WDM) communication system. It is the cause.

Further, in FIG. 21, since the cavity layer 1003 is formed from the nematic liquid crystal material 1001, it is necessary to form dielectric multilayer mirrors 1017 and 1019 inside the liquid crystal cell. The dielectric multilayer mirrors 1017 and 1019 are, for example, optical 1/4 wavelength film stacks using tantalum pentoxide (Ta ₂ O ₅ ) as a high refractive index material and silicon dioxide (SiO ₂ ) as a low refractive index material. Consists of. For the 1.55 μm band used for optical communication, the dielectric multilayer mirrors 1017 and 1019 each require a thickness of about several microns, which makes it difficult to produce a liquid crystal cell such as gap control and electrode formation of the liquid crystal Fabry-Perot filter 1000.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and to provide a variable wavelength filter device using a liquid crystal suitable for high-quality optical fiber communication that can make a liquid crystal cell a simple structure.

  In order to achieve the above object, the present invention basically employs a technical configuration as described below.

The liquid crystal variable wavelength filter device of the present invention includes a liquid crystal layer between the first substrate and the second substrate.
A liquid crystal beam deflector and a band-pass filter disposed on the output light side of the liquid crystal beam deflector. The first substrate or the second substrate of the liquid crystal beam deflector has a surface of the liquid crystal beam deflector. In contrast, a plurality of electrodes are provided so that a stripe-shaped electric field is generated in the horizontal direction, and the bandpass filter is fixed at a predetermined angle (α) in the vertical direction with respect to the surface of the liquid crystal beam deflector. Then, by changing the voltage applied to the plurality of electrodes, the emission angle (θ) of the light emitted from the liquid crystal beam deflector changes in the vertical direction with respect to the surface of the liquid crystal beam deflector, The changed light is incident on the bandpass filter. A wedge-shaped prism having a constant angle (α) is disposed between the liquid crystal beam deflector and the bandpass filter.

In addition, a voltage having an arbitrary gradient is applied to each of the plurality of electrodes, a relative phase difference having an arbitrary gradient is periodically generated at a constant pitch, and a voltage having an arbitrary gradient is generated. The emission angle (θ) of the emitted light is changed by changing the pitch and changing the pitch. The plurality of electrodes provided so as to generate a stripe-shaped electric field in the horizontal direction are a plurality of stripe-shaped individual electrodes provided on the first substrate or the second substrate.

The plurality of electrodes are divided into a plurality of groups, and each individual electrode in the group is bundled by a common collector electrode, and a pair of signal electrodes are connected to both ends of the collector electrode. By applying a voltage, a voltage having an arbitrary gradient is applied to each individual electrode in the group. Further, two liquid crystal beam deflectors are provided, and a band pass filter is disposed between the two liquid crystal beam deflectors.

  As is clear from the above description, in the liquid crystal tunable wavelength filter device of the present invention, a high isolation characteristic of a stop band close to a transmission band and a flat transmission band characteristic that could not be realized by a conventional tunable filter using liquid crystals. It is possible to use an arbitrary filter having ideal characteristics according to specifications to realize transmission and reflection characteristics, and is suitable for optical fiber communication with a simple structure and simple control even in driving. A variable wavelength filter device can be realized.

  Further, keeping the incident linearly polarized light and the outgoing linearly polarized light in the liquid crystal variable wavelength filter device of the present invention in parallel means that the optical coupling coefficient to the micro optical system in which the incident light and the emitted light are composed of an optical fiber and a collimator. Is effective because the coupling loss can be minimized and the coupling loss can be minimized.

  Note that the scope of the present invention is not limited by the devices described herein, and can be applied to a liquid crystal variable wavelength filter device for application to free space optical communication and other optical signal processing systems.

It is a schematic cross section which shows the liquid crystal variable wavelength filter apparatus in embodiment of this invention. It is the principal part expansion of the 1st liquid crystal beam deflector and band pass filter vicinity of the liquid crystal variable wavelength filter apparatus in embodiment of this invention. It is a graph which shows the transmission characteristic of the liquid crystal variable wavelength filter apparatus in embodiment of this invention. It is a characteristic view which shows the relationship between the center wavelength of the liquid crystal variable wavelength filter apparatus in embodiment of this invention, and the incident angle of a band pass filter. It is sectional drawing of the liquid-crystal beam deflector in the case of becoming P polarized light seeing from the band pass filter in embodiment of this invention. It is sectional drawing of the liquid-crystal beam deflector in case it becomes S polarized light seeing from the band pass filter in embodiment of this invention. It is a schematic plan view which shows the structure of the 1st composite electrode of the liquid crystal beam deflector in embodiment of this invention. It is a schematic plan view which shows the structure of the 2nd composite electrode of the liquid crystal beam deflector in embodiment of this invention. It is a schematic plan view which shows the structure of the 3rd composite electrode of the liquid crystal beam deflector in embodiment of this invention. It is a schematic top view which shows the structure of the 4th composite electrode of the liquid crystal beam deflector in embodiment of this invention. It is a schematic diagram which shows the basic principle of the liquid-crystal beam deflector in embodiment of this invention. It is sectional drawing which shows the principle of operation of the liquid-crystal beam deflector in embodiment of this invention. It is a graph which shows the relationship of the voltage-effective birefringence characteristic of the liquid crystal element in embodiment of this invention. It is a schematic diagram explaining the drive waveform of the liquid crystal variable wavelength filter apparatus in the embodiment of the present invention. It is a figure which shows the electric potential distribution of the liquid crystal beam deflector in embodiment of this invention. It is a graph which shows the relationship of the voltage-relative phase difference characteristic of the liquid crystal element in embodiment of this invention. It is a schematic diagram which shows the relationship between the composite electrode position of a liquid crystal beam deflector and phase distribution in embodiment of this invention. It is a schematic diagram which shows the other drive waveform of the liquid crystal variable wavelength filter apparatus in embodiment of this invention. It is a schematic diagram explaining the phase distribution in the 3rd composite electrode of the liquid-crystal beam deflector in embodiment of this invention. It is a schematic cross section which shows the module structure of the liquid crystal variable wavelength filter apparatus in embodiment of this invention. It is a schematic cross section which shows the basic structure of the liquid crystal variable wavelength filter apparatus in a prior art example. It is a characteristic view for comparing the transmittance | permeability characteristic and ideal characteristic of the liquid crystal variable wavelength filter apparatus in a prior art example.

  Hereinafter, a liquid crystal variable wavelength filter device and a driving method thereof in the best mode for carrying out the present invention will be described with reference to the drawings.

  First, the configuration of a liquid crystal variable wavelength filter device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view for explaining the configuration of a liquid crystal variable wavelength filter device 130 according to an embodiment of the present invention.

  As shown in FIG. 1, the liquid crystal variable wavelength filter device 130 of the present invention has a predetermined angle α between a first liquid crystal beam deflector 101 and a second liquid crystal beam deflector 103 arranged in parallel with each other. The band-pass filter 111 made of a dielectric multilayer film is tilted and sandwiched between a wedge-shaped first wedge prism 121 and a second wedge prism 123. A first driving device 141 is connected to the first liquid crystal beam deflector 101, and a second driving device 143 is connected to the second liquid crystal beam deflector 103.

  Each of the first and second liquid crystal beam deflectors 101 and 103 has a configuration in which a liquid crystal layer is sandwiched between a plurality of individual electrodes made of parallel stripe-shaped transparent conductive films and a common electrode. By applying this voltage, a spatial refractive index modulation region is induced in the liquid crystal layer, and a blazed diffraction grating can be realized.

  The first liquid crystal beam deflector 101 controls the incident angle of a specific polarization component incident on the bandpass filter 111, and the transmission band characteristic of the liquid crystal variable wavelength filter device 130 by controlling the incident angle to the bandpass filter 111. Can be changed. Further, the second liquid crystal beam deflector 103 acts to deflect a beam having a specific polarization component in the direction opposite to that of the first liquid crystal beam deflector 101. Therefore, the incident light to the first liquid crystal beam deflector 101 and the emitted light from the second liquid crystal beam deflector 103 can be kept parallel.

  Next, the light guide path of the incident light 151 of a specific polarization component to the liquid crystal variable filter device 130 of the present invention will be described in more detail. As shown in FIG. 1, when the first liquid crystal beam deflector 101 does not deflect incident light 151 having a vibration plane parallel to the paper surface of FIG. The emission angle θ from one liquid crystal beam deflector 101 is 0 degree, and only the component whose wavelength is selected by the bandpass filter 111 enters the second liquid crystal beam deflector 103 along the first path 161. At this time, the second liquid crystal beam deflector 103 also outputs the first emitted light 153 without deflecting the light of the first path 161.

  When the incident light 151 is deflected by + θ in the positive direction by the first liquid crystal beam deflector 101, the wavelength component transmitted through the bandpass filter 111 passes through the second path 163 and passes through the second liquid crystal beam. The light enters the deflector 103. The second liquid crystal beam deflector 103 deflects the light that has passed through the second path by −θ in the negative direction and outputs the deflected light as the second outgoing light 155.

  Further, when the incident light 151 is deflected in the negative direction by −θ by the first liquid crystal beam deflector 101, the wavelength component transmitted through the bandpass filter 111 passes through the third path 165 and passes through the second liquid crystal. It enters the beam deflector 103. The second liquid crystal beam deflector 103 deflects the light that has passed through the third path 165 by + θ in the positive direction, and outputs it as third emitted light 157. The incident light 151 and the first, second, and third outgoing lights 153, 155, and 157 are parallel lights.

  As described above, the first liquid crystal beam deflector 101 acts to deflect the incident light 151 by a predetermined angle ± θ as shown in FIG. Here, assuming that θ is increased counterclockwise in FIG. 1 and the maximum value of the variable range of θ is set to θmax, α ≧ in consideration of the maximum effective use of the variable range of θ. It is necessary to determine the angle α of the first and second wedge prisms 121 and 123 so as to be θmax.

FIG. 2 is an enlarged view of a main part in the vicinity of the first liquid crystal beam deflector 101 and the bandpass filter 111 in FIG. The relationship between the emission angle θ with respect to the surface of the second liquid crystal beam deflector 101 in contact with the nematic liquid crystal layer 501 of the second transparent substrate 203 and the incident angle β of the bandpass filter 111 is as follows:
When θ = + θ, β = α-θ
When θ = 0, β = α
When θ = −θ, β = α + θ
It becomes. However, α ≧ θmax.

  In this way, by tilting the band pass filter 111 with respect to the two liquid crystal beam deflectors by the angle α, the first liquid crystal beam deflector 101 deflects the incident linearly polarized light by the angle θ, thereby causing the band pass filter 111 to have a predetermined value for the band pass filter 111. Can be converted into light having a positive incident angle β.

Next, an example of a specific configuration of the bandpass filter is shown. As the band-pass filter 111, a predetermined optical filter made of a dielectric multilayer film can be selected according to specifications as described below. Since optical signals in the 1300 nm band and 1550 nm band are frequently used in optical fiber communication, the case where the center wavelength is 1550 nm will be described below. For example, a case where a dielectric multilayer film having a four-cavity structure with a center wavelength of 1550 nm when the incident angle β is 0 degrees is shown below. The band-pass filter 111 is configured, for example, by selecting tantalum pentoxide for the high refractive index film H and silicon dioxide for the low refractive index film L, and alternately laminating them. At this time, as one film design example, H is a high refractive index film at 1550 nm and the optical path length is a quarter wavelength, and L is a low refractive index film at 1550 nm and the optical path length is a quarter wavelength. When expressed as a film
Glass / 1.3H / L / (HL) ⁶ / H / 10L / H / (LH) ⁶ / L / (HL)
⁷ / H / 10L / H / (LH) ⁷ / L / (HL) ⁷ / H / 8L / H / (LH) ⁷ / L
A configuration of / (HL) ⁷ / H / 4L / H / (LH) ⁷ / glass can be used. In this way, other configurations may be used as long as a filter having characteristics suitable for wavelength multiplexing communication can be realized.

  Next, FIG. 3 shows a transmittance characteristic graph of the liquid crystal variable wavelength filter device 130 when the incident angle β of the bandpass filter 111 is changed by the first liquid crystal beam deflector 101. When the incident angle β is 0 degree, the first transmission curve 301 of the band-pass filter 111 has a flat top characteristic 313 in the vicinity of 1550 nm. Considering the incident angle β to the bandpass filter 111 as a reference, the second transmission curve 303 is obtained when the incident angle β is 4 degrees, and the third transmission curve 305 is obtained when the incident angle β is 6 degrees. Become. Thus, it was confirmed that, together with the flat top characteristics, high isolation of a stop band that could not be realized by the liquid crystal Fabry-Perot filter 1000 (FIG. 21) in the prior art can be brought close to the ideal characteristics.

Next, FIG. 4 shows the relationship between the incident angle β of the bandpass filter 111 described in FIG. 3 and the center wavelength of the liquid crystal variable wavelength filter device 130 of the present invention. It can be seen that as the incident angle β increases, the center wavelength of the liquid crystal tunable wavelength filter device 130 shifts to the short wavelength side as indicated by the incident angle dependency characteristic 401. At this time, the relationship between the emission angle θ of the first liquid crystal beam deflector 101 and the incident angle β to the bandpass filter 111 is, for example, that the angle α of the first wedge prism 121 is 3 degrees and θmax is 3 degrees. When
When β = 0 °, θ = 3 ° When β = 3 °, θ = 0 ° When β = 4 °, θ = −1 ° When β = 6 °, θ = −3 °. That is, if the outgoing light θ of the first liquid crystal beam deflector 101 is changed from 3 degrees to -3 degrees, the incident angle to the bandpass filter 111 becomes 0 to 6 degrees, and the center wavelength in FIG. It can be arbitrarily selected within the 5 nm to 1550 nm band. The characteristics shown in FIGS. 3 and 4 show the case where P-polarized light (TM wave) is used as the light of a specific polarization component. However, when the incident angle β is about 10 degrees or less, S-polarized light is used. (TE wave) has almost the same characteristics.

  Next, the structure of the first liquid crystal beam deflector 101 will be described with reference to FIG. Since the structure of the second liquid crystal beam deflector 103 is the same as that of the first liquid crystal beam deflector 101, only the first liquid crystal beam deflector 101 will be described in this embodiment.

The nematic liquid crystal layer 501 is applied with an electric field by an alignment layer 217 formed on the composite electrode 211 of the first transparent substrate 201 and the common electrode 213 of the second transparent substrate 203 of the first liquid crystal beam deflector 101. Homogeneous alignment is performed so that the tilt angle 209 of the director 207 of the p-type (positive-type) liquid crystal molecules is 5 degrees or less. In the case of the first liquid crystal beam deflector 101 shown in FIG. 5, the incident linearly polarized light 511 has a component parallel to the paper surface. The incident linearly polarized light 511 is P-polarized light when viewed from the subsequent band-pass filter 111.

  In the first liquid crystal beam deflector 101, only the P-polarized light, which is a component parallel to the director 207 of the nematic liquid crystal layer 501 among the incident light components, becomes phase-modulable light. Therefore, the specific polarization component of the incident light 151 shown in FIG. 1 is also P-polarized light when the first liquid crystal beam deflector 101 shown in the configuration of FIG. 1 is used.

Although not clearly shown in FIG. 5, the first transparent substrate 201 and the second transparent substrate 203 are fixed via a spacer so that the nematic liquid crystal layer 501 maintains a predetermined constant thickness of several μm to several tens of μm. Although not shown in FIG. 5, in order to prevent the composite electrode 211 and the common electrode 213 from being short-circuited, tantalum pentoxide (Ta ₂ O ₅ ) or dioxide dioxide is formed on the composite electrode 211 or the common electrode 213 or both. A transparent insulating film such as silicon (SiO ₂ ) may be formed. It is also desirable to improve the transmittance by making the transparent insulating film a dielectric multilayer film composed of a high refractive index film and a low refractive index film. The common electrode 213 formed on the second transparent substrate 203 may be a full-surface electrode made of a transparent conductive film. The structure of the composite electrode 211 will be described later.

  When indium tin oxide (ITO) is used for the transparent conductive film forming the optical path portion of the composite electrode 211 and the common electrode 213, the film thickness is set to 50 nm or less, and in the near infrared region of 1.3 μm to 1.6 μm. In order to improve the transmittance, it is desirable to use a film having a sheet resistance of several hundred Ω to 1 kΩ with an increased oxygen concentration during film formation.

In addition to ITO, thin films such as indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), and zinc oxide (ZnO) can be used as the transparent conductive film. In this case as well, it is desirable to use a film with a film thickness of 50 nm or less and a sheet resistance of about several hundred Ω to 1 kΩ.

Further, the surface of the first transparent substrate 201 or the second transparent substrate 203 made of glass opposite to the nematic liquid crystal layer 501 is required to prevent reflection at the interface between the air and the transparent substrate on the surface in contact with the air layer. In response to this, a non-reflective coating 215 is formed. As the non-reflective coating 215, for example, a coating layer made of a dielectric multilayer film of tantalum pentoxide (Ta ₂ O ₅ ) and silicon dioxide (SiO ₂ ) can be used.

  The incident light 151 shown in FIG. 1 or the incident linearly polarized light 511 of FIG. 5 is shown as a representative configuration in the case where it is P-polarized as viewed from the subsequent bandpass filter 111. However, the incident linearly polarized light 511 is a downstream bandpass filter. FIG. 6 shows the configuration of the liquid crystal beam deflector 101 when S-polarized light is viewed from 111. The structure is the same as that shown in FIG. 5 except that the director 207 of the nematic liquid crystal layer 501 is parallel to the S-polarized light of the incident linearly polarized light 511. The use of the liquid crystal beam deflector for the P-polarized light and S-polarized light may be determined depending on the specifications and applications.

  Next, the structure of the first composite electrode for forming the blazed diffraction grating of the first liquid crystal beam deflector 101 will be described in detail with reference to FIG. The first composite electrode 211 a is a plan view of an electrode in which two diffraction grating regions of a first element grating 751 and a second element grating 761 are arranged in a first active region 671. In FIG. 7, the first element lattice 751 includes the first individual electrode 721 to the Nth individual electrode 730. The second element lattice 761 includes the (N + 1) th individual electrode 731 to the 2Nth individual electrode 740. In this first composite electrode 211a, N = 10 is set for convenience for ease of explanation. The first to second N individual electrodes 740 to 740 are formed of a transparent conductive film such as ITO having the above-described film thickness and resistance value.

Further, the first N-th individual electrode 721 to the second N-th individual electrode 740 are grouped into a plurality of groups (two groups in FIG. 7) outside the first active region 671. They are connected by a common collector electrode such as ITO, which is the same material as the individual electrodes. In FIG. 7, the first individual electrode 721 to the Nth individual electrode 730 are connected by the first collector electrode 701 outside the first active region 671, and the (N + 1) th individual electrode 731 to the second Nth individual electrode are connected. 740 is similarly connected by the second collector electrode 703. Furthermore, the first signal electrode 711 and the second signal electrode 713 made of a low-resistance metal material such as Mo or Ag alloy are connected to both ends of the first collector electrode 701, respectively. The third signal electrode 715 and the fourth signal electrode 717 are connected to each other. The collector electrode may be configured not only to have a sheet resistance of several hundred to 1 kΩ, but also to make the film thickness thinner, or to narrow the electrode width so as to have a linear resistance in the long side direction of the electrode. I do not care.

  In FIG. 7, for convenience, only two diffraction grating regions of the first element grating 751 and the second element grating 761 are shown. However, in the actual first liquid crystal beam deflector 101, the first active region 671 is not included. It is necessary to form a predetermined number of element gratings according to the incident beam diameter. As an example, as a specific design example when the 1550 nm band is used as incident light, a case where light from a single mode optical fiber is incident on the first active region 671 as parallel light by a collimator will be described. At this time, when the Gaussian beam diameter of the parallel light is set to 300 μm, the width L of the first active region is set to 400 μm to 1.5 mm. In addition, the plurality of individual electrodes of each element grating preferably have a line and space of 2 μm or less in consideration of the wavelength of incident light, and the width W of the first composite electrode 211a when the element grating pitch P0 is 50 μm to 100 μm. Is preferably about 800 μm to 2 mm. Accordingly, the number of element lattices is 16 to 40 when the pitch P0 is 50 μm, and the number of element lattices is 8 to 20 when the pitch P0 is 100 μm. Here, as shown in FIG. 1, the width W of the first composite electrode 211a deflects the beam by Du when the emitted light has a beam deflection angle of + θ, and by Dd when the beam deflection angle is −θ. Since this is not the case (when θ is 0 degree), it is necessary to determine the width according to the beam deviation.

  As is clear from the above description, in the first liquid crystal beam deflector 101 forming the blazed diffraction grating, even when one diffraction grating region is composed of N individual electrodes, the control signal from the drive circuit is used as the control signal. The number of signal electrodes to be connected is 2M with respect to the number of element lattices (M) by connecting a pair of signal electrodes to both ends of the collector electrode. This configuration has the advantage that the number of signal electrodes can be greatly reduced, particularly when the number of individual electrodes increases.

  Next, the operation principle of the first liquid crystal beam deflector 101 will be described with reference to FIG. When an external electric field is applied in a state where the director 207 is homogeneously oriented in the direction parallel to the xz plane, a p-type (positive-type) nematic liquid crystal is aligned so that the major axis direction of the director is parallel to the electric field direction. Consider that the linearly polarized light 1110 oscillating in the direction parallel to the x-axis is incident on the liquid crystal beam deflector 101 used in the z-axis direction. The incident wavefront 1113 before entering the liquid crystal beam deflector 101 is a plane. By applying an electric field to the liquid crystal beam deflector 101 and controlling the in-plane distribution of the director so as to have a predetermined refractive index distribution, the incident wavefront 1113 can be converted into an outgoing wavefront 1123 of a plane wave deflected by a predetermined angle θ. .

This phenomenon will be described in more detail with reference to FIG. The plane on the emission side of the nematic liquid crystal layer 501 of the liquid crystal beam deflector 101 is the xy plane, and the liquid crystal is aligned so as to be parallel to the xz plane. At this time, the incident linearly polarized light 1201 enters the nematic liquid crystal layer 501 perpendicularly. In this nematic liquid crystal layer 501, an operating point is determined in advance so that the distribution 1211 of the extraordinary refractive index ne (x) as a function of the position x linearly changes between a and b at the pitch P of the element grating. deep. Further, although the thickness d of the nematic liquid crystal layer 501 is constant, the refractive index ne (x) changes linearly with the pitch P, so that the incident linearly polarized light 1201 propagating in the nematic liquid crystal layer 501 is It will be modulated with different retardations Δn (x) · d. Here, when n0 is the ordinary refractive index of the liquid crystal,
Δn (x) = ne (x) −n0 (3)
It is.

When the incident linearly polarized light 1201 propagates in the nematic liquid crystal, that is, in a dielectric medium, the incident linearly polarized light 1201 propagates slowly where the retardation is large, and conversely, propagates quickly where the retardation is small. Therefore, the output linearly polarized light 1203 emitted from the nematic liquid crystal layer 501 has a wavefront of tan θ = δΔn · d / P (4)
Will just lean. Here, δΔn is a value obtained by calculating the difference between retardations Δn (x) at point a and point b as in the following equation.
δΔn = Δn (a) −Δn (b) (5)
Thus, if the distribution 1211 of the extraordinary light refractive index ne (x) in the nematic liquid crystal layer 501 of the liquid crystal beam deflector is linear, the wavefront of the output linearly polarized light 1203 is also flat as in the case of the incident linearly polarized light 1201, and the result Thus, the outgoing linearly polarized light 1203 can be deflected by θ with respect to the incident linearly polarized light 1201.

  Next, the conditions under which the extraordinary refractive index ne (x) of the nematic liquid crystal layer 501 used in the present invention can be linearly approximated were considered. Incident linearly polarized light undergoes modulation determined by applied voltage-effective birefringence characteristics as shown in FIG. In FIG. 13, the horizontal axis represents the effective value of the voltage applied to the nematic liquid crystal layer 501 and the vertical axis represents the effective birefringence Δn. The shape of the electro-optic response curve is determined by parameters such as the elastic constant of the liquid crystal to be used, the dielectric anisotropy characteristics, and the pretilt angle determined by the alignment film layer when no electric field is applied. This applied voltage-effective birefringence characteristic is that of a nematic liquid crystal material BL007 (trade name) manufactured by Merck. Further, this characteristic is a theoretical curve obtained by assuming that Δnmax = 0.287 and the thickness of the liquid crystal layer is 20 μm. In FIG. 13, the horizontal axis indicates the voltage 1501 applied to the homogeneous alignment cell, and the vertical axis indicates the effective birefringence Δn 1503 of the liquid crystal molecules. FIG. 13 shows the characteristics when the pretilt angle is 0.5 degrees, 2 degrees, 5 degrees, and 10 degrees. When the liquid crystal beam deflector 101 having the first composite electrode 211a is used, it is necessary to use the vicinity of the linear region 1520 that can approximate the linear curve in order to obtain the operation described in FIG. Accordingly, it can be understood that the pretilt angle of the nematic liquid crystal is preferably 5 degrees or less, more preferably 2 degrees or less in order to take a wide linear region 1520.

  Next, a driving method of the liquid crystal beam deflector 101 having the first composite electrode 211a and a phenomenon of generating a potential gradient of the collector electrode will be described. First, a part of the first element lattice 751 is taken out and described. FIG. 14 shows drive waveforms. A first drive waveform 1601 is applied to the first signal electrode 711, and a second drive waveform 1603 is applied to the second signal electrode 713. The first drive waveform 1601 and the second drive waveform 1603 have the same frequency and phase and differ only in voltage, and the second drive waveform 1603 has a larger voltage than the first drive waveform 1601. In the period t1, the first drive waveform 1601 is + V1 [V], and the second drive waveform 1603 is + V2 [V]. Here, the common electrode 213 is set to 0 [V]. Therefore, since the potential is divided by the first collector electrode 701 formed of a linear resistance material such as a transparent conductive film, the plurality of individual electrodes of the first element lattice 751 formed in the first active region 671 are respectively The voltage applied to the first signal electrode 711 and the second signal electrode 713 is linearly divided depending on the arrangement position. Here, in the longitudinal direction of the individual electrode, the individual electrode is formed of a low resistance material as compared with the impedance of the nematic liquid crystal layer 501, so that the potential can be substantially the same. Furthermore, a period for applying the bias AC voltage to the common electrode may be provided separately from the period 1 and the period 2 as necessary.

Next, the relationship between the potential gradient on the collecting electrode 701 in the first composite electrode 211a (FIG. 7) and the potential of each individual electrode will be described in more detail. In the period t1 shown in FIG. 14, the potential distribution of the first collector electrode 701 that connects the first signal electrode 711 and the second signal electrode 713 is the first potential distribution of FIG. A linear potential distribution indicated by 1801 is obtained. In the period t2 shown in FIG. 14, the potential distribution of the first collector electrode 701 becomes the second potential distribution 1803 in FIG. Here, point a in FIG. 15 corresponds to the position of the individual electrode connected to the first signal electrode 711, and point b corresponds to the position of the individual electrode connected to the second signal electrode 713. Yes. When the drive waveform shown in FIG. 14 is a rectangular wave with 50% duty, the two first and second potential distributions 1801 and 1803 shown in FIG. 15 are alternately repeated in time. Therefore, the voltage applied to the nematic liquid crystal layer 501 through the common electrode 213 maintained at 0 [V] is changed to an alternating voltage at any individual electrode position, and no DC component is applied to the nematic liquid crystal layer 501. . Further, since nematic liquid crystal has an effective value response, V1 [V] is always applied as an effective value to the first signal electrode 711 side, and a voltage of V2 [V] is applied to the second signal electrode 713. Further, it can be considered that the potential divided by the first collector electrode 701 is applied to each individual electrode.

Next, the phase distribution generated in the collector electrode will be described. FIG. 16 is a graph showing the relationship between the voltage [Vrms] applied to the liquid crystal and the relative phase difference Δ when BL007 (trade name, manufactured by Merck Japan Ltd.) is used as the liquid crystal and the pretilt angle is set to 1 degree. . It can be seen that the characteristic curve 1711 has a linear approximation region 1701 in the vicinity of 1.5 to 2 [V]. Consider a case where the thickness d of the liquid crystal layer is 30 [μm] and the wavelength λ is 1550 [nm]. The relative phase difference Δ is set such that the effective birefringence is Δn.
Δ = Δn · d / λ (6)
Defined in From the linear approximation region 1701 of the relative phase difference Δ in FIG. 16, it can be seen that the linearly tunable range 1705 can be taken at a wavelength λ of 2 wavelengths or more, that is, about 4π in phase at λ = 1550 nm. As described above, if a linear approximation of the extraordinary refractive index can be performed by the pretilt angle, and a voltage within the operating voltage range 1703 operating in the linear approximation region 1701 within the range of the pretilt angle is applied, the first composite A phase distribution proportional to the position of each individual electrode can be realized in the first active region 671 of the electrode 211a.

Next, a specific method for realizing an arbitrary deflection angle with the liquid crystal beam deflector 101 having the first composite electrode 211a using the above driving method will be described with reference to FIG. In this case, the pitch of the element grating is P0, and the maximum deflection angle θmax is tan θmax = λ / P0 (7)
It is defined as At this time, the maximum phase modulation amount for the phase modulation curve 2001 of θmax is one wavelength, that is, 2π, at the distance P0 of the element grating. In the case of the first composite electrode 211a, since the positions of the first and second signal electrodes are determined in advance, it is impossible to apply a reset of 2π at any electrode position in order to change the phase. is there. Therefore, in order to perform resetting at a predetermined position, first, in order to swing an angle θp slightly smaller than θmax without generation of high-order light, it is necessary to perform resetting between λ and 2λ in the phase modulation curve 2003 of θp. As described above, in order to control the light of a specific polarization component to a predetermined deflection angle using the first composite electrode 211a, an element grating whose phase modulation amount falls within the range of λ to less than 2λ among the predetermined element gratings. You must use a drive method that resets every time.

Next, another driving method of the liquid crystal beam deflector 101 having the first composite electrode 211a will be described. FIG. 18 is a diagram showing a waveform application period to signal electrode terminals arranged in one element lattice. In this driving method, one frame is divided into period 1 and period 2 for driving. Specifically, in order to prevent the deterioration of the nematic liquid crystal layer 501, an alternating voltage drive signal 2101 having an average value of 0 is applied to the first signal electrode 711, and the second signal electrode 713 is connected to the common electrode 213. A period 1 in which the potential is 0 [V] so as to be the same potential, and a drive signal 2101 having an alternating voltage is applied to the second signal electrode 713 so that the first signal electrode 711 has the same potential as the common electrode 213. This is a driving method in which periods 2 of 0 [V] are alternately provided. By using such a driving method, the liquid crystal potential distribution generated in the element lattice of one frame obtained by adding the period 1 and the period 2 is the sum of the effective values of the respective periods. The applied waveforms in the period 1 and the period 2 may be arbitrary. For example, two waveforms having different voltages can be applied. Further, a waveform whose effective value is controlled by pulse width modulation may be used. Furthermore, a period for applying the bias AC voltage to the common electrode may be provided separately from the period 1 and the period 2 as necessary.

  Next, another structure of the composite electrode 211 for forming the blazed diffraction grating will be described in detail with reference to FIG. In addition to the structure of the first composite electrode 211a (FIG. 7) described above, the second composite electrode 211b has collectors arranged on both ends of a group of individual electrodes outside the first active region 671. Adopt the configuration. In FIG. 8, the third collector electrode 801 is opposed to the second collector electrode 703 via the individual electrode at a position facing the outside of the first active region 671 via the individual electrode of the first collector electrode. A fourth collector electrode 803 is disposed at a position where the second collector electrode 803 is located. Further, the third collector electrode 801 is connected to the fifth signal electrode 811 and the sixth signal electrode 813 made of a low resistance metal material such as Mo or Ag alloy, and the fourth collector electrode 803 is connected to the seventh signal electrode. 815 and the eighth signal electrode 817 are connected.

  In the second composite electrode structure, the first signal electrode 711 and the fifth signal electrode 811, the second signal electrode 713 and the sixth signal electrode 813, the third signal electrode 715 and the seventh signal electrode 815, The pair of the fourth signal electrode 717 and the eighth signal electrode 817 is driven by being short-circuited outside. Note that the driving method described above can be applied as it is to the driving method of the liquid crystal beam deflector using the second composite electrode 211b.

  The structure of the second composite electrode 211b for forming the liquid crystal beam deflector shown in FIG. 8 is different from the impedance at the driving frequency of the nematic liquid crystal layer when the individual electrode is thin or long. This is particularly effective when the impedance of the signal becomes so large that it cannot be ignored.

  Next, a third composite electrode having another configuration that is particularly effective in the case of an application that requires high-speed response will be described. FIG. 9 is a plan view showing the relationship between the first active region 671 and the third composite electrode 211c for realizing a blazed diffraction grating. In FIG. 9, the third composite electrode 211c is formed from the first stripe electrode 621 to the Nth individual electrode 640 (N = 20 for convenience) formed by a transparent conductive film such as ITO constituting the composite electrode. ing.

  In order to realize a blazed diffraction grating for performing beam deflection in the first active region 671, it is necessary to apply a predetermined voltage to each of the individual electrodes 621 to 640 in the third composite electrode 211c. The voltage pattern applying means includes first to N-th individual electrodes 621 to 640 separately formed as shown in FIG. 9, and each individual electrode is independently driven by a driving circuit such as an IC. A stepwise potential difference is generated in the individual electrodes.

A method for realizing an arbitrary deflection angle by using the liquid crystal beam deflector 101 using the third composite electrode 211c will be described with reference to FIG. In the third composite electrode 211c, each individual electrode can be independently applied with an arbitrary voltage by a direct drive circuit. Therefore, an arbitrary deflection angle can be realized when the modifiable amount can be as small as 2π (one wavelength). For example, when a voltage that realizes the first phase modulation waveform 1901 in the first active region 671 is applied to each individual electrode, the deflection angle θ1 is
tan θ1 = λ / P1 (8)
Takes the value given by. Here, λ represents a relative phase difference for one wavelength. In addition, the x-axis direction was a direction orthogonal to the individual electrode. By using this configuration, it is possible to bring the diffraction efficiency closer to 100% by resetting the phase by one wavelength at the pitch P1 in which predetermined individual electrodes are bundled. Next, the second phase modulation waveform 1903 is converted into the first active region 671.
Is applied to each individual electrode, the deflection angle θ2 is
tan θ2 = λ / P2 (9)
Takes the value given by. As described above, it is possible to easily realize an arbitrary deflection angle θ by changing the predetermined pitch P1 for resetting the phase.

  Further, in the case of the liquid crystal beam deflector 101 using the third composite electrode 211c, for example, not only the linear approximation region 1701 shown in FIG. 16 but also the entire region of the characteristic curve 1711 can be used, and the thickness of the liquid crystal cell. This is advantageous in achieving a high-speed response by reducing the thickness. This is because an arbitrary voltage can be applied to each individual electrode, so that the nonlinearity of the characteristic curve 1711 can be absorbed by weighting of the applied voltage.

  Finally, a module configuration 320 when the liquid crystal variable wavelength filter device 130 of the present invention is arranged between collimators often used in actual optical fiber communication will be described with reference to FIG. FIG. 20 shows a basic configuration as viewed from the side surface of FIG. The liquid crystal variable wavelength filter device 130 according to the present invention includes a bandpass filter 111 made of a dielectric multilayer film that is inclined by a predetermined angle α between the first liquid crystal beam deflector 101 and the second liquid crystal beam deflector 103. The first wedge prism 121 and the second wedge prism 123 are sandwiched between the first wedge prism 121 and the second wedge prism 123. A first driving device 141 is connected to the first liquid crystal beam deflector 101, and a second driving device 143 is connected to the second liquid crystal beam deflector 103.

  First, consider that the input light 171 is incident on the input A. Although not clearly shown in FIG. 20, the input light 171 is light that is collimated from light emitted from the optical fiber. The input light 171 is considered by dividing it into a first linearly polarized light 104 that is P-polarized light for the first polarization separator 131 and a second linearly-polarized light 105 that is S-polarized light for the first polarization separator 131. Hereinafter, the P-polarized light for the first polarization separator 131 is indicated by a vertical arrow on the drawing, and the S-polarization for the first polarization separator 131 is indicated by a black circle on the drawing.

  The first linearly polarized light 104 incident on the first polarization separator 131 passes through the first polarization separator 131 because it is P-polarized light. Next, the first half-wave plate 181 rotates the azimuth by 90 °, and the first half-wave plate 181 is converted into polarized light that vibrates in the same direction as the S-polarized light with respect to the first polarization separator 131. Further, it passes through the first active region 145 of the first liquid crystal beam deflector 101 and reaches the bandpass filter 111. Here, the alignment treatment is performed so that the rubbing directions of the alignment films of the first liquid crystal beam deflector 101 and the second liquid crystal beam deflector 103 are parallel to the incident polarized light. Next, of the first linearly polarized light 104, the component whose incident angle is selected by the first liquid crystal beam deflector 101 and transmitted through the bandpass filter 111 is transferred to the bandpass filter 111 by the second liquid crystal beam deflector 103. Is deflected in the direction opposite to the incident deflection angle. That is, when the first liquid crystal beam deflector 101 deflects by + θ, the second liquid crystal beam deflector 103 deflects by −θ. The light emitted from the second liquid crystal beam deflector 103 is rotated by 90 ° in the azimuth angle by the second half-wave plate 183, converted to P-polarized light with respect to the second polarization separator 133, and output as third linearly polarized light 113. Ejects from B.

  On the other hand, the second linearly polarized light 105 entering the input A is changed to a right angle by the first polarization separator 131 because it is an S-polarized light, enters the first total reflection mirror 125, and is further directed at a right angle. And the S-polarized light passes through the second active region 147 of the first liquid crystal beam deflector 101 and reaches the bandpass filter 111. Here, the alignment treatment is performed so that the rubbing directions of the alignment films of the first liquid crystal beam deflector 101 and the second liquid crystal beam deflector 103 are parallel to the incident polarized light. Next, of the second linearly polarized light 105, the component whose incident angle is selected by the first liquid crystal beam deflector 101 and transmitted through the bandpass filter 111 is transferred to the bandpass filter 111 by the second liquid crystal beam deflector 103. Is deflected in the direction opposite to the incident deflection angle.

  That is, when the first liquid crystal beam deflector 101 deflects by + θ, the second liquid crystal beam deflector 103 deflects by −θ. The light emitted from the second liquid crystal beam deflector 103 is turned at a right angle by the second total reflection mirror 127, and is turned again at a right angle by the second polarization separator 133, so that the fourth linearly polarized light 115 is obtained. As output from the output B. Although not shown, the output light 173 obtained by combining the two linearly polarized lights 113 and 115 is coupled to an optical fiber through a collimator lens as necessary.

  Thus, the point where the light passing through the first active region 145 and the second active region 147 intersects the bandpass filter 111 is different on the bandpass filter 111. Therefore, since the reflection and transmission characteristics of the band-pass filter 111 often vary in the plane, the composite electrode of the first liquid crystal beam deflector 101 and the second liquid crystal beam deflector 103 is, for example, shown in FIG. As in the fourth composite electrode, it is desirable to add a function of being divided into two regions and independently controlled by a drive circuit.

  FIG. 10 is a plan view of the fourth composite electrode 211 d having the first active region 671 and the second active region 673. In order to control the first active region 671 and the second active region 673 independently, in the fourth composite electrode 211d, the first composite electrodes 211a shown in FIG. 7 are arranged in two planes. It has a structure. The first active region 671 is the same as the first composite electrode 211a, and the fourth composite electrode structure includes a third element lattice 951 and a fourth element lattice 961 in the second active region 673. Have. The third element lattice 951 has a ninth signal electrode 911 and a tenth signal electrode 913 for applying a drive waveform, and the fourth element lattice 961 has an eleventh signal electrode 915 and a twelfth signal electrode. 917. In the fourth composite electrode 211d, the first and second active regions 671 and 673 have been described as having two element lattices for the sake of simplicity. However, the number of element lattices is set according to the specification. You can increase it. As described above, the fourth composite electrode 211d having this configuration has a structure effective when it is desired to divide and control the input to the liquid crystal variable wavelength filter device.

  In the above, the case where the light of a specific polarization component incident on the liquid crystal beam deflector is a linearly polarized light component and the use efficiency of the light of the component is increased has been described. It goes without saying that can be applied.

DESCRIPTION OF SYMBOLS 101 1st liquid crystal beam deflector 103 2nd liquid crystal beam deflector 111 Band pass filter 121 1st wedge prism 123 2nd wedge prism 130 Liquid crystal variable wavelength filter apparatus 141 1st drive device 143 2nd drive device 151 incident light 153 first outgoing light 155 second outgoing light 157 third outgoing light 161 first path 163 second path 165 third path 201 first transparent substrate 203 second transparent substrate 207 director 209 Tilt angle 211 Composite electrode 213 Common electrode 501 Nematic liquid crystal layer 621 to 640 Individual electrode 721 to 740 Individual electrode 751 First element grating 761 Second element grating 951 Third element grating 961 Fourth element grating

Claims (6)

A liquid crystal beam deflector comprising a liquid crystal layer between the first substrate and the second substrate;
A bandpass filter disposed on the outgoing light side of the liquid crystal beam deflector,
A plurality of electrodes are provided on the first substrate or the second substrate of the liquid crystal beam deflector so that a stripe-shaped electric field is generated in a horizontal direction with respect to the surface of the liquid crystal beam deflector,
The bandpass filter is tilted and fixed at a predetermined angle (α) in the vertical direction with respect to the surface of the liquid crystal beam deflector,
By varying the voltage applied to the plurality of electrodes, the emission angle (θ) of the light emitted from the liquid crystal beam deflector changes in a direction perpendicular to the surface of the liquid crystal beam deflector, The liquid crystal variable wavelength filter device, wherein the changed light is incident on the band pass filter.   2. The liquid crystal variable wavelength filter device according to claim 1, wherein a wedge-shaped prism having the predetermined angle (α) is disposed between the liquid crystal beam deflector and the bandpass filter.   A voltage having an arbitrary gradient is applied to each of the plurality of electrodes, a relative phase difference having an arbitrary gradient is periodically generated at a constant pitch, and the voltage having the arbitrary gradient is applied. 3. The liquid crystal variable wavelength filter device according to claim 1, wherein an emission angle (θ) of the emitted light is changed by modulating the pitch and changing the pitch. 4.   The plurality of electrodes provided so as to generate a stripe-shaped electric field in the horizontal direction are a plurality of stripe-shaped individual electrodes provided on the first substrate or the second substrate. 4. The liquid crystal variable wavelength filter device according to any one of 1 to 3.   The plurality of electrodes are divided into a plurality of groups, and each individual electrode in the group is bundled by a common collector electrode, and a pair of signal electrodes are connected to both ends of the collector electrode, and the pair of signals 5. The liquid crystal variable wavelength filter device according to claim 3, wherein a voltage having an arbitrary gradient is applied to each individual electrode in the group by applying a voltage to the electrode.   6. The liquid crystal variable wavelength filter according to claim 1, wherein the liquid crystal beam deflector includes two liquid crystal beam deflectors, and the bandpass filter is disposed between the two liquid crystal beam deflectors. 7. apparatus.

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