JP4869116B2 - Liquid crystal optical component and wavelength selective switch using the same - Google Patents

Description

  The present invention relates to a liquid crystal optical component capable of changing light transmittance, and a wavelength selective switch using the liquid crystal optical component and capable of branching or coupling light of different wavelengths in optical wavelength division multiplexing communication.

  With the spread of wavelength division multiplexing optical communication, wavelength selective switches that multiplex or demultiplex optical signals for each wavelength have become key devices for optical communication.

  Here, FIG. 6 shows a schematic configuration diagram of a conventional optical shutter.

  6 includes a birefringent plate 110 that outputs incident light divided into two deflections, a half-wave plate 111 that transmits one light from the birefringent plate 110, and a birefringent plate 110. A polarizer 112 that adjusts the deflection angle of the other light and the light from the half-wave plate 111, and a polarization rotation element 113 that rotates the deflection of the two lights from the polarizer 112 by 45 °, respectively. Prepare. FIG. 6 shows a form in which the optical shutter 100 is provided in the front stage of the mirror 114.

  The incident beam to the mirror 114 is a beam including vertically and horizontally polarized waves in the drawing. This is divided into two orthogonal polarized waves by the birefringent plate 110. The polarized light travels along the crystal axis direction of the birefringent plate 110 and enters the half-wave plate 111. Since this polarized light is rotated 90 degrees and enters the polarizer 112, polarization independence is realized. The light beam is incident on the polarization rotation element 113 from the polarizer 112 and is reflected by the mirror 114 as it is when the polarization direction is rotated by 45 degrees, is incident on the polarization rotation element 113 again, and the polarization direction is Rotate 45 °. The first 45 ° rotation and the 45 ° rotation after reflection by the mirror 114 result in 90 ° rotation, and the light is blocked by the polarizer 112. The light beam is attenuated by the polarizer 112.

  When this optical shutter 100 is applied to a wavelength selective switch, it is possible to prevent optical coupling to a non-target optical fiber that occurs when the mirror 114 operates by closing the optical shutter 100. Further, the amount of attenuation of the beam of light reflected from the mirror 114 can be controlled by controlling the polarization angle with voltage (see, for example, Patent Document 1).

JP 2006-106304 A

  However, the conventional optical shutter controls the intensity of the light beam by a method of controlling the polarization direction. In addition, the light quantity control method using polarization is affected by fluctuations in the polarization of the incident beam. For this reason, the birefringent plate 110 for making the polarization independent and the polarizer 112 for controlling the polarization are necessary, and the number of parts is further increased. Further, the insertion loss increases due to the increase in the number of parts.

  Accordingly, an object of the present invention is to provide a liquid crystal optical component having a small number of components and a small insertion loss, and a wavelength selective switch using the same.

  In order to achieve the above object, in the present invention, a liquid crystal optical element that changes the light transmittance by applying a voltage to a polymer liquid crystal composite material in which liquid crystal particles are dispersed in a polymer is provided in the front stage of the mirror. I made it.

  Specifically, the liquid crystal optical component according to the first invention of the present application is a polymer liquid crystal composite layer in which liquid crystal particles are dispersed in a polymer, and the polymer liquid crystal composite layer is irradiated and transmitted through the polymer liquid crystal composite layer. A plurality of mirrors capable of reflecting light at a predetermined angle, and a light transmittance of the polymer liquid crystal composite layer to the plurality of mirrors with respect to light directed to the plurality of mirrors by applying a voltage to the polymer liquid crystal composite layer. And a pair of electrodes provided on the polymer liquid crystal composite layer so as to change for each light.

  Accordingly, it is possible to provide a liquid crystal optical component that can control the attenuation amount of light incident on the plurality of mirrors for each light to the plurality of mirrors, has a small number of components, and has a small insertion loss.

  In the above-described liquid crystal optical component, the plurality of mirrors are arranged in a row so that the normal lines of the reflecting surfaces of the plurality of mirrors are parallel, the electrode is a light transmissive material, and the polymer liquid crystal A stripe is formed in the arrangement direction of the plurality of mirrors at substantially the same interval as the arrangement intervals of the plurality of mirrors on both surfaces of the polymer liquid crystal composite layer so as to apply a voltage to the polymer liquid crystal composite layer across the composite layer. It is desirable that it be formed.

  Thereby, the deflection angle of the MEMS mirror can be several degrees, and the fiber can be sufficiently switched. For example, when the distance between the mirror surface and the polymer liquid crystal composite layer is 0.3 mm and the mirror swing angle is 5 degrees, the beam spot position deviation of the incident and reflected beams is approximately 0.03 mm, and one electrode It can be smaller than the width. In this way, even if the mirror angle changes, it can be arranged so as to pass through the same electrode portion, and the light transmittance of each wavelength can be controlled.

  The liquid crystal optical component further includes a housing having one surface opened, and the plurality of mirrors are disposed at a bottom portion of the housing such that a reflecting surface of the plurality of mirrors faces the one surface, The reflective surface of the plurality of mirrors is such that the surface opposite to the irradiated surface of the polymer liquid crystal composite layer that is irradiated with light covers the one surface opened of the housing. It is desirable to be arranged opposite to. Here, the intensity of the incident light beam has a Gaussian distribution in the radial direction, and the beam diameter is not larger than the area of the pair of electrodes of the polymer liquid crystal composite layer, and is reflected from the mirror and returned. It is important to sufficiently narrow the distance between the polymer liquid crystal composite layer and the mirror so that the diameter of the incoming light beam does not become larger than the area of the pair of electrodes.

  As a result, the liquid crystal optical component can be modularized.

  In order to achieve the above object, a wavelength selective switch according to the present invention inputs and outputs light including one or more wavelengths, and faces the plurality of light input / output ports provided side by side and in a straight line. A first lens arranged so that the light from the input / output port becomes parallel light; and disposed on the opposite side of the plurality of light input / output ports with the first lens in between; Light that has passed through the first lens on a grating surface in which a plurality of gratings parallel to the arrangement direction of the plurality of light input / output ports are formed on a surface that receives light that has passed through the first lens among the output light Of the plurality of light input / output ports by transmitting the light transmitted through the first lens out of the light output from the light input / output port and reflected by the diffraction grating. Concave lens in the arrangement direction Convergent light from the first lens is converted into a parallel light beam, and converged light from the first lens is converged as it is without lens action in a direction orthogonal to the arrangement direction of the plurality of light input / output ports. A cylindrical concave lens arranged on the opposite side of the diffraction grating with the first lens interposed therebetween, and the liquid crystal optical component disposed on the opposite side of the first lens with the cylindrical concave lens interposed therebetween. A plurality of mirrors of the liquid crystal optical component, the light output from the light input / output port, reflected by the diffraction grating and transmitted through the first lens and the cylindrical concave lens, the first mirror and the cylindrical concave lens interposed therebetween, the first mirror Reflected at positions opposite to the lens by a focal length of the cylindrical concave lens, and each of the reflected lights is The light reflection angle is set so that it passes through the cylindrical concave lens and the first lens, is reflected by the diffraction grating, passes through the first lens again, and converges to one of the plurality of light input / output ports. .

  In the present invention, since the cylindrical concave lens is provided, the angle / offset conversion function can be realized by one of the cylindrical concave lenses, and the number of components can be reduced and the configuration can be simplified. In addition, by providing a liquid crystal optical element with an electrode in the polymer liquid crystal composite layer, the light transmittance can be changed in the polymer liquid crystal composite layer, so other fibers when a plurality of mirrors are movable with a small insertion loss. Leakage of light can be prevented. Furthermore, since the light transmittance can be changed only with the polymer liquid crystal composite layer, the beam spot size slightly changes on the mirror surface due to the insertion of the liquid crystal optical element, so it can be inserted simply by adjusting the mirror position slightly, Can be used. Therefore, it is possible to provide a small wavelength selective switch with a small number of parts.

  In order to achieve the above object, a wavelength selective switch according to the present invention inputs and outputs light including one or more wavelengths, and faces the plurality of light input / output ports provided side by side and in a straight line. A first lens arranged so that the light from the input / output port becomes parallel light; and disposed on the opposite side of the plurality of light input / output ports with the first lens in between; Light that has passed through the first lens on a grating surface in which a plurality of gratings parallel to the arrangement direction of the plurality of light input / output ports are formed on a surface that receives light that has passed through the first lens among the output light And a second diffraction grating disposed at a distance equal to the distance between the first lens and the diffraction grating on the opposite side of the first lens with the diffraction grating in between. Lens and the optical input / output port Of the light output through the diffraction grating and transmitted through the second lens, and acts as a concave lens in the arrangement direction of the plurality of light input / output ports, and converges light from the second lens. The light beam is converted into a parallel light beam and has no lens action in a direction perpendicular to the arrangement direction of the plurality of light input / output ports, and the diffraction is performed with the second lens interposed so as to converge the convergent light from the second lens as it is. A cylindrical concave lens arranged on the opposite side of the grating, and the liquid crystal optical component disposed on the opposite side of the second lens with the cylindrical concave lens interposed therebetween, and the plurality of mirrors of the liquid crystal optical component include the mirror The light output from the light input / output port and transmitted through the first lens, the diffraction grating, the second lens, and the cylindrical concave lens is converted into the cylindrical concave So that each of the reflected light passes through the cylindrical concave lens, the second lens, and the first lens and converges to one of the plurality of light input / output ports. The reflection angle of light is set for each.

  In the present invention, since the cylindrical concave lens is provided, the angle / offset conversion function can be realized by one of the cylindrical concave lenses, and the number of components can be reduced and the configuration can be simplified. In addition, by providing a liquid crystal optical element with an electrode in the polymer liquid crystal composite layer, the light transmittance can be changed in the polymer liquid crystal composite layer, so other fibers when a plurality of mirrors are movable with a small insertion loss. Leakage of light can be prevented. Furthermore, since the light transmittance can be changed only with the polymer liquid crystal composite layer, the beam spot size slightly changes on the mirror surface due to the insertion of the liquid crystal optical element, so it can be inserted simply by adjusting the mirror position slightly, Can be used. Therefore, it is possible to provide a small wavelength selective switch with a small number of parts.

  In the present invention, it is possible to provide a liquid crystal optical component having a small number of components and a small insertion loss, and a wavelength selective switch using the same.

  Hereinafter, the present invention will be described in detail with specific embodiments, but the present invention is not construed as being limited to the following description. In the following embodiments, light is output from one light input / output port (light input / output port 20d described later) and light is transmitted to other light input / output ports (light input / output ports 20a to 20g described later) for each wavelength. However, the same applies to the configuration in which the light output from any one of the other optical input / output ports 20a to 20g is divided into wavelengths and input to the one optical input / output port 20d. Can be explained.

  FIG. 1 is a schematic configuration diagram of a wavelength selective switch according to the present embodiment. 1A shows a wavelength selective switch in the xz plane, and FIG. 1B shows a wavelength selective switch in the yz plane. The wavelength selective switch 10 in FIG. 1 has a reflective configuration, that is, a configuration in which light is reflected by a diffraction grating 31 described later.

  The wavelength selective switch 10 in FIG. 1 has a convex lens 30 arranged so that light from the light input / output port 20d becomes parallel light, and light transmitted through the convex lens 30 among the light from the light input / output port 20d for each wavelength. A diffraction grating 31 reflecting at different angles, a cylindrical concave lens 33 disposed on the opposite side of the diffraction grating 31 with the convex lens 30 therebetween, and a liquid crystal optical element disposed on the opposite side of the convex lens 30 with the cylindrical concave lens 33 interposed therebetween. And a component 49. In the present embodiment, the liquid crystal optical component 49 includes mirrors 35 a and 35 b and a liquid crystal optical element 48. The liquid crystal optical component 49 will be described in detail later.

  In FIG. 1, the light path that is output from the light input / output port 20d and reflected by the diffraction grating 31 and reaches the mirror 35b is shown by a broken line to indicate the action of the convex lens 30 and the cylindrical concave lens 33. The chief ray is shown. For the other optical paths, only the principal ray is indicated by a solid line, a one-dot chain line or a two-dot chain line in order to avoid complication of the drawing.

  In this embodiment, the convex lens 30 (lens corresponding to the first lens described above) is used, but the lens used here is not limited to a convex lens. For example, a doublet lens in which an appropriate convex lens and a concave lens are bonded and combined to reduce optical aberration may be used, or a triplet in which three lenses are combined may be used.

A plurality of optical input / output ports 20a to 20g are provided. In FIG. 1, seven optical input / output ports 20 a to 20 g are described, but any number greater than or less than this can be arranged. For example, as shown in FIG. 1, optical fibers 40a to 40g are connected to the optical input / output ports 20a to 20g or optical waveguides are connected to the optical input / output ports 20a to 20g. The light input / output ports 20a to 20g input and output light including one or more wavelengths propagating through the optical fibers 40a to 40g, respectively. Further, the light input / output ports 20a to 20g are provided in a straight line, and the convex lens 30 disposed facing the light input / output ports 20a to 20g converts the light from the light input / output ports 20a to 20g into parallel light. as it can be disposed from the convex lens 30 to a position apart focal length f _m of the convex lens 30. In FIG. 1, as shown in FIG. 1B, the light input / output ports 20a to 20g are arranged such that the direction of light output from the light input / output ports 20a to 20g is parallel to the z-axis direction. However, as long as it is converted into parallel light by the convex lens 30, it may be directed in any direction. For example, if the optical input and output ports 20a~20g is positioned away by the focal length _{f m} as shown in FIG. 1, also the orientation of the optical input-output ports 20a~20g is an oblique to the convex lens 30 Good.

The diffraction grating 31 is disposed on the opposite side of the light input / output ports 20a to 20g with the convex lens 30 therebetween. Further, in FIG. 1, for constituting a confocal system, the diffraction grating 31 is disposed from the convex lens 30 to a position apart focal length f _m of the convex lens 30. Constructing a confocal system as shown in FIG. 1 is effective because the wavelength selective switch 10 can be reduced in size.

  On the grating surface 32 of the diffraction grating 31, a grating (not shown, the same applies in the following description) arranged to be parallel to the arrangement direction of the optical input / output ports 20 a to 20 g is formed. ing. In FIG. 1, a plurality of lattices parallel to the y-axis direction of FIG. 1B are formed in parallel on the lattice surface 32 in the x-axis direction of FIG. The grating may be a plurality of concave and convex grooves formed on the grating surface 32, or may alternately arrange light reflecting portions and absorbing portions. As a result, as shown in FIG. 1A, the light transmitted through the convex lens 30 is reflected on the grating surface 32 of the diffraction grating 31 and reflected at different angles in the x-axis direction for each wavelength. It is returned as it is in the z-axis direction of FIG. In FIG. 1, the grating surface 32 of the diffraction grating 31 faces the convex lens 30 for simplicity, but in general, the normal line of the grating surface 32 is in the xz plane with respect to the optical axis (z axis). Is inclined.

The cylindrical concave lens 33 transmits light that has passed through the convex lens 30 out of the light reflected by the diffraction grating 31 and converges it toward mirrors 35a and 35b described later. The cylindrical concave lens 33 is a simple flat plate in the xz plane of FIG. 1A, that is, in a direction (x direction) orthogonal to the arrangement direction of the light input / output ports 20a to 20g, and from the focal position f _m from the convex lens 30. Also, the light from the convex lens 30 is converged as it is at a slightly longer position. On the other hand, it functions as a concave lens in the yz plane of FIG. 1B, that is, the arrangement direction (y direction) of the light input / output ports 20a to 20g, and converts the light from the convex lens 30 into parallel light to mirrors 35a and 35b. Lead to. In FIG. 1, the cylindrical concave lens 33 is arranged so that the concave surface 34 faces the mirrors 35 a and 35 b, but it may naturally be arranged so as to face the convex lens 30 side. In FIG. 1, a plano-concave cylindrical lens is used, but a biconcave cylindrical lens may be used.

The mirrors 35 a and 35 b reflect the light reflected by the diffraction grating 31 and transmitted through the convex lens 30 and the cylindrical concave lens 33 on the opposite side of the convex lens 30 with the cylindrical concave lens 33 in between. Although two are illustrated in FIG. 1, a plurality may be arranged for each wavelength according to the number of wavelengths of light propagating in the optical fiber 40. Hereinafter, although the description will focus on the mirror 35a, the same applies to the mirror 35b. The mirror 35 a is disposed at a position separated by the focal length f ₃ of the cylindrical concave lens 33. Then, the convergent light from the cylindrical concave lens 33 is reflected at an arbitrary angle at a position where the light from the cylindrical concave lens 33 converges. Further, the light reflected by the mirror 35a is reflected so that the light passes through the cylindrical concave lens 33 and the convex lens 30, is reflected by the diffraction grating 31, passes through the convex lens 30 again, and converges to one of the light input / output ports 20a to 20g. Each angle is set. In FIG. 1, the mirror 35a is set to converge to the optical input / output port 20c, and the mirror 35b is set to converge to the optical input / output port 20e. However, any of the optical input / output ports 20a to 20g is set according to the angle. It is possible to make it converge. For example, when the angle is tilted upward as in the mirror 35a, the light can be converged to the light input / output port 20c through the convex lens 30 and the diffraction grating 31. On the other hand, when tilted downward as in the mirror 35b, the light passes through the convex lens 30 and the diffraction grating 31. It can be converged to the optical input / output port 20e. In this way, the wavelength can be selected by changing the angle of the mirror 35a. As the mirror 35a, for example, a micro electro mechanical systems (MEMS) mirror can be used to realize a small wavelength selective switch.

  The liquid crystal optical component 49 includes a liquid crystal optical element 48 and a plurality of mirrors 35a and 35b. Here, an embodiment of the liquid crystal optical component 49 will be described in detail.

  FIG. 3 is a schematic configuration diagram of the liquid crystal optical component. 3A is a top view, FIG. 3B is a cross-sectional view taken along line AA ′ in FIG. 3A, and FIG. 3C is a cross-sectional view taken along line BB ′ in FIG. Each figure is shown.

  As shown in FIG. 3C, the liquid crystal optical component 50 of FIG. 3 emits light 61 that irradiates the liquid crystal optical element 51 and the polymer liquid crystal composite layer 70 described later and transmits the polymer liquid crystal composite layer 70 in a predetermined manner. And a MEMS mirror 71 capable of reflecting at an angle. The liquid crystal optical element 51 includes a polymer liquid crystal composite layer 70 in which liquid crystal grains are dispersed in a polymer, and a polymer liquid crystal composite layer for light 61 and 62 directed to the MEMS mirror 71 by applying a voltage to the polymer liquid crystal composite layer 70. And a pair of electrodes 82 a to 82 d and 83 a to 83 d provided on the polymer liquid crystal composite layer 70 so that the light transmittance of the mirror 70 changes for each light to the respective mirrors 76 a to 76 d of the MEMS mirror 71. Note that the electrode 82a and the electrode 83a constitute a pair of electrodes. The same applies to the other electrodes 82b to 82d and 83b to 83d. Further, the liquid crystal optical component 50 includes a housing 73 in which the MEMS mirror 71 is sealed, and the MEMS mirror 71 is sealed by the polymer liquid crystal composite layer 70 so as to cover the released surface 74 of the housing 73. The Thus, by sealing the MEMS mirror 71 in the housing 73, the liquid crystal optical component 50 can be modularized. The modularized liquid crystal optical component 50 has a slight change in the mirror position because the beam spot size slightly changes on the mirror surface by inserting the liquid crystal optical element 51 into the liquid crystal optical component 49 of the wavelength selective switch 10 of FIG. It can be easily inserted and applied simply by adjusting to.

In this embodiment, the polymer liquid crystal composite layer 70 of FIG. 3 has a configuration in which a continuous layer of liquid crystal having a diameter of about 1 μm is dispersed in a network polymer network, and the alignment direction of the liquid crystal is random alignment. Therefore, a strong light scattering state is exhibited in the non-electric field state. As a method of obtaining the polymer liquid crystal composite layer 70, a method of separating the liquid crystal from a polymer or a mixture of a polymer precursor and a liquid crystal is generally used (see, for example, Patent Document 2). On the surface of the polymer liquid crystal composite layer 70, a pair of electrodes 82a to 82d and 83a to 83d are arranged as shown in FIG. It is known that when a voltage is applied to the pair of electrodes 82a to 82d and 83a to 83d, the orientation of liquid crystal molecules in the polymer liquid crystal composite layer 70 is aligned and the light transmission state is changed. A reverse mode polymer liquid crystal composite layer that is in a light-transmitting state when no electric field is also known (see, for example, Patent Document 2). Specifically, a mixture of an ultraviolet curable adhesive and a nematic liquid crystal was applied to glass plates 80 and 81 on which transparent electrodes to be described later were formed, and cured by irradiating with ultraviolet rays. The polymer liquid crystal composite layer 70 is included in the MEMS mirror 71 so that the surface opposite to the irradiated surface 75 of the polymer liquid crystal composite layer 70 irradiated with light covers one surface 74 of the housing 73 that is open. It arrange | positions facing the reflective surface 77 (FIG.3 (b)) of several mirror 76a-76d.
Japanese Patent Laid-Open No. 11-52339

  The MEMS mirror 71 can reflect the light 61 that is irradiated to the polymer liquid crystal composite layer 70 and transmitted through the polymer liquid crystal composite layer 70 at a predetermined angle. In this embodiment, the MEMS mirror 71 is arrange | positioned in a line so that the normal line of each reflective surface 77 (FIG.3 (b)) of several mirror 76a-76d may become parallel. The MEMS mirror 71 is disposed on the bottom 78 of the housing 73 with one surface 74 open so that the reflecting surfaces 77 (FIG. 3B) of the plurality of mirrors 76 a to 76 d face the one surface 74. .

  The pair of electrodes 82 a to 82 d and 83 a to 83 d respectively change the light transmittance of the polymer liquid crystal composite layer 70 with respect to the light 61 and 62 toward the MEMS mirror 71 by applying a voltage to the polymer liquid crystal composite layer 70. The polymer liquid crystal composite layer 70 is provided so as to change for each of the light 61 and the light 62 to the mirrors 76a to 76d. The pair of electrodes 82a to 82d and 83a to 83d are made of a light transmissive material. Then, as shown in FIGS. 3A and 3C, MEMS mirrors 71 are formed on both surfaces of the polymer liquid crystal composite layer 70 so that a voltage is applied to the polymer liquid crystal composite layer 70 with the polymer liquid crystal composite layer 70 interposed therebetween. The mirrors 76a to 76d are formed in stripes in the arrangement direction of the mirrors 76a to 76d at substantially the same intervals as the arrangement intervals of the mirrors 76a to 76d. Note that the electrode 72a and the electrode 72b constitute a pair of electrodes.

  In the present embodiment, a striped transparent electrode is formed as a pair of electrodes 82a to 82d and 83a to 83d on one surface of two glass plates 80 and 81 with a light transmissive material such as tin oxide, and polymer liquid crystal The composite layer 70 is sandwiched. With this configuration, the scattering state of the polymer liquid crystal composite layer 70 can be controlled by taking out the electrode leads from the inner transparent electrodes and applying an AC voltage. By forming the transparent electrode in a stripe shape, the attenuation amount of the light 61 and 62 incident on the plurality of mirrors 76a to 76d included in the MEMS mirror 71 can be controlled for each light to the plurality of mirrors 76a to 76d. Further, the liquid crystal optical component 50 having a small number of components and a small insertion loss can be provided.

  The light 62 incident on the liquid crystal optical component 50 is scattered by a randomly oriented liquid crystal region existing as a micro domain of several μm in the polymer. In this state, by applying an AC voltage to the electrodes 82d and 83d corresponding to the light 62, the alignment direction of the liquid crystal microdomains can be aligned in a direction perpendicular to the electrodes 82d and 83d, so that light scattering is reduced and transparent. Transition to a different state.

  Here, the function of the liquid crystal optical element 51 of FIG. 3 will be described.

  When two convex lenses are arranged facing each other between two optical fibers whose end faces face each other, a light beam that has passed through the lens becomes a collimated Gaussian beam having a beam waist. It is known that optical coupling between fibers can be realized with minimum loss by arranging a lens and an optical fiber at the beam waist position. The light receiving fiber coupling efficiency T can be expressed as the following formula (1) by the normalized overlap integral of the light receiving fiber and the light beam.

  In Formula (1), Fr (x, y) is a function describing the complex amplitude of the light receiving fiber on the light receiving side, W (x, y) is a function describing the complex amplitude of the beam coupled to the light receiving optical fiber, The symbol “” represents a complex conjugate. These functions are all complex numbers, which is a coherent overlap integral. Maximum receiving fiber coupling efficiency (T = 1.0) is achieved when the beam mode is perfectly matched in both amplitude and phase at all positions. Any difference in mode shape or phase will cause the value of T to be less than one.

  In this state, when the polymer liquid crystal composite layer 70 of FIG. 3 is disposed between the two convex lenses, the mode shape and the phase can be disturbed, and T in Expression (1) can be reduced. That is, since the optical coupling rate can be changed, an optical variable attenuator capable of obtaining an arbitrary amount of light attenuation can be configured. A maximum coupled state can be obtained by applying a square wave voltage of 1 kHz with a maximum amplitude of 10 Vrms to the polymer liquid crystal composite layer 70. At this time, the optical loss between fibers was 1 dB. When the voltage is 0, the maximum extinction ratio is 40 dB. When a reverse mode type polymer liquid crystal composite layer is used instead of the polymer liquid crystal composite layer 70, an insertion loss of 1.2 dB is obtained at an applied voltage of 0 V, and a square wave of 1 kHz with a maximum amplitude of 12 Vrms is passed through the electrodes. When applied, a maximum extinction ratio of 38 dB was obtained.

  In the wavelength selective switch 10 of FIG. 1, the input / output of light is switched between the plurality of optical fibers 40a to 40g. When the changeover switch between the optical fibers 40a to 40g is performed by changing the angle of the reflected light by the mirrors 35a and 35b, it is advantageous in terms of operation speed and operation algorithm to operate at the shortest distance. However, as shown in FIG. 1, for example, if another optical fiber 40f exists in the middle of the switching path from the optical fiber 40e to the optical fiber 40g, optical coupling occurs in the optical fiber 40f during switching, and unnecessary interference occurs. Occurs.

  In this embodiment, since the liquid crystal optical element 48 having the polymer liquid crystal composite layer 70 of FIG. 3 is disposed in front of the plurality of mirrors 35a and 35b, generation of optical coupling to the other optical fiber 40f being switched is prevented. can do.

  Here, the incident light passes through the liquid crystal optical element 48, is reflected by the mirrors 35a and 35b, and again passes through the liquid crystal optical element 48, and the insertion loss and the voltage applied to the liquid crystal optical element 48 are as follows. Explain the relationship.

  FIG. 4 shows the relationship between the insertion loss of the liquid crystal optical element and the voltage applied to the liquid crystal optical element.

  As shown in FIG. 4, the insertion loss is up to 1.8 dB up to 1.8 V, but when a voltage is applied, the loss increases due to light scattering, becomes saturated near 9 V, and the loss value is 38 dB. The response speed of this change was several ms. When the mirror 35b is rotated by the wavelength selective switch 10 of FIG. 1 to switch from the optical fiber 40e to the optical fiber 40g, when the mirror 35b is rotated uniaxially, the optical fiber 40f is momentarily crossed during the switching. When the optical fiber 40f is operating at a plurality of different wavelengths, the light that momentarily crosses these optical communications will interfere. Conventionally, in order to eliminate these interferences, a two-axis operation mirror is used to bypass the optical fiber 40f and switch to the optical fiber 40g. For this reason, there are drawbacks such as a complicated mirror structure, insufficient avoidance, and interference.

  When the liquid crystal optical component 49 including the liquid crystal optical element 48 and the mirrors 35a and 35b of FIG. 1 is applied to the wavelength selective switch 10, for example, when the optical fiber 40c is switched to the optical fiber 40g, the mirrors 35a and 35b are rotated. At the same time as starting, a voltage is applied to the liquid crystal optical element 48 to bring the insertion loss to a maximum state of 38 dB or more. The response speed at this time is several ms. When the liquid crystal optical component 50 shown in FIG. 3 is applied as the liquid crystal optical component 49 shown in FIG. 1, the response speed when a voltage is applied to the liquid crystal optical element 48 depends on the mirrors 76a to 76d of the MEMS mirror 71 shown in FIG. It is about the same or faster than the typical rotation speed. Therefore, when the mirrors 76a to 76d of the MEMS mirror 71 rotate and cross the fiber 40f, the light can already be blocked at an extinction ratio of 38 dB. At the same time as switching to the target optical fiber 40g, the applied voltage is set to 0 V to return the insertion loss to 0.5 dB. Thus, even if a uniaxial MEMS mirror is used by maximizing insertion loss during the switching operation of the MEMS mirror 71, the optical fiber other than the intended purpose is not disturbed.

  This wavelength selective switch 10 also has a function of making the light intensity at each wavelength constant by giving appropriate attenuation to each wavelength of wavelength multiplexed light having different light intensity at each wavelength. Conventionally, the rotation angle of each mirror of the MEMS mirror is slightly adjusted to change the optical coupling rate, thereby giving an attenuation effect. In this method, since the spot position on the optical fiber of the reflected beam from the MEMS mirror is slightly shifted from the position of the maximum coupling, loss is caused. As a result, the minute fluctuation of each mirror of the MEMS mirror causes a larger light output fluctuation and gives a ripple to the output light intensity. On the other hand, when the liquid crystal optical element 51 of FIG. 3 is used, the optical coupling position to the optical fiber can be maximized and attenuation can be given by the liquid crystal optical element 51. Therefore, each mirror 76a of the MEMS mirror 71 can be provided. The influence of the minute displacement of ˜76d becomes extremely small, and a good attenuated light output with little ripple can be obtained.

  Conventionally, as described with reference to FIG. 6, four components are required for the light amount control, but as shown in FIG. 3, the optical coupling to the optical fiber is changed by applying the polymer liquid crystal composite layer 70. It is possible. Further, the phase of the incident beam is made random by the dispersed liquid crystal, and the optical coupling to the optical fiber is reduced. As a result, the amount of light can be changed regardless of polarization control. Therefore, it is possible to provide a liquid crystal optical component 50 that can control the attenuation amount of light incident on the plurality of mirrors 76a to 76d, has a small number of components, and is small in insertion loss. Since the liquid crystal optical component 50 itself does not require a polarizing plate, the insertion loss can be reduced, and it can also be used as an attenuator with a stable light output.

  From the above, the wavelength selective switch 10 distributes light of a plurality of wavelengths output from any of the optical input / output ports 20a to 20g to other optical input / output ports (any of the optical input / output ports 20a to 20g), Since the light output from a plurality of the optical input / output ports 20a to 20g can be multiplexed by another optical input / output port (any one of the optical input / output ports 20a to 20g), the optical wavelength division multiplexing network It can be applied as an optical multiplexing / demultiplexing circuit for wavelength multiplexing at the time of realization or a wavelength rearrangement type add-drop wavelength multiplexing circuit.

  Here, the locus of light reflected by the mirror 35a will be described in detail.

  FIG. 5 is a schematic view showing the mirror 35 a and the cylindrical concave lens 33.

As shown in FIG. 5, the principal ray 55 reflected by the mirror 35a at an angle θ _m is transmitted through the cylindrical concave lens 33 at a height of h = | f ₃ | θ _m from the optical axis 60 of the incident light 56 to the mirror 35a. To do. This is because the mirror 35 a is disposed at a position away from the cylindrical concave lens 33 by the focal length f ₃ of the cylindrical concave lens 33. The principal ray 55 transmitted through the cylindrical concave lens 33 has a refraction angle of h / | f ₃ | = θ _m when transmitted through the cylindrical concave lens 33, and an emission angle of θ _m + h / | f ₃ | = 2θ _m . That is, the principal ray 55 transmitted through the cylindrical concave lens 33 can be considered to coincide with the ray emitted from the focal point of the cylindrical concave lens 33 with the point of height −h as the light source, and the reflection of the incident light 56 incident on the mirror 35a. It can be seen that the position can be equivalently offset in the y direction by -h.

  As described above, since the wavelength selective switch 10 of FIG. 1 includes the cylindrical concave lens 33, the angle / offset conversion function can be realized by one of the cylindrical concave lenses 33, and the number of components is reduced and the configuration is simplified. Can do. In addition, downsizing is possible. In addition, since the light transmittance can be changed by the polymer liquid crystal composite layer 70 of FIG. 3 by providing the liquid crystal optical element 48, other than when the plurality of mirrors 35a and 35b (FIG. 1) are movable with a small insertion loss. Leakage of light into the optical fiber can be prevented. Further, since the light transmittance can be changed only by the polymer liquid crystal composite layer 70, the wavelength selective switch 10 in FIG. 1 can be used by inserting it as it is without changing the arrangement of the other components except the liquid crystal optical component 49. Can do. Therefore, a small wavelength selective switch 10 with a small number of parts can be provided.

(Second embodiment)
FIG. 2 shows a schematic configuration diagram of the wavelength selective switch according to the present embodiment. FIG. 2A shows a wavelength selective switch in the xz plane, and FIG. 2B shows a wavelength selective switch in the yz plane. 2 that are the same as those in FIG. 1 are the same as those in FIG. The wavelength selective switch of FIG. 2 has a transmission type configuration, that is, a configuration in which light is transmitted through a diffraction grating described later.

  The wavelength selective switch 11 in FIG. 2 is different from the wavelength selective switch 10 in FIG. 1 in that the light transmitted through the convex lens 30 among the light input / output from the light input / output ports 20a to 20g is different for each wavelength. A diffraction grating 36 that transmits light at an angle, and a convex lens 37 that is disposed at a distance equal to the distance between the convex lens 30 and the diffraction grating 36 on the opposite side of the convex lens 30 with the diffraction grating 36 therebetween. However, the diffraction grating 36 is the same as the diffraction grating 31 of FIG. 1 except that the light transmitted through the convex lens 30 is transmitted. In this case, the grating formed on the grating surface 32 may be a plurality of concave and convex grooves formed on the grating surface 32, or alternatively, a portion that transmits light and a portion that reflects or absorbs light alternately. The arranged slit shape may be sufficient. Further, the same lens as the convex lens 30 is applied to the convex lens 37.

  With the above configuration, the wavelength selective switch 11 in FIG. 2 can perform wavelength selection by performing the same function as the wavelength selective switch 10 described in FIG.

  The wavelength selective switch according to the present invention can branch or combine light of different wavelengths, and can be used for wavelength multiplexing optical multiplexing / demultiplexing circuits or wavelength rearrangement type add-drop wavelength multiplexing when realizing an optical wavelength multiplexing communication network. It can be applied as a circuit.

It is a schematic block diagram of the wavelength selective switch which concerns on one Embodiment. It is a schematic block diagram of the wavelength selective switch which concerns on one Embodiment. It is a schematic block diagram of a liquid crystal optical component. It is the figure which showed the relationship between the insertion loss of a liquid crystal optical element, and the applied voltage to a liquid crystal optical element. It is the schematic which showed the mirror and the cylindrical concave lens. It is a schematic block diagram of the conventional optical shutter.

Explanation of symbols

10, 11: Wavelength selection switches 20a-20g: Optical input / output port 30: Convex lens 31: Diffraction grating 32: Grating surface 33: Cylindrical concave lens 34: Concave surfaces 35a, 35b: Mirror 36: Diffraction grating 37: Convex lenses 40, 40a-40g : Optical fiber 48: liquid crystal optical element 49: liquid crystal optical component 50: liquid crystal optical component 51: liquid crystal optical element 55: principal ray 56: incident light 60: optical axis 61, 62: light 70: polymer liquid crystal composite layer 71: MEMS Mirror 72a, 72b: Electrode 73: Housing 74: Surface 75: Irradiated surfaces 76, 76a to 76d: Mirror 77: Reflecting surface 78: Bottom 80, 81: Glass plates 82a to 82d: Electrodes 83a to 83d: Electrode 100: Optical shutter 110: birefringent plate 111: half-wave plate 112: polarizer 113: polarization rotation element 114: mirror

Claims (7)

A polymer liquid crystal composite layer in which liquid crystal grains are dispersed in a polymer;
A plurality of mirrors that can irradiate the polymer liquid crystal composite layer and transmit the light transmitted through the polymer liquid crystal composite layer at a predetermined angle;
The polymer liquid crystal composite layer is configured such that light transmittance of the polymer liquid crystal composite layer with respect to light traveling toward the plurality of mirrors is changed for each light to the plurality of mirrors by applying a voltage to the polymer liquid crystal composite layer. A pair of electrodes provided on;
A liquid crystal optical component comprising :
The plurality of mirrors are arranged in a row so that the normal lines of the reflecting surfaces of the plurality of mirrors are parallel to each other.
The electrode is a light transmissive material, and an arrangement interval of the plurality of mirrors on both sides of the polymer liquid crystal composite layer so as to apply a voltage to the polymer liquid crystal composite layer with the polymer liquid crystal composite layer interposed therebetween. A liquid crystal optical component, wherein the optical components are formed in stripes in the arrangement direction of the plurality of mirrors at substantially the same interval . A polymer liquid crystal composite layer in which liquid crystal grains are dispersed in a polymer;
A plurality of mirrors that can irradiate the polymer liquid crystal composite layer and transmit the light transmitted through the polymer liquid crystal composite layer at a predetermined angle;
The polymer liquid crystal composite layer is configured such that light transmittance of the polymer liquid crystal composite layer with respect to light traveling toward the plurality of mirrors is changed for each light to the plurality of mirrors by applying a voltage to the polymer liquid crystal composite layer. A pair of electrodes provided on;
A liquid crystal optical component comprising :
It further includes a housing having one surface open,
The plurality of mirrors are arranged at the bottom of the housing such that the reflecting surfaces of the plurality of mirrors face the one surface,
The reflective surface of the plurality of mirrors is such that the surface opposite to the irradiated surface of the polymer liquid crystal composite layer that is irradiated with light covers the one surface opened of the housing. A liquid crystal optical component, wherein the liquid crystal optical component is disposed opposite to the liquid crystal optical component . It further includes a housing having one surface open,
The plurality of mirrors are arranged at the bottom of the housing such that the reflecting surfaces of the plurality of mirrors face the one surface,
The reflective surface of the plurality of mirrors is such that the surface opposite to the irradiated surface of the polymer liquid crystal composite layer that is irradiated with light covers the one surface opened of the housing. The liquid crystal optical component according to claim 1, wherein the liquid crystal optical component is disposed opposite to the liquid crystal optical component. A first lens arranged to input / output light including one or more wavelengths and to collimate light from the light input / output port so as to face a plurality of light input / output ports arranged side by side in a straight line When,
The plurality of light input / output ports disposed on the opposite side of the plurality of light input / output ports with the first lens interposed therebetween, wherein the plurality of light beams are input and output from the light input / output ports. A diffraction grating that reflects light transmitted through the first lens at a different angle for each wavelength in a grating plane on which a plurality of gratings parallel to the arrangement direction of the light input / output ports of
Of the light output from the light input / output port and reflected by the diffraction grating, the light transmitted through the first lens is transmitted and acts as a concave lens in the arrangement direction of the plurality of light input / output ports. The first lens so that the convergent light from the first lens is converged as it is without any lens action in a direction orthogonal to the arrangement direction of the plurality of light input / output ports. A cylindrical concave lens arranged on the opposite side of the diffraction grating in between,
The polymer liquid crystal composite layer disposed on the opposite side of the first lens with the cylindrical concave lens in between and the liquid crystal grains dispersed in the polymer, and the polymer liquid crystal composite layer irradiated with the polymer liquid crystal composite layer A plurality of mirrors capable of reflecting the transmitted light at a predetermined angle; and a light transmittance of the polymer liquid crystal composite layer with respect to the light directed to the plurality of mirrors by applying a voltage to the polymer liquid crystal composite layer. A pair of electrodes provided in the polymer liquid crystal composite layer so as to change for each light to the mirror, and a liquid crystal optical component comprising:
With
The plurality of mirrors of the liquid crystal optical component reflect the light output from the light input / output port and reflected by the diffraction grating and transmitted through the first lens and the cylindrical concave lens with the cylindrical concave lens interposed therebetween. Reflected at positions opposite to the focal length of the cylindrical concave lens on the opposite side, each of the reflected light passes through the cylindrical concave lens and the first lens, is reflected by the diffraction grating, and passes through the first lens again. A wavelength selective switch in which a light reflection angle is set so as to converge on one of the plurality of light input / output ports. A first lens arranged to input / output light including one or more wavelengths and to collimate light from the light input / output port so as to face a plurality of light input / output ports arranged side by side in a straight line When,
The plurality of light input / output ports disposed on the opposite side of the plurality of light input / output ports with the first lens interposed therebetween, wherein the plurality of light beams are input and output from the light input / output ports. A diffraction grating that reflects light transmitted through the first lens at a different angle for each wavelength in a grating plane on which a plurality of gratings parallel to the arrangement direction of the light input / output ports of
Of the light output from the light input / output port and reflected by the diffraction grating, the light transmitted through the first lens is transmitted and acts as a concave lens in the arrangement direction of the plurality of light input / output ports. The first lens so that the convergent light from the first lens is converged as it is without any lens action in a direction orthogonal to the arrangement direction of the plurality of light input / output ports. A cylindrical concave lens arranged on the opposite side of the diffraction grating in between,
The liquid crystal optical component according to any one of claims 1 to 3, wherein the liquid crystal optical component is disposed on the opposite side of the first lens with the cylindrical concave lens in between.
With
The plurality of mirrors of the liquid crystal optical component reflect the light output from the light input / output port and reflected by the diffraction grating and transmitted through the first lens and the cylindrical concave lens with the cylindrical concave lens interposed therebetween. Reflected at positions opposite to the focal length of the cylindrical concave lens on the opposite side, each of the reflected light passes through the cylindrical concave lens and the first lens, is reflected by the diffraction grating, and passes through the first lens again. A wavelength selective switch in which a light reflection angle is set so as to converge on one of the plurality of light input / output ports. A first lens arranged to input / output light including one or more wavelengths and to collimate light from the light input / output port so as to face a plurality of light input / output ports arranged side by side in a straight line When,
The plurality of light input / output ports disposed on the opposite side of the plurality of light input / output ports with the first lens interposed therebetween, wherein the plurality of light beams are input and output from the light input / output ports. A diffraction grating that transmits light transmitted through the first lens at a different angle for each wavelength on a grating surface on which a plurality of gratings parallel to the arrangement direction of the light input / output ports of
A second lens disposed at a distance equal to the distance between the first lens and the diffraction grating on the opposite side of the first lens with the diffraction grating in between;
Of the light output from the light input / output port and transmitted through the diffraction grating, the light transmitted through the second lens is transmitted and acts as a concave lens in the arrangement direction of the plurality of light input / output ports. The second lens so as to converge the convergent light from the second lens without any lens action in a direction orthogonal to the arrangement direction of the plurality of light input / output ports. A cylindrical concave lens arranged on the opposite side of the diffraction grating in between,
The polymer liquid crystal composite layer disposed on the opposite side of the second lens with the cylindrical concave lens in between and the liquid crystal grains dispersed in the polymer, and the polymer liquid crystal composite layer irradiated with the polymer liquid crystal composite layer A plurality of mirrors capable of reflecting the transmitted light at a predetermined angle; and a light transmittance of the polymer liquid crystal composite layer with respect to the light directed to the plurality of mirrors by applying a voltage to the polymer liquid crystal composite layer. A pair of electrodes provided in the polymer liquid crystal composite layer so as to change for each light to the mirror, and a liquid crystal optical component comprising:
With
The plurality of mirrors of the liquid crystal optical component are separated from the light output from the light input / output port and transmitted through the first lens, the diffraction grating, the second lens, and the cylindrical concave lens by a focal length of the cylindrical concave lens. The reflection angle of light is reflected so that each of the reflected light passes through the cylindrical concave lens, the second lens, and the first lens and converges to one of the plurality of light input / output ports. Wavelength selective switch to be set. A first lens arranged to input / output light including one or more wavelengths and to collimate light from the light input / output port so as to face a plurality of light input / output ports arranged side by side in a straight line When,
The plurality of light input / output ports disposed on the opposite side of the plurality of light input / output ports with the first lens interposed therebetween, wherein the plurality of light beams are input and output from the light input / output ports. A diffraction grating that transmits light transmitted through the first lens at a different angle for each wavelength on a grating surface on which a plurality of gratings parallel to the arrangement direction of the light input / output ports of
A second lens disposed at a distance equal to the distance between the first lens and the diffraction grating on the opposite side of the first lens with the diffraction grating in between;
Of the light output from the light input / output port and transmitted through the diffraction grating, the light transmitted through the second lens is transmitted and acts as a concave lens in the arrangement direction of the plurality of light input / output ports. The second lens so as to converge the convergent light from the second lens without any lens action in a direction orthogonal to the arrangement direction of the plurality of light input / output ports. A cylindrical concave lens arranged on the opposite side of the diffraction grating in between,
The liquid crystal optical component according to any one of claims 1 to 3, wherein the liquid crystal optical component is disposed on the opposite side of the second lens with the cylindrical concave lens in between.
With
The plurality of mirrors of the liquid crystal optical component are separated from the light output from the light input / output port and transmitted through the first lens, the diffraction grating, the second lens, and the cylindrical concave lens by a focal length of the cylindrical concave lens. The reflection angle of light is reflected so that each of the reflected light passes through the cylindrical concave lens, the second lens, and the first lens and converges to one of the plurality of light input / output ports. Wavelength selective switch to be set.

Images