JP7101954B2 - Optical matrix switch - Google Patents

Description

The present invention relates to an optical switch element composed of a photonic crystal, an optical switch circuit using the same, a two-dimensional or three-dimensional optical beam type multi-stage switch circuit, and a variable optical attenuator.

An optical switch circuit that switches the paths of a plurality of optical signals is an important component in optical communication. FIG. 1 is a principle diagram showing a typical structure of an optical switch circuit, and shows a 4-input 4-output thermo-optical effect switch circuit connected in a planar manner by a waveguide.

As other important optical switch circuits used for optical communication, a wavelength selection switch (WSS: Wavelength Selective Switch), a MEMS type switch, and the like are known. The MEMS type optical switch circuit includes a three-dimensional type as shown in FIG. In the three-dimensional MEMS shown in Section 2, in order to increase the degree of freedom in selecting the signal path coupled from the optical fiber group 201 on the input side to the optical fiber group 204 on the output side, the MEMS micromirror array 202 , 203 It is necessary to control the two-dimensional tilt of the corresponding mirror in multi-gradation analog control, which is accompanied by great difficulty.

K. Suzuki, K. Tanizawa, S. Suda, H. Matsuura, T. Inoue, K. Ikeda, S. Namiki, and H. Kawashima, “Broadband silicon photonics 8 × 8 switch based on double-Mach-Zehnder element switches , ”Opt. Express 25, 7538-7546 (2017) Ming C. Wu, Olav Solgaard, and Joseph E. Ford, “Optical MEMS for Lightwave Communication,” Journal of Lightwave Technology, vol. 24, No. 12, December 2006.

Japanese Unexamined Patent Publication No. 2006-292872 US Pat. No. 7,092,599 Japanese Patent No. 3325825

As a path switch on a plane, a switch on a PLC (Planar Lightwave Circuit) and a silicon optical circuit switch are known. These multi-input, multi-output optical path switches have a network structure as shown in FIG. 1, and signals are exchanged between adjacent optical lines.

In FIG. 1, the 2-input × 2-output unit switch element 101 is in an anti-cross state (upper left → upper right or lower left → lower right) and a cross state (upper left) as the heating on / off of the thermooptical portion represented by the rectangle is performed. → Lower right or lower left → upper right) can be switched. Seen from the input of one switch element, the destination of the signal is only one of the two adjacent lines, and the path change is zero or plus or minus 1, that is, the jump of the signal is at most one stage. In the circuit, the signal lines intersect at almost right angles to minimize crosstalk, but it is still difficult to avoid crosstalk between signals. In more complex circuits, such as 8x8 switch circuits (or 16x16 switch circuits), the signal must pass through 8 (or 16) switch elements before reaching the output end. It is even more difficult to maintain signal quality because each signal loss or crosstalk is accumulated 8 times (16 times).

In this way, in an optical switch circuit having a large number of input / output ports, signal loss and crosstalk between signal lines have been considered to be problems. Therefore, an object of the present invention is to effectively suppress signal loss and crosstalk between signal lines even in an optical switch circuit having a large number of input / output ports.

[1. Optical switch element]
The first aspect of the present invention relates to an optical switch element. In the three-dimensional space xyz, the optical switch element of the present invention propagates incident light, which is a clockwise or counterclockwise circularly polarized light having a traveling direction inclined by a predetermined angle θ with respect to the z-axis, in the xz plane. .. The optical switch element includes a first polarization separation prism, a second polarization separation prism, and a liquid crystal cell interposed between the first and second polarization separation prisms in the z-axis direction. The first and second polarization separation prisms are photonic crystal polarization separation prisms, respectively. The liquid crystal cell can transition from at least an isotropic state with respect to incident light and a birefringent state having a phase difference of 180 degrees by voltage driving. Due to such a transition of the liquid crystal cell, the optical switch element according to the present invention emits incident light as circularly polarized light having the same traveling direction and the same or opposite rotation direction, or z. It has a traveling direction tilted by an angle −θ with respect to the axis, and is configured so that it can be selected whether to emit as circularly polarized light in the same or opposite rotation direction.

[1-1. First Specific Example of Photonic Crystal Polarization Separation Prism]
The photonic crystal polarization separation prism constituting the optical switch element may be a “split type”. The split-type photonic crystal polarization separation prism includes a half-wave plate of photonic crystals formed on the xy plane and laminated in the z-axis direction in the three-dimensional space xyz, and is single or repeated in the x-axis direction. It has one or more regions, and this region is divided into a plurality of strip-shaped sub-regions in the x-axis direction. The groove direction of the photonic crystal changes stepwise in the region with respect to the y-axis direction in the range of 0 ° to 180 °, and the angle with respect to the y-axis direction is uniform in the sub-region. be. In such a photonic crystal polarization separation prism, light incident in the z-axis direction is directed clockwise by a certain angle from the z-axis toward the x-axis and toward the -x-axis by the same angle from the z-axis. It is separated and converted into counterclockwise circular polarization in the direction and emitted.

[1-2. Second Specific Example of Photonic Crystal Polarization Separation Prism]
The photonic crystal polarization separation prism constituting the optical switch element may be of a “curve type”. The curved photonic crystal polarization separation prism includes a half-wave plate of photonic crystals formed on the xy plane and laminated in the z-axis direction in the three-dimensional space xyz, and is single or repeated in the x-axis direction. Has one or more regions. The groove direction of the photonic crystal is a curve represented by y = (D / π) log (| cos (πx / D) |) + constant in the approximate range of the average period of the groove, where D is a constant. Such a photonic crystal polarization separation prism can be used for clockwise circular polarization in the direction from the z-axis toward the x-axis by a certain angle and counterclockwise circular polarization in the same angle from the z-axis toward the -x-axis. Separate and convert and emit.

[2. Optical switch circuit]
A second aspect of the present invention relates to an optical switch circuit. In the optical switch circuit of the present invention, a plurality of optical switch elements according to the first side surface described above are arranged two-dimensionally or three-dimensionally. Specific examples of the optical switch circuit are a two-dimensional structure optical beam type multi-stage switch circuit and a three-dimensional structure optical beam type multi-stage switch circuit.

[Light beam type multi-stage switch circuit with 2-1.2 dimensional structure]
The light beam type multi-stage switch circuit having a two-dimensional structure includes an N-stage switch sub-circuit in the z-axis direction in the three-dimensional space xyz. In the switch subcircuit of each stage, a plurality of optical switch elements related to the first side surface are arranged in the x-axis direction. The average traveling direction of the entire light beam is the z-axis direction, and the light beam forms a two-dimensional network in the xz plane. In this circuit, a sequence of ^2N input ports having a predetermined polarization on the input surface and a sequence of 2N output ports having a predetermined polarization on the output surface are arranged in the x ^- axis direction. Each optical switch element selects the emission direction of the optical beam so that the optical beam incident on it is guided to one of the other two optical switch elements having different positions in the x-axis direction of the next stage. Is what you do. In the Mth stage (M <N) of the switch circuit, the mth of the ports arranged in the x direction is connected to the mth port of the next (M + 1) stage, or m to 2 (N-). You can choose whether to combine with the port that jumped only by M). The port surface or intermediate port surface forming the boundary between each stage and the regions before and after the stage includes a photonic crystal wave plate or a photonic crystal polarization separation prism that adjusts the polarization and bends the light in a desired direction. Specific examples of the photonic crystal polarization separation prism are as described above. The light beam type multi-stage switch circuit having a two-dimensional structure emits a sequence of optical signals incident on 2N ports on the incident surface from 2N ports on the emitting surface as an overall effect, and at the same time, light different from the input. It can be converted into a signal sequence. In this two-dimensional structure light beam type multi-stage switch circuit, the order of the first stage, the second stage, ..., And the Nth stage can be arbitrarily replaced.

The light beam type multi-stage switch circuit having the above-mentioned two-dimensional structure is expressed in another expression as follows. The present invention is a light beam type multi-stage switch circuit in a three-dimensional space xyz, in which the average traveling direction of the entire light beam is the z direction, and the light beam forms a two-dimensional network in the xz plane. A plurality of switch elements related to the first n side surface are arranged in the x direction to form one stage, and a plurality of these stages are arranged in the z direction to form a switch circuit. The coupling destination of the mth switch element in the Ath stage is either the pth or the qth (q> p) switch element of the next (A + 1) stage, and the jump width q. The value of −p is uniform for one stage A regardless of m, and a different jump width can be given to a stage different from the stage A. The port surface or intermediate port surface forming the boundary between each stage and the regions before and after the stage includes a photonic crystal wave plate or a photonic crystal polarization separation prism that adjusts the polarization and bends the light in a desired direction. Specific examples of the photonic crystal polarization separation prism are as described above.

[2-2.3 light beam type multi-stage switch circuit with three-dimensional structure]
The light beam type multi-stage switch circuit having a three-dimensional structure includes a 2N-stage switch sub-circuit in the z-axis direction in the three-dimensional space xyz. In the switch subcircuit of each stage, the optical switch elements related to the first side surface are arranged parallel to the xy plane to form 2 ^N rows in the x direction and 2 ^N columns in the y direction. The light beam forms a three-dimensional network in xyz space, and the average traveling direction of the entire light beam is the z direction. The input port group of predetermined polarization on the input surface and the output port group of predetermined polarization on the output surface are arranged in the xy plane, and the light beam incident on each of the optical switch elements is directed in the x-axis direction on the next intermediate port surface. You can choose to lead to one of the other two intermediate ports with different positions, or to one of the other two intermediate ports with different values on the next intermediate port plane. Also, M is 1, 2, ... .. , N-1, on the intermediate port surface of No. (2M-1), the mth row of the light beam is connected to the mth row on the intermediate port surface of No. 2M. Alternatively, it is possible to select whether to connect to the m + 2 (NM) row, and on the 2M intermediate port surface, the nth column of the light beam is changed to the nth column on the (2M + 1) intermediate port surface. You can choose to tie or tie in the n + 2 (NM) column. Furthermore, as an effect of all 2N stages, a row of optical signals incident on ^2N × ^2N ports on the incident surface and another optical signal of ^2N × ^2N predetermined polarized ports on the emitting surface Can be converted to columns. In this three-dimensional structure optical beam type multi-stage switch circuit, the order of the first stage, the second stage, ..., And the second N stage can be arbitrarily replaced.

The light beam type multi-stage switch circuit having the above-mentioned three-dimensional structure is expressed in another expression as follows. The present invention is a light beam type multi-stage switch circuit in a three-dimensional space xyz, in which the average traveling direction of the entire light beam is the z direction, and the light beam forms a three-dimensional network in the xyz plane. The switch elements related to the first side surface are arranged in a plurality of rows in the x direction and in a plurality of columns in the y direction to form one surface. The surface is an x-shaped switch surface such that the signal points on the surface can be combined with two points that have the same y-value and x-values of the subsequent surfaces that differ by the jump width Cx, or the surface is The signal point on the surface is a y-shaped switch surface that can be combined with two points that have the same x value on the subsequent surface and different y values by the jump width Cy. It is composed of an x-type switch surface and a y-type switch surface so that the jump width Cx for each of the plurality of x-type switch surfaces is not constant and the jump width Cy for each of the plurality of y-type switch surfaces is not constant. The port surface or intermediate port surface forming the boundary between each stage and the regions before and after the stage includes a photonic crystal wave plate or a photonic crystal polarization separation prism that adjusts the polarization and bends the light in a desired direction. Specific examples of the photonic crystal polarization separation prism are as described above.

[3. Variable optical attenuator]
A third aspect of the present invention relates to a Variable Optical Attenuator (VOA). The variable optical attenuator of the present invention has a first polarization separation prism pair, a second polarization separation prism pair, and these first and second polarization separation prism pairs in the three-dimensional space xyz in the z-axis direction. It is provided with a liquid crystal cell intervening between them. The first and second polarization separation prism pairs are pairs in which photonic crystal polarization separation prisms are overlapped in the z-axis direction, respectively. The first polarization separation prism pair is a single light in a polarized state in which left-handed and right-handed circularly polarized light travels along the z-axis, and two parallels of left-handed and right-handed circularly polarized light. Separate into light. The liquid crystal cell is voltage-driven to convert each of the two parallel lights into a birefringent state with a phase difference θ while keeping the principal axis direction constant. The second pair of polarizing prisms makes the incident beam passing through the liquid crystal cell light in the same polarization state as the incident beam having a power ratio (sinθ) ² or (cosθ) ² , and two unnecessary waves having residual power. Separate into parallel beams.

According to the present invention, signal loss and crosstalk between signal lines can be effectively suppressed even in an optical switch circuit having a large number of input / output ports.

It is a principle diagram of the optical switch using the plane optical circuit which is a prior art. It is the schematic of the optical switch using the MEMS technique which is a prior art. It is a block diagram when the optical switch of this invention and it are arranged two-dimensionally. It is a block diagram when the optical switches of this invention are arranged three-dimensionally. It is a figure which shows an example of the polarization separation prism (divided type) which concerns on 1st Embodiment and the polarization separation prism (curve type) which concerns on 2nd Embodiment. It is a figure explaining the operation at the time of the vertical incident of the polarization separation prism which concerns on 1st Embodiment. It is a figure explaining the operation at the time of oblique incident of the polarization separation prism which concerns on 1st Embodiment. It is a figure explaining the structure and operation of the optical switch which concerns on 1st Embodiment. It is a figure explaining the input port surface of the optical switch which has the port of 8X8 which concerns on 4th Embodiment. It is a figure explaining that the optical switch having an 8X8 port which concerns on 4th Embodiment is hierarchized into four 4X4 blocks. It is a figure explaining that the optical switch having an 8X8 port which concerns on 4th Embodiment is hierarchized into four 4X4 blocks, and the blocks are exchanged in each section. It is a figure explaining the variable optical attenuator using the liquid crystal which concerns on 5th Embodiment.

[1. Basic Principles of Optical Switch Elements and Optical Switch Circuits]
FIG. 3 is a principle diagram of a two-dimensional switch circuit of the present invention. It is the optical switch element 304 shown in ellipse that plays a central role. The optical switch element 304 is interposed between the first polarization separation prism 301, the second polarization separation prism 303, and the first and second polarization separation prisms in the three-dimensional space xyz in the z-axis direction. It includes a liquid crystal cell 302. The first and second polarization separation prisms 301 and 303 are each composed of a photonic crystal polarization separation prism. Incident light is incident on the optical switch element 304 having such a structure in the z-axis direction. The incident light is circularly polarized light clockwise or counterclockwise having a traveling direction inclined by a predetermined angle θ with respect to the z-axis, and propagates in the xz plane of the optical switch element 304. The liquid crystal cell 302 can transition from at least an isotropic state (first state) with respect to incident light and a birefringent state (second state) having a phase difference of 180 degrees by voltage driving. The optical switch element 304 emits incident light as circularly polarized light having the same traveling direction and the same rotational direction by such a transition of the liquid crystal cell, or emits the incident light with respect to the z-axis. It is possible to select whether to emit as circularly polarized light having a traveling direction tilted by an angle −θ and in the opposite rotation direction. Further, the optical switch element 304 emits the incident light as circularly polarized light having the same traveling direction and the opposite rotation direction by the transition of the liquid crystal cell, or emits the incident light at an angle with respect to the z-axis. It is also possible to select whether to emit as circularly polarized light having a traveling direction inclined by −θ and in the same rotation direction.

As described above, the optical switch element 304 switches the polarization state of the incident light beam by the voltage applied to the liquid crystal cell 302. The photonic crystal prism pairs 301 and 303 sandwiching the liquid crystal cell 302 perform either or both of a function of adjusting the direction of the incident beam and a function of bending the emitted light ray in a desired direction.

A plurality of optical beams whose connection can be switched enter the optical switch circuit from the input surface (input port surface) P, and pass through the plurality of intermediate port surfaces R and T and the plurality of optical switch elements Q and U to the output surface (the output surface (input port surface). Output port surface) reaches V. In the optical switch circuit shown in FIG. 3, the optical beam is an input port surface P, a first optical switch element Q, a first intermediate port surface R, a second optical switch element S, and a second intermediate port surface T. , The third optical switch element U and the output port surface V are configured to pass in this order. Each stage is a switch subcircuit divided by two port surfaces and an optical switch element located between them, and is called a first stage, a second stage, and so on in order from the input side of the optical beam. With respect to the traveling direction of light, a plurality of switch elements are arranged side by side in the plane direction (y direction or xy direction) in the center of each stage to form a switch element surface or a switch element row surface. The light beam passing through the point 305 in FIG. 3 is guided to the point 306 or the point 307 depending on the state of the optical switch element 304 (whether it is the first state or the second state). The amount of jump from point 305 to point 307 is 4. That is, the light beam incident on the point 305 located at the highest position in the y direction on the input port surface P is guided to the point 307 located at the fourth highest position in the y direction on the first intermediate port surface R. .. Such a jump of the signal path from the input port surface to the next port surface is expressed as "jump" in the present specification. The magnitude of this jump is common within the first stage. Similarly, the amount of jump between the front and back stages is doubled (or halved).

The input port surface P, the output port surface V, the intermediate port surfaces R, and T have a photonic crystal wave plate or a photonic crystal polarization separation prism, adjust the polarization state of the light beam to be handled to a desired state, and perform a desired traveling direction. Has the function of bending to. Further, FIG. 4 is a diagram showing a simplified principle of the three-dimensional type of the switch circuit of the present invention.

By selecting the distance between the input port surface P and the first intermediate port surface R, or the distance between the first intermediate port surface R and the second intermediate port surface T, the jump amount of the signal path is set to 4. Since it can be set to 2 or 1, the number of switch stages required is small. Moreover, since the light beam propagates in free space or in a uniform medium, no crosstalk occurs between signal paths. Further, in reality, the photonic crystal created on the glass plate and the liquid crystal cell sandwiched between the glass plates are overlapped and bonded to each other, so that the mounting is easy.

[2. Photonic crystal polarization separation prism]
An optical switch circuit using a photonic crystal polarization separation prism will be described.
Although the photonic crystal is known, it may be formed by, for example, a self-cloning method (see Patent Document 3). A photonic crystal is a structure in which the refractive index changes periodically in a period shorter than the operating wavelength of the guided light. In particular, the wave plate is preferably a photonic crystal formed by a self-cloning action. A photonic crystal is a microperiodic structure that functions as an optical element (for example, a polarization separation prism or a wave plate). As a specific method for producing a photonic crystal, as disclosed in Patent Document 3, two or more kinds of different refractive indexes are used on a substrate having one-dimensional or two-dimensional periodic irregularities. An example is a method in which an optical element is manufactured by periodically and sequentially laminating substances (transparent bodies) and using spatter etching alone or at the same time as film formation on at least a part of the laminated material. This method is also called the self-cloning method. The photonic crystal formed by this self-cloning method is called a self-cloning photonic crystal. A technique for constructing a wave plate using a self-cloning photonic crystal is known. For example, as another method for producing a photonic crystal, there is a method for producing periodic voids by irradiating glass with a femtosecond laser.

The plurality of types of transparent substances forming the self-cloning photonic crystal are fluorides such as amorphous silicon, niobium pentoxide, tantalum pentaoxide, titanium oxide, hafnium oxide, silicon dioxide, aluminum oxide, and magnesium fluoride. It is preferably either. Two or more kinds having different refractive indexes can be selected from these and used for photonic crystals. For example, a combination of amorphous silicon and silicon dioxide, niobium pentoxide and silicon dioxide, and tantalum pentoxide and silicon dioxide is desirable, but other combinations are also possible. Specifically, the self-cloning photonic crystal has a structure in which a high refractive index material and a low refractive index material are alternately laminated. The high refractive index material is preferably tantalum pentoxide, niobium pentoxide, amorphous silicon, titanium oxide, hafnium oxide, or a combination of two or more of these materials. The low refractive index material is preferably a fluoride containing silicon dioxide, aluminum oxide, magnesium fluoride, or a combination of two or more of these materials.

More specifically, the photonic crystal polarization separation prism (optical element) used in the present invention is a wave plate (divided type) in which the principal axis orientation is different for each region, or a wave plate in which the spindle orientation is continuously changed. It is (curved), and the wave plate in each region is composed of a photonic crystal having a periodic structure in the plane and the periodic structure is laminated in the thickness direction. Photonic crystals may be formed by a self-cloning method.

The split-type photonic crystal polarization separation prism uses a self-cloning method to form a photonic crystal on a substrate having a pattern as shown in 501 of FIG. In the xy plane, a plurality of regions D are periodically and repeatedly formed at least in the x-axis direction. It is preferable that the lengths of the plurality of regions D in the x-axis direction are equal. Further, each region D is further divided into a plurality of sub-regions in the x direction. The number of divisions of each region D can be 3 to 21, and is preferably an odd number such as 5, 7, 9, 11, 13, 15, 17, or 19. It is preferable that the sub-regions included in each region D have substantially the same width in the x-direction. The "substantially equal width" means that an error of ± 2% is allowed with respect to the width d of the sub-region located in the center in the x direction.

Further, a plurality of grooves are periodically formed in each sub-region. The widths of the grooves are virtually all equal. Further, the groove is formed from end to end in the x direction in each sub region. In the sub-region located at the center of the x-direction in the region D, grooves extending parallel to the x-axis direction are periodically and repeatedly formed in the y-direction. On the other hand, in the region D, in the sub-regions located at the left and right ends in the x direction, grooves extending parallel to the y direction are formed. Therefore, the angle θ formed by the grooves formed in the left and right sub-regions is 90 degrees with respect to the groove formed in the central sub-region. In such a sub-region, the groove length is the largest and coincides with the effective dimension of the entire element in the y direction.

Further, a plurality of sub-regions are located on each of the left and right sides between the central sub-region and the sub-regions at both left and right ends. Then, a plurality of grooves are periodically and repeatedly formed in the y direction in each of the sub-regions located between them. Also, the angles of the grooves formed in a certain sub-region are all equal. However, the angle θ of the groove of each sub-region located between them is set so as to gradually approach 90 degrees as it approaches the sub-regions at both the left and right ends from the central sub-region. For example, four sub-regions are provided between the central sub-region and the sub-regions on the left and right ends, and the angle of the groove in the central sub-region is 0 degrees and the angle of the groove in the sub-regions on the left and right ends is 90. In terms of degrees, the inclination angle θ becomes steeper by 22.5 degrees in order from the region closest to the central sub-region. In this way, each region D is divided into a plurality of sub-regions having the same width in the x-direction, and grooves having the same angle are periodically formed in each sub-region, and left and right from the sub-region located at the center in the x-direction. The angle of the groove increases monotonically toward the sub-regions located at both ends.

Under these assumptions, in each sub-region, the inter-groove unit period p of the periodic structure (see FIG. 5) is less than a quarter of the wavelength of the incident light (eg selected from between 400 nm and 1800 nm). It becomes. The lower limit of the inter-groove unit period p is 40 nm. Further, in the thickness direction (z direction), the unit period of the two types of transparent media having different refractive indexes is also one-fourth or less of the wavelength of light. The lower limit of the unit period in the thickness direction is 40 nm. Then, among the entire plurality of regions D, the in-plane minimum value d (see FIG. 5) of the groove length becomes one or more times the above-mentioned inter-groove unit period p. The upper limit of the in-plane minimum value d of the groove length is considered to be 50 times the above-mentioned inter-groove unit period p. Here, as shown in FIG. 5, since the widths of the plurality of sub-regions formed in a certain region D in the x-direction are all equal, the in-plane minimum value d of the groove length in the region D is basically. , The length of the groove formed in the sub-region located at the center of this region D. The length of the groove tends to be longer as the groove is in the region on both the left and right sides in the x direction.

光学素子（偏光分離プリズム）が持つ位相差φがπの時、上記の式を整理すると、

となる。したがって射出される光は左回りの円偏光へ変換される。また、θはｘにだけ依存しているため、ｘに依存した位相差が生じる。１周期Ｄの間でθがｘに比例して０～πまで比例して変化するとき、出力波第１項、第２項の位相の傾きはｘ＝Ｄのところで、ｘ＝０のところと２πだけ変化する。したがってｚ軸に対してψ＝ｓｉｎ^－１（λ／Ｄ）だけ屈曲して射出される。同様に左回りの円偏光が入射した際、光は右回り円偏光に変換され、ｚ軸に対して－ψ＝－ｓｉｎ^－１（λ／Ｄ）だけ屈曲して射出される。 In the three-dimensional space xyz, the traveling direction of light is defined as the z-axis. An optical element (polarization separation prism) having a period D is installed in the xy plane, the inclination of the slow axis direction from the x axis is θ, and the light emitted when the right-handed polarization is incident is as follows. It is represented by.

When the phase difference φ of the optical element (polarization separation prism) is π, the above equation can be summarized as follows.

Will be. Therefore, the emitted light is converted into counterclockwise circular polarization. Further, since θ depends only on x, a phase difference depending on x occurs. When θ changes proportionally from 0 to π in proportion to x during one period D, the slopes of the phases of the first and second output waves are at x = D and at x = 0. It changes by 2π. Therefore, it is bent and ejected by ψ = sin ^-1 (λ / D) with respect to the z-axis. Similarly, when counterclockwise circular polarization is incident, the light is converted to clockwise circular polarization and is emitted by bending by −ψ = −sin ^-1 (λ / D) with respect to the z-axis.

The operation when the light beam is vertically incident will be described with reference to FIG. There are straight lines L ₁ and L ₂ parallel to the x-axis and equal in height in the y direction, and a straight line PQR from a point P on L ₁ through a point Q on the optical element 601 to a point R on L ₂ . Define. In this case, the PQ is perpendicular to the element 601. For convenience of explanation, it is assumed that the refractive indexes of the media on both sides of the optical element are equal. R ₋ and R ₊ are taken on the straight line L ₂ with R in between, and the ray QR ₊ has a wave number of 2π / D in the x direction, and QR ₋ also has -2π / D. When the clockwise circular polarization is incident along the PQ, it becomes a counterclockwise circular polarization and is bent to QR ₊ (see FIG. 6A). On the other hand, the case where the incident polarization is counterclockwise circular polarization will be described with reference to FIG. 6 (b). When counterclockwise circular polarization is incident perpendicularly to the element 602, it becomes clockwise circular polarization _and is bent to QR− (see FIG. 6B).

In the above description, for convenience, the wave numbers in the y direction are all set to 0, but the same applies when they have a common wave number. Further, even when the refractive indexes of the media filling the spaces on both sides of the optical elements 601 and 602 are not common (for example, air and glass), the light rays are associated with each other not by the spatial shape but by the wave number. When using a plurality of optical elements, the direction for defining the period may be selected in a different direction for each element, and the element is divided into a plurality of regions, each of which has a different period direction and period. You may be.

Further, with reference to FIG. 7, the operation when the light beam is obliquely incident will be described. There are straight lines L ₁ and L ₂ parallel to the x-axis and equal in height in the y direction, and a straight line PQR from a point P on L ₁ through a point Q on the optical element 701 to a point R on L ₂ . Define. For convenience of explanation, it is assumed that the refractive indexes of the media on both sides of the optical element are equal. The light rays PQ and QR have the same wave number in the x direction with respect to light having a wavelength λ in the propagation medium. P ₋ and P ₊ are taken on the straight line L ₁ with P in between, the ray P ₊ Q has the wave number + 2π / D in the x direction, and the ray P ₋ Q also has -2π / D. When the light rays P + Q are counterclockwise circularly polarized, the emitted light becomes clockwise circularly polarized, is bent, and travels in the QR direction. On the other hand, when the light ray PQ is clockwise circularly polarized light, the emitted light becomes counterclockwise circularly polarized light, is bent, and also travels in the QR direction. In this case, the QR direction is perpendicular to the elements 701 and 702.

In the above description, for convenience, the wave numbers in the y direction are all set to 0, but the same applies when they have a common wave number. Further, even when the refractive indexes of the media filling the spaces on both sides of the optical elements 701 and 702 are not common (for example, air and glass), the light rays are associated with each other not by the spatial shape but by the wave number. When using a plurality of optical elements, the direction for defining the period may be selected in a different direction for each element, and the element is divided into a plurality of regions, each of which has a different period direction and period. You can.

Although the split-type photonic crystal polarization separation prism has been described here, the pattern 501 in FIG. 5 can be replaced with the pattern 502 in FIG. The pattern 502 in FIG. 5 shows a so-called curved photonic crystal polarization separation prism. That is, the basic configuration of the curved photonic crystal polarization separation prism (optical element) is a wave plate formed of photonic crystals formed on the xy plane in the three-dimensional spaces x, y, and z and laminated in the z-axis direction. (More specifically, a half-wave plate). In the wave plate, a plurality of strip-shaped width D regions parallel to the y-axis direction are repeated in the x-axis direction. The groove direction of the photonic crystal is a curve that matches the curve 503y = (D / π) log (| cos (πx / D) |) + constant within the range of discretization error.

As shown in 502 of FIG. 5, by making the pattern (convex or concave) of the photonic crystal curved, the pattern becomes sparse in the central part within one cycle, and the closer to the edge, the denser the pattern. It becomes difficult to make a pattern. Therefore, as in 504, the pitch between patterns at the center is taken as a reference, and that is set as _p0 . The two patterns are merged at a position where p ₀ is below a certain threshold pitch. The pitch immediately after merging becomes 2p ₀ , but since it becomes denser toward the end, it is rejoined when it becomes less than the threshold length. By repeating the above operation, the ideal optical axis distribution can be realized while the pitch changes within a certain range. Assuming that the threshold pitch is 0.5p ₀ , the pitch change range is between 0.5p ₀ and 2.0p ₀ . That is, they are geometrically arranged so that the ratio of the maximum value and the minimum value of the distance between one of the adjacent convex portions and the concave portions is within 4 times, preferably within 2 times, and the other branches and merges. .. In the example shown in 504, the white portion is a concave portion and the black portion is a convex portion. That is, in the case of a wave plate (curve type) in which the principal axis direction changes continuously, if the pitch p of the convex portion (pitch when the pattern is a straight line) is p ₀ , then 0.5 · p ₀ ≦ p ≦ 2 -The convex or concave parts are geometrically arranged so as to branch or merge so as to be within p ₀ .
By continuously changing the axial direction in this way, higher efficiency can be realized as compared with the divided one.
Photonic crystal polarization separation prisms are, for example: ・ Free space wavelength λ ₀ 1.55 μm
・ High refractive index material a-Si
・ Low refractive index material SiO ₂
・ Prism period D 10 μm
・ Slow-axis refractive index n _s 2.713
・ Fast-axis refractive index n _f 2.486
・ Thickness of the entire laminate λ ₀ / ( _ns − n _f ) × φ / (2π)
Assuming that, when the medium is quartz, the separation angle is Φ = 6.1 degrees.

Further, as in the optical switch element 804 shown in FIG. 8, two curved photonic crystal separation prisms 801 and 803 are arranged so that the directions of the curves are opposite to each other, and a glass substrate is placed between them. A liquid crystal cell 802 sandwiching a nematic liquid crystal molecule can also be arranged. A transparent electrode is formed on the glass substrate so that an electric field is applied perpendicularly to the glass. For example, when a birefringence control type liquid crystal is used, it becomes isotropic when an electric field is applied, and birefringence can be provided according to the orientation when an electric field is not applied.

As a result, the liquid crystal cell 802 can turn on / off the phase difference, and when an appropriate voltage is selected, the phase difference (2n + 1) π (n = 0, 1, 2, ...) When the voltage is off, and the voltage is turned on. In the case of, it functions as a variable birefringence plate with zero phase difference. When the phase difference is zero, when clockwise circular polarization is incident, it is emitted clockwise, and when counterclockwise circular polarization is incident, it is emitted counterclockwise. Therefore, as in the optical switch element 804 shown in the middot ellipse of FIG. 8, when the phase difference is zero, the light coming from the top goes up and the light coming from the bottom goes down. On the other hand, when the phase difference of the liquid crystal cell is π, when the clockwise circular polarization is incident, it is emitted as counterclockwise circular polarization, and when the counterclockwise circular polarization is incident, it is emitted as clockwise circular polarization. As a result, the light coming from above goes down and the light coming from below goes up. In this way, the optical path can be switched by turning the voltage applied to the liquid crystal cell 803 on and off.

The substrate of the liquid crystal cell 802 may be shared with the substrate of the photonic crystal, or may be independent. Further, the function of the liquid crystal cell is to switch the phase difference, and the type of liquid crystal and the method of applying an electric field may be appropriately known. Of course, the directions of the patterns of the polarizing prisms on the input side and the output side may be the same. Only the optical path when the voltage is on and off is reversed. Further, when the liquid crystal cell is off with a phase difference (2n + 1) π (n = 0, 1, 2, ...) When a voltage is applied, there may be no phase difference. It only changes the output direction when it is on and off.

[3. Two-dimensional optical switch circuit]
The optical switch circuit is a two-dimensional type (planar arrangement type), and the configuration for reducing interference and crosstalk between adjacent lines of signal light is shown below.

FIG. 3 shows an optical switch circuit having 8 inputs and 8 outputs. Light having a predetermined free space wavelength and a predetermined polarization (for example, right-handed circular polarization) is incident on the leftmost input port surface P. The input port P is composed of a row of polarization separation prisms, and the first to fourth ports 308 are arranged so that the output light becomes left-handed circularly polarized light and is emitted diagonally downward, and the fifth to fourth ports 308 are arranged. The 8-port 309 is arranged so that the output light becomes right-handed circularly polarized light and is emitted diagonally upward. In the optical switch element row Q, whether a voltage is applied to the liquid crystal cell 302 to make the liquid crystal cell isotropic, or whether the voltage applied to the liquid crystal cell 302 is zero and the liquid crystal cell becomes a wave plate having a phase difference of 180 °. select. As a result, the light from the mth port in row P is
When m = <4, it is input to the mth port or the (m + 4) th port of the R column.
When m> = 5, it is input to the mth port or the (m-4) port of the R column.
Be combined. Unlike the coupling only between adjacent lines as shown in FIG. 1, in the optical switch circuit of the present invention, the destinations selected by turning the voltage on and off are separated by 4 ports. That is, the jump width of the switch is 4.

As shown in FIG. 3, in the optical switch element train S after the intermediate port surface R, switching between lines separated by 2 is selected. Further, in the optical switch element train U after the intermediate port surface T, switching between adjacent ports (between lines separated by one) is performed.

As is clear from the above description, in the N-stage optical switch element, it is possible to select a route (switching) such that the difference between the ports is 2 ^N-1 at the maximum, and the adjacent line as shown in FIG. Compared to a switch with only a pause, the number of switches can be significantly reduced, and insertion loss and crosstalk can be significantly reduced.

A concrete example of the structure and characteristics of the optical switch circuit is shown. With an N = 3 (8 × 8) switch, the channel spacing is 0.5 mm, the prism pattern period is 5 um, the propagation space is quartz glass, the light wavelength is 1550 nm, and the bending angle in the medium is 12.3 degrees. If the radius of the input beam is selected so that the overlap of the hem of the light beam after propagation is minimized, the propagation distance is 18.4 mm and the inter-signal crosstalk is -87.2 dB. Losses and crosstalk can be extremely small.

[4.3-dimensional optical switch circuit]
An example of configuring a three-dimensional (spatial wiring type) optical switch circuit using the optical switch element according to the present invention is shown.

FIG. 4 shows an optical switch circuit having 16 inputs and 16 outputs (4 rows and 4 columns each). Light having a predetermined free space wavelength and a predetermined polarization (for example, right-handed circular polarization) is incident on the leftmost input port surface P portion. Optical switch element rows Q, S, U, and W are installed between the polarization separation prism rows arranged on the port surfaces P, R, T, V, and X. In the example shown in FIG. 4, the light beam incident on the input port surface P travels parallel to the xz surface, and the path is selected between the ports in the x direction by the first optical switch element sequence Q, and the light beam is selected in the x direction. With a jump width of 2, it is coupled to the first intermediate port surface R of the next stage. In the vertical dot array (first optical switch element array Q) between the input port surface P and the first intermediate port surface R, the uppermost optical switch element in the y direction is the layer below the y direction. It means that it is also provided in the same manner. The same applies to the following second to fourth optical switch element trains S, U, and W. Subsequently, in the section between the first intermediate port surface R and the second intermediate port surface T, the light beam travels parallel to the yz surface, and the path between the ports in the y direction by the second optical switch element sequence S. The selection is made and coupled with the second intermediate port surface T of the next stage with a jump width of 2 in the y direction. After that, similarly, in the section between the second intermediate port surface T and the third intermediate port surface V, the light beam travels parallel to the xz surface, switching is performed between the ports adjacent to each other in the x direction, and the third intermediate port surface T is used. In the section between the intermediate port surface V and the output port surface X, the light beam travels parallel to the yz surface, and switching is performed between adjacent ports in the y direction.
A concrete example of the structure and characteristics of the optical switch circuit is shown. In the 16-input x 16-output switch shown in FIG. 4, the channel spacing is 0.25 mm, the prism pattern period is 10 um, the propagation space is quartz glass, the light wavelength is 1550 nm, the bending angle in the medium is 6.1 degrees, and the optical switch circuit. If the radius of the input beam is selected so that the overlap of the hem of the optical beam after propagation is minimized, the propagation distance is 14.1 mm and the inter-signal crosstalk is -56.8 dB. Losses and crosstalk can be extremely small.

In the embodiment shown in FIG. 4, the number of input ports and output ports is 4 × 4 = 16, respectively. With the same idea, the number of input / output ports can be increased to 8 × 8 = 64, respectively. The penalty, that is, the increase in the number of steps required, is only two.

[5. Multiple block method]
There is a multiple block system as an embodiment for variably connecting a signal port on the input surface and a signal port on the output surface with a high degree of freedom. In the multiple block method, it is possible to have free compatibility between blocks of the same size. In order to make the effect of the invention easy to understand, the structural principle of FIG. 4 will be maintained as it is, and the size will be increased from 4 × 4 to 8 × 8. FIG. 9 is an input / output surface of a switch circuit having 8 × 8 ports on both the input surface and the output surface. Divide the input surface into four 4x4 blocks. Furthermore, individual 4x4 blocks can be hierarchized by dividing them into four 2x2 blocks. To return to the original state and freely rearrange the 4 × 4 blocks divided into four as shown in FIG. 10, the following configuration may be used.

In FIG. 11, the PR section of the circuit of FIG. 4 is enlarged from 4 × 4 to 8 × 8 (section A), the RT section is similar (section B), and the PR section is again changed from 4 × 4 to 8 ×. It shows three sections of the one set to 8 (section C). In order to display a light ray moving horizontally or vertically in a three-dimensional space, the section A in FIG. 11 represents the horizontal movement, and the p-axis represents the x-axis in this section. The same applies to section C. The section B represents the movement of the vertical plane of the light beam, and here the p-axis represents the y-axis. In other words, in the section A between the input port surface and the first intermediate port surface, the y value of the light ray is constant and only the value of x changes. The same applies to section C. In the section B, the value of x of the light ray is constant and only the value of y changes. That is, in section A and section C, (1 + 3) and (2 + 4) in FIG. 10 can be replaced, and in section B, (1 + 2) and (2 + 4) in FIG. 10 can be replaced without changing the internal configuration. In the three-section configuration of FIG. 11, it is shown in FIG. The blocks 1, 2, 3, and 4 having a size of 4 × 4 on the input surface of the section A can be arbitrarily replaced on the output surface of the section C without changing the internal configuration.

According to the same idea, the sub-block of size 2 × 2 inside the block of size 4 × 4 can also be arbitrarily replaced in three sections. The same operation as above is possible for sub-blocks of size 2x2. Alternatively, if four signals are arranged in the size 2 × 2 subblock, two signals each having two degrees of freedom of polarization from the two optical fibers, the replacement corresponds to the replacement between the fibers. Only the section is sufficient.

To summarize the above, there are 2 ^N x 2 ^N signal ports on the input side and output side, respectively, and it is possible to divide them into 4 layers and realize free replacement between blocks of the same size (N). -1) + 1 switch surface is sufficient, and the larger N is, the more remarkable the advantage is.

[6. Variable optical attenuator]
Next, a variable optical attenuator that applies the principle of the optical switch element will be described.
FIG. 12 shows an example of a variable optical attenuator. The variable optical attenuator has a first polarization separation prism pair 1201 and 1202, a second polarization separation prism pair 1204.1205, and their first and second polarizations in the z-axis direction in the three-dimensional space xyz. It includes a liquid crystal cell 1203 interposed between the separation prism pairs. The first and second polarization separation prism pairs 1201, 1202, 1204, and 1205 are paired with photonic crystal polarization separation prisms overlapping in the z-axis direction, respectively. The first polarization separation prism pair 1204.1205 travels along the z-axis and transmits a single light in a polarized state in which counterclockwise and clockwise circular polarizations are mixed, and counterclockwise and clockwise circularly polarized light 2 Separate into parallel light of the book. The liquid crystal cell 1203 converts each of the two parallel lights into a birefringent state with a phase difference θ while keeping the principal axis direction constant by voltage driving. The second polarizing prism pair 1204-1205 uses light having the same polarization state as the incident beam having a power ratio (sinθ) ² or (cosθ) ² of the incident beam passing through the liquid crystal cell 1203, and unnecessary power having residual power. Separate into two undulating parallel beams.

By continuously changing the voltage applied to the liquid crystal cell 1203, the given phase difference can also be continuously changed. The photonic crystal polarization separation prisms 1201, 1202, 1204 and 1205 are all in the same direction. It can be said that the mixed polarized light incident on the first polarization separation prism pair 1201 and 1202 is synthesized by changing the ratio of arbitrary clockwise circular polarization and counterclockwise circular polarization. Therefore, no matter what kind of polarization is incident, the first polarization separation prism pairs 1201 and 1202 are separated into clockwise and counterclockwise circular polarization by the first prism 1201 and are separated by the second prism 1202. The orientation is corrected to be parallel, and the light is incident on the liquid crystal cell 1203. In the liquid crystal cell 1203, the polarization state changes depending on the given phase difference. For example, when clockwise circular polarization is incident, it becomes elliptically polarized as the phase difference increases, and becomes linearly polarized when the phase difference is π / 2. When the phase difference becomes larger and the phase difference becomes π, counterclockwise circular polarization occurs. In this way, in the liquid crystal cell 1203, the polarization state changes according to the applied voltage and is emitted. Therefore, the third polarizing prism 1204 is further separated into upper and lower parts depending on the polarization state of the incident light. This separation ratio depends on the phase difference given by the liquid crystal cell. Then, the required light is combined by the fourth polarizing prism 1205 and output from the output port 1206. Unnecessary light is separated vertically by the polarization separation prism 1204, then returned to parallel light by the polarization prism 1205, and emitted from other than the output port 1206. These unnecessary lights may be absorbed by, for example, a black object.

The amount of light output in this way can be controlled by the phase difference given by the liquid crystal cell. Therefore, the configuration of FIG. 12 functions as a variable attenuator capable of controlling the amount of transmitted light by the voltage applied to the liquid crystal cell. The polarization state of the emitted light is the same as that of the incident light. This variable attenuator does not require alignment between each element and has excellent industrial characteristics.

It was difficult to realize an optical switch with a large number of I / O ports that had excellent characteristics due to insertion loss and leakage, but the simple composite structure of the photonic crystal prism and liquid crystal cell made it possible to increase the number of I / O ports. It can be realized and is effective in optical communication systems.

Claims (7)

An optical beam type multi-stage switch circuit having N stages of switch subcircuits in the z-axis direction in a three-dimensional space xyz, and a plurality of optical switch elements arranged in the x-axis direction in the switch subcircuits of each stage.
The optical switch element is
An optical switch element in which incident light, which is a right-handed or left-handed circularly polarized light having a traveling direction tilted by a predetermined angle θ with respect to the z-axis in a three-dimensional space xyz, propagates in the xz plane.
In the z-axis direction, a first polarization separation prism, a second polarization separation prism, and a liquid crystal cell interposed between the first and second polarization separation prisms are provided.
The first and second polarization separation prisms are photonic crystal polarization separation prisms, respectively.
The liquid crystal cell can transition from at least an isotropic state with respect to the incident light and a birefringent state having a phase difference of 180 degrees by voltage driving.
Due to the transition of the liquid crystal cell, the incident light is emitted as circularly polarized light having the same traveling direction and one of the same or opposite rotation directions, or the traveling direction tilted by an angle −θ with respect to the z-axis. And can be selected to be emitted as circularly polarized light in the same or opposite rotation direction.
In the light beam type multi-stage switch circuit
The average traveling direction of the entire light beam is the z-axis direction.
The light beam creates a two-dimensional network in the xz plane,
The ^2N input port trains with predetermined polarization on the input surface and the 2N output port rows with predetermined polarization on the output surface are arranged in the x ^- axis direction.
Each of the optical switch elements sets the emission direction of the light beam so as to guide the light beam incident therein to one of the other two optical switch elements having different positions in the x-axis direction of the next stage. It ’s a choice,
In the Mth stage (M <N) of the switch circuit, the mth of the ports arranged in the x direction is connected to the mth port of the next (M + 1) stage, or m to 2 ^(N-) . Whether to combine with the port that jumped only ^M) ,
The port surface or intermediate port surface that forms the boundary between each stage and the regions before and after it is provided with a photonic crystal wave plate or a photonic crystal polarization separation prism that regulates polarization and bends light in a desired direction.
An optical beam type multi-stage switch circuit capable of converting an optical signal train incident on 2 ^N ports on an incident surface into an optical signal train emitted from 2 ^N ports on an exit surface, which is different from the input. In the optical beam type multi-stage switch circuit according to claim 1, the optical beam type multi-stage switch circuit in which the order of the first stage, the second stage, ..., And the Nth stage is arbitrarily replaced. In the three-dimensional space xyz, the average traveling direction of the entire light beam is the z direction, the light beam forms a two-dimensional network on the xz plane, and a plurality of optical switch elements are arranged in the x direction to form one stage. A light beam type multi-stage switch circuit in which a plurality of the above stages are arranged in the z direction to form a switch circuit.
The optical switch element is
An optical switch element in which incident light, which is a clockwise or counterclockwise circularly polarized light having a traveling direction tilted by a predetermined angle θ with respect to the z-axis in a three-dimensional space xyz, propagates in the xz plane.
In the z-axis direction, a first polarization separation prism, a second polarization separation prism, and a liquid crystal cell interposed between the first and second polarization separation prisms are provided.
The first and second polarization separation prisms are photonic crystal polarization separation prisms, respectively.
The liquid crystal cell can transition from at least an isotropic state with respect to the incident light and a birefringent state having a phase difference of 180 degrees by voltage driving.
Due to the transition of the liquid crystal cell, the incident light is emitted as circularly polarized light having the same traveling direction and one of the same or opposite rotation directions, or the traveling direction tilted by an angle −θ with respect to the z-axis. And can be selected to be emitted as circularly polarized light in the same or opposite rotation direction.
In the light beam type multi-stage switch circuit
The coupling destination of the mth switch element in the Ath stage is either the pth or the qth (q> p) switch element of the next (A + 1) stage, and the jump width q. The value of -p is uniform for one stage A regardless of m, and a different jump width can be given to a stage different from the stage A.
The port surface or intermediate port surface that forms the boundary between each stage and the regions before and after it is an optical beam type multi-stage switch equipped with a photonic crystal wave plate or a photonic crystal polarization separation prism that regulates polarization and bends light in a desired direction. circuit. In the three-dimensional space xyz, a 2N stage switch sub circuit is provided in the z axis direction, and optical switch elements are arranged parallel to the xy plane in the switch sub circuit of each stage, 2 ^N rows in the x direction, and 2 ^N in the y direction. A row of light beam type three-dimensional multi-stage switch circuits
The optical switch element is
An optical switch element in which incident light, which is a right-handed or left-handed circularly polarized light having a traveling direction tilted by a predetermined angle θ with respect to the z-axis in a three-dimensional space xyz, propagates in the xz plane.
In the z-axis direction, a first polarization separation prism, a second polarization separation prism, and a liquid crystal cell interposed between the first and second polarization separation prisms are provided.
The first and second polarization separation prisms are photonic crystal polarization separation prisms, respectively.
The liquid crystal cell can transition from at least an isotropic state with respect to the incident light and a birefringent state having a phase difference of 180 degrees by voltage driving.
Due to the transition of the liquid crystal cell, the incident light is emitted as circularly polarized light having the same traveling direction and one of the same or opposite rotation directions, or the traveling direction tilted by an angle −θ with respect to the z-axis. And can be selected to be emitted as circularly polarized light in the same or opposite rotation direction.
In the light beam type three-dimensional multi-stage switch circuit,
The light beam creates a three-dimensional network in xyz space,
The average traveling direction of the entire light beam is the z direction.
The input port group of predetermined polarization on the input surface and the output port group of predetermined polarization on the output surface are arranged in the xy plane, and the light beam incident on each of the optical switch elements is directed in the x-axis direction on the next intermediate port surface. You can choose to lead to one of the other two intermediate ports with different positions, or to one of the other two intermediate ports with different values on the next intermediate port plane.
M is 1, 2, ... .. , N-1 any one
On the intermediate port surface of No. (2M-1), whether to connect the mth row of the light beam to the mth row on the intermediate port surface of No. 2M or to the m + 2 ^(NM) row. Selectable and
On the 2M intermediate port surface, it is possible to select whether to connect the nth row of the light beam to the nth row on the (2M + 1) intermediate port surface or to the n + 2 ^(NM) row. And
As an effect of all 2N stages, the optical signal incident on the ^2N × ^2N ports on the incident surface is transferred to another optical signal sequence of the ^2N × ^2N ports of predetermined polarization on the emitting surface. Optical beam type multi-stage switch circuit that can be converted. The optical beam type multistage switch circuit according to claim 4, wherein the order of the first stage, the second stage, ..., And the second N stage is arbitrarily replaced. In the three-dimensional space xyz, the average traveling direction of the entire light beam is in the z direction, the light beam forms a three-dimensional network in the xyz plane, and the optical switch elements are arranged in multiple rows in the x direction and in multiple columns in the y direction. It is a light beam type multi-stage switch circuit that forms one surface.
The optical switch element is
An optical switch element in which incident light, which is a right-handed or left-handed circularly polarized light having a traveling direction tilted by a predetermined angle θ with respect to the z-axis in a three-dimensional space xyz, propagates in the xz plane.
In the z-axis direction, a first polarization separation prism, a second polarization separation prism, and a liquid crystal cell interposed between the first and second polarization separation prisms are provided.
The first and second polarization separation prisms are photonic crystal polarization separation prisms, respectively.
The liquid crystal cell can transition from at least an isotropic state with respect to the incident light and a birefringent state having a phase difference of 180 degrees by voltage driving.
Due to the transition of the liquid crystal cell, the incident light is emitted as circularly polarized light having the same traveling direction and one of the same or opposite rotation directions, or the traveling direction tilted by an angle −θ with respect to the z-axis. And can be selected to be emitted as circularly polarized light in the same or opposite rotation direction.
In the light beam type multi-stage switch circuit
The surface is an x-shaped switch surface such that the signal points on the surface can be combined with two points that have the same y-value and x-values of the subsequent surfaces that differ by the jump width Cx, or the surface is The signal point on the surface is a y-shaped switch surface that can be combined with two points where the x value of the subsequent surface is the same and the y value is different by the jump width Cy.
It is composed of an x-type switch surface and a y-type switch surface so that the jump width Cx for each of the plurality of x-type switch surfaces is not constant and the jump width Cy for each of the plurality of y-type switch surfaces is also not constant.
The port surface or intermediate port surface that forms the boundary between each stage and the regions before and after it is an optical beam type multi-stage switch equipped with a photonic crystal wave plate or a photonic crystal polarization separation prism that regulates polarization and bends light in a desired direction. circuit. In the three-dimensional space xyz, a first polarization separation prism pair, a second polarization separation prism pair, and a liquid crystal cell interposed between the first and second polarization separation prism pairs are provided in the z-axis direction. ,
The first and second polarization separation prism pairs are pairs of photonic crystal polarization separation prisms overlapping in the z-axis direction.
The first polarization separation prism pair is a single light in a polarized state in which left-handed and right-handed circularly polarized light travels along the z-axis, and two left-handed and right-handed circularly polarized light. Separated into parallel light,
The liquid crystal cell is driven by a voltage to convert each of the two parallel lights into a birefringent state with a phase difference θ while keeping the principal axis direction constant.
In the second polarization separation prism pair, the incident beam that has passed through the liquid crystal cell has a power ratio (sinθ) ² or (cosθ) ² , and is in the same polarization state as the incident beam. A variable optical attenuator that separates into two parallel beams that undulate.

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