JP2009168840A - Wavelength selection switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength selection switch which does not use MEMS (Micro Electro Mechanical Systems) mirror array, whose layout is easy and which has high reliability and stability. <P>SOLUTION: A one input port-M output port type wavelength selection switch inputs an optical signal from one input port to separate the optical signal into a plurality of optical signals having wavelengths different from one another, changes optical axes of the optical signals having the respective wavelengths to make the optical signals correspond to desired M (M is an integer of 2 or more) output ports, and outputs the optical signals corresponding to the respective output ports from the respective output ports by joining the plurality of optical signals having the wavelengths different from one another. The switch includes: an AWG (Arrayed Wavelength Grating) for separating the optical signal made incident on the input port into the plurality of optical signals having the wavelengths different from one another and for emitting the optical signals at emission angles corresponding to the wavelengths; a lens 40 condensing the optical signals separated for each wavelength; and a reflection type liquid crystal phase modulation element 200 giving phase differences to each of the condensed optical signals to change progress directions thereof. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wavelength selective switch applicable to an optical communication system.

  While the capacity of optical communication has been increased and the transmission capacity has been increased by a wavelength division multiplexing (WDM) system, an increase in the throughput of the path switching function in the node is strongly demanded. In the past, the path switching was mainly performed by an electrical switch after converting the transmitted optical signal to an electrical signal. However, taking advantage of the characteristics of the optical signal such as high speed and wide bandwidth, an optical switch, etc. A ROADM system that performs add / drop and the like using an optical signal as it is is introduced. Specifically, an optical signal is added / dropped at each node using a ring type network, and those that do not need to pass through the optical signal as it is, so that the node device is small and has low power consumption. is there. A wavelength selective switch (WSS) module is required as a device necessary for future development of these reconfigurable optical add / drop multiplexer (ROADM) systems.

  Conventionally, WSS using a MEMS mirror array is known. FIG. 1 is a diagram showing a configuration of a WSS using such a MEMS (Micro Electro Mechanical Systems) mirror array. FIG. 1A is a plan view of the WSS, and FIG. 1B is a side view. In the WSS shown in FIG. 1, a wavelength division multiplexed (WDM) optical signal is input to an input optical fiber as input light, and a wavelength demultiplexer (for example, a quartz glass-based slab waveguide 12 on a substrate 10). And an optical waveguide having an arrayed waveguide 14 (Planar lightwave circuit: PLC) is demultiplexed into channel optical signals having different wavelengths from each other by an arrayed waveguide grating (AWG). The channel optical signal thus formed is condensed by a lens (cylindrical lens 20, main lens 40) onto a MEMS mirror 60 constituting a MEMS mirror array. Here, the MEMS mirror array is arranged so that the optical signals of the respective wavelength channels are input to the respective mirrors 60. Therefore, by adjusting the angle of each MEMS mirror, the optical signal of each wavelength channel can be steered in an arbitrary direction. For example, in the WSS shown in FIG. 1, it is possible to input to another AWG on the same substrate by swinging the mirror in the left and right direction with respect to the optical axis.

  As shown in FIG. 1B, the WSS is a WSS having a configuration in which an input side arrayed waveguide grating substrate 10 and a plurality of output side arrayed waveguide grating substrates 10 'are stacked. Therefore, by further adjusting the angle of each MEMS mirror in the vertical direction with respect to the optical axis, an optical signal can be input to the AWG of another stacked PLC substrate.

  In the WSS shown in FIG. 1, the optical signals of the respective wavelength channels are multiplexed by the output side AWGs and output again as WDM signals from the respective output ports. In the example of FIG. 1, since 24 arrayed waveguide gratings exist for one input side arrayed waveguide grating, it functions as a WSS with 1 input and 24 outputs (1 × 24).

  Conventionally, WSS using a bulk diffraction grating and a liquid crystal device is known. 3 and 4 are diagrams showing the configuration of a WSS using such a bulk diffraction grating and a liquid crystal device. 3 is a perspective view of the WSS, and FIG. 4 is a cross-sectional view of the WSS. Light from the input / output fiber arrays 101 to 110 is deflected by the spherical mirror 112 and collimated to enter the diffraction grating 14. The light incident on the diffraction grating 114 is reflected at an emission angle corresponding to the wavelength, and enters the reflective liquid crystal device 115 via the lens 113 and the spherical mirror 112. The liquid crystal device 115 functions as a diffraction grating, and changes the traveling direction after reflection of light incident on the liquid crystal device 115. The light reflected by the liquid crystal device 115 returns to the input / output fiber arrays 101 to 110 via the spherical mirror 112, the lens 113, and the diffraction grating 114. Therefore, by controlling the diffraction order of the liquid crystal device 115, it functions as a WSS capable of entering light into a desired input / output fiber array.

By Hector, Hector Optics II, September 2004, p88, p247

  However, the conventional wavelength selective switch has the following problems. In the wavelength selective switch of FIG. 1, since the WDM optical signal is divided by the diffraction grating for each wavelength and processed by being applied to the MEMS mirror array, it is necessary to make the gap between the MEMS mirrors as narrow as possible. That is, as shown in FIG. 2, the MEMS mirror has a structure in which mirrors corresponding to the number of wavelength channels are arranged without a gap, and typically hinges (springs that support the mirror) are provided above and below the MEMS mirror. This is because the light divided for each wavelength from the diffraction grating is incident on A-A ′ on the mirror surface, so that there is a gap in the wavelength spectrum of the emitted light by the gap between the mirrors. That is, in order to incline up and down, right and left, although it is advantageous to provide hinges on the top, bottom, right and left, hinges (springs) cannot be inserted between the mirrors, and there are hinges only on the top and bottom.

  Nevertheless, in the conventional example, it is necessary to tilt the mirror up, down, right, and left to bend the reflected light in a two-dimensional direction. This is because the output part of the arrayed waveguide grating corresponding to the output port is two-dimensionally arranged in the traveling direction of the optical axis. Thus, in principle, it is necessary to rotate in the biaxial direction regardless of the hinge structure suitable for the rotation in the uniaxial direction, and there is a problem in reliability and the like because excessive stress is applied to the hinge.

  In addition, the wavelength selective switch of FIG. 3 has a problem that it is difficult to accurately lay out the input / output fiber array in a three-dimensional manner.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a wavelength selective switch that does not use a MEMS mirror. It is another object of the present invention to provide a wavelength selective switch that can be easily laid out. It is another object of the present invention to provide a wavelength selective switch with high reliability and stability.

  In order to solve the above-described problem, the wavelength selective switch of the present invention is configured by using an AWG and a reflective liquid crystal phase modulation element that are accurately laid out with mask accuracy in a manufacturing process, without using a MEMS mirror. .

  The wavelength selective switch according to the present invention receives an optical signal from one input port, separates it into a plurality of optical signals of different wavelengths, and changes the optical axis for the optical signals of each wavelength. To match M (M is an integer of 2 or more) desired output ports, and the optical signals corresponding to each output port are combined with a plurality of optical signals of different wavelengths and output from each output port. Input switch that has a plurality of input ports and M output ports, an input array that splits an optical signal incident on the input port into a plurality of optical signals having different wavelengths and emits them at an emission angle corresponding to the wavelength A waveguide diffraction grating, a lens for condensing the optical signal dispersed by wavelength by the input array waveguide diffraction grating, and a phase difference for each of the optical signals collected by the lens Desired output And a liquid crystal phase modulation element of the traveling direction is changed so as to correspond to the over and.

  In one embodiment, the liquid crystal phase modulation element may be an element in which a liquid crystal driving circuit, a reflection mirror, and a liquid crystal are sequentially stacked on a substrate.

  In one embodiment, the wavelength selective switch includes an output array waveguide that joins a plurality of optical signals having different wavelengths on the same substrate as the substrate on which the input array waveguide diffraction grating is arranged, and outputs the optical signal from the output port. A plurality of diffraction gratings can be arranged so that the liquid crystal phase modulation means gives a phase difference to each of the optical signals and changes the traveling direction in a direction parallel to the plane.

  Furthermore, in one embodiment, the wavelength selective switch joins a plurality of optical signals, each having a different wavelength, on a substrate stacked in parallel with the substrate on which the input array waveguide diffraction grating is arranged, from the output port. A plurality of output arrayed waveguide diffraction gratings are arranged, and the liquid crystal phase modulation means gives a phase difference to each optical signal and proceeds in a direction in a plane horizontal to the plane and / or a direction in a plane perpendicular to the plane. It can be configured to change direction.

  As described above, according to the present invention, by using the AWG and the reflective liquid crystal phase modulation element that are accurately laid out with the mask accuracy in the manufacturing process, the MEMS mirror is not used, and the layout is easy and reliable. In addition, a highly selective wavelength selective switch can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Embodiment 1)
5A and 5B are diagrams for explaining a schematic configuration of the wavelength selective switch WSS according to the first embodiment of the present invention. FIG. 5A is a plan view and FIG. 5B is a side view.

  The wavelength selective switch of the present embodiment includes a PLC 10 on which a plurality of AWGs each having an optical waveguide that can be an input port or an output port are arranged, a cylindrical lens 20, and a birefringent crystal (polarization separation crystal) (not shown). A polarization separation unit, a cylindrical lens (main lens) 40, and a liquid crystal phase modulation element 200 are provided.

  In the WSS of the present embodiment, the PLC 10 including an arrayed waveguide diffraction grating (AWG) has a quartz glass core and cladding formed on a Si substrate, and includes an optical waveguide 11, a slab waveguide 12, and an array waveguide. A plurality of AWGs composed of the waveguides 14 are formed. This substrate is called a PLC substrate. This AWG may or may not include a slab waveguide at the substrate end on the right side of the arrayed waveguide 14. A cylindrical lens 20 is disposed on the side of the PLC substrate on the array waveguide (right side in the figure), and further, a cylindrical lens (main lens) 40 and a reflective liquid crystal phase modulation element 200 are disposed further ahead.

  The liquid crystal phase modulation element 200 has a function of giving a phase difference to the light emitted from the AWG and digitally steering it in the left-right direction (a direction in a plane horizontal to the PLC substrate surface). The liquid crystal phase modulation element can be configured using a reflection type liquid crystal element (LCOS: Liquid Crystal On Silicon) in which a liquid crystal driving circuit such as wiring, a reflection mirror, and a liquid crystal are stacked on a silicon substrate.

  Here, the structure and function of the WSS of this embodiment will be described in the order of propagation of optical signals. In this embodiment, a circulator (not shown) is connected to the optical waveguide 11 of the AWG arranged at the center among a plurality (five) of AWGs included in the PLC board, and these are connected to the input port and the output. A description will be given assuming that a port is used (this AWG is referred to as an input AWG) and the remaining four AWG optical waveguides 11 are used as output ports (this AWG is referred to as an output AWG).

  As shown in FIG. 5A, since the AWG is a transmissive diffraction grating, the output light from the input AWG is emitted at different angles in the horizontal plane depending on the wavelength. Here, for example, the wavelength channel (Ch) of the optical signal exists at intervals of 100 GHz from about 1530 nm to 1560 nm, and the number of wavelength channels can be 40 wavelengths.

  The light beam emitted from the end face of the input AWG passes through the cylindrical lens 20 to prevent the light beam from spreading in the vertical direction.

  Next, since the liquid crystal elements constituting the liquid crystal phase modulation element 200 have polarization dependency, the light that has passed through the cylindrical lens 20 at the polarization separation unit is limited to, for example, a horizontal polarization component. The configuration and principle of this polarization separation unit are shown in FIG. FIG. 8 shows a schematic configuration of a polarization beam displacer constituting the polarization separation unit. The polarization beam displacer can be made of a birefringent crystal (see, for example, Non-Patent Document 1), and includes a birefringent crystal (polarization separation crystal) 840 and a half-wave plate 850.

  The light incident on the birefringent crystal 840 of the polarization beam displacer has a horizontal polarization component above the output end face of the birefringent crystal 840 and a vertical polarization component below the output end face of the birefringent crystal 840, respectively. Emitted. Here, as shown in FIG. 8, when the half-wave plate 850 is provided in a plane perpendicular to the optical axis so that the main axis is 45 degrees from the horizontal direction, the vertical direction emitted from the birefringent crystal 840 is provided. Are converted into horizontal polarization components and output. Therefore, all the light incident on the polarization beam displacer is output as parallel light having a horizontal component. Since the behavior of the two adjacent beams is exactly the same, it is omitted in the following description and drawings.

  Next, the light transmitted through the polarization separation unit is separated into polarization components by the polarization separation crystal and is transmitted through the cylindrical lens (main lens) 40. In the present embodiment, the focal point of the main lens 40 is set to the pixel of the liquid crystal phase modulation element 200 (FIG. 6). For this reason, as shown in FIG. 5A, all the light having different emission angles depending on the wavelength in the horizontal plane becomes light whose central optical axis is parallel, enters the liquid crystal phase modulation element 200, is phase-modulated, and the reflection angle is controlled. .

  FIG. 6 is a diagram showing an outline of the light incident surface in the liquid crystal phase modulation element 200. As illustrated, a plurality of pixels are arranged in a comb shape on the light incident surface of the liquid crystal phase modulation element 200. Each pixel can be controlled independently, and the amount of phase imparted to the light at each pixel can be controlled.

  Here, the principle that the liquid crystal phase modulation element 200 gives a phase difference to the light emitted from the AWG and steers the traveling direction digitally will be described.

  In FIG. 6, the width of each pixel is 15 μm. The light collected by the main lens 40 is perpendicularly incident on the pixel, and the light diameter is 90 μm at the pixel position. That is, it is assumed that the liquid crystal phase modulation element 200 and the main lens 40 are adjusted and arranged at positions where light is collected and vertically incident on six adjacent pixels.

  Here, with respect to six adjacent pixels positioned substantially at the center of the liquid crystal phase modulation element 200 on which the light having the central wavelength is collected and incident, the phase difference given between the adjacent pixels is ε, and the six adjacent pixels Table 1 shows an example of the relationship between the phase difference ε and the folding angle θ when the diffraction angle in a plane parallel to the PLC substrate surface is θ. The relationship between the phase difference ε and the folding angle θ can be calculated in advance using a known calculation formula in consideration of the arrangement of the main lens, the liquid crystal phase modulation element, and the AWG ( Non-patent document 1).

Here, when the focal length f of the main lens is 200 mm and the pitch d AWG between the _AWGs is 7 mm, the light incident on each pixel controlled so that the phase difference ε = 0 is equal to the liquid crystal phase. The light is reflected by the modulation element 200 so as to be incident on the input AWG via the main lens 40. Similarly, light incident on each pixel controlled to have a phase difference ε = ± 60 ° is incident on the output AWG adjacent to the input AWG through the main lens 40 in the liquid crystal phase modulation element 200. Then, the light incident on each pixel that is controlled to have a phase difference ε = ± 120 ° is transmitted through the main lens 40 in the liquid crystal phase modulation element 200 for the next output. Reflected to enter the AWG.

  Similarly, a wavelength selective switch of 1 × 5 (one input and five outputs) can be configured by controlling the phase amount applied to each of the six pixels on which light of each channel is collected and incident.

  In this embodiment, an example of a 1 × 5 wavelength selective switch is shown for convenience of explanation. However, if the light traveling direction is reversed and the input / output direction is also reversed, five inputs and one output (5 × 1) are provided. It is also possible to operate as a wavelength selective switch. Further, by omitting some of the ports, a 1 × N (N is an integer of 2 or more) or N × 1 wavelength selective switch can be configured.

  The present embodiment is merely a typical example, and is not limited to the present embodiment as long as it has the same configuration and the same functional block.

  In this embodiment, LCOS is used as an example of the liquid crystal phase modulation element. However, an ordinary liquid crystal element, for example, a liquid crystal element shown in FIG. 9A (components excluding the polarizer 502 among the components of the liquid crystal VOA 500). ) In which the phase of the incident light is controlled can be an element in which some reflection surface is formed. The reflecting surface may be formed by forming a gold electrode from an ITO electrode far away from the light incident surface (ITO electrode shown as the ground in FIG. 9A), or once the liquid crystal element is formed. It may be an external mirror provided outside the liquid crystal element so as to reflect the transmitted light. This is the same in the other embodiments.

  However, in general, the LCOS type has a feature that the gap width can be reduced because it uses a microfabrication process of Si. This has the advantage that (1) the diffraction angle can be increased as the pitch of the liquid crystal pixels is smaller, and (2) light loss due to the gap can be reduced. Therefore, it is possible to produce a WSS with better characteristics by using LCOS in a small size.

  In addition, in the two-dimensional LCOS as shown in FIG. 12, a greater effect can be obtained as compared with the case of using the above normal liquid crystal element. This is because in the above-described normal liquid crystal element, in order to take out the electrode to the outside, it is necessary to increase the gap, and the characteristics may be further deteriorated.

(Embodiment 2)
7A and 7B are diagrams for explaining a schematic configuration of the wavelength selective switch WSS according to the second embodiment. FIG. 7A is a plan view and FIG. 7B is a side view.

  The wavelength selective switch of this embodiment includes a PLC (input side AWG 10 and output side AWG 10 ′) including a plurality of AWGs stacked in order from the input port or output port side, a cylindrical lens 20, and a polarization beam displacer (not shown). ), The main lens 40, a liquid crystal variable optical attenuator (VOA) 500 through which light transmitted through the main lens 40 is transmitted, a first liquid crystal switch 700, a second liquid crystal switch 800, and a second liquid crystal switch It includes a reflective liquid crystal phase modulation element 200 and a fixed mirror 602 that give a phase difference to light transmitted through 800 and digitally steer in the left-right direction (direction horizontal to the PLC substrate surface).

  In the WSS of this embodiment, a PLC including an AWG includes a PLC substrate (input side AWG) 10 including one AWG on which an input signal is incident, and five AWGs stacked in parallel on the PLC substrate at predetermined intervals. Including four PLC substrates (output side AWG) 10 '. A cylindrical lens 20 is arranged on the array waveguide side (right side in the drawing) of each PLC substrate, and a main lens 40 is fixed further to the cylindrical lens 20.

  The first liquid crystal switch 700, the second liquid crystal switch 800, and the LCOS 200, which is a liquid crystal phase modulation element, constitute a spatial light switch unit. The first liquid crystal switch 700 and the second liquid crystal switch 800 (also referred to as a liquid crystal polarization switch unit in this specification) are a liquid crystal element 550 and a polarization splitting crystal 900 that receives light transmitted through the liquid crystal element 550, respectively. The space switch unit steers light emitted from the input side AWG in the vertical direction (PLC stack direction). Further, the liquid crystal phase modulation element 200 has a function of giving a phase difference to light emitted from the input side AWG in the space switch unit and steering only in the wavelength direction (left and right direction (direction in a plane perpendicular to the stack direction of the PLC)). Take on.

Here, the function and structure of the WSS will be described according to the propagation of the optical signal.
As shown in FIG. 7A, the AWG 10 on the input side demultiplexes the incident light into light of different wavelengths and emits the light at different angles depending on the wavelength. Here, a channel corresponding to 40 wavelengths at intervals of 100 GHz from 1530 nm to 1560 nm is assumed. In FIG. 7 (a), only the beam having the minimum wavelength λ ₁ , the center wavelength λ ₂₀ and the maximum wavelength λ ₄₀ is shown.

  The light beam emitted from the input-side AWG passes through the cylindrical lens 20 in order to prevent the light beam from spreading in the vertical direction.

  Next, since the liquid crystal elements constituting the liquid crystal VOA 500, the first liquid crystal switch 700, the second liquid crystal switch 800, and the liquid crystal phase modulation element 200 have polarization dependency, the light transmitted through the cylindrical lens 20 in the polarization separation unit is, for example, horizontal Only the polarization component of the direction. Since the configuration and principle of the polarization separation unit have been described in the first embodiment, description thereof will be omitted.

  Referring to FIG. 7 again, the light output from the polarization separation unit passes through the main lens 40 as shown. In the present embodiment, the distance between the output end (right side of the drawing) of the arrayed waveguide 14 and the main lens 40 and the distance between the main lens 40 and the reflection surface of the liquid crystal phase modulation element 200 are each at the focal point of the main lens 40. Are equal. For this reason, as shown in FIG. 7A, all the light having different emission angles depending on the wavelength becomes light having a parallel central optical axis and enters the liquid crystal VOA 500 to control the intensity.

  Since the wavelength selective switch often requires adjustment of the light intensity of each wavelength channel, this embodiment also exemplifies the wavelength selective switch including the liquid crystal VOA 500 that adjusts the light intensity.

  FIG. 9 is a diagram showing a schematic configuration of the liquid crystal VOA 500, FIG. 9A is an enlarged side view of the liquid crystal VOA 500, and FIG. 9B is an enlarged front view of the liquid crystal VOA 500. The liquid crystal VOA 500 has a structure in which a liquid crystal element 550 is sandwiched between two polarizing elements 502. The liquid crystal element 550 has a structure in which the liquid crystal 510 is sandwiched between two glass substrates 504 on which an ITO (Indium Tin Oxide) electrode 506 and an alignment film 508 are formed.

  As described above, the optical signal is separated into optical signals of respective wavelengths in the horizontal direction by the input side AWG 10. The locations where the optical signals of the respective wavelengths are incident respectively correspond to the locations of the respective pixels of the ITO electrode in FIG. 9B.

  Here, the principle that the liquid crystal VOA 500 of the present embodiment functions as a variable optical attenuator for optical signals of each wavelength will be described. In the liquid crystal VOA 500 of this embodiment, the liquid crystal element 550 is a twisted nematic liquid crystal element, and the liquid crystal element 550 is sandwiched between the front and rear by a polarizer 502 that transmits only polarized light in the horizontal direction. The liquid crystal VOA 500 applies a desired voltage to the ITO electrode 506 of the transparent conductive film when horizontally polarized light is incident on each pixel, so that the polarization plane of the optical signal is 0 to 90 degrees on the vertical plane with respect to the optical axis. Can rotate up to. Since the polarizer 502 is also provided on the output side, it acts as a variable optical attenuator. Specifically, for example, when the applied voltage to the liquid crystal 510 is increased from 1 V to 5 V, the rotation angle of the incident light changes from 90 degrees to 0 degrees. By adjusting this voltage, the light of each wavelength The transmitted light intensity can be controlled individually for each signal. In this way, the liquid crystal VOA 500 can function as an array of variable optical attenuators that can change the attenuation of the optical signal of each wavelength. In the present embodiment, the liquid crystal VOA 500 is disposed in front of the first liquid crystal SW 700 on the optical path. However, the liquid crystal VOA 500 may be disposed in front of the second liquid crystal SW 800, and before or after the liquid crystal phase modulation element 200.

  Thereafter, the light beam is incident on a liquid crystal light polarization switch unit for separating the light beam in the vertical direction for each wavelength ch.

  With reference to FIG. 10, the principle of changing the angle in the liquid crystal polarization switching unit will be described. FIG. 10A is a diagram showing a polarization splitting crystal 900 that constitutes a part of the first liquid crystal switch 700 and the second liquid crystal switch 800. Here, a birefringent crystal YVO4 is used as an example of the polarization separation crystal. Here, the refractive index in the horizontal direction of the birefringent crystal YVO4 is n (//) = 1.9447, and the refractive index in the vertical direction is n = 2.1486. If the incident surface on which the light of the birefringent crystal YVO4 is incident is perpendicular to the optical path and the output surface to be output is inclined with respect to the incident surface as shown in the figure, the output is made according to the direction of the input polarized light according to Snell's law. The angle shifts. Therefore, in the liquid crystal element 550 arranged in the preceding stage of the birefringent crystal, the first as a 1 × 2 optical switch that changes the emission angle by controlling the polarization direction of the light incident on the birefringent crystal to 0 or 90 degrees. The first liquid crystal switch 700 and the second liquid crystal switch 800 can function.

  FIG. 10B is a graph obtained by calculating the refraction angle of each polarization (horizontal and vertical) of the optical axis with respect to the offset angle of the exit surface of the birefringent crystal YVO4 of FIG. By adjusting the offset angle in this way, the refraction angle of each polarized light can be changed to a desired value, and the refraction angle difference between the vertical light and the horizontal light (in FIG. 10B, a dotted line). (Shown) also increases uniformly. In this embodiment, an angle is given to the optical axis by this liquid crystal light polarization switch section. Here, since the pixel of the liquid crystal phase modulation element 200 is at the focal position, the light parallel to the incident light returns at the main lens 40 regardless of the reflection angle. That is, the change in the reflection angle by the liquid crystal light polarization switch unit corresponds to the shift amount from the central axis of the main lens 40. Therefore, by adjusting the phase difference applied in the liquid crystal phase modulation element, the switched light can be returned to any AWG by adjusting the shift amount in parallel with the incident light, and thus can function as an optical switch.

  Here, the incident surface of the birefringent crystal YVO4 is not completely perpendicular to the optical path of the incident light but is inclined so as to obtain desired characteristics. Since the optical signal is separated into each wavelength ch by the AWG in the horizontal direction, if the ITO electrode 506 of the liquid crystal element is separated and arranged in accordance with each wavelength ch, the first liquid crystal SW700 and the second liquid crystal SW800. Each can function as a 1 × 2 switch for each wavelength.

  For example, a 1 × 4 optical switch can be configured by combining this in a cascade. Note that the change in the emission angle depends on the inclination of the emission surface. Therefore, a 1 × 4 switch can be configured by changing the switching angle of the first liquid crystal switch 700 and the switching angle of the second liquid crystal switch 800. For example, by providing a large switching angle with the first liquid crystal switch 700 and a smaller switching angle with the second liquid crystal switch 800, a 1 × 4 switch can be configured. Even if the angle of the optical axis is changed, the mirror surface is the focal point of the lens, so the main lens becomes parallel light, and the angle change given by the liquid crystal polarization switch section proceeds from right to left. After passing through the main lens 40, it corresponds to the shift amount in the vertical direction.

  In this 1 × 4 optical switch, the refraction angle is determined only by the offset angle of the birefringent crystal and does not depend on the thickness of the crystal. Therefore, the crystal can be thinned as much as possible, and there is an advantage that the distance between the liquid crystal element 550 and the liquid crystal phase modulation element 200 can be reduced. This corresponds to the fact that there is little defocusing in the liquid crystal element, and the characteristic is that the transmission band of the optical signal of each wavelength is wide.

In this embodiment, since the output side AWGs are arranged in the plane of each substrate, it is necessary to steer the optical axis at an angle of ± several degrees in the horizontal direction. For this reason, the liquid crystal phase modulation element 200 is further used in the same manner as in the first embodiment. When the main lens has a focal length f of 200 mm and a pitch d AWG between _AWGs of 7 mm, the liquid crystal phase modulation element 200 of the present embodiment has been described with reference to Table 1 in the first embodiment. Similarly to the above, by controlling the phase difference ε between the pixels, the light traveling direction can be steered in a direction horizontal to the PLC substrate surface.

  In the present embodiment, the light of each wavelength whose angle is shifted by the liquid crystal phase modulation element 200 passes through the fixed mirror 602 and the main lens 40, and the arbitrary output of the five-array AWG for output that is superimposed four times. Can be incident. In each AWG, all wavelengths are combined and output. As a result, 1 × 20 WSS can be realized with a smaller number of PLC stacks.

  In the present embodiment, an example in which one spherical lens is used as the main lens 40 has been described. However, in consideration of aberrations, other lenses, aspherical lenses, best focus lenses, or combinations of two or more lenses, For example, an aromatic lens or the like may be used.

  Note that although a configuration example of 1 × 20 WSS is shown here, a configuration of 20 × 1 WSS in which the traveling direction of light is reversed is of course possible.

  Further, although an example of 1 × 20 WSS is shown, a larger WSS can be configured by increasing the number of AWG arrays in one PLC or the number of stacks of PLCs in the vertical direction.

  The present embodiment is merely a typical example, and is not limited to the present embodiment as long as it has the same configuration and the same functional block.

(Embodiment 3)
11A and 11B are diagrams for explaining a schematic configuration of a wavelength selective switch WSS according to the third embodiment of the present invention. FIG. 11A is a plan view and FIG. 11B is a side view.

  The wavelength selective switch of the present embodiment includes a PLC (input side AWG 10 and output side AWG 10 ′) in which a plurality of AWGs each having an optical waveguide that can be an input port or an output port are stacked and a birefringent crystal (not shown) A polarization separation unit including a polarization separation crystal), a cylindrical lens 20, a cylindrical lens (main lens) 40, and a liquid crystal phase modulation element 201.

  In the WSS of this embodiment, five PLC substrates including a plurality of AWGs are bonded and fixed in a stacked manner (detailed structures such as spacers for bonding are omitted). A cylindrical lens 20 is disposed on the array waveguide side (right side in the figure) of each PLC substrate, and a cylindrical lens (main lens) 40 is disposed further ahead.

  In the present embodiment, the liquid crystal phase modulation element 201 gives a phase difference to the light emitted from the AWG, the left and right direction and / or the up and down direction (a direction in a plane horizontal to the PLC substrate surface and / or a plane perpendicular to the PLC substrate surface). It is responsible for digitally steering in the inner direction). The liquid crystal phase modulation element can be configured using a reflective liquid crystal element (LCOS: Liquid Crystal On Silicon).

  Here, the structure and function of the WSS of this embodiment will be described in the order of propagation of optical signals. In the present embodiment, the AWG arranged at the center of the plurality (five) of AWGs included in the third PLC board among the five stacked PLC boards also serves as an input / output port. In the following description, it is assumed that a circulator (not shown) is connected to the optical waveguide 11 of the AWG, and this is used as an input port and an output port (this AWG is referred to as an input AWG). Needless to say, this port may be an input-only port. The remaining 24 AWG optical waveguides 11 are used as output ports (this AWG is referred to as an output AWG).

  As shown in FIG. 11A, since the AWG is a transmission type diffraction grating, the output light from the AWG 10 on the input side is emitted at different angles in the horizontal plane depending on the wavelength. Here, for example, the wavelength channel (Ch) of the optical signal exists at intervals of 100 GHz from about 1530 nm to 1560 nm, and the number of wavelength channels can be 40 wavelengths.

  The light beam emitted from the end face of the input side PLC 10 passes through the cylindrical lens 20 in order to prevent the vertical spread.

  Next, the polarization component of the light transmitted through the cylindrical lens 20 is separated by the polarization separation crystal and is transmitted through the cylindrical lens (main lens) 40. In the present embodiment, the focal point of the main lens 40 is set to the pixel (FIG. 12) of the liquid crystal phase modulation element 201. Therefore, as shown in FIG. 11 (a), all the light whose emission angles differ depending on the wavelength in the horizontal plane becomes light with the central optical axis parallel, enters the liquid crystal phase modulation element 201, is phase-modulated, and the reflection angle is controlled. .

  FIG. 12 is a diagram showing an outline of a light incident surface in the liquid crystal phase modulation element 201 in the present embodiment. As shown in the figure, a plurality of pixels are arranged on a lattice on the light incident surface of the liquid crystal phase modulation element 201. Each pixel can be controlled independently, and the amount of phase imparted to the light at each pixel can be controlled.

  Here, the principle that the liquid crystal phase modulation element 201 gives a phase difference to the light emitted from the AWG and steers the traveling direction digitally will be described.

In FIG. 12, one side of each pixel is 15 μm. The light collected by the main lens 40 is perpendicularly incident on the pixel, and the light diameter is 90 μm at the pixel position. That is, it is assumed that the liquid crystal phase modulation element 201 and the main lens 40 are adjusted and arranged at positions where light is collected and vertically incident on a total of 36 pixels adjacent to each other six in the vertical and horizontal directions. Further, it is assumed that the focal length f of the main lens is 200 mm, the pitch d AWG between _AWGs is 7 mm, and the pitch d _PLC between _PLCs is 2 mm.

  Here, a phase difference ε ′ given between adjacent pixels in the vertical direction (a direction perpendicular to AA ′, a stacking direction of the PLC) and a diffraction angle in a plane perpendicular to the PLC substrate surface in six adjacent pixels. The relationship with θ ′ is that the diffraction angle θ ′ = 0 ° when the phase difference ε ′ = 0 °, the diffraction angle θ ′ = ± 0.57 ° when the phase difference ε ′ = ± 36 °, and the phase difference ε ′ = When ± 72 °, the diffraction angle θ ′ = ± 1.14 °.

  Therefore, the phase difference given between the adjacent pixels on the left and right (AA ′ direction) for the 36 adjacent pixels positioned substantially at the center of the liquid crystal phase modulation element 201 on which the light having the central wavelength is collected and incident. ε is controlled so as to satisfy the relationship between the phase difference ε and the diffraction angle θ described with reference to Table 1. At the same time, the phase difference ε ′ applied between the pixels adjacent in the vertical direction (the direction perpendicular to AA ′, the stacking direction of the PLC) is controlled so as to satisfy the relationship between the phase difference ε ′ and the diffraction angle θ ′. To do.

  In this way, by controlling the phase amount given to each of the 36 pixels, it is possible to reflect the light incident from the AWG 20 on the input side so as to be incident on any of the 25 AWGs. Similarly, a 1 × 25 (one input 25 output) wavelength selective switch can be configured by controlling the phase amount given to each of the 36 pixels on which light of other wavelength channels is incident.

  In this embodiment, an example of a 1 × 25 wavelength selective switch is shown for convenience of explanation. However, if the light traveling direction is reversed and the input / output direction is also reversed, 25 inputs and 1 output (25 × 1). It is also possible to operate as a wavelength selective switch. Further, by omitting some ports or PCL, a 1 × N (N is an integer of 2 or more) or N × 1 wavelength selective switch can be configured.

  The present embodiment is merely a typical example, and is not limited to the present embodiment as long as it has the same configuration and the same functional block.

It is a figure for demonstrating schematic structure of the conventional wavelength selective switch, (a) is a top view, (b) is a side view. It is a figure for demonstrating schematic structure of the MEMS mirror used for the conventional wavelength selective switch. It is a perspective view for demonstrating schematic structure of the conventional wavelength selective switch. It is sectional drawing for demonstrating schematic structure of the conventional wavelength selective switch. It is a figure for demonstrating schematic structure of the wavelength selective switch which concerns on Embodiment 1 of this invention, (a) is a top view, (b) is a side view. It is a figure which shows the outline of the light-incidence surface in the liquid crystal phase modulation element concerning Embodiment 1 and 2 of this invention. It is a figure for demonstrating schematic structure of the wavelength selective switch which concerns on Embodiment 2 of this invention, (a) is a top view, (b) is a side view. It is a figure for demonstrating the operation principle of the polarization separation part used for the wavelength selective switch which concerns on each embodiment of this invention. It is a figure for demonstrating schematic structure of the liquid crystal optical variable attenuator (liquid crystal VOA) used for the wavelength selection switch which concerns on Embodiment 2 of this invention, (a) is a side view, (b) is a front view. It is a figure for demonstrating the principle of operation of the liquid crystal switch used for the wavelength selective switch which concerns on Embodiment 2 of this invention, (a) is a polarization separation crystal which comprises a part of liquid crystal switch, and is light of a polarization | polarized-light. It is a figure for demonstrating that an output direction changes, (b) is each polarization (horizontal, vertical) of an optical axis with respect to the offset angle of an output surface at the time of using birefringent crystal YVO4 as a polarization splitting crystal. It is the graph which calculated the change of the refraction angle. It is a figure for demonstrating schematic structure of the wavelength selective switch which concerns on Embodiment 3 of this invention, (a) is a top view, (b) is a side view. It is a figure which shows the outline of the light-incidence surface in the liquid crystal phase modulation element which concerns on Embodiment 3 of this invention.

Explanation of symbols

10, 10 ′ Optical waveguide substrate 20 Cylindrical lens 40 Main lens 60 MEMS mirror 200, 201 Liquid crystal phase modulation element, LCOS
500 Liquid crystal VOA
602 Fixed mirror 700,800 Liquid crystal switch

Claims (6)

Optical signals are input from one input port and separated into a plurality of optical signals having different wavelengths, and M (M is 2 or more) by changing the optical axis for the optical signals of each wavelength. A plurality of optical signals having different wavelengths are combined to output from each output port, and one input port and M output ports. A wavelength selective switch having:
An input array waveguide diffraction grating that splits an optical signal incident on the input port into a plurality of optical signals having different wavelengths and emits the optical signal at an exit angle corresponding to the wavelength;
A lens for condensing each optical signal dispersed by wavelength by the input array waveguide diffraction grating;
A wavelength selective switch, comprising: a liquid crystal phase modulation element that gives a phase difference to each of the optical signals collected by the lens and changes a traveling direction so as to correspond to the desired output port. An output array waveguide diffraction grating that is arranged on the same substrate as the substrate on which the input array waveguide diffraction grating is arranged and that combines a plurality of optical signals of different wavelengths and outputs them from the output port;
The liquid crystal phase modulation element indicates the traveling direction of each optical signal collected by the lens in a plane horizontal to the substrate surface on which the input array waveguide diffraction grating and the output array waveguide diffraction grating are arranged. 2. The wavelength selective switch according to claim 1, wherein the wavelength selective switch is changed. A plurality of output array waveguide diffractions arranged on a substrate stacked in parallel with the substrate on which the input array waveguide diffraction grating is arranged, each of which joins a plurality of optical signals of different wavelengths and outputs them from the output port Lattice,
Spatial light switch means for changing the traveling direction of each of the optical signals collected by the lens in a plane perpendicular to the substrate surface on which the input array waveguide diffraction grating is disposed, and
The liquid crystal phase modulation element changes the traveling direction of each optical signal whose traveling direction has been changed by the spatial light switch means within a plane horizontal to the substrate surface on which the input array waveguide diffraction grating is disposed. The wavelength selective switch according to claim 1.   The spatial light switch means includes an array of variable optical attenuators and / or one or more one-input two-output liquid crystal switches through which each of the optical signals collected by the lens is transmitted. The wavelength selective switch according to claim 3. A plurality of optical signals are arranged on the same substrate as the substrate on which the input array waveguide diffraction grating is disposed and on a substrate that is overlapped with the substrate in parallel. An output array waveguide diffraction grating for outputting;
In the liquid crystal phase modulation element, the traveling direction of each of the optical signals collected by the lens is set in a plane horizontal to the substrate surface on which the input array waveguide diffraction grating is arranged and the input array waveguide diffraction grating is 2. The wavelength selective switch according to claim 1, wherein the wavelength selective switch is changed in a plane perpendicular to the surface of the substrate.   6. The wavelength selective switch according to claim 1, wherein the optical signal input and output travel directions are reversed, light is input from the output port, and light is output from the optical input port. A wavelength selective switch having M input ports and one output port.

Images