JP4949355B2 - Wavelength selective switch - Google Patents

Description

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

  While an increase in capacity of optical communication has progressed and transmission capacity has been increased by a wavelength division multiplexing (WDM) method, an increase in throughput of a path switching function in a 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 (for example, refer to Patent Document 1). 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, the optical signal of each wavelength channel can be input to other AWGs on the same substrate by swinging the mirror in the left and right direction (x direction) with respect to the optical axis (z direction). It is. In this specification, the horizontal direction of the signal light emission end face on the substrate of the optical circuit is x, the vertical direction is y, and the traveling direction of the light wave, that is, the optical axis is z.

  As shown in FIG. 1B, the WSS is a WSS having a configuration in which an arrayed waveguide grating substrate 10 on the input side and a plurality of arrayed waveguide grating substrates 10 ′ on the output side are stacked (in the y direction). is there. Therefore, by further adjusting the angle of each MEMS mirror in the vertical direction (y direction) with respect to the optical axis (z direction), 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).

U.S. Pat. No. 7,088,882 By Hector, Hector Optics II, September 2004, p88

  However, the wavelength selective switch of FIG. 1 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.

  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.

The wavelength selective switch according to the present invention receives an optical signal from an 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 change a plurality of optical signals. Corresponding to a desired output port among the output ports, the optical signal corresponding to each output port is a wavelength selective switch that outputs a plurality of optical signals of different wavelengths and outputs from each output port. The wavelength selective switch according to the present invention splits an optical signal incident on an input port into a plurality of optical signals having different wavelengths and emits them at an emission angle according to the wavelength, and the spectral means separates each wavelength. Each of the optical signals converted into an optical signal of a single polarization component , a condensing unit for condensing the optical signal of a single polarization component, and an optical signal collected by the condensing unit. and space deflecting means for changing the traveling direction against an optical signal traveling direction changed by the spatial deflection means, respectively, multiplexed and output to one of two output ports, the traveling direction by the space deflecting means Optical signals that do not change the frequency of the optical signals are combined and output to the other of the two output ports .

  The plurality of spectral planes of the multiplexing means of the wavelength selective switch according to the present invention are in the same plane, and in one embodiment, can be configured using one or a plurality of arrayed waveguide gratings. Moreover, the spectral means of the wavelength selective switch according to the present invention can also be configured using an arrayed waveguide diffraction grating in one embodiment.

  The spatial deflecting means of the wavelength selective switch according to the present invention is a compound that changes the traveling direction of each optical signal within the spectral plane of the multiplexing means in accordance with the polarization state of the signal light arranged in order from the condensing means side. A refractive crystal, a liquid crystal element that changes the polarization state of the signal light, and a mirror that turns back the optical path can be used. The signal light can be configured so as to pass through the birefringent crystal and the liquid crystal element in order from the condensing means, and then pass through the liquid crystal element and the birefringent crystal in order after being turned back by a mirror.

  The spatial deflecting means of the wavelength selective switch according to the present invention is configured so that the optical signal whose traveling direction is changed by the spatial deflecting means and the optical signal whose traveling direction is not changed are parallel to each other before entering the condenser lens. A means for changing the traveling direction of the signal may be further provided.

  As described above, according to the present invention, it is possible to provide a wavelength selective switch that does not use a MEMS mirror and uses a PLC substrate including a plurality of AWGs.

  As described above, the wavelength selective switch of the present invention includes the PLC substrate including the AWG and the liquid crystal switch, and the liquid crystal switch steers the light of the desired wavelength channel that has been wavelength-separated by the AWG on the input side, and outputs it. It functions as a switch that couples in the direction of the AWG (x direction) (disperses light of a desired wavelength channel from light of other wavelength channels). The wavelength selective switch of the present invention can be implemented as a reflection type. Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, the same or similar elements are referred to by the same or similar reference numerals.

  FIG. 3 is a diagram illustrating a configuration example of a wavelength selective switch using a liquid crystal optical polarization switch without using a MEMS mirror. 3A is a plan view and FIG. 3B is a side view.

  The wavelength selective switch shown in FIG. 3 includes, in order from the input port or output port side, a PLC (input side AWG 10 and output side AWG 10 ′) including stacked AWGs (in the y direction), a cylindrical lens 20, and polarization separation. Unit (for example, polarization beam displacer) 30, main lens (for example, cylindrical lens, spherical lens) 40, liquid crystal variable optical attenuator (VOA) 500, first liquid crystal switch 700 and second liquid crystal switch 800 and a reflection mirror 610.

  In the WSS shown in FIG. 3, the PLC 10 (10 ′) includes an AWG, and the AWG includes an optical waveguide 11, a slab waveguide 12, and an arrayed waveguide 14.

  The first liquid crystal switch 700 and the second liquid crystal switch 800 constitute a liquid crystal switch unit. Each of the first liquid crystal switch 700 and the second liquid crystal switch 800 includes a liquid crystal element 550 and a polarization separation crystal (or a wedge-type birefringent crystal) 900 that receives light transmitted through the liquid crystal element 550, and the liquid crystal switch This unit functions to steer light emitted from the input side AWG in the vertical direction (PLC stacking direction: y direction).

  In the WSS shown in FIG. 3, output light from the AWG 10 on the input side is emitted at different angles in the horizontal plane depending on the wavelength. 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, since the liquid crystal elements constituting the liquid crystal VOA 500, the first liquid crystal switch 700, and the second liquid crystal switch 800 have polarization dependency, the light transmitted through the cylindrical lens 20 by the polarization separation unit 30 is converted into, for example, a horizontal polarization component. Only. Each light output from the polarization separation unit 30 passes through the main lens 40 as shown in the figure. The focal points before and after the main lens 40 are made to be the emission end face of the PLC and the reflection face of the reflection mirror 610. Therefore, as shown in FIG. 3A, all the light whose emission angles are different depending on the wavelength in the horizontal plane become light whose central optical axis is parallel. The light transmitted through the main lens 40 enters the liquid crystal VOA 500 and the intensity is controlled.

  The liquid crystal switches 700 and 800 have the structure shown in FIG. 4, and by applying a desired voltage to the ITO electrode 506 of the transparent conductive film in the liquid crystal element 550, the polarization plane of the optical signal is 0 on the vertical plane with respect to the optical axis. Can rotate up to 90 degrees. That is, by controlling the voltage applied to the ITO electrode 506, the liquid crystal element 550 can be controlled with the rotation angle of the polarization plane being 0 or 90 degrees. Therefore, when the liquid crystal element 550 and the polarization separation crystal 840 are used, a 1 × 2 switch for separating light as shown in FIG. 4 can be configured. Finally, a WSS can be configured by installing a PLC on the output side of each optical path. In the WSS shown in FIG. 3, the separation (shift) of the optical axis in the vertical direction (y direction) in the liquid crystal optical polarization switch unit is the refraction angle of the polarized light in the horizontal and vertical directions by the wedge-type birefringent crystal 900 shown in FIG. It can also be caused by differences.

  FIG. 5 is a diagram for explaining a wedge-type polarization separation crystal that constitutes a part of the liquid crystal switch of FIG. 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 tilted with respect to the incident surface as shown in the figure, the output is made according to the direction of the input polarization according to Snell's law. The angle shifts. Therefore, the refraction angle of each polarized light can be changed to a desired value by adjusting the offset angle of the exit surface of the birefringent crystal YVO4, and the refraction angle difference between the vertical light and the horizontal light is also one. Can be increased. 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.

  The WSS shown in FIG. 3 shows an example in which liquid crystal switches 700 and 800 are arranged in cascade to realize a 1 × 4 switch. Here, the combination of shift amounts in the vertical direction can be adjusted by the offset angle of the polarization splitting crystal.

  On the other hand, in the horizontal direction (in-plane direction perpendicular to the stacking direction of the PLC: x direction), the signals of each wavelength ch are wavelength-separated by the AWG 10 as shown in FIG. Therefore, the liquid crystal element 550 constituting the liquid crystal switches 700 and 800 also patterns the ITO electrode in the direction of the spectral axis (x direction in WSS shown in FIG. 3) so as to hit one pixel of the ITO electrode for each signal light of a desired wavelength ch. Thus, the output port can be switched for each wavelength channel. Then, by arranging the AWGs 10 'at the output signal condensing positions, the desired AWGs 10' can be restored. The light returned to each AWG 10 'is combined and output from each port on the left side of the PLC board.

  In the configuration of FIG. 3, when focusing on one liquid crystal switch, light is transmitted in the order of a liquid crystal element, a birefringent crystal wedge, a mirror, a birefringent crystal wedge, and a liquid crystal element. A double separation angle can be obtained by passing the birefringent crystal wedge twice after the polarization rotation. As can be seen from FIG. 5, in order to obtain a large separation angle, a thick crystal is generally required, resulting in high costs. According to the configuration of the liquid crystal switch of the present invention, a thin crystal can be used, and a cost merit can be obtained.

  The wavelength selective switch WSS shown in FIG. 3 has a problem that the cost increases because a plurality of PLC substrates (10, 10 ') each including an arrayed waveguide grating (AWG) are used. Further, in the wavelength selective switch WSS shown in FIG. 3, since it is necessary to stack a plurality of PLC boards (10, 10 ′) with high accuracy in the switch axis direction (y direction), the assembly process becomes complicated and the yield decreases. However, there is a problem that the cost increases and a problem that the optical module becomes thick. On the other hand, when light is steered in the x direction using a liquid crystal switch having the same configuration as that of FIG. 3, the following problem occurs.

  FIG. 6 is a diagram for explaining an optical path of light incident on the liquid crystal switch when configured in the same manner as the WSS liquid crystal switch (700, 800) shown in FIG.

  The liquid crystal element shown in FIG. 6 is arranged in the order of a liquid crystal element 550, a wedge-type birefringent crystal 900, and a mirror 610. The liquid crystal element 550 includes ITO electrodes 506 that are arranged in the direction of the AWG on the PLC substrate (x direction) and that are long in the direction perpendicular to the PLC substrate surface (y direction). Corresponds to wavelength ch.

  As shown in FIG. 6, the light incident on the liquid crystal switch from the incident optical path is incident on the birefringent crystal wedge 900 after the rotation angle of the polarization plane is controlled to 0 or 90 degrees in the liquid crystal element 550. The light incident on the birefringent crystal wedge 900 exits at a refraction angle corresponding to the rotation angle of the polarization plane, is reflected by the mirror 610, and passes through the birefringent crystal wedge 900 and the liquid crystal 550 again. In this way, the light is steered so as to switch the outgoing optical path A or B in the AWG arrangement direction (x direction) on the PLC substrate. Here, as shown in FIG. 6, when switching to the emission optical path B, the light incident position and the emission position in the liquid crystal element 550 are different in the x direction, so that the light incident on the pixels of the liquid crystal element 550 is different. May be transmitted through and output. Since light transmitted through different pixels is output as light of an unintended polarization plane, the light steer accuracy is lowered and the wavelength resolution in WSS is lowered.

  Therefore, in the present invention, the birefringent crystal wedge for polarization separation is arranged on the output PLC side only in the liquid crystal switch section steering in the direction of the spectral axis. The operation of this arrangement will be described with reference to FIG. The liquid crystal element shown in FIG. 7 is arranged in the order of a wedge-type birefringent crystal 900, a liquid crystal element 550, and a mirror 610. The liquid crystal element 550 is configured such that when light is transmitted twice, the rotation angle of the polarization plane of the light is controlled to 0 or 90 degrees.

  The light incident on the liquid crystal switch shown in FIG. 7 is first transmitted through the wedge-type birefringent crystal 900, the rotation angle of the polarization plane is controlled by the liquid crystal element 550, reflected by the mirror 610, and again by the liquid crystal element 550. Is rotated, and enters the wedge-type birefringent crystal 900. The light incident on the wedge-type birefringent crystal 900 again is emitted at a refraction angle corresponding to the rotation angle of the polarization plane. In this way, the light is steered in the AWG arrangement direction (x direction) on the PLC substrate.

  Here, as shown in FIG. 7, the incident position and the exit position of light in the liquid crystal element 550 coincide with each other in the x direction. In the liquid crystal element 550, when the polarization plane is not rotated (when the control amount of the liquid crystal element 550 is 0 degree), the light is accurately output to the optical path opposite to the original optical path. Further, in the liquid crystal element 550, when the polarization plane is rotated by 90 degrees (when the control amount of the liquid crystal element 550 is 90 degrees), the light is output to an optical path different from the original optical path. By disposing the liquid crystal switch unit steering in the direction of the spectral axis as shown in FIG. 7 so that the light is not transmitted through the other liquid crystal switch unit after being separated into the output optical path A or B, It is possible to prevent a decrease in wavelength resolution due to an optical path position difference with respect to B, thereby realizing a highly accurate light steering function.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  8A and 8B are configuration diagrams of the WSS of the first embodiment, where FIG. 8A is a plan view and FIG. 8B is a side view. The WSS shown in FIG. 8 includes a PLC substrate 10 including two AWGs and the liquid crystal switch described with reference to FIG.

  The PLC substrate 10 has a quartz glass core and clad formed on a Si substrate, and includes an AWG A composed of an optical waveguide 11A, a slab waveguide 12A, and an arrayed waveguide 14A, and an optical waveguide 11B and a slab waveguide. AWG B composed of 12B and the arrayed waveguide 14B is configured. AWG A is provided as both an input AWG and an output AWG. Therefore, the circulator 15 is connected to the optical waveguide 11A. AWG B is provided as an output AWG.

  The angular dispersion values of the AWGs A and B as the spectroscopes are set to be equal. The free transmission bands FSR of the AWGs A and B are configured to be equal to or greater than the wavelength bandwidth of the wavelength multiplexed optical signal (WDM optical signal) input from the optical waveguide 11A.

  The liquid crystal switch includes a wedge-type birefringent crystal 900, a liquid crystal element 550, and a mirror 610, which are sequentially arranged from the PLC substrate 10 side.

  The liquid crystal element 550 includes ITO electrodes 506 that are arranged in a long pixel column in a direction (y direction) perpendicular to the PLC substrate surface, which is arranged in the AWG arrangement direction (x direction) on the PLC substrate. Further, the liquid crystal element 550 is configured such that when the light is transmitted twice, the rotation angle of the polarization plane of the light is controlled to 0 or 90 degrees by controlling the voltage applied to the ITO electrode 506. Yes.

  In the wedge-type birefringent crystal 900, the crystal axis direction is set so that the refraction angle with respect to the horizontal polarization component (x polarization) is small and the refraction angle with respect to the vertical polarization component (y polarization) is large. .

  The mirror 610 is arranged at an angle adjusted so that when the control amount of the liquid crystal element 550 is 0 degree, light is output to an optical path opposite to the original optical path, that is, an optical path coupled to AWG A. .

  Cylindrical lenses (not shown) are arranged on the array waveguide side 14A side of AWG A and the array waveguide side 14B side of AWG B, respectively. Further, a polarization separation crystal 30A and a half-wave plate 31A, and a polarization separation crystal 30B and a half-wave plate 31B are disposed at the tip of each cylindrical lens. The half-wave plate 31A is inserted into the y-polarized light path (y-polarized light path) separated by the polarization separation crystal 30A, converted into x-polarized light, and emitted to the liquid crystal switch side. Therefore, all the light rays on the liquid crystal switch side from the polarization separation portion made up of the polarization separation crystal 30A and the half-wave plate 31A become x-polarized light. Due to the reciprocity of light, the AWG A can receive x-polarized light in the optical path from the liquid crystal switch to the polarization separation unit composed of the polarization separation crystal 30A and the half-wave plate 31A. The half-wave plate 31B is inserted into the x-polarized light path of the polarization separation crystal 30B, converts y-polarized light from the liquid crystal switch side into x-polarized light, and enters the polarization separation crystal 30B. Therefore, AWG B can receive the y-polarized light in the optical path from the liquid crystal switch to the polarization separation unit composed of the polarization separation crystal 30B and the half-wave plate 31B.

  Further, a condenser lens 41 is disposed between the half-wave plates 31A and 31B and the wedge-type birefringent crystal 900 of the liquid crystal switch.

  As shown in FIG. 8B, the two optical paths separated in the y direction are combined on the reflection mirror 610 with their optical axes coinciding with each other by the action of the condenser lens 41. Therefore, the TE mode light and the TM mode light in the AWG are emitted as x-polarized light and y-polarized light, respectively, are exchanged and received by the AWG, and a polarization diversity configuration is established.

Here, the structure and function of the WSS of this embodiment will be described in the order of propagation of optical signals.
Since AWG is a transmission type diffraction grating, output light from AWG A on the input side is emitted at different angles in the PLC substrate surface (xz plane) depending on the wavelength. That is, wavelength separation is performed. A surface including the wavelength-separated optical axis is called a spectral surface.

  The light of each wavelength channel emitted from the end face of the input side PLC 10 passes through the cylindrical lens in order to prevent the vertical spread. Next, since the liquid crystal element 550 and the birefringent crystal 900 constituting the liquid crystal switch have polarization dependency, the light transmitted through the cylindrical lens 20 in the polarization separation section (the polarization separation crystal 30A and the half-wave plate 31A). For example, only the polarization component in the horizontal direction. These lights are output as parallel light. Since the behavior of the two adjacent beams is exactly the same, it is omitted in the following description and drawings.

  The light of each wavelength channel output from the polarization separation unit passes through the condenser lens 41.

  The light of each wavelength channel transmitted through the condenser lens 41 is incident on a different pixel (patterned ITO electrode) of the liquid crystal element 550, the rotation angle of the polarization plane is controlled, reflected by the mirror 610, and again the liquid crystal element. At 550, the rotation angle of the polarization plane is controlled, and the light enters the wedge-type birefringent crystal 900.

  The light incident on the wedge-type birefringent crystal 900 again is emitted at a refraction angle corresponding to the rotation angle of the polarization plane. In this way, the light is steered in the AWG arrangement direction (x direction) on the PLC substrate. In the liquid crystal element 550, when the polarization plane is not rotated (when the control amount of the liquid crystal element 550 is 0 degree), the light is output to the optical path opposite to the original optical path, that is, the optical path coupled to AWG A. In the liquid crystal element 550, when the plane of polarization is rotated by 90 degrees, the light is output to an optical path different from the original optical path, that is, an optical path coupled to AWG B.

  In order to sufficiently reduce the crosstalk of the optical switch, the optical path coupled to AWG A and the optical path coupled to AWG B need not overlap. This condition is that the Gaussian beam radius of the light coupled to the arrayed waveguide 14A is w, the focal length of the condenser lens 41 is f, and the birefringence amount and apex angle of the wedge-type birefringent crystal 900 are Δn, α, Then,

It is represented by When using a condensing lens with YVO4 (Δn = 0.2) as a birefringent crystal, a Gaussian beam radius of light coupled to the arrayed waveguide 14A of 2 mm, a condensing lens 41 and a focal length f of 100 mm, a wedge The apex angle α of the type birefringent crystal 900 is

It becomes.

  In this way, 1 × 2 WSS can be realized. In this embodiment, an example of a 1 × 2 wavelength selective switch is shown for convenience of explanation. However, if the light traveling direction is reversed and the input / output direction is reversed, two inputs and one output (2 × 1) are provided. It is possible to operate as a wavelength selective switch.

  FIG. 9 is a configuration diagram of the WSS of the second embodiment. The WSS shown in FIG. 9 includes a PLC substrate 10 including one AWG and the liquid crystal switch described with reference to FIG.

  The PLC substrate 10 has a quartz glass core and clad formed on a Si substrate, and constitutes an AWG comprising optical waveguides 11A and 11B, a slab waveguide 12, and an arrayed waveguide 14.

  The free transmission band FSR of the AWG is configured to be at least twice the wavelength bandwidth of the wavelength multiplexed optical signal (WDM optical signal) input from the optical waveguide 11A.

  The optical waveguide 11A is provided for both input and output. Therefore, the circulator 15 is connected to the optical waveguide 11A. The optical waveguide 11B is provided as an output AWG. The optical waveguides 11A and 11B are connected to the slab waveguide 12 with an interval equal to or greater than the wavelength bandwidth of the wavelength multiplexed optical signal (WDM optical signal).

  Similar to the first embodiment, a cylindrical lens (not shown) is arranged on the array waveguide side 14 side of the AWG. In addition, a polarization separation unit (not shown) is disposed at the tip of each cylindrical lens. A condensing lens 41 is disposed between the polarization separation unit and the wedge-type birefringent crystal 900 of the liquid crystal switch.

  Further, the WSS of the present embodiment is made of optical glass in which light whose polarization plane is rotated by 90 degrees by the liquid crystal switch is sequentially transmitted between the condenser lens 41 and the wedge-type birefringent crystal 900 of the liquid crystal switch. A wedge 90 and a half-wave plate are arranged. The optical glass wedge 90 is a wedge having no birefringence.

Here, the structure and function of the WSS of this embodiment will be described in the order of propagation of optical signals.
Similar to the first embodiment, the output light from the AWG is emitted at different angles within the substrate surface (xz surface) of the PLC substrate 10 depending on the wavelength, and is transmitted through the cylindrical lens. Next, the light enters the polarization splitting unit and is output as two optical signals of x polarization parallel to each other.

  The light of each wavelength channel output from the polarization separation unit passes through the condenser lens 41.

  The light of each wavelength channel transmitted through the condenser lens 41 is incident on a different pixel (patterned ITO electrode) of the liquid crystal element 550, the rotation angle of the polarization plane is controlled, reflected by the mirror 610, and again the liquid crystal element. At 550, the rotation angle of the polarization plane is controlled, and the light enters the wedge-type birefringent crystal 900.

  The light incident on the wedge-type birefringent crystal 900 again is emitted at a refraction angle corresponding to the rotation angle of the polarization plane. In this way, steering is performed in the direction of the spectral axis (x direction). In the liquid crystal element 550, when the plane of polarization is not rotated (when the control amount of the liquid crystal element 550 is 0 degree), the light of the horizontal polarization component (x-polarized light: a beam) is output to the optical path opposite to the original optical path. Is done. Further, in the liquid crystal element 550, when the polarization plane is rotated by 90 degrees, the light of the polarization component in the vertical direction (y-polarized light: b beam) is different from the original optical path, that is, the optical glass wedges 90 and 1/2. The light is transmitted through the wave plate 91 and output to the optical path coupled to the AWG.

  The y-polarized light (b beam) is deflected in the direction of recombination with the AWG in the glass wedge 90 and converted into x-polarized light in the half-wave plate (that is, the polarization of the a beam and the b beam is changed). Match).

  Here, since the incident angles to the AWG are different from each other, the a beam and the b beam are condensed at different positions of the slab waveguide 12. The optical waveguides 11A and 11B are connected at the position of the slab waveguide 12 where the a beam and the b beam are condensed. However, if the diffracted light of the adjacent diffraction order of the a beam is applied to the position of the optical waveguide 11B, crosstalk occurs, so the AWG's FSR is set to twice the normal value (bandwidth of wavelength used + margin). Is desirable.

  In this way, 1 × 2 WSS can be realized. In this embodiment, an example of a 1 × 2 wavelength selective switch is shown for convenience of explanation. However, if the light traveling direction is reversed and the input / output direction is reversed, two inputs and one output (2 × 1) are provided. It is possible to operate as a wavelength selective switch.

  FIG. 10 is a configuration diagram of the WSS of the third embodiment. The WSS shown in FIG. 10 is a modification of the WSS of the second embodiment described with reference to FIG. In the WSS of this embodiment, the liquid crystal switch of the second embodiment is configured by a polarization displacer 910 instead of the wedge-type birefringent crystal 900.

  The polarization displacer 910 can be made of a birefringent crystal (see, for example, Non-Patent Document 1), and includes a birefringent crystal and a half-wave plate. Since the polarization displacer 910 separates two polarized lights in parallel, it is not necessary to arrange the optical glass wedge 90 used in the WSS of the second embodiment.

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 figure for demonstrating schematic structure of a wavelength selective switch, (a) is a top view, (b) is a side view. It is a figure for demonstrating the basic principle of the liquid crystal polarization switch used for the wavelength selective switch which concerns on embodiment of this invention. It is a figure for demonstrating the principle of operation of the liquid crystal switch used for the 1 * 2 wavelength selection switch which concerns on one Example of this invention. It is a figure for demonstrating the principle of operation of the liquid crystal switch used for the 1 * 2 wavelength selection switch which concerns on one Example of this invention. It is a figure for demonstrating the operation principle of the liquid crystal switch used for the reflection type 1x2 wavelength selection switch which concerns on one Example of this invention. It is a figure for demonstrating schematic structure of the 1 * 2 wavelength selective switch which concerns on one Example of this invention, (a) is a top view, (b) is a side view. It is a figure for demonstrating schematic structure of the 1 * 2 wavelength selective switch which concerns on one Example of this invention. It is a figure for demonstrating schematic structure of the 1 * 2 wavelength selective switch which concerns on one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,10 'Optical waveguide board | substrate 20 Cylindrical lens 30 Polarization separation part 41 Condensing lens 550 Liquid crystal element 610 Mirror 900 Birefringent crystal

Claims (7)

An optical signal is inputted from one input port and separated into a plurality of optical signals of different wavelengths, and the optical signals are changed to two desired output ports by changing the optical axis. A 1 × 2 wavelength selective switch having one input port and two output ports, in which a plurality of optical signals having different wavelengths are combined and output from each output port. Because
A spectroscopic unit 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 emission angle corresponding to the wavelength;
Means for converting each of the optical signals dispersed for each wavelength by the spectroscopic means into an optical signal having a single polarization component;
A focusing means for focusing the optical signal before Kitan one polarization component in each
Spatial deflection means for changing the traveling direction for each of the optical signals collected by the light collecting means;
An optical signal traveling direction changed by the space deflection means, respectively, multiplexes, and output to one of the two output ports, an optical signal that does not change the traveling direction by the space deflection means, respectively, Combining means for combining and outputting to the other of the two output ports ,
The two spectral planes of the multiplexing means are in the same plane,
The spatial deflecting means is a birefringent crystal that changes the traveling direction of each of the optical signals in the same plane in accordance with the polarization state of the signal light arranged in order from the light collecting means side, It consists of a liquid crystal element that changes the polarization state, and a mirror that folds the optical path,
The wavelength selection is characterized in that the signal light passes through the birefringent crystal and the liquid crystal element in order from the condensing means, and after passing through the mirror, sequentially passes through the liquid crystal element and the birefringent crystal. switch.   2. The wavelength selective switch according to claim 1, wherein the spectroscopic means and the multiplexing means are configured using an arrayed waveguide diffraction grating.   The said combining means is comprised using the two array waveguide diffraction gratings respectively connected to the mutually different output port of the said two output ports. Wavelength selective switch. The multiplexing means is an array waveguide grating composed of two output waveguides, one slab waveguide, and a set of array waveguides,
The two output waveguides have one end connected to a different output port of the two output ports, and the other end of the two output waveguides at different positions having an interval equal to or greater than the wavelength bandwidth of the signal light. Connected by
Before the light signal whose traveling direction is changed by the spatial deflecting unit and the optical signal whose traveling direction is not changed is combined by the combining unit, the traveling direction of the optical signal is changed before entering the condenser lens. The wavelength selective switch according to claim 1, further comprising means for changing. The multiplexing means is an array waveguide grating composed of two output waveguides, one slab waveguide, and a set of array waveguides,
The two output waveguides have one end connected to a different output port of the two output ports, and the other end of the two output waveguides at different positions having an interval equal to or greater than the wavelength bandwidth of the signal light. Connected by
The wavelength selective switch according to claim 1, wherein the birefringent crystal is a polarization displacer that separates different deflection components in parallel.   6. The wavelength selective switch according to claim 1, wherein the liquid crystal element has a function of rotating a polarization plane of an optical signal transmitted twice, by 0 degrees or 90 degrees.   7. The wavelength selective switch according to claim 1, wherein the direction of travel of the optical signal is reversed, light is input from the output port, and light is output from the optical input port. Select wavelength switch.

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