JP6691471B2 - Optical switch - Google Patents

Description

  The present invention relates to an optical switch used in an optical communication network or the like.

  With the spread of the Internet, the demand for data communication networks is exploding, and to support this, demands for large capacity and flexible customization functions for optical communication networks are increasing. From the viewpoint of increasing the capacity, which is one of the requirements for such an optical communication network, Wavelength Division Multiplexing (WDM) communication has been put into practical use.

  From the perspective of flexible customization, a 1-input N-output (or N-input 1-output) wavelength selective switch (WSS) with a switching function that selects a route for each WDM signal wavelength has been developed. Has been done. Hereinafter, such 1-input N-output (or N-input 1-output) WSS is simply referred to as WSS.

  Development of a 2-input 1-output WSS in which two WSSs are realized by one module is in progress. In order to realize a WSS having a cross-connect function with one module, it is also considered to use an N input / one output WSS in which more WSSs are integrated in one module (Non-Patent Document 1). In Non-Patent Document 1, the signal light of each emission angle is treated as another WSS by emitting light from one input / output port at a plurality of angles.

N. Nemoto, Y. Ikuma, K. Suzuki, O. Moriwaki, T. Watanabe, M. Itoh, T. Takahashi, “8x8 Wavelength Cross Connect with Add / Drop Ports Integrated in Spatial and Planar Optical Circuit,” Proceedings of ECOC 2015, Tu. 3.5.1.

  In an optical switch such as the above WSS, leakage of signal light into ports other than the connection port (crosstalk between ports) becomes a problem. Further, in a two-input one-output WSS in which a plurality of WSSs are incorporated in one module, crosstalk between switches in which signal light of one WSS enters another WSS becomes a problem.

  These crosstalks (port-to-port crosstalk, switch-to-switch crosstalk) pose problems for optical switches.

  The present invention has been made under such a circumstance, and by making the input / output mode of the signal light different depending on the port, the signal is coupled to the port only in a specific mode and crosstalk is reduced. It is an object of the present invention to provide an optical switch having the above structure.

To achieve the above object, the present invention provides one or more input ports, one or more output ports, and a spatial light output device that outputs light from the input ports to a space in a specific propagation mode, A spatial light modulator that modulates the spatial phase distribution of incident light, and a spatial light input device that couples the light modulated by the spatial light modulator to the output port, and the coupling mode to the output port is the have a plurality of different modes of the particular propagation mode, and are set to be different from each other, the spatial light modulator, the light propagation mode of the time of entering the spatial light input device, coupled It is configured to switch to a coupling mode to the output port .

  The output ports other than the output ports to be coupled may be set so that the coupling mode and the propagation mode are orthogonal to each other.

The spatial light input device and the spatial light output device may be configured using a planar optical waveguide.

  According to the present invention, a signal can be coupled to a port only in a specific mode to reduce crosstalk.

It is a figure which shows the structural example of the optical switch in 1st Embodiment of this invention. It is a figure for explaining an example of spatial phase modulation realized in LCOS. It is a figure for explaining an example of the state where crosstalk between ports (XT) may occur by diffracted light. It is a figure which shows the structural example of the optical switch in 2nd Embodiment. It is a figure which shows the structural example of an SBT circuit. It is a figure which shows the structural example of the SBT circuit which used the MMI waveguide. It is a figure which shows the structural example of a spatial light input / output device.

<First Embodiment>
FIG. 1 is a diagram showing a configuration example of an optical switch 1 which is a first embodiment of the present invention.

  In FIG. 1, an optical switch 1 includes an input / output port unit 101 and a spatial light input / output unit for inputting / outputting a signal light from a post-writing output port of the input / output port unit 101 into a space in a specific propagation mode and a specific input / output angle. Output devices 102-1, 102-2, 102-3, and 102-4, and an optical element 103 for irradiating the spatial light modulation element 104 with light corresponding to the emission angle from each of the input / output ports, And a spatial light modulator 104 capable of modulating the spatial phase distribution of the input signal light. In the following description, the spatial light input / output devices 102-1 to 102-4 are also collectively referred to as the spatial light input / output device 102.

  The input / output port unit 101 includes an input port In-1 for optical signals and three output ports Out-1, Out-2, Out-3.

  A signal input from the input port In-1 is emitted from the spatial light input / output unit 102-1 in an angle and a propagation mode according to the input port 102-1 and is incident on the spatial light modulation element 104 via the optical element 103. To do.

  The optical element 103 is configured to cause light to be incident on a specific place in the plane where the spatial light input / output units 102-1 to 102-4 are located according to the incident angle of the signal light from the spatial light modulator 104. There is. A lens or the like is used as such an optical element 103. In the case of a lens, it is known that the change of the incident angle is converted into the change of the condensing position (for example, Reference 1: “Toyohiko Tanigai, Advanced Optoelectronics Series 11, Optical Computing” (Kyoritsu Publishing Co., Ltd.). , October 15, 2004, 1st edition, 1st edition, p.18-21 ”).

  The spatial light modulator 104 can control the propagation angle by modulating the spatial phase distribution of the incident optical signal. As the spatial light modulator 104 such as a WSS (wavelength selective switch) using a spatial optical system, for example, LCOS (Liquid Crystal On Silicon) is often used.

  In the optical switch 1 according to the present embodiment, the signal light deflected by the LCOS as the spatial phase modulation element 104 is incident on a specific place in the plane of the input / output port unit 101 according to the incident angle to the optical element 103. To do.

  In the spatial light modulator 104, the signal light is incident on the spatial light input / output unit 102 connected to the output ports Out-1 to Out-3 in the input / output port unit 101 which is desired to be incident (to be coupled) at a specific place. The deflection angle is controlled so that Thereby, the destination of the optical signal can be switched.

  FIG. 2A and FIG. 2B are diagrams for explaining an example of the propagation direction deflection in the pattern of spatial phase modulation realized by the LCOS.

  In FIGS. 2A and 2B, by applying a sawtooth-shaped phase modulation pattern in the LCOS, the signal light is given a change in the deflection angle according to the inclination of the sawtooth wave. As a result, the propagation direction of the light reflected by the LCOS is deflected.

  FIG. 3 is a diagram for explaining an example of a state in which crosstalk (XT) between ports can occur due to diffracted light.

  In FIG. 3, various diffracted lights (for example, various diffracted lights) are deflected as an example of incident light deflected at an angle (unintended angle) different from an angle (for example, θ) preset by the LCOS as the spatial light modulator 104. Secondary light having a deflection angle of “2θ”, −secondary light having a deflection angle of “−2θ”, etc.) are shown. It is known that high-order diffracted light is diffracted at a deflection angle that is an integral multiple of the set deflection angle (for example, Document 2- "Wang, Xinghua" Liquid Crystal Diffractive Optical Elements: Applications and Limitations. "Electronic Thesis or Dissertation, Kent State University, 2005. ").

  In the optical switch 1 of the present embodiment, if such higher-order diffracted light is incident on the output ports Out-1 to Out-3, the signal light is coupled to the ports other than the ports to be originally coupled, which causes Cross talk (XT) between ports can occur.

  In order to suppress such XT, it is effective to change the coupling mode of each of the input / output ports In-1, Out-1 to Out-3. For example, each port In-1, Out-1 to Out-3 shown in FIG. 1 can have a different coupling mode to reduce the XT between the ports. This is because the coupling rate for coupling the signal light to each port is determined by the overlap integral of the complex amplitude of the incident signal light and the coupling mode of the port (see, for example, Reference 3- "Kenji Kawano, Hikaru"). Basics and applications of coupling systems for devices (Hyundai Engineering Co., Ltd.), 2nd edition, 2nd edition, July 25, 2003, p. 29-32. ”).

  The light coupling rate described above is given by the following equation (1) (reference 3 above).

Here, η: coupling efficiency, φ _i (x, y): port coupling mode, φ ^* _i (x, y): complex amplitude of incident signal light.

  According to the above equation (1), the highest coupling rate occurs when the coupling mode and the complex amplitude (mode) of the incident light are the same. On the other hand, the coupling rate becomes low when the coupling mode and the mode of the incident light input are different.

  From this, in the optical switch 1 of the present embodiment, by designing to couple only in a specific mode, the coupling efficiency when light of another propagation mode m1 (FIG. 1) enters is reduced, and Is used to suppress XT.

  Generally, it is known that the propagation mode of light can be converted by spatial phase modulation using LCOS or the like (Reference 4- "Naoya Matsumoto et al.," Generation of high-quality higher-order Laguerre-Gaussian beams using liquid ". -crystal-on-silicon spatial light modulators, "J. Opt. Soc. Am. A 25, 1642-1651 (2008)").

  In the optical switch 1 of the present embodiment, the spatial phase modulation element 104 such as LCOS switches the propagation mode when entering the spatial optical input / output device 102 connected to each optical input / output port of the input / output port unit 101. . By performing such switching of the propagation mode and adjustment of the deflection angle at the same time by the spatial phase modulation element 104, a specific propagation mode p (FIG. 1) is obtained at a specific place in the plane where the spatial light input / output device 102 is present. Signal light can be incident.

  For example, in order to suppress XT most effectively, it is preferable to adopt a mode orthogonal to the coupling modes m1, m2, m3 (FIG. 1) of each output port. By adopting such an orthogonal mode, all the propagation modes other than the specific propagation mode among the propagation modes coupled to each port input to the same place are not coupled. This is because the integral term of the numerator shown in the above formula (1) becomes "0", and thus the binding rate η becomes "0".

  As the propagation modes of the orthogonal light described above, for example, Gaussian modes of the base and higher orders are used (see the above-mentioned Document 4). For example, in the example of FIG. 1, in each of the output ports Out-1 to Out-3, by coupling only in the 0th, 1st, and 2nd order Gaussian modes (coupling modes), all the coupling modes are orthogonal. That is, in FIG. 1, the propagation mode of the output light from the input port In-11 is a 0th-order Gaussian mode, and the coupling mode of each output port Out-1 to Out-3 is a 0th-order to 2nd-order Gaussian mode. Is set as.

  As described above, according to the optical switch 1 of the present embodiment, the input port, the output port, the spatial light output device 102 that outputs the light from the input port to the space in the specific propagation mode, and the incident light It includes a spatial light modulator 104 that modulates the spatial phase distribution, and a spatial light input device 102 that couples the light modulated by the spatial light modulator 104 to the output port. Here, the coupling mode to the output port has a plurality of modes different from the specific propagation mode (in the output ports other than the output port Out-2 to be coupled, the coupling modes m1 and m3 and the propagation mode p are orthogonal to each other. .). This allows signals to be combined at the output ports only in certain modes, reducing crosstalk between ports (or between switches).

<Second Embodiment>
The optical switch 1A according to the second embodiment of the present invention will be described below. The configuration of the optical switch 1A is almost the same as that shown in FIG. In the following description of the present embodiment, the reference numerals and the like used in the description of the first embodiment are used as they are, unless otherwise specified.

  Although the optical switch 1 according to the first embodiment is composed of one series of one input and three outputs, it is not always necessary. The optical switch 1A of the second embodiment achieves the same effect as that of the first embodiment, but is configured with two 1-input and 2-output.

  FIG. 4 is a diagram showing a configuration example of the optical switch 1A.

  As shown in FIG. 4, in the optical switch 1A, as in the first embodiment, the input / output port unit 101 and the signal light from the input / output port of the input / output port unit 101 are specified in a specific propagation mode and specified. The spatial light input / output devices 102-1, 102-2, and 102-3 that enter and exit the space at the input / output angles of the light and the spatial light modulator 104 corresponding to the output angles from the input / output ports. The optical element 103 for irradiating and the spatial light modulator 104 capable of modulating the spatial phase distribution of the input signal light are provided. Also in this embodiment, the spatial light input / output devices 102-1 to 102-3 are collectively referred to as the spatial light input / output device 102.

  The input / output port unit 101 includes two input ports In-1, In-2 and four output ports Out-1-1, Out-1-2, Out-2-1, Out-2-2. .

  A signal input from one input port of the input / output port unit 101 is emitted from the spatial light input / output unit 102-1 at an angle and propagation modes P11 and P21 according to the input port, and is transmitted via the optical element 103 to the spatial light. The light enters the modulation element 104.

  Then, in the spatial light modulator 104, the spatial light input / output device connected to the output ports Out-1-1 to Out-2-2 in the input / output port unit 101 to be incident (to be coupled) at a specific place. The deflection angle is controlled so that the signal light is incident on 102. Thereby, the destination of the optical signal can be switched.

  This optical switch 1A also adopts a mode orthogonal to the coupling mode of each output port, as in the first embodiment. For example, in the example of FIG. 3, the propagation modes P11 and P21 of the output light from the input ports In-1 and In-2 are the 0th-order Gaussian, and the coupling modes of the output ports Out-2-1 and Out-2-2. The m21 and m32 are set to the 0th-order Gaussian mode. Then, the coupling modes m11 and m31 of the output ports Out-1-1 and Out-1-2 are set to the first-order Gaussian mode.

  Even in this case, the coupling mode to the output port has a plurality of modes different from the specific propagation mode (in the output ports other than the output port to be coupled, the coupling mode and the propagation mode are orthogonal to each other). This allows signals to be combined at the output ports only in certain modes, reducing crosstalk between ports (or between switches).

  Next, modified examples of the optical switches 1 and 1A of the above-described embodiments will be described.

(Modification 1)
The spatial light input / output device 102 may use a planar lightwave circuit (PLC). For example, when a PLC is used, an SBT (Spatial Beam Transformer) circuit may be used (see, for example, Reference 5- "K. Senohoka et al.," Spatial beam transformer for wavelength selective switch composed of silica-based planar "). lightwave circuit, ”Proceedings of OFC / NFOEC 2012, JTh2A.5”).

  FIG. 5A is a diagram showing a configuration example of the SBT circuit 40.

  The SBT circuit 40 is an optical circuit including an input / output waveguide, a slab waveguide 402, and an array waveguide 403.

  In the SBT circuit 40, the optical signal input from the predetermined waveguide on the PLC side is emitted from the output end of the PLC to the spatial optical circuit (spatial light modulation element 104) side at a predetermined angle. On the other hand, the optical signal input to the PLC from the spatial optical circuit side at a predetermined angle is output to the predetermined waveguide 403 on the PLC side.

  5, in the SBT circuit 40, the propagation mode after the light input from the input waveguide 401 to the slab waveguide 402 propagates in the slab waveguide 402 is output to the space. Further, when light is input from the space to the SBT circuit 40, the mode in which the mode coupled with the input waveguide 401 is expanded or contracted becomes the coupled mode.

  As described above, in the SBT circuit 40, the propagation mode of light output to the space can be changed by changing the propagation mode of light from the input waveguide 401 to the slab waveguide 402 (FIG. 5B). (FIG.5 (c)).

(Modification 2)
In the SBT circuit 40 of the first modification, a multimode interference (MMI) waveguide may be used as an input waveguide of the slab waveguide (for example, Reference 6- “T. Hiraki et al., 4 persons,“ Monolithically Integrated Mode ”). Multiplexer / De-multiplexer on Three-dimensional SiOx-waveguide Platform, "in Optical Fiber Communication Conference, OSA Technical Digest (online) (Optical Society of America, 2015), paper W1A.2.").

  FIG. 6A shows a configuration example of the SBT circuit 40 using the MMI waveguide 405. Also in this SBT circuit 40, by changing the propagation mode of light from the input waveguide 401 to the slab waveguide 402 (FIGS. 6B and 6C), the propagation mode of light output to the space is changed. (FIG. 6 (d) and FIG. 6 (e)).

(Modification 3)
In the SBT circuit 40 of the modified example 2, the case of using the MMI waveguide 405 has been described, but the present invention is not limited to this. For example, mode conversion may be performed using a waveguide set by the wavefront matching method (for example, the wavefront matching method is described in Reference 7- "J. Sakamoto et al., 3 Computers-generated optical mode-managed funnel"). coupler for reducing intrinsic coupling loss, "in Conference on Lasers and Electro-Optics, OSA Technical Digest (2016) (Optical Society of America, 2016), paper SM1F.2.").

(Modification 4)
In the spatial light input / output device 102, the function of changing the input / output angle of the signal light and the function of converting the propagation mode may be realized by separate elements. For example, it is possible to change the incident / emission angle of the signal light with a lens and to change the propagation mode with a phase mask (see Document 4).

  FIG. 7A illustrates a configuration example of the spatial light input / output device 102A in the third modification.

  In this spatial light input / output device 102A, the lens 502 changes the incident / emission angle of the signal light from the input / output waveguides 501-1 and 501-2, and the propagation modes are changed by the phase masks 503-1 and 503-2. 7 (b) → FIG. 7 (c) or FIG. 7 (b) → FIG. 7 (d).

(Modification 5)
In the optical switches 1 and 1A, the number of input waveguides and / or output waveguides of the input / output port unit 101 can be appropriately changed as necessary.

1A Optical switch 101 Input / output port section 102-1 to 102-4: Spatial optical input / output device 103 Optical element 104 Spatial phase modulation element 401 Input waveguide 402 Slab waveguide 403 Array waveguide 405 MMI waveguide 501 Input / output port 502 Lens 503-1, 503-2 Phase mask

Claims (3)

One or more input ports,
One or more output ports,
A spatial light output device that outputs light from the input port to a space in a specific propagation mode,
A spatial light modulator that modulates the spatial phase distribution of incident light;
A spatial light input device for coupling the light modulated by the spatial light modulator to the output port;
Binding mode to said output port, said to have a plurality of different modes of the particular propagation mode, and are set to be different from each other
The spatial light modulator is configured to switch a propagation mode of light upon entering the spatial light input device to a coupling mode to the output port for coupling . The optical switch according to claim 1, wherein the output ports other than the output ports to be coupled are set such that the coupling mode and the propagation mode are orthogonal to each other. The spatial light input unit and the spatial light output instrument, an optical switch according to claim 1 or 2, characterized in that it is configured using a planar optical waveguide.