CN115248481A - Crosstalk suppression method and device for wavelength selective switch and wavelength selective switch - Google Patents

Crosstalk suppression method and device for wavelength selective switch and wavelength selective switch Download PDF

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CN115248481A
CN115248481A CN202110454511.0A CN202110454511A CN115248481A CN 115248481 A CN115248481 A CN 115248481A CN 202110454511 A CN202110454511 A CN 202110454511A CN 115248481 A CN115248481 A CN 115248481A
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modulation function
diffraction order
initial
energy
phase
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卢特安
贾伟
张宁
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Huawei Technologies Co Ltd
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
    • G02B6/3534—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being diffractive, i.e. a grating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/06—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the phase of light
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G02B6/3538—Optical coupling means having switching means based on displacement or deformation of a liquid
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/35—Optical coupling means having switching means
    • G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types

Abstract

The application discloses a crosstalk inhibition method and device of a wavelength selective switch and the wavelength selective switch, which are used for inhibiting crosstalk generated on other output ports when an incident beam in a WSS is diffracted to a target output port. According to the method, a phase modulation function is obtained by superposing a first modulation function on the basis of an initial modulation function, and a phase grating characterized by the phase modulation function is superposed on the LCoS to modulate an incident beam. The diffraction order with the strongest energy in each diffraction order generated by modulating the incident beam through the initial modulation function is positioned at the target output port; the energy of the first diffraction order produced by modulating the incident beam with the first modulation function is capable of canceling the energy of the first diffraction order produced by modulating the incident beam with the initial modulation function. No additional components need to be modified or added at the WSS.

Description

Crosstalk restraining method and device of wavelength selective switch and wavelength selective switch
Technical Field
The embodiment of the application relates to the technical field of photoelectrons, in particular to a crosstalk suppression method and device for a wavelength selective switch and the wavelength selective switch.
Background
A reconfigurable optical add-drop multiplexer (ROADM) is a device or apparatus used in a Dense Wavelength Division Multiplexing (DWDM) system, and can implement automatic path scheduling and restoration at an optical layer through remote configuration. A Wavelength Selective Switch (WSS) is a core component in an existing ROADM device, wherein the WSS based on a liquid crystal on silicon (LCoS) technology becomes a mainstream switching engine of the existing WSS due to its advantages of supporting a flexible grid, supporting a large number of ports, and the like. The core principle of the WSS based on the LCOS is that different voltages are applied to different pixel points (pixels) of the LCOS, and due to the birefringence effect of the liquid crystal, the different voltages correspond to different amounts of phase retardation, so that a structure similar to a Blazed grating (Blazed grating) can be formed. Because the diffraction angle of the blazed grating depends on the grating period of the blazed grating, the diffraction angle of the incident light can be controlled only by changing the grating periods corresponding to different positions on the LCoS, so that the diffracted light is output at different ports of the WSS, and the wavelength selective switch function is realized.
However, due to the discretization of pixels, the edge field effect and the elastic interaction between liquid crystal molecules, the appearance of the phase grating generated by the voltage has a certain deviation from that of an ideal stepped blazed grating, and the region with sudden voltage change becomes smooth. The other orders of diffraction light are inevitably generated, so that a part of energy in the process of deflecting the incident light beam can be diffracted to other directions and coupled into a non-target port, the insertion loss and the port isolation degree are deteriorated, and the performance of the whole system is influenced.
Disclosure of Invention
The embodiment of the application provides a crosstalk suppression method and device for a wavelength selective switch and the wavelength selective switch, which are used for suppressing crosstalk generated to other output ports when an incident beam in a WSS is diffracted to a target output port.
In a first aspect, the present application provides a wavelength selective switch WSS comprising an input port, a plurality of output ports, and a liquid crystal on silicon LCoS. An input port for receiving an incident beam; the LCoS is used for modulating the incident beam by superposing the phase grating so that the modulated incident beam is diffracted to a target output port in the plurality of output ports; the phase grating is characterized by a phase modulation function, the phase modulation function being determined from the initial modulation function and the first modulation function; the diffraction order with the strongest energy in each diffraction order generated by modulating the incident beam through the initial modulation function is positioned at the target output port; the energy of the first diffraction order generated by modulating the incident light beam through the first modulation function is used for reducing the energy of the first diffraction order generated by modulating the incident light beam through the initial modulation function; the first diffraction order generated by diffraction is located at the first output port, and the first output port is one of the plurality of output ports except for the target output port.
According to the scheme provided by the embodiment of the application, when the incident beam in the WSS is diffracted to the target output port and the crosstalk generated to other output ports is large, the first modulation function can be configured for the output port needing to be inhibited from the crosstalk, so that the energy of the first diffraction order generated by modulating the incident beam through the first modulation function is used for reducing the energy of the first diffraction order generated by modulating the incident beam through the initial modulation function, the crosstalk energy of the corresponding port is inhibited, and the port isolation is improved. No additional components need to be added to the WSS, and no changes need to be made to the structure inherent in the WSS itself.
In one possible design, the amplitude of the first modulation function and the energy of the first diffraction order produced by modulating the incident beam with the initial modulation function satisfy a first type of Bessel function relationship. The amplitude of the first modulation function is determined through the Bessel function relation between the amplitude of the first modulation function and the crosstalk energy, so that the energy generated by the first modulation function in the first output port in a modulation mode is the same as the crosstalk energy generated by the initial modulation function in the first output port, and the scheme is simple and effective.
In one possible design, the first modulation function is a sine function or a cosine function.
In one possible design, the amplitude of the first modulation function and the energy of the first diffraction order produced by modulating the incident beam with the initial modulation function satisfy the following condition:
E n ＝20log 10 (J 0 (A)/J 1 (A))；
wherein E is n Representing the energy and the energy of a first diffraction order generated by modulating an incident beam with an initial modulation functionThe relative magnitude of the energy of the strongest diffraction order, A representing the amplitude of the first modulation function, J 1 () Representing a 1 st order Bessel function of the first kind, J 0 () Representing a bessel function of the first kind of order 0.
In one possible design, the diffraction angle modulated by the first modulation function is the same as the angular difference between the diffraction angle at which the incident light beam is diffracted into the energy-strongest diffraction order and the diffraction angle at which the incident light beam is diffracted into the first diffraction order.
In one possible design, the diffraction angle and the angle difference of the first modulation function modulation satisfy the following correspondence:
Figure BDA0003040078940000021
wherein T represents the phase grating period corresponding to the target output port, and T n The period of the phase grating corresponding to the first output port is indicated, t the period of the first modulation function, and λ the wavelength of the incident light beam.
According to the design, the period of the first modulation function is determined by the diffraction angle and the angle difference modulated by the first modulation function, and the scheme is simple and effective.
In one possible design, the period of the first modulation function satisfies the following condition:
Figure BDA0003040078940000022
wherein T represents the phase grating period corresponding to the target output port, T n Indicating the phase grating period corresponding to the first output port and t indicating the period of the first modulation function. The period of the first function is determined through the design, and the method is simple and effective.
In one possible design, the phase of the optical signal at the first diffraction order generated by modulating the incident light beam with the first modulation function is opposite to the phase of the optical signal at the first diffraction order generated by modulating the incident light beam with the initial modulation function, and the energy of the first diffraction order generated by modulating the incident light beam with the first modulation function is the same as the energy of the first diffraction order generated by modulating the incident light beam with the initial modulation function.
In one possible design, the initial phase of the first modulation function is swept in the range 0-2 π such that the phase of the optical signal in the first diffraction order produced by modulating the incident light beam with the first modulation function of the initial phase is opposite to the phase of the optical signal in the first diffraction order produced by modulating the incident light beam with the initial modulation function. The initial phase of the first modulation function is obtained by scanning within the range of 0-2 pi through the design, the scheme is simple, and the determined initial phase achieves a good effect.
In one possible design, the initial phase of the initial modulation function is adjusted such that energy of a first diffraction order generated by modulating the incident light beam by the first modulation function diminishes energy of the first diffraction order generated by modulating the incident light beam by the initial modulation function, and such that energy of a second diffraction order generated by modulating the incident light beam by the first modulation function diminishes energy of the second diffraction order generated by modulating the incident light beam by the initial modulation function, the second diffraction order and the first diffraction order being two diffraction orders that are symmetrical about a diffraction order with the strongest energy. Through the design, when crosstalk exists in the two symmetric orders and the first modulation function determined by adjusting the initial phase of the initial modulation function cannot inhibit the crosstalk of the two symmetric orders by superposing the first modulation function, the first modulation function is superposed, and the effect of inhibiting the crosstalk of the two diffraction orders which are symmetric with the target order can be achieved.
In one possible design, the initial phase of the initial modulation function is adjusted such that the initial phase of the first modulation function, the initial phase of the first diffraction order, and the initial phase of the second diffraction order satisfy the following condition:
Figure BDA0003040078940000031
Figure BDA0003040078940000032
wherein the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical with the diffraction order with the strongest energy as the center, phi represents the initial phase of the first modulation function, and phi +m Initial phase, phi, representing the most intense diffraction order of energy +(m-y) Indicating the initial phase of the first diffraction order, phi +(m-y) Indicating the initial phase of the second diffraction order.
In a second aspect, the present application further provides a crosstalk suppression method for a wavelength selective switch WSS, where beneficial effects of the method can be found in beneficial effects of various designs of the first aspect, and details are not repeated here. The method comprises the following steps: the WSS modulates the incident beam by superposing a phase grating on the LCoS so that the modulated incident beam is diffracted to a target output port in a plurality of output ports of the WSS; the phase grating is expressed by a phase modulation function, and the phase modulation function is determined according to an initial modulation function and a first modulation function; the WSS outputs the modulated incident beam through a target output port; the system comprises a plurality of output ports, a plurality of diffraction orders, a plurality of optical fiber coupling units and a plurality of optical fiber coupling units, wherein the maximum energy diffraction order in each diffraction order generated by modulating an incident beam through an initial modulation function is positioned at a target output port in the plurality of output ports; the energy of the first diffraction order generated by modulating the incident light beam through the first modulation function is used for reducing the energy of the first diffraction order generated by modulating the incident light beam through the initial modulation function; the first diffraction order generated by diffraction is located at the first output port, and the first output port is one of the output ports which needs crosstalk suppression except for the target output port.
In one possible design, the amplitude of the first modulation function and the energy of the first diffraction order produced by modulating the incident beam with the initial modulation function satisfy a first type of Bessel function relationship.
In one possible design, the amplitude of the first modulation function and the energy of the first diffraction order produced by the initial modulation function on modulation of the incident beam satisfy the following condition:
E n ＝20log 10 (J 0 (A)/J 1 (A))；
wherein E is n Denotes the relative magnitude of the first diffraction order and +1 st diffraction energy produced by the modulation of an incident beam by an initial modulation function, A denotes the amplitude of the first modulation function, J 1 () Representing a 1 st order Bessel function of the first kind, J 0 () Representing a bessel function of the first kind of order 0.
In one possible design, the first modulation function modulates the energy at the same diffraction angle as the angular difference between the diffraction angle at which the incident beam is diffracted into the energy-strongest diffraction order and the angle at which the incident beam is diffracted into the first diffraction order.
In one possible design, the diffraction angle and the angle difference for modulating the energy by the first modulation function satisfy the following correspondence:
Figure BDA0003040078940000033
wherein T represents the phase grating period corresponding to the target output port, and T n The period of the phase grating corresponding to the first output port is indicated, t the period of the first modulation function, and λ the wavelength of the incident light beam.
In one possible design, the period of the first modulation function satisfies the following condition:
Figure BDA0003040078940000041
wherein T represents the phase grating period corresponding to the target output port, and T n Indicating the phase grating period corresponding to the first output port and t indicating the period of the first modulation function.
In one possible design, the phase of the optical signal at the first diffraction order generated by modulating the incident light beam by the first modulation function is opposite to the phase of the optical signal at the first diffraction order generated by modulating the incident light beam by the initial modulation function, and the amplitude of the energy at the first diffraction order generated by modulating the incident light beam by the first modulation function is the same as the amplitude of the energy at the first diffraction order generated by modulating the incident light beam by the initial modulation function.
In one possible design, the initial phase of the first modulation function is swept in the range 0-2 π such that the phase of the optical signal in the first diffraction order produced by modulating the incident light beam with the first modulation function of the initial phase is opposite to the phase of the optical signal in the first diffraction order produced by modulating the incident light beam with the initial modulation function.
In one possible design, the method further includes:
when the energy of the second diffraction order generated by modulating the incident light beam through the first modulation function cannot reduce the energy of the second diffraction order generated by modulating the incident light beam through the initial modulation function, the initial phase of the initial modulation function is adjusted, so that the energy of the first diffraction order generated by modulating the incident light beam through the first modulation function reduces the energy of the first diffraction order generated by modulating the incident light beam through the initial modulation function, and the energy of the second diffraction order generated by modulating the incident light beam through the first modulation function reduces the energy of the second diffraction order generated by modulating the incident light beam through the initial modulation function, wherein the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical by taking the strongest diffraction order as the center.
In one possible design, the initial phase of the initial modulation function is adjusted such that the initial phase of the first modulation function, the initial phase of the first diffraction order, and the initial phase of the second diffraction order satisfy the following condition:
Figure BDA0003040078940000042
Figure BDA0003040078940000043
wherein the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical with the diffraction order with the strongest energy as the center, phi represents the initial phase of the first modulation function, and phi +m Initial phase, phi, representing the most intense diffraction order of energy +(m-y) Indicating the initial phase of the first diffraction order, phi +(m-y) Indicating the initial phase of the second diffraction order.
In a third aspect, the present application further provides a crosstalk suppression method for a wavelength selective switch WSS, where beneficial effects of the method may refer to beneficial effects of the designs in the first aspect, and are not described herein again. The method comprises the following steps: superposing a first phase grating represented by an initial modulation function on the LCoS to modulate an incident beam, so that the strongest diffraction order of the diffraction orders of the modulated incident beam is positioned at a target output port of a plurality of output ports of the WSS; measuring crosstalk energy generated by the initial modulation function on other output ports except the target output port in the plurality of output ports; determining a first output port needing crosstalk suppression according to measured crosstalk energy of other output ports, wherein the energy of a first diffraction order generated by modulating incident beams by an initial modulation function is larger than a set threshold; determining a first modulation function for the first output port, so that after a second phase grating characterized by the first phase modulation function is superposed on the LCoS, the energy of a first diffraction order on the first output port is smaller than a set threshold value; the first phase modulation function is determined from the initial modulation function and the first modulation function; the first diffraction order is located at a first output port; the set threshold is determined based on the maximum crosstalk energy supported by the output port of the WSS.
In one possible design, determining a first modulation function for a first output port includes: the amplitude of the first modulation function is determined from a first type of Bessel function relationship that the amplitude of the first modulation function satisfies with the energy of a first diffraction order generated by the modulation of the incident beam by the initial modulation function.
In one possible design, the amplitude of the first modulation function and the energy of the first diffraction order produced by modulating the incident beam with the initial modulation function satisfy the following condition:
E n ＝20log 10 (J 0 (A)/J 1 (A))；
wherein E is n Representing the relative magnitude of the energy of the first diffraction order produced by the modulation of the incident beam by the initial modulation function and the energy of the diffraction order of the strongest order of energy, a representing the amplitude of the first modulation function, J 1 () Representing a 1 st order Bessel function of the first kind, J 0 () Representing a bessel function of the first kind of order 0.
In one possible design, determining a first modulation function for a first output port includes: determining the period of the first modulation function according to the corresponding relation satisfied by the diffraction angle and the angle difference modulated by the first modulation function; the diffraction angle modulated by the first modulation function is the same as the angular difference between the diffraction angle at which the incident beam is diffracted into the most energetic diffraction order and the diffraction angle at which the incident beam is diffracted into the first diffraction order.
In one possible design, the diffraction angle and the angle difference of the first modulation function modulation satisfy the following correspondence:
Figure BDA0003040078940000051
wherein T represents the phase grating period corresponding to the target output port, and T n The period of the phase grating corresponding to the first output port is indicated, t the period of the first modulation function, and λ the wavelength of the incident light beam.
In one possible design, determining a first modulation function for the first output port includes: and determining the period of the first modulation function according to the phase grating period corresponding to the target output port and the phase grating period corresponding to the first output port.
In one possible design, the period of the first modulation function satisfies the following condition:
Figure BDA0003040078940000052
wherein T represents the phase grating period corresponding to the target output port, T n Indicating the phase grating period corresponding to the first output port and t indicating the period of the first modulation function.
In one possible design, determining a first modulation function for a first output port includes: scanning the initial phase value of the first modulation function to be determined within the range of 0-2 pi, measuring the energy of a first diffraction order on a first output port after a phase grating represented by the initial modulation function and the first modulation function to be determined corresponding to the current scanning is superposed on the LCoS after the initial phase value of the first modulation function to be determined is scanned once; and after the scanning of the initial phase of the first modulation function to be determined within the range of 0-2 pi is completed, taking the initial phase value corresponding to the minimum scanning time which satisfies that the energy of the first diffraction order on the first output port is less than a set threshold as the initial phase value of the first modulation function.
In one possible design, the method further includes: determining a second output port needing crosstalk suppression according to the measured crosstalk energy of other output ports, wherein the second output port is positioned at a second diffraction order generated by the modulation of the initial modulation function; the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical by taking the diffraction order with the strongest energy as the center; when measuring that the energy of a second diffraction order generated by the second phase grating for incident beam modulation after the first modulation function is superposed on the basis of the initial modulation function is larger than a set threshold, adjusting the initial phase of the initial modulation function, and determining the first modulation function for the first output port again, so that after a third phase grating characterized by the second phase modulation function is superposed on the LCoS, the energy of the first diffraction order on the first output port and the energy of the second diffraction order on the second output port are both smaller than the set threshold; the second phase modulation function is determined according to the initial modulation function after the initial phase is adjusted and the first modulation function which is determined again.
In one possible design, the initial phase of the initial modulation function is adjusted such that the re-determined initial phase of the first modulation function, the initial phase of the first diffraction order, and the initial phase of the second diffraction order satisfy the following condition:
Figure BDA0003040078940000061
Figure BDA0003040078940000062
where Φ denotes the initial phase of the first modulation function which is determined anew, Φ +m Initial phase, phi, representing the most intense diffraction order of energy +(m-y) Indicating the initial phase of the first diffraction order, phi +(m-y) Indicating the initial phase of the second diffraction order.
In a fourth aspect, the present application provides a crosstalk suppression apparatus for a wavelength selective switch WSS, the apparatus comprising a memory and a processor; a memory for storing a program executed by the processor; and a processor configured to execute the program stored in the memory to perform the method provided by the third aspect or any design of the third aspect.
In a fifth aspect, the present application provides a computer storage medium having stored thereon computer-executable instructions for causing a computer to perform the method provided by any one of the third aspect or the design of the third aspect.
In a sixth aspect, the present application provides a computer program product containing instructions, which when run on a computer, causes the computer to perform the method provided by the third aspect or any one of the third aspects.
Drawings
FIG. 1 is a schematic diagram of the diffraction principle of an LCoS;
FIG. 2 is a schematic structural diagram of a WSS in an embodiment of the present application;
FIG. 3 is a schematic diagram illustrating crosstalk suppression principles in an embodiment of the present application;
fig. 4A is a schematic flowchart of a method for determining a first modulation function in an embodiment of the present application;
FIG. 4B is a schematic diagram of a system for determining a first modulation function according to an embodiment of the present disclosure;
FIG. 5 is a schematic diagram illustrating a crosstalk suppression effect according to an embodiment of the present application;
FIG. 6 is a schematic diagram of phase modulation for double sideband crosstalk suppression in an embodiment of the present application;
FIG. 7 is a schematic diagram of a first modulation function and a process for determining an initial phase of the initial modulation function in an embodiment of the present application;
FIG. 8 is a schematic diagram of another crosstalk suppression effect in the embodiment of the present application;
fig. 9 is a schematic structural diagram of a control device in an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Before introducing the scheme provided by the embodiment of the application, the working principle of the LCoS is explained.
The principle of operation of LCoS is based on the diffraction effect, and some higher diffraction orders are generated due to the phase error while the required diffracted light is obtained. The core principle of the WSS based on the LCOS is that different voltages are applied to different pixel points (pixels) of the LCOS, and due to the birefringence effect of the liquid crystal of the LCOS, the different voltages correspond to different phase retardation amounts, so that a structure similar to a Blazed grating (also referred to as a phase grating) can be formed. For ease of distinction, the phase grating is referred to herein as the first phase grating. Referring to fig. 1, a schematic diagram of a possible WSS is shown. It should be understood that fig. 1 is a schematic diagram for explaining the cause of crosstalk, and the structure of the WSS is not particularly limited. In fig. 1, light incident from an input port is processed (e.g., by a lens component that focuses the light) and then incident on an LCOS panel. And a phase grating is superposed on a corresponding pixel point on the LCoS to diffract the required + 1-order diffraction light to a corresponding output port. The phase grating may be characterized by an initial modulation function.
The diffraction angle between the phase grating superposed by the corresponding pixel points on the LCoS and the incident beam should satisfy the following formula (1):
Figure BDA0003040078940000071
where T denotes a period of the phase grating, N denotes the number of pixels included in one period of the phase grating, d denotes a width of a single pixel, θ denotes a diffraction angle of incident light,
Figure BDA0003040078940000072
representing the angle of incident light with respect to the LCoS plane normal, m representing the diffraction order, and λ representing the wavelength of the incident light. Taking the +1 st order diffracted light corresponding to the target port as an example, m =1. In some embodiments, equation (1) may also be referred to as a grating equation.
As an example, the initial modulation function may satisfy the following formula (2):
Figure BDA0003040078940000073
Φ origin representing the initial modulation function, T the period of the phase grating and x the pixel coordinates. It should be noted that the initial modulation function shown in formula (2) is only an example, and other modulation functions may be used as the initial modulation function, and it is sufficient that the diffraction order with the strongest energy generated by the initial modulation function on the modulation of the incident light beam is located at the target port.
However, in this case, light of other diffraction orders may enter other output ports, thereby causing crosstalk to other output ports. Light of other diffraction orders, such as 0.x order, +1 order, +1.x order, +2 order, etc., may cause crosstalk in subsequent optical links after entering the corresponding input ports. For example, in fig. 1, when +1 st order diffracted light needs to be output from a target port, other diffraction orders may be output from other ports as crosstalk light, so that co-frequency crosstalk is formed, and the signal is difficult to eliminate once entering a non-target port, which affects system performance.
The present application provides a wavelength selective switch and a crosstalk suppression method for the wavelength selective switch, wherein the wavelength selective switch is based on LCoS and can effectively suppress crosstalk diffraction light. It should be noted that "connected" in the embodiments of the present application refers to connection on an optical path, and those skilled in the art will understand that specific optical devices may not necessarily have a physical connection relationship with substantial contact, but the spatial positions of the optical devices and their own device characteristics make them form a connection relationship on an optical path.
Referring to fig. 2, a schematic diagram of a possible WSS structure based on LCoS is shown. The WSS includes an input port, a plurality of output ports, and an LCoS. The input port receives an incident light beam. And the LCoS superposition phase grating modulates the incident beam, so that the modulated incident beam is diffracted to a target output port in the plurality of output ports.
Wherein the phase grating is characterized by a phase modulation function, which is determined from the initial modulation function and the first modulation function. And the diffraction order with the strongest energy in the diffraction light of each diffraction order generated by the diffraction of the incident light beam is positioned at the target output port. For example, the strongest diffraction order is the +1 order. The energy of the first diffraction order generated by modulating the incident light beam through the first modulation function is used for reducing the energy of the first diffraction order generated by modulating the incident light beam through the initial modulation function; the first diffraction order generated by the diffraction is located at the first output port, and the first output port is one of the plurality of output ports except for the target output port.
The fringe field effect of the LCoS and the elastic interaction between liquid crystal molecules cause the diffraction light of the multi-order crosstalk derived, and the crosstalk is generated on other ports except the target port. Crosstalk diffraction light into non-target ports causes crosstalk, causing deterioration in port isolation. In the embodiment of the application, the first modulation function related to the energy and the position of the crosstalk port is superposed on the initial modulation function of the original phase grating so as to inhibit the crosstalk of the diffraction light signal of the diffraction order which is diffracted to the target port to other output ports. Referring to fig. 3, a schematic diagram of a crosstalk suppression principle provided in an embodiment of the present application is shown. In fig. 3, the solid line curve represents the signal energy resulting from the modulation of an incident beam by an initial modulation function. The dashed curve represents the signal energy resulting from modulation of the incident beam by the first modulation function. As can be seen from fig. 3, the signal energy of the first diffraction order generated by the modulation of the incident light beam by the first modulation function can be reduced by the signal energy of the first diffraction order generated by the modulation of the incident light beam by the initial modulation function.
Illustratively, a drive circuit may also be included in the WSS. The driving circuit determines the phase grating overlapped by the LCoS according to the phase modulation function, so that the driving voltage of each pixel point included by the LCoS is determined. The drive circuit outputs a corresponding drive voltage to each pixel on the LCoS.
In some embodiments, the first modulation function may be used to suppress crosstalk for the first output port. When the crosstalk of other output ports needs to be suppressed, the modulation functions for suppressing other output ports can be superimposed on the phase modulation function.
As an example, the first modulation function is a sine function or a cosine function. For example, taking the first modulation function as a sine function as an example, the first modulation function can be expressed by the following formula (3).
Figure BDA0003040078940000081
Wherein phi is mod Representing a first modulation function. Phi (phi) of initial Representing the initial phase of the first modulation function and a representing the amplitude of the first modulation function. t denotes the period of the first modulation function.
The phase modulation function corresponding to the phase grating may satisfy the following formula (4):
Figure BDA0003040078940000082
it will be appreciated that the determination of the port position is related to the period of the phase grating, as can be seen from the grating equation (1). The distance between the lens and the LCoS is fixed, i.e. the focal length of the lens; and under the condition that the diffraction angle of the incident light and the included angle between the incident light and the normal line of the LCoS plane are also fixed, determining the actual position of the port according to the period of the phase grating. It will thus be appreciated that the period t of the first modulation function may be characteristic of the actual spatial location of the signal energy equivalent modulated by the first modulation function.
In order to more effectively suppress the signal energy of the first diffraction order generated by the initial modulation function for modulating the incident light beam, the signal energy of the first diffraction order generated by the first modulation function for modulating the incident light beam can be the same as or approximately the same as the signal energy of the first diffraction order generated by the initial modulation function for modulating the incident light beam. Further, the amplitude of the first modulation function and the energy of the first diffraction order generated by the initial modulation function on the incident light beam satisfy the first Bessel function relation. Approximately the same, it can be understood that the difference between the magnitude of the signal energy of the first diffraction order generated by the modulation of the incident light beam by the first modulation function and the magnitude of the signal energy of the first diffraction order generated by the incident light beam by the initial modulation function is smaller than the set value. The set value may be determined based on the magnitude of acceptable crosstalk.
As an example, the amplitude of the first modulation function and the energy of the first diffraction order generated by the initial modulation function on the incident light beam modulation satisfy the condition shown in the following formula (5):
E n ＝E +1 -E crosstalk ＝10log 10 (J 0 (A) 2 )-10log 10 (J 1 (A) 2 )＝20log 10 (J 0 (A)/J 1 (A) Equation (5)
Wherein E is n Representing the relative magnitude of the energy of the first diffraction order resulting from the modulation of the incident beam by the initial modulation function and the energy of the diffraction order of the strongest order of energy, a representing the amplitude of the first modulation function, J 1 () Representing a 1 st order Bessel function of the first kind, J 0 () Representing a Bessel function of 0 th order, E +1 Representing the energy of the most intense diffraction order of energy (in the case of +1 diffraction order) resulting from the modulation of the incident beam by the initial modulation function. E Crosstalk Representing the energy of a first diffraction order resulting from modulation of the incident beam by the initial modulation function.
It should be noted that, as above, the formula (5) can be derived by performing fourier transform on the phase modulation function.
In order to more effectively suppress the signal energy of the first diffraction order generated by the initial modulation function for modulating the incident light beam, it can be satisfied that the phase of the signal energy of the first diffraction order generated by the first modulation function for modulating the incident light beam is opposite to the phase of the signal energy of the first diffraction order generated by the initial modulation function for modulating the incident light beam.
In some embodiments, the diffraction angle modulated by the first modulation function is the same as the angular difference between the diffraction angle at which the incident beam is diffracted into the most energetic diffraction order and the diffraction angle at which the incident beam is diffracted into the first diffraction order. Further, the diffraction angle and the angle difference of the first modulation function modulation satisfy the condition shown in the following formula (6):
Figure BDA0003040078940000091
wherein T represents the phase grating period corresponding to the target output port, T n Representing the period of the phase grating corresponding to the first output port, and t representing the period of the first modulation functionAnd λ represents the wavelength of the incident light beam.
Exemplarily, the above formula (6) can be approximately described as formula (7):
Figure BDA0003040078940000092
wherein T represents the phase grating period corresponding to the target output port, T n The period of the phase grating corresponding to the first output port is represented, and t represents the period of the first modulation function.
It is determined by equation (7) that the period of the first modulation function satisfies the condition shown in equation (8):
Figure BDA0003040078940000093
according to the scheme provided by the embodiment of the application, the first modulation function of the first output port needing to be suppressed is superposed on the basis of the phase grating generated by the initial modulation function, so that the energy generated by the first modulation function is the same as the crosstalk energy acted on the first output port by the initial modulation function, and the phases are opposite, thereby realizing suppression of crosstalk of the first output port and improvement of port isolation.
In some embodiments, the initial phase of the first modulation function is scanned over a range of 0-2 π such that the phase of the energy of the first diffraction order resulting from the modulation of the incident beam with the first modulation function of the initial phase is opposite to the phase of the energy of the first diffraction order resulting from the modulation of the incident beam with the initial modulation function.
In some embodiments, when crosstalk of other output ports than the first output port needs to be suppressed, for example, the second output port, the second modulation function of the second output port that needs to be suppressed may be further superimposed on the basis of the current phase modulation function, so that energy generated by the second modulation function is the same as crosstalk energy acting on the second output port by the initial modulation function, and phases of the energy are opposite, thereby achieving suppression of crosstalk of the second output port and improving port isolation.
The flow of determining the first modulation function is described below with reference to fig. 4A. The determination of the first modulation function may exemplarily be performed by a controller or a control device. Referring to fig. 4B, the determination system of the first modulation function may include a control device and a WSS to be determined. The method flow shown in fig. 4A may be performed by a control device.
401, establishing light intersection between an input port and a target output port of a WSS based on LCoS, and superimposing a phase grating represented by an initial modulation function on the LCoS. For ease of distinction, the phase grating characterized by the initial modulation function is referred to as the first phase grating. Therefore, the LCoS superposes the first phase grating to modulate incidence, so that the diffraction order with the strongest energy in the diffraction orders of the modulated incident beam diffraction is positioned at a target output port in the plurality of output ports of the WSS.
Illustratively, the control device is configured to superimpose a phase grating characterized by an initial modulation function on the LCoS via the drive circuit.
The crosstalk energy is measured 402 for the target output port and other output ports than the target output port. Alternatively, it can be understood that the initial modulation function may cause crosstalk to other output ports of the plurality of output ports than the target output port, thereby measuring crosstalk energy at the other output ports.
In one example, each output port may be configured with an energy detector for measuring crosstalk energy at the output port. See fig. 4B. The control device obtains the energy of each output port through the energy detector. Alternatively, the energy detector may be configured in the control device.
In another example, the signal output by the output port is sent to a control device, such that the control device determines the energy based on the signal output by the output port.
403, the output port for which crosstalk suppression is required is determined. Take the first output port as an example. For example, the initial modulation function modulates the incident light beam to generate a first diffraction order with an energy greater than a set threshold. The set threshold may be determined based on the maximum crosstalk energy supported by the output port of the WSS.
Illustratively, the control device determines the output port from which crosstalk needs to be suppressed based on the energy of the respective output port.
A first modulation function corresponding to the first output port where crosstalk is to be suppressed is determined 404.
The first modulation function is determined by the control device.
Illustratively, the first modulation function may employ a sine function or a cosine function. The amplitude of the first modulation function may be determined by:
the amplitude of the first modulation function is determined according to a first Bessel function relationship that the amplitude of the first modulation function and the energy of a first diffraction order generated by the initial modulation function for the incident light beam are satisfied.
For example, equation (3) is used as an example of the first modulation function. And determining the amplitude of the first modulation function corresponding to the first output port by combining the formula (5) according to the measured energy of the target output port and the measured crosstalk energy of the first output port.
Illustratively, the period of the first modulation function may be determined by:
determining the period of the first modulation function according to the corresponding relation satisfied by the diffraction angle and the angle difference modulated by the first modulation function; the diffraction angle modulated by the first modulation function is the same as the angular difference between the diffraction angle at which the incident beam is diffracted into the diffraction order with the strongest energy and the diffraction angle at which the incident beam is diffracted into the first diffraction order. For example: the period of the first modulation function is determined according to equation (6) or equation (8).
The initial phase of the first modulation function may be determined by scanning at 0-2 pi.
For example, the initial value of the initial phase of the first modulation function may be set to 0, then the initial phase is stepped by a step value every time the scanning is performed to obtain an updated first modulation function, the phase grating represented by the initial modulation function is superimposed according to the updated first modulation function to modulate the incident beam, and the energy of the first diffraction order on the first output port is measured. And after the scanning of the initial phase of the first modulation function to be determined within the range of 0-2 pi is completed, taking the initial phase value corresponding to the minimum scanning time which meets the condition that the energy of the first diffraction order on the first output port is less than a set threshold value as the initial phase value of the first modulation function. The process of scanning the initial phase described above is described below in connection with steps 405-408.
405, a first modulation function is superimposed on the basis of the initial phase function to obtain a phase modulation function, and a phase grating represented by the phase modulation function is superimposed on the LCoS.
Illustratively, the control device is configured to superimpose a phase grating characterized by the phase modulation function described above on the LCoS via the drive circuit.
The crosstalk energy of the first output port is measured 406.
The initial phase of the first modulation function is adjusted 407 during the current scan. It will be appreciated that 405 is performed by stepping the set step value based on the initial phase determined for the previous scan.
And 408, after the scanning of 0-2 pi of the initial phase is completed, determining the initial phase corresponding to the scanning times when the measured crosstalk energy of the first output port is minimum.
As an example, taking a target output port as port6, that is, establishing light intersection between a WSS-based input port and port6, then setting a corresponding initial modulation function and loading the modulation function onto an LCoS chip, where "+1" order diffracted light will be focused on port6, and light of other diffraction orders will be coupled into other output ports except port6 and cause crosstalk to the other output ports. And selecting the port needing to inhibit crosstalk to calculate and determine the required modulation function by measuring the crosstalk energy size and distribution of each output port. For example, the first output port is the port 14. port6 corresponds to a period of about 16.239 × d and port14 corresponds to a period of about 8.008 × d, then most of the energy of the +2 diffraction orders will couple into port14 and create crosstalk for port 14. Determination of what is detected at port14 by measurementThe crosstalk energy is E 14 . According to the formula (5) E 14 ＝20log 10 (J 0 (A 14 )/J 1 (A 14 ) Determine an amplitude a of a first modulation function for suppressing port14 crosstalk 14 According to the period of the phase grating corresponding to port6 port and port14 port, respectively, the formula
Figure BDA0003040078940000111
The period t of the first modulation function can be calculated, and the optimal initial phase phi can be determined by scanning in the range of 0-2 pi 6-14 Obtaining a modulation function for suppressing port14 crosstalk
Figure BDA0003040078940000112
And the first modulation function is superposed on the initial phase function, and a new phase grating is reloaded, so that the crosstalk of the port14 can be inhibited.
Referring to fig. 5, the experimental results for suppressing port14 crosstalk with port6 as the target port are shown. Fig. 5 (a) is a waveform diagram illustrating the energy of port6 and the crosstalk energy of port14 before the first modulation function is superimposed. Fig. 5 (b) is a waveform diagram illustrating the energy of port6 and the crosstalk energy of port14 after superimposing the first modulation function. From fig. 5 (b), it can be seen that the crosstalk for port14 is optimized by more than 10dB after the first modulation function is superimposed. Fig. 5 (c) is a waveform diagram illustrating the energy of port6 before the first modulation function is superimposed on the crosstalk energy of the other output ports. Fig. 5 (d) is a waveform diagram illustrating the energy of port6 and the crosstalk energy of other output ports after the first modulation function is superimposed. From (d) in fig. 5, it can be seen that the cross-talk over port14 is optimized by more than 10dB after the first modulation function is superimposed, with little effect on the energy of port6 or other ports.
It can be understood that the diffraction order corresponding to the target output port generates crosstalk to the diffraction orders symmetric on both sides, and in some possible scenarios, the superimposed modulation function is a sine function or a cosine function, so that the modulation in which the sine function is superimposed on the initial modulation function belongs to double-sideband modulation, and the +1 st diffraction light is taken as the center, and has a modulation effect on the diffraction orders symmetric on both sides. In some scenarios, however, the superimposed sinusoidal function may not satisfy both of the cancellation effects for crosstalk of bilaterally symmetric diffraction orders.
The phase modulation amount of the phase modulation function superimposed with the first modulation function for the bilaterally symmetric diffraction orders can be obtained by fourier transform of the modulated phase modulation function (see formula (3)), for example, see formula (9) below.
Figure BDA0003040078940000113
Taking the new 0 th diffraction order as the diffraction order corresponding to the target port, the new +1 diffraction order and the new-1 diffraction order are two diffraction orders which are symmetrical with the new 0 th diffraction order as the center. The new 0 th diffraction order of n =0 corresponds to the original +1 st diffraction light, and taking the initial phase of the new 0 th diffraction order as 0 as an example, the initial phase at the new +1 th diffraction order (n = 1) is Φ initial The initial phase at the new-1 diffraction order (n = -1) is- Φ initial + π. The new +1 diffraction order and the new-1 diffraction order are two diffraction orders that are symmetrical about the new 0 diffraction order (original +1 order).
Φ total Representing the phase modulation function after superimposing the first modulation function. J is a unit of n () Representing an n-th order bessel function of the first kind. w represents the spatial frequency and δ () represents the impulse function.
Take the initial modulation function (the target output port corresponds to the +1 diffraction order) and simultaneously generate the diffraction crosstalk for the +0.5 diffraction order (corresponding to the new-1 diffraction order) and the diffraction crosstalk for the +1.5 diffraction order (corresponding to the new +1 diffraction order) as an example. From the phase point of view, the suppression effect is best when the phase of the energy of the diffracted crosstalk generated by the superimposed first modulation function for the +0.5 diffraction order is opposite to the phase of the energy of the diffracted crosstalk generated by the initial modulation function for the +0.5 diffraction order (i.e., the phase difference is 180 ° (pi)), and the phase of the energy of the diffracted crosstalk generated by the superimposed first modulation function for the +1.5 diffraction order is opposite to the phase of the energy of the diffracted crosstalk generated by the initial modulation function for the +1.5 diffraction order. As shown in FIG. 6, after the first modulation function is superimposed +The total phase modulation amount of 0.5 diffraction order is-phi initial +π+Φ +1 The total phase modulation amount of the +1.5 diffraction order is Φ initial +Φ +1 . Wherein phi +1 Indicating the initial phase of the +1 st order diffracted light before the first modulation function is superimposed. If the +0.5 order diffraction light and the +1.5 order diffraction light are simultaneously suppressed by the superimposed first modulation function and the effect is best, the formula (10) and the formula (11) are simultaneously satisfied:
-Φ initial +π+Φ +1 ＝Φ +0.5 + pi formula (10)
Φ initial +Φ +1 ＝Φ +1.5 + pi formula (11)
Wherein phi +0.5 Denotes the initial phase of +0.5 th order diffracted light, phi +1.5 The initial phase of the +1.5 th order diffracted light is shown. In general, the initial phase of each order of diffracted light cannot be satisfied by equations (10) and (11), i.e., by adjusting the initial phase Φ of the first modulation function initial Only +0.5 th order diffracted light can be suppressed, but +1.5 th order diffracted light cannot be suppressed.
In view of this, in the embodiment of the present application, the first diffraction order and the second diffraction order are two diffraction orders that are centrosymmetric to the diffraction order with the strongest energy. The following inequalities (12) and (13) can be satisfied by adjusting the initial phase of the initial modulation function:
Figure BDA0003040078940000121
Figure BDA0003040078940000122
wherein the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical around the diffraction order with the strongest energy, phi initial Representing the initial phase, Φ, of said first modulation function +m Representing the most energetic diffraction order before superimposing said first modulation functionSecond initial phase, phi +(m-x) Representing the initial phase, Φ, of said first diffraction order before superimposing said first modulation function +(m-x) Representing an initial phase of the second diffraction order before superimposing the first modulation function.
Incident light field psi assuming LCoS plane in (x) =1, the emergent light field can be expressed as
Figure BDA0003040078940000123
After the initial modulation function adds an offset to the phase grating, the diffraction efficiency η can be expressed as formula (14) in combination with formula (1):
Figure BDA0003040078940000124
where offset represents the offset of the phase grating corresponding to the initial modulation function, and m represents the diffraction order. As can be seen from equation (14), the variation of the value of the offset varies the initial phases of different diffraction orders, so that the initial phases of the LCoS diffraction orders can be changed to different degrees by shifting the initial phases of the phase grating, and when the initial phases of the diffraction orders satisfy equation (15) (obtained by combining equations (10) and (11)), the +0.5 order diffracted light and the +1.5 order diffracted light can be effectively suppressed.
Φ＝Φ +1 -Φ +0.5 ＝Φ +1.5 -Φ +1 +π (15)
More generally, if two diffraction orders symmetric about + m order are to be suppressed, the initial phase Φ of the initial modulation function has a double sideband suppression effect when inequalities (12) and (13) are satisfied at the same time. When the formula (12) and the formula (13) satisfy-phi + pi + phi +m -Φ +(m-x) = pi and phi + phi +m -Φ +(m+x) When = pi, the phase modulation function has the best effect of suppressing crosstalk between two diffraction orders symmetric about + m order.
The flow of determining the first modulation function and the initial phase of the initial modulation function is described below with reference to fig. 7. The determination of the first modulation function and the initial phase of the initial modulation function may exemplarily be performed by a controller or a control device. Referring to fig. 4B, the determination system of the first modulation function may include a control device and a WSS to be determined.
And 701, establishing optical crossing between an input port and a target output port of the WSS based on the LCoS, and superposing a phase grating represented by an initial modulation function on the LCoS. See 401 for details, which are not described herein.
The crosstalk energy of the target output port and other ports than the target output port is measured 702. See 402 for details, which are not described herein.
703, an output port for which crosstalk suppression is required is determined. Take the first output port as an example. See 402 for details, which are not described herein.
And 704, determining a first modulation function corresponding to the first output port needing to suppress crosstalk according to the crosstalk energy of the first output port. See 404, which is not described in detail herein.
For example, equation (3) is taken as an example of the first modulation function. And determining the amplitude of the first modulation function corresponding to the first output port by combining the formula (5) according to the measured energy of the target output port and the measured crosstalk energy of the first output port. The period of the first modulation function is determined according to equation (6) or equation (8). The initial value of the initial phase of the first modulation function may be set to 0. The sweep range of the initial phase of the first modulation function may be 0-2 pi.
705, a first modulation function is superimposed on the basis of the initial phase function to obtain a phase modulation function, and a phase grating represented by the phase modulation function is superimposed on the LCoS.
The crosstalk energy is measured at each output port 706.
707, adjust the initial phase of the first modulation function, and execute 705.
708, after completing the scanning of 0-2 pi of the initial phase, determining whether the initial phase of the first modulation function exists where the crosstalk energy of the first output port and the crosstalk energy of the second output port both meet the crosstalk requirement, and if not, executing 709. If so, 710 is performed. For example, satisfying the crosstalk requirement may be that the crosstalk energies are each less than a set threshold.
709, adjust initial phase of initial modulation function, execute 704.
710, a first modulation function and an initial phase of the initial modulation function are obtained.
Referring to FIG. 8, with port12 as the target port, the diffraction order of the target port is +1 diffraction order. The diffraction orders corresponding to port5 and port19 are two diffraction orders symmetric about the +1 diffraction order. FIG. 8 is an experimental result of suppressing port5 and port19 crosstalk. Fig. 8 (a) is an energy diagram of port12, port5, and port19 with the first modulation function superimposed and the initial phase of the initial modulation function not adjusted. After the modulation function corresponding to port19 is superimposed for the first time and crosstalk is suppressed, the crosstalk caused by port19 is optimized to about 5dB as a whole, but the crosstalk caused by port5 cannot be suppressed (similarly, the crosstalk caused by port5 can be suppressed after the modulation function corresponding to port5 is superimposed and crosstalk cannot be suppressed, but the crosstalk caused by port19 is suppressed), as shown in fig. 8 (b). By introducing the initial phase shift of the initial modulation function, that is, by shifting the phase grating, and changing the initial phase of each diffraction order, the crosstalk of port5 and port19 can be suppressed by about 11dB and 6dB, respectively, which is significantly improved compared with the suppression effect before shifting the phase grating, as shown in (c) of fig. 8.
Fig. 9 is a schematic diagram of a possible control device. The control device includes a processor 901 and a memory 902. The processor 901 may be a Central Processing Unit (CPU), a digital processing unit, or the like. The control device may also include a communication interface 903 for connecting to a WSS. Processor 901 sends and receives information over communication interface 903. A memory 902 for storing programs executed by the processor 901.
The specific connection medium between the processor 901, the memory 902 and the communication interface 903 is not limited in the embodiments of the present application. In the embodiment of the present application, the memory 902, the processor 901, and the communication interface 903 are connected by the bus 904 in fig. 9, the bus is represented by a thick line in fig. 9, and the connection manner between other components is merely schematic illustration and is not limited thereto. The bus may be divided into an address bus, a data bus, a control bus, etc. For ease of illustration, only one thick line is shown in FIG. 9, but this does not indicate only one bus or one type of bus.
The memory 902 may be a volatile memory (RAM), such as a random-access memory (RAM); the memory 902 may also be a non-volatile memory (non-volatile memory), such as a read-only memory (ROM), a flash memory (flash memory), a Hard Disk Drive (HDD) or a solid-state drive (SSD), or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer, but is not limited thereto. The memory 902 may be a combination of the above memories.
The processor 901 is configured to execute the program code stored in the memory 902, and is specifically configured to execute the method described in the embodiment corresponding to fig. 4A or fig. 7, which may be specifically implemented with reference to the embodiment corresponding to fig. 4A or fig. 7, and is not described herein again.
Optionally, a plurality of energy detectors (not shown in fig. 9) may also be deployed in the control device for detecting energy at the output ports of the WSS.
The embodiments described herein are only for illustrating and explaining the present application and are not intended to limit the present application, and the embodiments and functional blocks in the embodiments in the present application may be combined with each other without conflict.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It will be apparent to those skilled in the art that various changes and modifications may be made in the embodiments of the present application without departing from the scope of the embodiments of the present application. Thus, if such modifications and variations of the embodiments of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to encompass such modifications and variations.

Claims (32)

1. A wavelength selective switch WSS is characterized in that the WSS comprises an input port, a plurality of output ports and a liquid crystal on silicon (LCoS);
the input port is used for receiving incident light beams;
the LCoS is used for modulating the incident beam by a superposed phase grating so that the modulated incident beam is diffracted to a target output port in the output ports; the phase grating is characterized by a phase modulation function, which is determined from an initial modulation function and a first modulation function;
the diffraction order with the highest energy in all diffraction orders generated by modulating the incident light beam through the initial modulation function is positioned at the target output port; modulating the incident light beam by the first modulation function to produce a first diffraction order of energy for attenuating the first diffraction order of energy produced by modulating the incident light beam by the initial modulation function; the first diffraction order generated by the diffraction is located at the first output port, and the first output port is one of the plurality of output ports except for the target output port.
2. The wavelength selective switch of claim 1, wherein an amplitude of the first modulation function and an energy of a first diffraction order generated by the modulation of the incident beam by the initial modulation function satisfy a first type of Bessel function relationship.
3. The wavelength selective switch of claim 1 or 2, wherein the amplitude of the first modulation function and the energy of the first diffraction order resulting from the modulation of the incident beam by the initial modulation function satisfy the following condition:
E n ＝20log 10 (J 0 (A)/J 1 (A))；
wherein, E n Representing the relative magnitude of the energy of the first diffraction order and the energy of the most energetic diffraction order resulting from modulation of the incident beam by the initial modulation function, A representing the first modulationAmplitude of the function, J 1 () Representing a 1 st order Bessel function of the first kind, J 0 () Representing a first class bessel function of order 0.
4. The wavelength selective switch of any one of claims 1-3, wherein the diffraction angle modulated by the first modulation function is the same as an angular difference between the diffraction angle at which the incident light beam is diffracted into the most energetic diffraction order and the diffraction angle at which the incident light beam is diffracted into the first diffraction order.
5. The wavelength selective switch of claim 4, wherein the diffraction angle and the angle difference of the first modulation function modulation satisfy the following correspondence:
Figure FDA0003040078930000011
wherein T represents the phase grating period corresponding to the target output port, T n Denotes the phase grating period corresponding to the first output port, t denotes the period of said first modulation function, and λ denotes the wavelength of the incident light beam.
6. The wavelength selective switch of any one of claims 1-5, wherein a period of the first modulation function satisfies the condition:
Figure FDA0003040078930000012
wherein T represents the phase grating period corresponding to the target output port, T n The period of the phase grating corresponding to the first output port is represented, and t represents the period of the first modulation function.
7. The wavelength selective switch of any one of claims 1-6, wherein the modulation of the incident light beam by the first modulation function produces an optical signal at a first diffraction order that is out of phase with the optical signal at the first diffraction order produced by the modulation of the incident light beam by the initial modulation function, and wherein the modulation of the incident light beam by the first modulation function produces a first diffraction order that has the same energy as the first diffraction order produced by the modulation of the incident light beam by the initial modulation function.
8. The wavelength selective switch of any one of claims 1-7, wherein an initial phase of the first modulation function is swept over a range of 0 to 2 π such that a phase of an optical signal in a first diffraction order generated by modulating the incident light beam with the first modulation function of the initial phase is opposite to a phase of an optical signal in the first diffraction order generated by modulating the incident light beam with the initial modulation function.
9. The wavelength selective switch of any one of claims 1-8, wherein an initial phase of the initial modulation function is adjusted such that energy of the first diffraction order resulting from modulation of the incident light beam by the first modulation function cancels energy of the first diffraction order resulting from modulation of the incident light beam by the initial modulation function, and such that energy of a second diffraction order resulting from modulation of the incident light beam by the first modulation function cancels energy of a second diffraction order resulting from modulation of the incident light beam by the initial modulation function, the second diffraction order and the first diffraction order being two diffraction orders centered on the most energetic diffraction order.
10. The wavelength selective switch of claim 9, wherein the initial phase of the initial modulation function is adjusted such that the initial phase of the first modulation function, the initial phase of the first diffraction order, and the initial phase of the second diffraction order satisfy the following condition:
Figure FDA0003040078930000021
Figure FDA0003040078930000022
wherein the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical around the diffraction order with the strongest energy, phi represents the initial phase of the first modulation function, and phi represents the initial phase of the first modulation function +m Initial phase, phi, representing the most intense diffraction order of energy +(m-y) Representing the initial phase, Φ, of said first diffraction order +(m-y) Representing the initial phase of the second diffraction order.
11. A crosstalk suppression method for a Wavelength Selective Switch (WSS), comprising:
the WSS modulates the incident beam by superposing a phase grating on the LCoS so that the modulated incident beam is diffracted to a target output port in a plurality of output ports of the WSS; the phase grating is represented by a phase modulation function, and the phase modulation function is determined according to an initial modulation function and a first modulation function;
the WSS outputs an incident beam after modulation processing through the target output port;
wherein the energy-strongest diffraction order of the diffraction orders generated by modulating the incident beam through the initial modulation function is located at a target output port of the plurality of output ports; modulating the incident light beam by the first modulation function to produce a first diffraction order of energy for attenuating the first diffraction order of energy produced by modulating the incident light beam by the initial modulation function; the first diffraction order generated by the diffraction is located at the first output port, and the first output port is one of the output ports which needs crosstalk suppression except for the target output port.
12. The method of claim 11 wherein the amplitude of the first modulation function and the energy of the first diffraction order produced by the modulation of the incident beam by the initial modulation function satisfy a first type of bessel function relationship.
13. The method of claim 11 or 12, wherein the amplitude of the first modulation function and the energy of the first diffraction order produced by the initial modulation function on the incident light beam modulation satisfy the following condition:
E n ＝20log 10 (J 0 (A)/J 1 (A))；
wherein E is n Representing the relative magnitude of the first diffraction order and +1 st order diffracted light energy resulting from modulation of the incident beam by the initial modulation function, A representing the amplitude of the first modulation function, J 1 () Representing a 1 st order Bessel function of the first kind, J 0 () Representing a first class bessel function of order 0.
14. The method of any of claims 11-13, wherein the first modulation function modulates energy at the same diffraction angle as an angular difference between the diffraction angle at which the incident beam is diffracted to the most energetic diffraction order and the angle at which the incident beam is diffracted to the first diffraction order.
15. The method of claim 14, wherein the diffraction angle and the angle difference for the first modulation function to modulate the energy satisfy the following correspondence:
Figure FDA0003040078930000031
wherein T represents the phase grating period corresponding to the target output port, T n Representing the phase grating period corresponding to the first output port, and t representing the first modulation functionThe period of the number, λ, represents the wavelength of the incident beam.
16. The method of any of claims 11-15, wherein a period of the first modulation function satisfies the following condition:
Figure FDA0003040078930000032
wherein T represents the phase grating period corresponding to the target output port, T n The period of the phase grating corresponding to the first output port is represented, and t represents the period of the first modulation function.
17. The method of any of claims 11-16, wherein modulating the incident light beam by the first modulation function produces an optical signal at a first diffraction order that is opposite in phase to an optical signal at a first diffraction order produced by modulating the incident light beam by the initial modulation function, and wherein modulating the incident light beam by the first modulation function produces an energy at the first diffraction order that is the same in amplitude as the energy at the first diffraction order produced by modulating the incident light beam by the initial modulation function.
18. The method of any of claims 11-17, wherein an initial phase of the first modulation function is scanned in a range of 0 to 2 pi, such that a phase of an optical signal at a first diffraction order generated by modulating the incident optical beam with the first modulation function of the initial phase is obtained when a phase of an optical signal at the first diffraction order generated by modulating the incident optical beam with the initial modulation function is opposite to a phase of an optical signal at the first diffraction order generated by modulating the incident optical beam with the initial modulation function.
19. The method of any one of claims 11-18, further comprising:
when the energy of a second diffraction order generated by modulating the incident light beam by the first modulation function cannot reduce the energy of the second diffraction order generated by modulating the incident light beam by the initial modulation function, adjusting the initial phase of the initial modulation function, so that the energy of the first diffraction order generated by modulating the incident light beam by the first modulation function reduces the energy of a first diffraction order generated by modulating the incident light beam by the initial modulation function, and so that the energy of a second diffraction order generated by modulating the incident light beam by the first modulation function reduces the energy of the second diffraction order generated by modulating the incident light beam by the initial modulation function, wherein the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical by taking the strongest diffraction order as the center.
20. The method of claim 19, wherein the initial phase of the initial modulation function is adjusted such that the initial phase of the first modulation function, the initial phase of the first diffraction order, and the initial phase of the second diffraction order satisfy the following condition:
Figure FDA0003040078930000033
Figure FDA0003040078930000034
wherein the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical around the diffraction order with the strongest energy, phi represents the initial phase of the first modulation function, and phi represents the initial phase of the first modulation function +m Initial phase, phi, representing the most intense diffraction order of energy +(m-y) Representing the initial phase, Φ, of said first diffraction order +(m-y) Representing the initial phase of the second diffraction order.
21. A crosstalk suppression method for a Wavelength Selective Switch (WSS), comprising:
superposing a first phase grating represented by an initial modulation function on the LCoS to modulate an incident beam, so that the strongest diffraction order of the diffraction orders of the modulated incident beam is positioned at a target output port of the multiple output ports of the WSS;
measuring crosstalk energy generated by the initial modulation function on other output ports except for a target output port in the plurality of output ports;
determining a first output port needing crosstalk suppression according to the measured crosstalk energy of the other output ports, wherein the energy of a first diffraction order generated by modulating the incident light beam by the initial modulation function is larger than a set threshold;
determining a first modulation function for the first output port, so that after a second phase grating characterized by the first phase modulation function is superposed on the LCoS, the energy of a first diffraction order on the first output port is smaller than a set threshold value; the first phase modulation function is determined according to an initial modulation function and a first modulation function; the first diffraction order is located at the first output port; the set threshold is determined according to a maximum crosstalk energy supported by an output port of the WSS.
22. The method of claim 21, wherein determining a first modulation function for the first output port comprises:
the amplitude of the first modulation function is determined according to a first Bessel function relationship that the amplitude of the first modulation function and the energy of a first diffraction order generated by the initial modulation function for the incident light beam are satisfied.
23. The method of claim 22 wherein the amplitude of the first modulation function and the energy of the first diffraction order produced by modulating the incident beam with the initial modulation function satisfy the following condition:
E n ＝20log 10 (J 0 (A)/J 1 (A))；
wherein E is n Representing the relative magnitude of the energy of the first diffraction order resulting from the modulation of the incident beam by the initial modulation function and the energy of the diffraction order of the strongest order of energy, a representing the amplitude of the first modulation function, J 1 () Representing a 1 st order Bessel function of the first kind, J 0 () Representing a bessel function of the first kind of order 0.
24. The method of any of claims 21-23, wherein determining a first modulation function for the first output port comprises:
determining the period of the first modulation function according to the corresponding relation satisfied by the diffraction angle and the angle difference modulated by the first modulation function;
the diffraction angle modulated by the first modulation function is the same as the angular difference between the diffraction angle at which the incident beam is diffracted into the diffraction order with the strongest energy and the diffraction angle at which the incident beam is diffracted into the first diffraction order.
25. The method of claim 24, wherein the diffraction angle and the angle difference of the first modulation function modulation satisfy the following correspondence:
Figure FDA0003040078930000041
wherein T represents the phase grating period corresponding to the target output port, T n Denotes the period of the phase grating corresponding to the first output port, t denotes the period of said first modulation function, and λ denotes the wavelength of the incident light beam.
26. The method of any of claims 21-23, wherein determining a first modulation function for the first output port comprises:
and determining the period of the first modulation function according to the phase grating period corresponding to the target output port and the phase grating period corresponding to the first output port.
27. The method of claim 26, wherein a period of the first modulation function satisfies the following condition:
Figure FDA0003040078930000051
wherein T represents the phase grating period corresponding to the target output port, T n And the period of the phase grating corresponding to the first output port is represented, and t represents the period of the first modulation function.
28. The method of any of claims 21-27, wherein determining a first modulation function for the first output port comprises:
scanning the initial phase value of the first modulation function to be determined within the range of 0-2 pi, measuring the energy of a first diffraction order on a first output port after a phase grating represented by the initial modulation function and the first modulation function to be determined corresponding to the current scanning is superposed on the LCoS every time the initial phase value of the first modulation function to be determined is scanned;
and after the scanning of the initial phase of the first modulation function to be determined within the range of 0-2 pi is completed, taking the initial phase value corresponding to the minimum scanning time which meets the condition that the energy of the first diffraction order on the first output port is less than a set threshold value as the initial phase value of the first modulation function.
29. The method of any one of claims 21-28, further comprising:
determining a second output port needing crosstalk suppression according to the measured crosstalk energy of the other output ports, wherein the second output port is located at a second diffraction order generated by the modulation of the initial modulation function; the second diffraction order and the first diffraction order are two diffraction orders which are symmetrical with the diffraction order with the strongest energy as the center;
when measuring that the energy of a second diffraction order generated by the incident light beam modulated by a second phase grating on which the first modulation function is superposed on the basis of the initial modulation function is larger than a set threshold, adjusting the initial phase of the initial modulation function, and determining the first modulation function for the first output port again, so that after a third phase grating characterized by the second phase modulation function is superposed on the LCoS, the energy of the first diffraction order on the first output port and the energy of the second diffraction order on the second output port are both smaller than the set threshold; the second phase modulation function is determined according to the initial modulation function after the initial phase is adjusted and the re-determined first modulation function.
30. The method of claim 29, wherein the initial phase of the initial modulation function is adjusted such that the re-determined initial phase of the first modulation function, the initial phase of the first diffraction order, and the initial phase of the second diffraction order satisfy the following condition:
Figure FDA0003040078930000052
Figure FDA0003040078930000053
wherein Φ represents an initial phase of the re-determined first modulation function, Φ +m Initial phase, phi, representing the most intense diffraction order of energy +(m-y) Representing the initial phase, Φ, of said first diffraction order +(m-y) Representing the initial phase of the second diffraction order.
31. A crosstalk suppression apparatus for a wavelength selective switch WSS, the apparatus comprising a memory and a processor;
the memory is used for storing programs executed by the processor;
the processor is configured to execute the program stored in the memory to perform the method of any of claims 21 to 30.
32. A computer storage medium having computer-executable instructions stored thereon for causing a computer to perform the method of any one of claims 21 to 30.
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