A method for suppressing crosstalk of a wavelength selective switch and a wavelength selective switch

Abstract

This invention discloses a crosstalk suppression method and a wavelength selective switch, belonging to the field of optical communication technology. Addressing the problems in existing technologies where the first-order diffraction efficiency of the phase diffraction grating formed on the LCoS surface of a silicon-based liquid crystal (LCoS) affects the insertion loss and increases signal crosstalk in WSSs, this invention provides a crosstalk suppression method and a wavelength selective switch. Along the beam direction, the switch consists of an ITO glass layer, an alignment layer, a liquid crystal region layer, another alignment layer, and a high-reflectivity layer. By altering the beam phase through the ITO glass, liquid crystal region layer, and high-reflectivity layer, and by setting a phase diffraction grating with a specific period, the beam direction of different wavelengths is deflected, thereby achieving port switching and effectively avoiding signal crosstalk between ports.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and more specifically, to a method for suppressing crosstalk in a wavelength selective switch and a wavelength selective switch. Background Technology

[0002] Reconfigurable optical add-drop multiplexers (ROADMs) can switch, attenuate, or block optical signals of any wavelength or wavelength combination at any communication port in optical communication networks, making them core optical switching devices for flexible scheduling in optical communication networks. Wavelength selective switches (WSS) are the core modules for realizing the functions of ROADM systems. Based on their technical principles, WSSs are mainly divided into those based on liquid crystal on silicon (LCoS), liquid crystal (LC), and micro-electro-mechanical systems (MEMS). Among them, WSSs based on LCoS technology feature flexible grid configuration, meaning that the communication center frequency and bandwidth can be flexibly set, thus gradually becoming the mainstream in market applications.

[0003] In WSS based on silicon-based liquid crystal LCoS technology, in addition to the coupling efficiency of the optical system, the magnitude of the first-order diffraction efficiency of the phase diffraction grating formed on the silicon-based liquid crystal LCoS surface directly determines the insertion loss of the WSS. At the same time, the higher-order diffraction energy of the phase diffraction grating can cause signal crosstalk between different wavelengths or different ports, affecting the isolation and crosstalk performance of the WSS.

[0004] A search revealed Chinese patent application No. 201210118299.1, filed on April 20, 2012, which discloses a wavelength selective switch based on LCOS and a method for reducing inter-port crosstalk. This invention calculates the diffraction characteristics of LCOS, designs the focal length of the wavelength selective switch optical path and the spacing between the fiber array ports, and adjusts the phase of the pixels in the LCOS region corresponding to each wavelength. This allows the optical signal with the minimum deflection angle θ1 to be output to any designated port of the fiber array, minimizing the arrival of other wavelengths at the output port, thus reducing inter-port crosstalk. However, this scheme does not consider that the phase curve of the phase diffraction grating formed by the actual silicon-based liquid crystal LCoS will deviate from the theoretical value, resulting in a decrease in diffraction efficiency and increased signal crosstalk. Summary of the Invention

[0005] 1. Technical problems to be solved

[0006] To address the problems in existing technologies where the first-order diffraction efficiency of the phase diffraction grating formed on the LCoS surface of a silicon-based liquid crystal (LCoS) affects the insertion loss and increases signal crosstalk in a WSS, this invention provides a crosstalk suppression method and a wavelength selective switch. By changing the phase of the light beam through ITO glass, a liquid crystal region layer, and a high-reflectivity layer, and by setting a phase diffraction grating with a specific period, the direction of the light beam at different wavelengths can be deflected, thereby achieving port switching and effectively avoiding signal crosstalk between ports.

[0007] 2. Technical Solution

[0008] The objective of this invention is achieved through the following technical solutions.

[0009] A wavelength selective switch includes a silicon-based liquid crystal (LCoS), wherein the LCoS includes an ITO glass, a high reflectivity layer, and a substrate, the ITO glass and the substrate are spaced apart, the high reflectivity layer is disposed between the ITO glass and the substrate, and a plurality of equally spaced pixels are disposed on one side of the substrate.

[0010] Furthermore, an alignment layer is provided on one side of the ITO glass, and an alignment layer is provided on the side of the high reflectivity layer closest to the ITO glass.

[0011] Furthermore, a liquid crystal region layer is disposed between the ITO glass and the high reflectivity layer.

[0012] Furthermore, along the beam direction, the layers are sequentially ITO glass, alignment layer, liquid crystal region layer, alignment layer, and high reflectivity layer.

[0013] Furthermore, the light beam is incident on the ITO glass, passes through the liquid crystal region layer and enters the high reflectivity layer, where it is reflected. After passing through the liquid crystal region layer, the light beam exits through the ITO glass.

[0014] A crosstalk suppression method based on the wavelength selective switch involves applying a voltage difference between the ITO glass and the pixel to form an electric field. The liquid crystal in the liquid crystal region layer is deflected by the electric field, and the deflection of the liquid crystal changes the refractive efficiency of the liquid crystal region layer.

[0015] Furthermore, an electric field is formed by applying a voltage difference between the ITO glass and a single pixel. The liquid crystal orientation in the liquid crystal region layer between the single pixel and the ITO glass is deflected, while the liquid crystal orientation in the liquid crystal region layer between the pixels on both sides of the single pixel and the ITO glass is not deflected.

[0016] Furthermore, a phase diffraction grating is set on the silicon-based liquid crystal (LCoS) surface to achieve different optical path direction deflections; the phase diffraction grating is composed of pixels, and the diffraction efficiency of the phase diffraction grating is:

[0017]

[0018] Where η represents the diffraction efficiency of the phase diffraction grating, and q represents the number of pixels contained in a single phase diffraction grating period.

[0019] Furthermore, the pixel phase distribution within a single period of the phase diffraction grating is adjusted to improve the diffraction efficiency η of the phase diffraction grating.

[0020] Furthermore, the formula for the pixel phase distribution within a single period of the phase grating is:

[0021]

[0022] Where x represents the pixel sequence number of the silicon-based liquid crystal LCoS, and P represents the number of pixels in a single period of the phase diffraction grating. Indicates the pixel phase, and A represents the slope factor. This represents the phase depth translation factor.

[0023] 3. Beneficial effects

[0024] Compared with the prior art, the advantages of this invention are:

[0025] This invention provides a method for suppressing crosstalk in a wavelength selective switch and a wavelength selective switch. An electric field is formed by applying a voltage between the ITO glass and the pixel. This electric field alters the deflection direction of the liquid crystal in the liquid crystal region layer, thereby changing the phase of the light beam. By setting a phase diffraction grating with a specific period, the beam direction of different wavelengths can be deflected, thus achieving port switching. This improves the first-order diffraction efficiency of the phase diffraction grating and reduces the diffraction efficiency of other orders, effectively reducing signal crosstalk between the WSS wavelength and ports, improving the overall performance of the WSS, and demonstrating strong practicality and wide applicability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall structure of silicon-based liquid crystal (LCoS).

[0027] Figure 2 This is a diagram of the liquid crystal region layer structure after applying voltage to the second pixel in the embodiment.

[0028] Figure 3 This is an electric field diagram of the liquid crystal region layer after applying voltage to the second pixel in the embodiment;

[0029] Figure 4 This is a diagram showing the liquid crystal region layer structure of the first, second, and third pixels after a voltage is applied to the second pixel in an embodiment.

[0030] Figure 5 The above is an electric field diagram of the liquid crystal region layer of the first pixel, the second pixel, and the third pixel after applying voltage to the second pixel in the embodiment.

[0031] Figure 6 For the example, phase diffraction gratings with different periods and widths are formed on the silicon-based liquid crystal LCoS surface by input wavelength light spots;

[0032] Figure 7 This is a diagram showing the shape of the phase diffraction grating for a silicon-based liquid crystal (LCoS) in an embodiment.

[0033] Figure 8 This is a diagram showing the shape of the phase diffraction grating of the silicon-based liquid crystal LCoS in the embodiment.

[0034] Figure 9 The diffraction efficiency diagram of the silicon-based liquid crystal LCoS phase diffraction grating is shown in the example.

[0035] Figure 10 Comparison of phase diffraction grating shapes for silicon-based liquid crystal LCoS in the embodiments;

[0036] Figure 11 The pixel phase distribution diagram within a single period of the silicon-based liquid crystal LCoS phase diffraction grating was adjusted for the example.

[0037] Figure 12 This is a diagram of the phase diffraction grating structure of a silicon-based liquid crystal (LCoS) as an example.

[0038] The following are the labels in the diagram: 1. ITO glass; 2. Alignment layer; 3. Liquid crystal region layer; 31. Liquid crystal; 4. High reflectivity layer; 5. Pixel; 51. First pixel; 52. Second pixel; 53. Third pixel; 6. Substrate; 7. Silicon-based liquid crystal LCoS surface; 8. Phase diffraction grating; 9. Wavelength spot. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0040] Example

[0041] like Figure 1 The image shows a wavelength selective switch provided in this embodiment. The wavelength selective switch includes a silicon-based liquid crystal (LCoS), which includes an ITO glass 1, a high reflectivity layer 4, and a substrate 6. The ITO glass 1 and the substrate 6 are spaced apart, and the high reflectivity layer 4 is disposed between the ITO glass 1 and the substrate 6. A plurality of equally spaced pixels 5 are disposed on one side of the substrate 6.

[0042] Specifically, in this embodiment, the silicon-based liquid crystal LCoS includes an ITO glass 1, an alignment layer 2, a liquid crystal region layer 3, a high reflectivity layer 4, a pixel 5, and a substrate 6.

[0043] The ITO glass 1 and the substrate 6 are spaced apart. In this embodiment, the ITO glass 1 serves as a transparent common electrode. The high-reflectivity layer 4 is disposed between the ITO glass 1 and the substrate 6. A liquid crystal region layer 3 is disposed between the ITO glass 1 and the high-reflectivity layer 4, and the liquid crystal region layer 3 contains liquid crystal 31. An alignment layer 2 is disposed on one side of the ITO glass 1, and an alignment layer 2 is disposed on the side of the high-reflectivity layer 4 near the ITO glass 1. In this embodiment, the alignment layer 2 is used to anchor the crystal axis direction of the liquid crystal 31 in the liquid crystal region layer 3. A plurality of equally spaced pixels 5 are disposed on one side of the substrate 6. In this embodiment, the pixels 5 are composed of a photosensitive element CMOS structure, and the pixels 5 include a first pixel 51, a second pixel 52, and a third pixel 53.

[0044] Therefore, this embodiment provides a wavelength selective switch, which, along the beam direction, consists of an ITO glass 1, an alignment layer 2, a liquid crystal region layer 3, an alignment layer 2, and a high-reflectivity layer 4. The beam is incident on the ITO glass 1, passes through the liquid crystal region layer 3, and then enters the high-reflectivity layer 4. The high-reflectivity layer 4 reflects the beam, and after passing through the liquid crystal region layer 3, the beam exits through the ITO glass 1. This applies a voltage between the ITO glass 1 and the pixel 5 to form an electric field. The electric field alters the deflection direction of the liquid crystal 31 in the liquid crystal region layer 3, thereby changing the phase of the beam.

[0045] like Figure 2-12 As shown, in this embodiment, a crosstalk suppression method based on the wavelength selective switch is implemented by applying a voltage difference between the ITO glass 1 and the pixel 5 to form an electric field. The liquid crystal 31 in the liquid crystal region layer 3 is deflected by the electric field, thereby changing the refractive efficiency of the liquid crystal region layer 3 and thus changing the optical path, thereby changing the phase of the light beam. Further, by applying a voltage difference between the ITO glass 1 and a single pixel 5, the direction of the liquid crystal 31 in the liquid crystal region layer 3 between the single pixel 5 and the ITO glass 1 is deflected, while the direction of the liquid crystal 31 in the liquid crystal region layer 3 between the pixels 5 on both sides of the single pixel 5 and the ITO glass 1 is not deflected. In this embodiment, as... Figure 3 As shown, a voltage difference is applied between the ITO glass 1 and the second pixel 52, forming an electric field between them. This causes the orientation of the liquid crystal 31 in the liquid crystal region layer 3 between the ITO glass 1 and the second pixel 52 to deflect. Simultaneously, the orientation of the liquid crystal 31 in the liquid crystal region layer 3 between the first pixel 51 and the third pixel 53 on both sides of the second pixel 52 and the ITO glass 1 does not deflect. Figure 2As shown, an electric field is formed by applying a voltage difference between the second pixel 52 and the ITO glass 1, causing the crystal axis of the liquid crystal 31 in the liquid crystal region layer 3 to deflect. No voltage difference is applied between the first pixel 51, the third pixel 53, and the ITO glass 1, so the crystal axis of the liquid crystal 31 in the liquid crystal region layer 3 does not deflect and maintains its original anchoring direction. Thus, the refractive efficiency of the light beam passing through the liquid crystal region layer 3 corresponding to pixel 5 is independently controlled, thereby changing the phase of the light beam.

[0046] It is important to note that, such as Figure 5 The diagram shows the electric field shape of the second pixel 52 corresponding to the liquid crystal layer 3 in a silicon-based liquid crystal LCoS under actual operation. It can be seen that part of the electric field extends to the first pixel 51 and the third pixel 53 adjacent to the second pixel 52, thus generating the edge field effect of the silicon-based liquid crystal LCoS. Figure 4 As shown, the edge field effect of the silicon-based liquid crystal LCoS causes the crystal axis of the liquid crystal 31 in the liquid crystal region layer 3 between the first pixel 51 and the third pixel 53 and the ITO glass 1 to deflect, thereby affecting the beam phase of the second pixel 52.

[0047] Therefore, as Figure 6 As shown, in this embodiment, a phase diffraction grating 8 is set on the silicon-based liquid crystal LCoS surface 7 to achieve different optical path direction deflections. Specifically, phase diffraction gratings 8 with different periods and widths are formed on the silicon-based liquid crystal LCoS surface 7 corresponding to the input wavelength light spot 9. In this embodiment, the width direction of the phase diffraction grating 8 represents the wavelength bandwidth, and the center position represents the center frequency f. The phase diffraction grating 8 is composed of pixels 5. It should be noted that in this embodiment, the phase diffraction grating 8 is composed of multiple pixels 5 with fixed sizes. The diffraction efficiency of the phase diffraction grating 8 is:

[0048]

[0049] Where η represents the diffraction efficiency of the phase diffraction grating 8, and q represents the number of pixels 5 contained in a single period of the phase diffraction grating 8. For example... Figure 7 The diagram shows the shape of the phase diffraction grating 8. In this embodiment, the phase diffraction grating 8 is preferably arranged in a regular triangular pattern, which maximizes its diffraction efficiency η. Therefore, by setting a specific period for the phase diffraction grating 8, beam deflection at different wavelengths can be achieved, thereby enabling port switching. Figure 8 As shown, the diffraction efficiency η, grating shape, and the number of constituent pixels 5 of the phase diffraction grating 8 are all related. Figure 9 As shown, as the number of pixels 5 increases within a single period, the diffraction efficiency η of the phase diffraction grating 8 also gradually increases.

[0050] It should be noted that in this embodiment... Figure 9The diffraction efficiency η of the phase diffraction grating 8 does not take into account the edge field effect of the silicon-based liquid crystal LCoS. However, in actual operation, the shape of the phase diffraction grating 8 will be deformed due to the edge field effect of the silicon-based liquid crystal LCoS. Figure 10 As shown, 'a' represents the shape of the phase diffraction grating 8 under ideal conditions, i.e., without the influence of the edge field of the silicon-based liquid crystal LCoS; 'b' represents the shape of the phase diffraction grating 8 after being affected by the edge field of the silicon-based liquid crystal LCoS. When the shape of the phase diffraction grating 8 deviates from the ideal shape, it leads to a decrease in the first-order diffraction efficiency of the phase diffraction grating 8, thereby affecting the insertion loss of the WSS. Simultaneously, the decrease in the first-order diffraction efficiency of the phase diffraction grating 8 causes energy to be transferred to other higher diffraction orders, resulting in signal crosstalk between different wavelengths and different ports of the WSS, thus affecting the performance of the WSS. It should be noted that in this embodiment, the ideal shape refers to the phase diffraction grating 8 of the silicon-based liquid crystal LCoS having a regular triangular structure, and the phase difference between the maximum and minimum phases within a single period of the phase diffraction grating 8 being 2π, where π represents the phase unit.

[0051] In this embodiment, the influence of the edge field effect of the silicon-based liquid crystal LCoS between the first pixel 51, the second pixel 52, and the third pixel 53 is related to factors such as the difference in electric field between pixels 5, the thickness of the liquid crystal layer 3, the physical spacing between pixels 5, the size of pixels 5, and the starting voltage of pixels 5. Therefore, for the phase diffraction grating 8, under the same conditions, the more pixels 5 in a single period, the less the first-order diffraction efficiency of the phase diffraction grating 8 is affected by the edge field effect of the silicon-based liquid crystal LCoS; conversely, the fewer pixels 5 in a single period, the greater the influence of the edge field effect of the phase diffraction grating 8 on the first-order diffraction efficiency of the phase diffraction grating 8. Therefore, it is necessary to reduce the influence of the edge field effect of the silicon-based liquid crystal LCoS on the shape of the phase diffraction grating 8. In this embodiment, based on the law of the influence of the edge field effect of the silicon-based liquid crystal LCoS on the shape of the phase diffraction grating 8, an inverse compensation method is adopted to make the phase diffraction grating 8 affected by the edge field of the silicon-based liquid crystal LCoS closer to the ideal shape. Specifically, based on the established phase curve, the voltage of pixel 5 at lower voltage locations is further reduced, while the voltage of pixel 5 at higher voltage locations is increased, thereby making the shape of the phase diffraction grating 8 closer to the ideal shape. It is worth noting that the higher the voltage of pixel 5, the greater the electric field of the liquid crystal layer 3 corresponding to that pixel 5, and the stronger the phase modulation capability.

[0052] like Figure 11 As shown, c represents the adjusted phase setting of pixel 5, and d represents the shape of the phase diffraction grating 8 after being affected by the edge field effect of LCoS (Liquid Crystal on Silicon). By readjusting the phase distribution of pixel 5 within a single period of the phase diffraction grating 8, the phase distribution of the phase diffraction grating 8 after being affected by the edge field effect of LCoS is made close to the ideal shape.

[0053] By setting the 5th phase of pixels within a single period, the difference between the phase diffraction grating 8 formed by the silicon-based liquid crystal LCoS and its ideal shape is corrected, so that the actual phase arrangement of the phase diffraction grating 8 under the influence of the edge field effect of the silicon-based liquid crystal LCoS is close to the ideal value, thereby improving the first-order diffraction efficiency of the phase diffraction grating 8. It should be noted that, in practical applications, the influence trend of the edge field effect of the silicon-based liquid crystal LCoS can be determined, but the degree of influence is difficult to measure accurately. Therefore, it is necessary to use a specific data function for correction, and at the same time, the diffraction efficiency of the phase diffraction grating 8 is detected for confirmation. In this embodiment, correction can be performed by mathematical functions such as the tangent function and the inverse cosine function. The characteristic of this mathematical function is that it gradually deviates from linearity at both ends with the midline as the center, and the deviation directions are opposite. Furthermore, the distribution of the 5th phase of pixels within a single period of the phase diffraction grating 8 is adjusted to improve the diffraction efficiency η of the phase diffraction grating 8. Further, the formula for the distribution of the 5th phase of pixels within a single period of the phase diffraction grating 8 is:

[0054]

[0055] Where x represents the pixel sequence number of the silicon-based liquid crystal LCoS, and P represents the number of pixels 5 in a single period of the phase diffraction grating 8. This indicates the 5th phase of a pixel, and A represents the slope factor. This represents the phase depth shift factor. In this embodiment, the number P of pixels 5 within a single period of the phase diffraction grating 8 is selected as 20, the slope factor A is selected as 1, and the phase depth shift factor is selected as... The value is 1.55, thus forming the shape of the phase diffraction grating 8. Therefore, as... Figure 12 As shown, m represents the 5-phase setting curve of the pixel, and n represents the actual 5-phase curve of the pixel under the influence of the edge field effect of silicon-based liquid crystal LCoS. The slope factor A and the phase depth shift factor are adjusted. The shape of the 5-phase setting curve m can be adjusted in real time, and the parameters can be corrected by testing the diffraction efficiency η of the phase diffraction grating 8, so that the actual 5-phase curve of the pixel is close to the shape of the 5-phase setting curve m. In this embodiment, the single-grating periodic phase depth of the 5-phase setting curve m is 2π, and it is close to a linear distribution.

[0056] Therefore, the crosstalk suppression method for wavelength selective switches provided in this embodiment achieves beam direction deflection of different wavelengths by setting a phase diffraction grating 8 with a specific period, thereby realizing port switching, reducing the influence of edge field effect of silicon-based liquid crystal LCoS, improving the first-order diffraction efficiency of phase diffraction grating 8, reducing the diffraction efficiency of other orders of phase diffraction grating 8, effectively reducing signal crosstalk between WSS wavelengths and ports, improving the overall performance of WSS, and has strong practicality and wide applicability.

[0057] The invention and its embodiments have been described above illustratively. This description is not restrictive, and the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. The accompanying drawings are only one embodiment of the invention, and the actual structure is not limited thereto. No reference numerals in the claims should limit the scope of the claims. Therefore, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of the invention, such design should fall within the scope of protection of this patent. Furthermore, the word "comprising" does not exclude other elements or steps, and the word "a" preceding an element does not exclude the inclusion of "a plurality" of that element. Multiple elements stated in the product claims may also be implemented by a single element through software or hardware. The terms "first," "second," etc., are used to indicate names and do not indicate any specific order.

Claims

1. A method for suppressing crosstalk in a wavelength selective switch, characterized in that, An electric field is formed by applying a voltage difference between the ITO glass (1) and a single pixel (5); the liquid crystal (31) in the liquid crystal region layer (3) is deflected by the electric field; the deflection of the liquid crystal (31) changes the refractive efficiency of the liquid crystal region layer (3), and phase diffraction gratings (8) with different periods and widths are formed on the silicon-based liquid crystal LCoS surface (7) corresponding to the light spot of the input wavelength, and the voltage applied to the pixels with the largest and smallest phases corresponding to the period of the diffraction grating is corrected; Among them, the phase diffraction grating (8) affected by the edge field of silicon-based liquid crystal LCoS is made close to the ideal shape by using the anti-compensation method; based on the phase curve, the voltage of the pixel (5) at the lower voltage is reduced and the voltage of the pixel (5) at the higher voltage is increased so that the shape of the phase diffraction grating (8) is close to the ideal shape. The phase distribution formula of the pixel (5) within a single period of the phase diffraction grating (8) is as follows: φ = A × tan(xP / 2) + Δφ; Where x represents the sequence number of the pixel (5) of the silicon-based liquid crystal LCoS; P represents the number of pixels (5) in a single period of the phase diffraction grating (8); φ represents the phase of the pixel (5); A represents the slope factor; and Δφ represents the phase depth shift factor.

2. The crosstalk suppression method for a wavelength selective switch according to claim 1, characterized in that, An electric field is formed by applying a voltage difference between the ITO glass (1) and the individual pixel (5); the direction of the liquid crystal (31) in the liquid crystal region layer (3) between the individual pixel (5) and the ITO glass (1) is deflected, while the direction of the liquid crystal (31) in the liquid crystal region layer (3) between the individual pixel (5) and the ITO glass (1) on both sides of the individual pixel (5) is not deflected.

3. The crosstalk suppression method for a wavelength selective switch according to claim 1, characterized in that, The phase diffraction grating (8) is set on the silicon-based liquid crystal LCoS surface (7) to achieve different optical path direction deflection; the phase diffraction grating (8) is composed of the pixels (5), and the diffraction efficiency of the phase diffraction grating (8) is: ； Wherein, η represents the diffraction efficiency of the phase diffraction grating (8); q represents the number of pixels (5) contained in a single period of the phase diffraction grating (8); where q has the same meaning as P in the phase distribution formula of the pixels (5) in a single period of the phase diffraction grating (8).

4. The crosstalk suppression method for a wavelength selective switch according to claim 1, characterized in that, Adjust the phase distribution of the pixel (5) within a single period of the phase diffraction grating (8) to improve the diffraction efficiency η of the phase diffraction grating (8).

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