A wavelength selective switch and its attenuation control method

Abstract

This application provides a wavelength selective switch and its attenuation control method, belonging to the field of optical communication technology. The wavelength selective switch includes: an optical fiber array, a 4f-2f optical system, and an attenuation control system. The attenuation control system includes a blazed grating and a binary Fresnel lens. The binary Fresnel lens is superimposed on the blazed grating. The blazed grating is used to receive the optical signal transmitted by the 4f-2f optical system and generate diffraction. The binary Fresnel lens is used to adjust the defocus amount by adjusting the gray value, thereby adjusting the diffraction intensity of the optical signal and achieving optical signal attenuation. The optical fiber array is used to output the optical signal through the input port and transmit the returned optical signal to the target port. The 4f-2f optical system is used to transmit the input optical signal to the blazed grating through a deflection direction cylindrical lens. This application can not only achieve optical signal attenuation but also suppress crosstalk between non-adjacent ports caused by higher-order diffraction.

Description

Technical Field

[0001] This application belongs to the field of optical communication technology, and more specifically, relates to a wavelength selective switch and its attenuation control method. Background Technology

[0002] Wavelength selective switches (WSS) are crucial components for dynamic wavelength management and signal routing in wavelength division multiplexing (WDM) systems. In WSS systems, the selection and attenuation of optical signals are achieved through optical devices and algorithms. Currently, common attenuation methods include mechanical blocking and liquid crystal modulation. However, mechanical blocking suffers from slow response speed, insufficient accuracy, and complex structure. Conventional liquid crystal on silicon (LCoS) modulation methods suffer from other port degradation and increased insertion loss, limiting the performance improvement of WSS systems. For example, three commonly used attenuation methods are: setting up abandoned ports, stacking binary gratings, and stacking Fresnel lenses. Setting up abandoned ports for attenuation requires additional design and integration of abandoned ports in the optical path, increasing the complexity of the optical path design and reducing the number of available ports. The method of using stacked deflection direction binary gratings is prone to inducing high-order diffraction interference. While the method of stacking Fresnel lenses can achieve high isolation attenuation, the attenuation accuracy is difficult to control, and the selection of lens focal length and position is critical. These shortcomings limit the flexibility and efficiency of these methods in practical applications. Therefore, there is an urgent need for a new LCoS attenuation method that can achieve accurate and wide-range signal attenuation while maintaining insertion loss parameters and suppressing port crosstalk, so as to improve the performance and reliability of WSS systems. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the purpose of this application is to provide a wavelength selective switch and its attenuation control method, which aims to solve the problems that the method of superimposing a binary grating with a deflection direction is prone to causing high-order diffraction interference, and that although the method of superimposing a Fresnel lens can achieve high isolation attenuation, the attenuation accuracy is difficult to control.

[0004] To achieve the above objectives, in a first aspect, this application provides an attenuation control device for a wavelength selective switch, comprising: an optical fiber array, a 4f-2f optical system, and an attenuation control system;

[0005] The attenuation control system includes a blazed grating and a binary Fresnel lens; the binary Fresnel lens is superimposed on the blazed grating;

[0006] The fiber array is located at the front focal point of the deflection direction cylindrical lens in the 4f-2f optical system or at the higher-order diffraction focal point of the binary Fresnel lens; the attenuation control system is located on the rear side of the deflection direction of the 4f-2f optical system.

[0007] Blazed gratings are used to receive light signals transmitted by 4f-2f optical systems and generate diffraction; binary Fresnel lenses are used to adjust the defocus amount by adjusting the gray value, thereby adjusting the diffraction intensity of the light signal and achieving light signal attenuation.

[0008] Fiber optic arrays are used to output optical signals through input ports and transmit the returned optical signals to the target port;

[0009] The 4f-2f optical system is used to transmit the input optical signal to the blazed grating through a deflection direction column lens;

[0010] Where 4f-2f is the focal length of the deflection direction cylindrical lens.

[0011] More preferably, the fiber array is located at the +1st or -1st diffraction focus of the binary Fresnel lens.

[0012] More preferably, the binary Fresnel lens is a binary Fresnel spherical lens or a binary Fresnel cylindrical lens.

[0013] More preferably, the attenuation control system is a silicon-based liquid crystal, on which a blazed grating and a binary Fresnel lens are disposed.

[0014] More preferably, the grayscale level of the silicon-based liquid crystal is 8 bits (256). It should be noted that existing silicon-based liquid crystal products with 10 bits, 12 bits, or other grayscale levels are also acceptable.

[0015] Secondly, this application provides an attenuation control method for a wavelength selective switch, specifically:

[0016] The fiber array is placed at the front focal point of the deflection direction cylindrical lens of the 4f-2f optical system. A binary Fresnel lens is superimposed on the blazed grating. The defocusing amount of the target port is adjusted by adjusting the binary Fresnel lens, thereby adjusting the diffraction intensity of the optical signal and achieving optical signal attenuation.

[0017] Thirdly, this application provides an attenuation control method for a wavelength selective switch, specifically:

[0018] The fiber array is offset from the focal position of the deflection column lens of the 4f-2f optical system. A binary Fresnel lens is superimposed on the blazed grating. By superimposing the phase map of the binary Fresnel lens, the defocusing of the optical path is compensated, so that the target port is located at the higher-order diffraction focal position of the binary Fresnel lens.

[0019] By continuously superimposing binary Fresnel lenses of corresponding focal lengths, the defocusing of the optical path is corrected. At the same time, by changing the gray value of the binary Fresnel lenses, the intensity of multi-order diffraction is controlled, thereby achieving the attenuation effect of the optical signal.

[0020] More preferably, blazed grating diffraction generates higher-order diffracted light, and a binary Fresnel lens is introduced in the case of defocusing to cause field curvature, thereby suppressing crosstalk between non-adjacent ports introduced by higher-order diffraction.

[0021] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art:

[0022] This application provides an attenuation control device for a wavelength selective switch. A blazed grating and a binary Fresnel lens are superimposed within the silicon-based liquid crystal of the wavelength selective switch. The defocusing amount is adjusted by controlling the grayscale value of the binary Fresnel lens to achieve optical signal attenuation. Simultaneously, when the fiber array is located at the higher-order diffraction focal point of the binary Fresnel lens, the blazed grating diffracts high-order diffracted light. The introduction of this high-order diffraction light into the binary Fresnel lens under defocusing conditions causes field curvature, meaning the multi-order diffraction focal planes at the receiving end rotate, thereby suppressing crosstalk between non-adjacent ports caused by higher-order diffraction. The overall attenuation control device has the advantages of simple structure, fast response speed, and high reliability. It can be widely used in high-performance optical communication systems to improve system flexibility and stability. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the WSS system device provided in the embodiments of this application;

[0024] Figure 2 This is a schematic diagram of the diffraction principle of a binary Fresnel lens provided in an embodiment of this application;

[0025] Figure 3 This is a phase diagram of a binary Fresnel lens loaded on an LCoS provided in this application embodiment;

[0026] Figure 4 This is a schematic diagram of the first configuration of WSS provided in the embodiments of this application;

[0027] Figure 5 This is a schematic diagram of the second configuration of WSS provided in the embodiments of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0029] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0030] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more.

[0031] The technical solutions provided in the embodiments of this application will be described.

[0032] This application provides an attenuation control method for a wavelength selective switch (WSS) system. By superimposing a binary Fresnel lens on a blazed grating in the deflection direction and controlling the grayscale value of the binary Fresnel lens, precise attenuation of the optical signal in a specified channel is achieved. Simultaneously, in a defocused configuration, the multi-order diffraction focal plane of the fiber array receiver is rotated by offsetting the center of the binary Fresnel lens to suppress crosstalk between non-adjacent ports caused by higher-order diffraction. This application combines the high-precision diffraction control of the binary grating with the beam focusing capability of the binary Fresnel lens, overcoming the shortcomings of each method and achieving high-precision and high-isolation optical signal attenuation. By optimizing the phase diagram of the binary Fresnel lens and the system structure design, interference from higher-order diffraction is avoided, and the attenuation accuracy and range of the wavelength selective switch are improved.

[0033] This application provides an attenuation method for a wavelength selective switch, specifically:

[0034] Superposition of binary Fresnel lenses: A binary Fresnel lens is superimposed on the blazed grating of the wavelength selection switch. By controlling the gray value of the binary Fresnel lens, the diffraction intensity of the light signal is adjusted, thereby achieving precise attenuation of the light signal.

[0035] The grayscale control is achieved by adjusting the grayscale value of the binary Fresnel lens, which controls the intensity of the +1st order diffracted light, thereby attenuating the optical signal. The diffraction intensity of different focal orders of the binary Fresnel lens can be expressed as follows:

[0036]

[0037] Where φ0 and φ1 are two phase values ​​of the binary Fresnel lens, and Δφ = φ1 - φ0; by controlling the magnitude of Δφ, the light intensity attenuation at different diffraction focal points can be achieved.

[0038] More specifically, the two implementation configuration methods are as follows:

[0039] The first configuration involves placing the fiber array of the wavelength selective switch at the focal point of the deflection direction cylindrical lens in the 4f-2f system, and adjusting the defocusing amount of the binary Fresnel lens to achieve attenuation; where f is the focal length of the deflection direction cylindrical lens.

[0040] The second configuration involves placing the fiber array of the wavelength selective switch at the +1st order focal position of the binary Fresnel lens. Without the binary Fresnel lens, the wavelength selective switch is in a defocused configuration. The defocusing is corrected by superimposing a binary Fresnel lens of the corresponding focal length, and the +1st order diffraction intensity is controlled by changing the gray value, thereby achieving the attenuation effect of the optical signal.

[0041] Figure 1 The working principle of LCoS-WSS in two orthogonal directions was analyzed. Existing wavelength selective switches are basically based on a 4f-2f optical system configuration. That is, in the dispersion direction, it is a 4f system. The light emitted from the fiber array is collimated by a lens and enters the dispersive element, which splits it into light of different wavelengths. The light of different wavelengths then passes through a focusing lens and converges at different positions of the LCoS through different paths. At this time, the light spot is controlled by loading a phase map of two-dimensional spatial grayscale distribution onto the LCoS, and functions such as attenuation and flexible grating are completed. In the deflection direction, it is a 2f system. The position of the deflection cylindrical lens is generally located near the dispersive element. The light emitted from the fiber array is collimated by the deflection cylindrical lens and enters the LCoS. The LCoS applies a blazed grating to generate a certain deflection angle and then focuses it to the target port through a deflection mirror.

[0042] Figure 2 The working principle of a binary Fresnel lens is explained; compared to a traditional Fresnel lens, the continuous curvature change of a binary Fresnel lens is replaced by a binary step, which introduces multi-order diffraction similar to a binary grating during the lens focusing process; the formulas for the focal length and Fresnel ring radius of a binary Fresnel lens are the same as those for a traditional Fresnel lens, and can be expressed as:

[0043]

[0044] Among them, f m r represents the diffraction focus of order m; r1 represents the radius of the first-order Fresnel ring; the diffraction field of a binary Fresnel lens can be expressed as:

[0045]

[0046] It can be seen that a binary Fresnel lens only exhibits diffraction at odd orders. Figure 2 The diffraction positions for the +1st and ±3rd orders are given in the previous paper, and the diffraction efficiency for each order is given in this application; r is the polar coordinate of the diffracted light field, f1 is the focal length of the first order diffraction, λ is the wavelength of the incident light, and odd indicates the odd diffraction order.

[0047] Figure 3This paper presents a method for loading a binary Fresnel lens onto an LCoS (Liquid Crystal on Silicon), with a binary Fresnel spherical lens above and a binary Fresnel cylindrical lens below, both with a focal length of 100mm. The grayscale values ​​corresponding to the binary phases φ0 and φ1 are set as G0 and G1, respectively, and the grayscale difference corresponding to Δφ is ΔG; G0 = 0, G1 = 128; at this point, the first-order diffraction intensity is maximized. In existing WSS devices, the small spot size in the dispersion direction makes it difficult to modulate using a periodic phase diagram. Therefore, this application attenuates the light in the deflection direction. In practical applications, a binary Fresnel cylindrical lens is generally used for attenuation. The grayscale level of the LCoS is set to 256.

[0048] Figure 4 This is a schematic diagram of the wavelength selection switch operation in the first configuration. At this time, the fiber array is located at the focal point of the deflection direction cylindrical lens of the 4f-2f system. Attenuation is achieved by adjusting Δφ of the binary Fresnel lens. When the binary Fresnel lens is not applied or Δφ = 0, the beam is normally deflected to the target port. As ΔG corresponding to Δφ changes from 0 to 128, the energy deflected to the target port is gradually transferred to other diffraction focal points, thereby achieving signal attenuation.

[0049] Figure 5 This is a schematic diagram of WSS operation under the second configuration. In this configuration, the fiber array deviates from the focal position of the deflection cylindrical lens in the 4f-2f system. By superimposing the phase diagram of the binary Fresnel lens, the defocusing of the optical path is compensated, ensuring the target port is precisely located at the +1st order diffraction focal position of the binary Fresnel lens. A binary Fresnel lens of the corresponding focal length is superimposed to correct system defocusing. Simultaneously, the +1st order diffraction intensity is controlled by changing the grayscale value, achieving an attenuation effect on the optical signal. Meanwhile, for the higher-order diffracted light generated by the diffraction grating, the introduction of the binary Fresnel lens in the defocusing situation causes field curvature, i.e., the multi-order diffraction focal planes at the receiving end rotate, thereby suppressing crosstalk between non-adjacent ports caused by higher-order diffraction. Furthermore, if the center offset of the binary Fresnel lens is introduced at this point, port crosstalk can be further suppressed while maintaining high-precision attenuation.

[0050] Example 1

[0051] In the first configuration, the fiber array is placed at the focal point of the cylindrical lens of the 4f-2f system. The optical signal is attenuated by superimposing a binary Fresnel lens on the blazed grating and adjusting its defocus. This method can precisely control the attenuation and is suitable for application scenarios that require high-precision attenuation.

[0052] Example 2

[0053] In the second configuration, the fiber array is placed at the +1st order focal position of the binary Fresnel lens. By utilizing its inherent defocus configuration, the intensity of the +1st order diffraction is controlled by controlling the gray value of the binary Fresnel lens, while suppressing higher-order crosstalk in the system and achieving signal attenuation with high isolation. This method changes the traditional system structure and is suitable for attenuation scenarios with high isolation requirements.

[0054] This application achieves high-precision attenuation and high-order crosstalk suppression of optical signals by introducing a binary Fresnel lens into a wavelength selection switch. It has the advantages of simple structure, fast response speed and high reliability. This method can be widely used in high-performance optical communication systems to improve the system's flexibility and stability.

[0055] Alternative methods: This attenuation method mainly uses a deflection method with a binary Fresnel cylindrical lens for attenuation. In some wavelength selection switches, binary Fresnel spherical lenses and dispersion-direction binary Fresnel cylindrical lenses can also be used. In the attenuation configuration based on Example 2, +1 order diffraction is not necessarily used as defocus compensation; -1 order, +3 order, etc. can also be used for attenuation. In order to achieve better crosstalk suppression, the center offset of the binary Fresnel lens can be introduced or the center offset of the binary Fresnel lens can be used directly to replace the blazed grating for deflection.

[0056] In summary, this application has the following advantages compared with the prior art:

[0057] High-precision attenuation: By controlling the gray value of the binary Fresnel lens, the gray gradient directly affects the attenuation step, thus achieving high-precision attenuation of the optical signal.

[0058] Crosstalk suppression: In the case of defocus configuration, superimposing a binary Fresnel lens can rotate the multi-order diffraction focal plane of the fiber array receiver, suppressing crosstalk between non-adjacent ports caused by higher-order diffraction.

[0059] Simplified structure: Eliminating the need for mechanical apertures and complex iterative algorithms simplifies the structure of the wavelength selective switching system and improves the system's reliability and stability.

[0060] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A wavelength selective switch, characterized in that, include: Fiber array, 4f-2f optical system and attenuation control system; The attenuation control system includes a blazed grating and a binary Fresnel lens; the binary Fresnel lens is superimposed on the blazed grating; The fiber array is located at the front focal point of the deflection direction cylindrical lens in the 4f-2f optical system or at the higher-order diffraction focal point of the binary Fresnel lens; the attenuation control system is located on the rear side of the deflection direction of the 4f-2f optical system. The blazed grating is used to receive the optical signal transmitted by the 4f-2f optical system and generate diffraction; the binary Fresnel lens is used to adjust the defocus of the target port by adjusting its own gray value, thereby adjusting the diffraction intensity of the optical signal and achieving optical signal attenuation; the fiber array is used to output the optical signal through the input port and transmit the returned optical signal to the target port; the 4f-2f optical system is used to transmit the input optical signal to the blazed grating through the deflection direction cylindrical lens; where f is the focal length of the deflection direction cylindrical lens.

2. The wavelength selective switch according to claim 1, characterized in that, The fiber array is located at the +1st or -1st diffraction focus of the binary Fresnel lens.

3. The wavelength selective switch according to claim 1 or 2, characterized in that, A binary Fresnel lens is either a binary Fresnel spherical lens or a binary Fresnel cylindrical lens.

4. The wavelength selective switch according to claim 1, characterized in that, The attenuation control system is a silicon-based liquid crystal with a blazed grating and a binary Fresnel lens.

5. An attenuation control method based on the wavelength selective switch according to claim 1, characterized in that, Specifically: The fiber array is placed at the front focal point of the deflection direction cylindrical lens of the 4f-2f optical system. A binary Fresnel lens is superimposed on the blazed grating. The defocusing amount of the target port is adjusted by adjusting the binary Fresnel lens, thereby adjusting the diffraction intensity of the optical signal and achieving optical signal attenuation.

6. An attenuation control method based on the wavelength selective switch according to claim 1, characterized in that, Specifically: The fiber array is offset from the focal position of the deflection column lens of the 4f-2f optical system. A binary Fresnel lens is superimposed on the blazed grating. By superimposing the phase map of the binary Fresnel lens, the defocusing of the optical path is compensated, so that the target port is located at the higher-order diffraction focal position of the binary Fresnel lens. By continuously superimposing binary Fresnel lenses of corresponding focal length, the defocus of the optical path is corrected. At the same time, by changing the gray value of the binary Fresnel lens, the intensity of multi-order diffraction is controlled, thereby achieving the attenuation effect of the optical signal.

7. The attenuation control method according to claim 6, characterized in that, Blazed grating diffraction generates higher-order diffracted light. When defocused, a binary Fresnel lens is introduced to cause field curvature, which suppresses crosstalk between non-adjacent ports introduced by higher-order diffraction.

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