A wavelength selective switch and method based on two-dimensional dispersion

Abstract

The present invention discloses a wavelength selection switch and method based on two-dimensional dispersion, comprising: a collimating fiber array arranged in a horizontal one-dimensional form; a virtual image phase array disposed behind the collimating fiber array; a Fourier lens disposed behind the virtual image phase array; an optical lens assembly disposed behind the Fourier lens, the optical lens assembly and the Fourier lens being located on the same optical axis; and a liquid crystal on silicon optical switch disposed behind the optical lens assembly, the end face of the liquid crystal on silicon optical switch being arranged opposite the mirror surface of the optical lens assembly. The present invention utilizes a virtual image phase array with two-dimensional dispersion characteristics to replace a one-dimensional dispersion device, allowing the wavelength signal to be spread out in a two-dimensional plane, thereby improving the performance of the wavelength selection device.

Description

Technical Field

[0001] The present invention relates to the field of wavelength selective switches, and in particular to a wavelength selective switch and method based on two-dimensional dispersion. Background Art

[0002] Ever since Charles Kao, the "Father of Fiber Optics," theoretically demonstrated the feasibility of long-distance, high-capacity communications using optical fiber as a transmission medium, the field of optical fiber communications has experienced explosive growth, culminating in the first commercial fiber-optic communication system in 1977. Today, modern optical fiber communication systems are deployed worldwide. However, with the widespread adoption of mobile internet and the development of emerging technologies such as the Internet of Things, cloud computing, and big data analytics, demands for higher communication capacity and data transmission rates are increasing. Wavelength division multiplexing (WDM), a key technology in modern optical fiber communication networks, significantly increases network transmission capacity at the wavelength dimension.

[0003] The widespread adoption of wavelength division multiplexing (WDM) has also spawned another technology: the reconfigurable optical add / drop multiplexer (ROADM). ROADMs enable telecommunications operators to implement wavelength-level path scheduling and recovery at network nodes, significantly improving network reconfigurability and robustness. Furthermore, ROADM systems exchange wavelength information at an all-optical level, bypassing traditional optical-to-electrical-to-optical conversion. This effectively reduces system power consumption while eliminating the need for complex modulation schemes. Therefore, ROADMs are a key technology for realizing all-optical networks. ROADMs have a history of over two decades, with their first commercialization around 2000. The first generation of ROADMs, based on wavelength blockers (WBs), offered a simple structure, low cost, and high modularity. However, the system required external fixed filters to implement fixed-wavelength optical switching, preventing dynamic reconfiguration of upstream and downstream wavelengths. The second-generation ROADM is based on Planar Lightwave Circuit (PLC) technology. It's a silicon-based integrated circuit that integrates a demultiplexer, optical switch, attenuator, and multiplexer on a single chip. While commercialization costs are low, it suffers from the same drawback as the first generation: it cannot dynamically reconfigure wavelengths. The third-generation ROADM emerged, with its core technology being the Wavelength Selective Switch (WSS). This technology can switch any wavelength channel at an input port to any output port, enabling dynamic wavelength reconfiguration in all-optical networks.

[0004] To meet the requirements for reconfigurability and flexibility in network operations and maintenance, ROADMs must be wavelength-independent, direction-independent, and contention-free. To this end, WSS, a key ROADM component, is undergoing continuous innovation. Currently, there are three mainstream solutions for implementing WSS, fundamentally differentiated by their optical switch technology: microelectromechanical mirrors (MEMS) systems, liquid crystal (LC), and liquid crystal on silicon (LCoS) optical switches. MEMS systems utilize a large number of micromirrors as optical path control elements, resulting in poor system stability and high power consumption, making it difficult to achieve specifications exceeding 20 ports. Furthermore, the large physical size of the mirrors limits the adjustable channel bandwidth. In contrast, LC optical switches offer greater stability, but the thicker stacked liquid crystal layers make it difficult to precisely focus the beam at the desired depth, limiting the channel bandwidth accuracy of high-port WSSs. LCoS technology, with its ultra-large port count and flexible grid capabilities, has become the mainstream technology of choice in the industry. LCoS-based ROADMs, coupled with WSS (World Wide Web Service), offer wavelength independence, directionality independence, contention independence, and flexible grid functionality (also known as CDCF ROADMs), making them the most promising all-optical switching systems. In recent years, WSS research has focused on achieving higher port counts, more flexible grids, and wider bandwidths while maintaining optimal loss and crosstalk performance.

[0005] Therefore, the existing technology needs to be improved. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that, in view of the defects of the prior art, the present invention provides a wavelength selective switch and method based on two-dimensional dispersion to improve the performance of the wavelength selective switch.

[0007] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0008] In a first aspect, the present invention provides a wavelength selective switch based on two-dimensional dispersion, the wavelength selective switch based on two-dimensional dispersion comprising:

[0009] a collimating optical fiber array, wherein the collimating optical fiber array is arranged in a transverse one-dimensional form;

[0010] A virtual image phase array, the virtual image phase array being arranged behind the collimating optical fiber array;

[0011] A Fourier lens, the Fourier lens being arranged behind the virtual image phase array;

[0012] an optical lens group, wherein the optical lens group is disposed behind the Fourier lens, and the optical lens group and the Fourier lens are located on the same optical axis;

[0013] and a liquid crystal on silicon optical switch, wherein the liquid crystal on silicon optical switch is arranged behind the optical lens group, and an end face of the liquid crystal on silicon optical switch is arranged opposite to the mirror surface of the optical lens group;

[0014] After passing through the virtual image phase array, the composite light inputted by the collimating fiber array is linearly dispersed in the longitudinal direction and forms a plane dispersion through the Fourier lens and the optical lens group, so as to be selectively reflected on the silicon-based liquid crystal optical switch and enter the output end of the collimating fiber array.

[0015] In one implementation, the wavelength selective switch based on two-dimensional dispersion further includes:

[0016] A cylindrical lens is provided between the collimating fiber array and the virtual image phase array. The composite light emitted from the collimating fiber array is subjected to beam waist shaping by the cylindrical lens, and the shaped signal light enters the virtual image phase array.

[0017] In one implementation, the wavelength selective switch based on two-dimensional dispersion further includes:

[0018] A diffraction grating is provided between the lenses of the optical lens group, and the diffraction grating, the Fourier lens and the optical lens group are located on the same optical axis.

[0019] In one implementation, the optical lens assembly includes: a first spherical mirror and a second spherical mirror;

[0020] The first spherical mirror is arranged in front of the diffraction grating, and the second spherical mirror is arranged behind the diffraction grating; the first spherical mirror, the diffraction grating and the second spherical mirror are located on the same optical axis;

[0021] The signal light expanded by linear dispersion passes through the Fourier lens so that the lateral distance between the signal light and the optical axis is converted into a lateral angle, which is then converted into a lateral displacement by the first spherical mirror and imaged on the diffraction grating. The diffraction and spectral effects of the diffraction grating expand the lateral dispersion to form the planar dispersion.

[0022] In one implementation, the virtual image phase array is tilted backward at a certain angle in the longitudinal direction to form a free spectrum region in the virtual image phase array.

[0023] In one implementation, the virtual image phase array includes: an incident surface and an exit surface;

[0024] The incident surface is coated with a first reflective film, and the exit surface is coated with a second reflective film; the composite light emitted by the collimating fiber array and the cylindrical lens is reflected multiple times by the first reflective film and the second reflective film, and is spread out in linear dispersion on the exit surface.

[0025] In one implementation, the collimating fiber array includes: an input end and an output end;

[0026] After being collimated by the input end, the composite light enters the cylindrical lens and the virtual image phase array; the optical signal reflected by the silicon-based liquid crystal optical switch passes through the virtual image phase array and the cylindrical lens and is output from the output end to the signal receiving end.

[0027] In a second aspect, the present invention provides a wavelength selection method based on two-dimensional dispersion, the wavelength selection method based on two-dimensional dispersion comprising:

[0028] The composite light at the optical signal input end is incident from the collimating optical fiber array, and the composite light is subjected to beam waist shaping by a cylindrical lens to obtain a shaped signal light;

[0029] The shaped signal light is reflected multiple times by a virtual image phase array, and a signal light with linear dispersion spread along the longitudinal direction is formed on the output surface of the virtual image phase array;

[0030] The lateral distance between the expanded signal light and the optical axis is converted into a light incidence angle by a Fourier lens, and then converted into a lateral displacement by a first spherical mirror to form an image on the diffraction grating;

[0031] The image is dispersed in the lateral direction by utilizing the diffraction and spectral splitting effect of the diffraction grating to form a plane dispersion in the lateral direction;

[0032] The plane dispersion is incident on a liquid crystal on silicon optical switch through a second spherical mirror, and the liquid crystal on silicon optical switch is controlled to load a preset phase on a corresponding pixel so that light signals with different wavelength components are selectively reflected in the horizontal direction;

[0033] The reflected signal light is converted into a lateral displacement through the second spherical mirror, the diffraction grating, the first spherical mirror, the Fourier lens and the virtual image phase array, and is selectively output to the output end of the collimating fiber array via the virtual image phase array.

[0034] In one implementation, the step of injecting the composite light at the optical signal input end into the collimating optical fiber array includes:

[0035] Determining the tilt angle and incident window size of the virtual image phase array;

[0036] Determine the free spectrum area of the virtual image phase array according to the tilt angle:

[0037]

[0038] Wherein, n and t are the refractive index and thickness of the virtual image phase array respectively;

[0039] θ is the tilt angle of the virtual image phase array;

[0040] c is a constant.

[0041] In one implementation, the step of injecting the composite light at the optical signal input end into the collimating optical fiber array further includes:

[0042] Determine the two-dimensional dispersion field distribution δθ of the diffraction grating according to the tilt angle and the incident beam waist x and δθ y ;

[0043]

[0044]

[0045] Where, d is the grating constant;

[0046] β is the angle between the grating and the x-axis;

[0047] θ x is the field of view angle in the x direction;

[0048] ω is the beam waist;

[0049] α is the angle between the virtual image phase array and the y-axis;

[0050] n is the refractive index of the medium inside the virtual image phase array;

[0051] R1 is the reflectivity of the first reflective film of the virtual image phase array;

[0052] R2 is the reflectivity of the second reflective film of the virtual image phase array.

[0053] The present invention adopts the above technical solution to achieve the following effects:

[0054] The virtual image phase array provided by the present invention has a large dispersion angle, can effectively improve the spectral resolution and spatial resolution of wavelength components, and can reduce channel crosstalk in the wavelength selective switch while maintaining the other architectures of the wavelength selective switch. Moreover, the provided virtual image phase array can fully utilize the pixel area of the silicon-based liquid crystal optical switch for phase modulation, significantly increasing the number of controllable light beams, enabling the wavelength selective switch to support a larger number of ports, and improving the performance of the entire wavelength selection system. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0056] Figure 1 It is a schematic structural diagram of a wavelength selective switch based on two-dimensional dispersion in one implementation of the present invention.

[0057] Figure 2 It is a structural diagram of an existing wavelength selection system.

[0058] Figure 3 This is a schematic diagram of the spot distribution of the existing wavelength selection system.

[0059] Figure 4 It is a structural diagram of an existing reconfigurable all-optical add-distribution multiplexer system.

[0060] Figure 5 It is a schematic diagram of the principle of two-dimensional dispersion in one implementation of the present invention.

[0061] Figure 6 It is a schematic diagram of two-dimensional spectral field distribution in one implementation of the present invention.

[0062] Figure 7 It is a flow chart of a wavelength selection method based on two-dimensional dispersion in one implementation of the present invention.

[0063] In the picture:

[0064] 1. Collimating fiber array; 2. Cylindrical lens; 3. Virtual image phase array; 4. Fourier lens; 5. First spherical mirror; 6. Diffraction grating; 7. Second spherical mirror; 8. Liquid crystal on silicon optical switch.

[0065] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solutions and advantages of the present invention more clear and distinct, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0067] At present, the performance of wavelength selective switches is constantly improving, mainly reflected in the increase in the number of input and output ports, the expansion of coverage bandwidth and the improvement of optical switch performance. The basic architecture of their optical systems is similar, such as Figure 2 As shown in the figure, the distance between the Fourier lens and imaging lens 1 is the sum of the focal lengths of the two lenses. Imaging lenses 1 and 2 form a 4f system (linear optical information processing system). The dispersion element is located on the confocal plane between the two lenses of the 4f system, and the reflective beam control device is located on the back focal plane of lens 2. Multiple fiber array ports are arranged along the y-axis, and the output signal of each port is transmitted along the z-axis.

[0068] The system works as follows:

[0069] First, the collimated signal light passes through a Fourier lens, converting the distance in the y-direction into an angle that intersects the optical axis at the object plane of the 4f system. The signal light is then dispersed by the dispersive element (typically a diffraction grating) on the confocal plane of the 4f system, resulting in wavelength splitting only in the x-direction and ultimately landing at different locations on the reflective beam deflector.

[0070] Then, wavelength components falling at different positions on the x-axis are reflected at different y-axis angles by the deflection device, and the optical path is reversed. The Fourier lens converts the different inclination angles of each wavelength beam into displacements on the y-axis, which then enter different output ports, thus achieving wavelength-selective output. This architecture is widely used in wavelength-level optical switching systems.

[0071] Since the optical system design of wavelength selective switches is generally based on the "dispersion-deflection" architecture, gratings or prisms are generally used as dispersion elements at this stage to perform one-dimensional dispersion expansion on the signal light (assuming expansion in the x-direction). The expanded light beam is deflected in the y-direction on the optical switch to achieve wavelength selection (such as Figure 3 In recent years, wavelength selective switches (WSSs) using diffraction gratings and liquid crystal on silicon (LCOS) optical switches have become the mainstream choice in the industry. They can have up to 1 x 32 ports, cover a maximum spectrum range approaching 10 THz, and have a minimum channel grid spacing of around 10 GHz. The limits of these specifications are primarily limited by the performance of the dispersion element and the optical switch.

[0072] Currently, all dispersive elements used are based on a one-dimensional expansion, meaning that light can only be wavelength-split in a single direction. Furthermore, commercially available liquid crystal on silicon (LCOS) optical switches have a limited number of pixels. High-performance commercial LOS optical switches typically have 2k pixels, with a few reaching 4k pixels. Consequently, the number of controllable beams is limited. To further improve the performance of WSSs, the most direct approach is to integrate multiple WSSs (M 1xN WSSs, or MxN WSSs). Encapsulating two WSSs in a single module has become a mainstream approach. In recent years, the integration level of WSSs has continued to increase, with leading-edge solutions enabling 24x12 WSSs. However, WSSs are expensive, and as integration increases, the system becomes more expensive. This makes commercialization difficult due to cost-effectiveness. Therefore, further improving the key performance metrics of individual WSSs (such as number of ports, coverage bandwidth, and grid spacing) remains a key research direction.

[0073] To address the above technical issues, this embodiment provides a wavelength selective switch based on two-dimensional dispersion. By using a two-dimensional disperser instead of a traditional one-dimensional dispersive element, the wavelength signal is spread out in a two-dimensional plane. This spread provides higher spectral resolution and more controllable channels. This wavelength selective switch based on two-dimensional dispersion significantly improves performance in terms of channel crosstalk, number of ports, wavelength coverage, and grid flexibility.

[0074] Exemplary Systems

[0075] like Figure 1 As shown, an embodiment of the present invention provides a wavelength selective switch based on two-dimensional dispersion.

[0076] In one implementation of this embodiment, the wavelength selective switch based on two-dimensional dispersion can be applied to the third-generation ROADM (reconstructable optical add / drop multiplexing system), also known as CDCF ROADM reconstructable optical add / drop multiplexing system; wherein the framework of the third-generation ROADM is as follows: Figure 4 shown.

[0077] Of course, in another implementation of this embodiment, the wavelength selective switch based on two-dimensional dispersion can also be applied to other generations of reconfigurable optical add-drop multiplexing systems, or to a reconfigurable optical add-drop multiplexing system based on the third generation improvement.

[0078] like Figure 1 As shown, the wavelength selective switch based on two-dimensional dispersion includes:

[0079] The collimating fiber array 1, the virtual image phase array 3, the Fourier lens 4, the optical lens group and the liquid crystal on silicon optical switch 8 are arranged in sequence along the z-axis in the figure.

[0080] Specifically, the collimating fiber array 1 is arranged in a horizontal one-dimensional form, that is, the collimating fiber array 1 is arranged in a single row along the x-axis direction in the figure; the virtual image phase array 3 is arranged behind the collimating fiber array 1; the Fourier lens 4 is arranged behind the virtual image phase array 3; the optical lens group is arranged behind the Fourier lens 4, and the optical lens group and the Fourier lens 4 are located on the same optical axis; the silicon-based liquid crystal optical switch 8 is arranged behind the optical lens group, and the end face of the silicon-based liquid crystal optical switch 8 is arranged opposite to the mirror surface of the optical lens group.

[0081] In this embodiment, the composite light input from the collimating fiber array 1 is linearly dispersed along the longitudinal direction after passing through the virtual image phase array 3, and is then plane-dispersed by passing through the Fourier lens 4, the diffraction grating 6, and the optical lens group, so as to be selectively reflected on the silicon-based liquid crystal optical switch 8 and enter the output end of the collimating fiber array 1.

[0082] In an implementation of this embodiment, the wavelength selective switch based on two-dimensional dispersion further includes: a cylindrical lens 2 and a diffraction grating 6 .

[0083] Specifically, the cylindrical lens 2 is arranged between the collimating fiber array 1 and the virtual image phase array 3. The composite light emitted by the collimating fiber array 1 is waist-shaped by the cylindrical lens 2, and the shaped signal light enters the virtual image phase array 3; the diffraction grating 6 is arranged between the lenses of the optical lens group, and the diffraction grating 6, the Fourier lens 4 and the optical lens group are located on the same optical axis.

[0084] Furthermore, the optical lens group includes: a first spherical mirror 5 and a second spherical mirror 7; wherein the first spherical mirror 5 is arranged in front of the diffraction grating 6, and the second spherical mirror 7 is arranged behind the diffraction grating 6; the first spherical mirror 5, the diffraction grating 6 and the second spherical mirror 7 are located on the same optical axis; the signal light expanded by linear dispersion passes through the Fourier lens 4 so that the lateral distance between the signal light and the optical axis is converted into a lateral angle, and is imaged on the diffraction grating 6 through the first spherical mirror 5. The diffraction and spectral effects of the diffraction grating 6 act on the lateral dispersion to form the plane dispersion, and then the plane dispersed light signal passes through the second spherical mirror 7 and is incident on the silicon-based liquid crystal optical switch 8, so that light of different wavelength components is selectively deflected and reflected in the x-axis direction.

[0085] It is worth mentioning that, in the process of the optical signal returning along the optical path, the Fourier lens 4 can convert the angle deviation of the light beam generated on the silicon liquid crystal optical switch 8 into a displacement, which is then output to different receiving ports in the collimating fiber array 1.

[0086] Furthermore, the virtual image phase array 3 is tilted backward at a certain angle in the longitudinal direction to form a free spectrum region in the virtual image phase array 3; in an implementation of this embodiment, the tilt angle of the virtual image phase array 3 is 1° to 5°.

[0087] In one implementation of this embodiment, the virtual image phase array 3 includes: an incident surface and an exit surface, the incident surface being coated with a first reflective film, and the exit surface being coated with a second reflective film; the composite light emitted by the collimating fiber array 1 and the cylindrical lens 2 is reflected multiple times by the first reflective film and the second reflective film, and is then spread out as linear dispersion on the exit surface;

[0088] In one implementation of this embodiment, the collimating fiber array 1 includes: an input end and an output end; the composite light is collimated by the input end and then enters the cylindrical lens 2 and the virtual image phase array 3; the optical signal reflected by the silicon-based liquid crystal optical switch 8 passes through the virtual image phase array 3 and the cylindrical lens 2 and is output from the output end to the signal receiving end.

[0089] like Figure 5 As shown, in this embodiment, the optimization is mainly focused on the dispersion element in the wavelength selective switch architecture. Traditional dispersion elements usually include diffraction gratings and grisms, while this embodiment uses a rare spectroscopic element - a virtually imaged phased array (VIPA).

[0090] The structure of a virtual image phased array is similar to that of a Fabry-Perot etalon, with a fully reflective coating R1 (i.e., the first reflective coating) exceeding 99% applied to the incident surface (excluding the antireflection coating on the incident window), and a highly reflective coating R2 (i.e., the second reflective coating) with a 90%-98% reflectivity applied to the exit surface. Because the composite light beam is reflected multiple times within the two reflective surfaces, at the output, it appears as n equally spaced virtual images interfering with a constant phase difference. Light of a specific wavelength is collimated and emitted at a specific angle, thus achieving beam splitting.

[0091] The original purpose of using the virtual image phase array in this embodiment is to utilize its large angular dispersion and high resolution characteristics to achieve functions such as wavelength division multiplexing and dispersion compensation. However, the virtual image phase array has a free spectral range (FSR) similar to the etalon structure:

[0092]

[0093] Wherein, n and t are the refractive index and thickness of the virtual image phase array respectively;

[0094] θ is the tilt angle of the virtual image phase array;

[0095] c is a constant.

[0096] In this embodiment, the wavelengths within each free spectrum period are linearly spread, but the spectral lines of different periods are mixed together, so this element cannot be widely used. In this embodiment, a two-dimensional disperser composed of a virtual image phase array and a diffraction grating is used to replace the traditional one-dimensional dispersion element, and the composite light is dispersed on a two-dimensional plane. The principle is as follows: Figure 5 shown.

[0097] First, the wide-spectrum signal light passes through the input window of the virtual image phase array and is reflected multiple times on the two surfaces of the virtual image phase array. At the output surface, the different wavelengths within a single free spectrum region are linearly expanded in the longitudinal direction. Aliasing will occur between the periods of different free spectrum regions, and the difference in the aliased wavelengths is an integer multiple of the free spectrum region.

[0098] Then, the linearly expanded wavelength components are incident on the diffraction grating (the dispersion direction is horizontal), and the overlapping wavelength components are expanded in the horizontal direction due to the diffraction effect, so a dispersion signal with a two-dimensional plane distribution can be obtained. Assuming that the grating is a +1-order blazed grating, the grating equation is:

[0099] d[sin(θ x,i +β)+sinβ]=λ i (2);

[0100] Where β is the incident angle of the signal light and d is the grating constant.

[0101] Therefore, for a certain wavelength λ i , the lateral dispersion angle θ can be obtained x,i The dispersion law of the virtual image phase array is:

[0102]

[0103] Where α is the virtual image phase array tilt angle, and nsinα in =sinα.

[0104] Therefore, for a certain wavelength λ i , we can get the angle of longitudinal dispersion θ y,i , the two-dimensional distribution of the signal light can be calculated by combining formulas (2) and (3).

[0105] It is worth noting that in practical applications, in addition to considering the size of the free spectrum area, the size of the tilt angle must also be considered for virtual image phase arrays. Virtual image phase arrays are usually very thin, and their incident window size is 2ndtgα. In order for the incident light beam to enter the virtual image phase array, the incident light beam waist size must meet the following conditions:

[0106] 2ω<2ndtgα (4);

[0107] Therefore, a cylindrical lens is usually placed in front of the virtual image phase array to compress the spot in the longitudinal direction. Secondly, in order to obtain greater angular dispersion and spatial resolution, too small a tilt angle should be avoided. In order to reduce loss and ensure the number of virtual images produced and increase the field of view, a large tilt angle cannot be used. Therefore, the tilt angle is generally set at around 1 to 5 degrees.

[0108] In this embodiment, the experimental device is as follows Figure 1 This solution is similar to Figure 2 The biggest difference between the wavelength selective switch device and the embodiment is that: the virtual image phase array dispersion element is introduced in this embodiment. The incident window size of the device is limited, thereby limiting the longitudinal control range of the input and output ports;

[0109] Therefore, the number of ports in the y direction should not be too many. The collimating fiber array in this embodiment is arranged one-dimensionally in the x direction, so the deflection direction of the light beam by the silicon-based liquid crystal optical switch is in the x-axis direction. From the perspective of the optical path structure, in addition to the introduction of the virtual image phase array and the cylindrical mirror, the other components are the same as Figure 2 The placement positions are similar. The distance between the Fourier lens and the first spherical mirror is the sum of their focal lengths. The first spherical mirror and the second spherical mirror form a 4f system. The diffraction grating is placed on the confocal plane of the 4f system. The silicon-based liquid crystal optical switch is placed on the back focal plane of the 4f system. The distance between the virtual image phase array and the cylindrical mirror is determined according to the actual required beam waist size.

[0110] From the perspective of optical path analysis, the optical path principle in this embodiment is as follows:

[0111] First, the composite light at the input port is incident from the collimating fiber array and shaped by the cylindrical lens. After the shaped signal light enters the virtual image phase array, it is linearly dispersed along the y-axis at the output surface.

[0112] Secondly, the linearly dispersed signal light passes through a Fourier lens to convert the distance from the optical axis in the x-direction into an angle, and then passes through the first spherical mirror to convert it into an x-direction displacement and imaged on the grating. After undergoing diffraction and splitting, it is dispersed in the x-axis direction, thus forming plane dispersion.

[0113] Furthermore, the plane-dispersed light signal passes through the second spherical mirror and is incident on the silicon-based liquid crystal optical switch. The PC controls different pixels of the silicon-based liquid crystal optical switch to load different phases, so that light with different wavelength components is selectively deflected and reflected in the x-axis direction.

[0114] Finally, light with different reflection angles is converted into displacement in the x-direction through the 4f system and the Fourier lens. That is, the angle deviation of the light beam generated on the silicon-based liquid crystal optical switch is converted into displacement through the Fourier lens. The displacement is then output in reverse through the virtual image phase array and selectively enters the collimating fiber array.

[0115] It's worth noting that the two-dimensional dispersion plane isn't rectangular; it has a slope in the vertical direction, which increases monotonically with the number of wavelength components covered. Furthermore, in practical applications, system aberrations and errors also affect the distribution of the light spot. Therefore, applying phase shift to the pixel introduces unnecessary insertion loss and crosstalk into the wavelength selective switch. To achieve precise beam deflection, the position of the light spot distribution for different wavelength components on the liquid crystal on silicon optical switch must be calibrated.

[0116] In one implementation of this embodiment, the parameters required for the wavelength selective switch based on two-dimensional dispersion are selected as follows:

[0117] In this embodiment, the main parameters affecting the performance of the wavelength selective switch are the size and free spectral range of the virtual image phase array, the waist size of the light beam, the tilt angle of the two-dimensional dispersion element, the focal length of the 4f system, and the number and pixel size of the silicon-based liquid crystal optical switch.

[0118] First, the size of the incident window of the virtual image phase array determines the number of incident and outgoing beams, which directly affects the number of ports of the wavelength selective switch.

[0119] Secondly, under the condition that the tilt angle of the virtual image phase array is determined, its length in the y direction determines the number of virtual images that can be produced. The more virtual images there are, the smaller the leakage loss of light emitted from the top; therefore, the size of the virtual image phase array should be as large as possible; the size of the free spectrum area directly affects the coverage bandwidth and channel spacing of the wavelength selective switch. A larger free spectrum area can cover a wider wavelength range, while a smaller free spectrum area can support a smaller grid size.

[0120] The spot divergence angle directly affects the spectral resolution and spatial resolution. In the application of wavelength selective switches, the smaller the divergence angle, the more advantages it has. The two-dimensional dispersion field distribution of the signal light at the grating output is as follows: Figure 6 As shown, δθ x and δθ y The divergence angle of the light spot in the xy plane is expressed as:

[0121]

[0122]

[0123] Where, d is the grating constant;

[0124] β is the angle between the grating and the x-axis;

[0125] θ x is the field of view angle in the x direction;

[0126] ω is the beam waist;

[0127] α is the angle between the virtual image phase array and the y-axis;

[0128] n is the refractive index of the medium inside the virtual image phase array;

[0129] R1 is the reflectivity of the first reflective film of the virtual image phase array;

[0130] R2 is the reflectivity of the second reflective film of the virtual image phase array.

[0131] When the dispersion element parameters are determined, it can be known from formula (5) that the divergence angle δθ in the x direction is x It is mainly affected by the grating angle β and the incident beam waist, and there is an optimal solution;

[0132] From formula (6), we can know that the divergence angle δθ in the y direction is y The main influence is the tilt angle α of the virtual image phase array. As α increases, the divergence angle gradually converges. Therefore, the optimal incident beam waist and the tilt angle of the dispersion element can be determined by calculation.

[0133] The focal length of the 4f system affects the size of the image on the dispersion plane. If the area of the image on the silicon liquid crystal optical switch is too large, signal loss will occur, and if the image is too small, the flexibility of the adjustable grid will be reduced. Therefore, the focal length of the spherical mirror needs to be reasonably selected.

[0134] The parameters of LCS optical switches are crucial to wavelength selective switch performance. Smaller individual pixels mean finer adjustable beam units, which translates to greater grid flexibility. Currently, most commercial LCS optical switches have pixel sizes around 8μm. The area of an LCS optical switch is determined by both pixel size and number. A larger LCS optical switch area increases the bandwidth it can cover and the number of ports it can support. Currently, most commercial LCS optical switches have 2k pixels, with a few reaching 4k. Therefore, further development of LCS optical switch technology is expected, and the performance of wavelength selective switches based on these switches will also be further enhanced.

[0135] This embodiment has the following effects through the above technical solution:

[0136] The present invention replaces the one-dimensional dispersive element of a wavelength selective switch with a two-dimensional disperser, allowing the wavelength-level signal in the input channel to be spread out in a plane. This fully utilizes the pixel area of the liquid crystal on silicon optical switch to control the beam phase. This means that the wavelength selective switch can cover a wider bandwidth while maintaining other device parameters. Furthermore, because a two-dimensional disperser has a higher spatial resolution than a one-dimensional disperser, the grid's operable range is more flexible while maintaining a constant pixel size in the liquid crystal on silicon optical switch.

[0137] Exemplary Methods

[0138] like Figure 7 As shown, based on the above embodiment, this embodiment further provides a wavelength selection method based on two-dimensional dispersion, comprising the following steps:

[0139] Step S100, the composite light at the optical signal input end is incident from the collimating fiber array, and the composite light is subjected to beam waist shaping by a cylindrical lens to obtain a shaped signal light;

[0140] Step S200, performing multiple reflections on the shaped signal light through the virtual image phase array, and forming a signal light with linear dispersion spread along the longitudinal direction on the output surface of the virtual image phase array;

[0141] Step S300, converting the lateral distance between the expanded signal light and the optical axis into a light incidence angle through a Fourier lens, and then converting it into a lateral displacement through a first spherical mirror, so as to form an image on the diffraction grating;

[0142] Step S400, utilizing the diffraction and spectral splitting effect of the diffraction grating to disperse the image in the lateral direction to form a plane dispersion in the lateral direction;

[0143] Step S500, directing the plane dispersion light onto a liquid crystal on silicon optical switch through a second spherical mirror, and controlling the liquid crystal on silicon optical switch to load a preset phase on a corresponding pixel, so that light signals of different wavelength components are selectively reflected in the horizontal direction;

[0144] Step S600: convert the reflected signal light into a lateral displacement through the second spherical mirror, the diffraction grating, the first spherical mirror, the Fourier lens and the virtual image phase array, and selectively output it to the output end of the collimating fiber array through the virtual image phase array.

[0145] In this embodiment, the optimization is mainly focused on the dispersion element in the wavelength selective switch architecture. Traditional dispersion elements usually include diffraction gratings and grisms, while this embodiment uses a rare spectroscopic element - a virtually imaged phased array (VIPA).

[0146] The structure of a virtual image phased array is similar to that of a Fabry-Perot etalon. The incident surface (excluding the antireflection coating on the incident window) is coated with a fully reflective coating R1 (i.e., the first reflective coating) with a reflection ratio of at least 90%, and the exit surface is coated with a highly reflective coating R2 (i.e., the second reflective coating) with a reflection ratio of 90%-98%. Because the composite light beam is reflected multiple times within the two reflective surfaces, at the output, it appears as n equally spaced virtual images interfering with each other at a constant phase difference. Light of a specific wavelength is collimated and emitted at a specific angle, thus achieving beam splitting.

[0147] The original purpose of using the virtual image phase array in this embodiment is to utilize its large angular dispersion and high resolution characteristics to achieve functions such as wavelength division multiplexing and dispersion compensation. However, the virtual image phase array has a free spectral range (FSR) similar to the etalon structure:

[0148]

[0149] Wherein, n and t are the refractive index and thickness of the virtual image phase array respectively;

[0150] θ is the tilt angle of the virtual image phase array;

[0151] c is a constant.

[0152] In this embodiment, the wavelengths within each free spectrum period are linearly spread, but the spectral lines of different periods are mixed together, so this element cannot be widely used. In this embodiment, a two-dimensional disperser composed of a virtual image phase array and a diffraction grating is used to replace the traditional one-dimensional dispersion element, and the composite light is dispersed on a two-dimensional plane. The principle is as follows: Figure 5 shown.

[0153] First, the wide-spectrum signal light passes through the input window of the virtual image phase array and is reflected multiple times on the two surfaces of the virtual image phase array. At the output surface, the different wavelengths within a single free spectrum region are linearly expanded in the longitudinal direction. Aliasing will occur between the periods of different free spectrum regions, and the difference in the aliased wavelengths is an integer multiple of the free spectrum region.

[0154] Then, the linearly expanded wavelength components are incident on the diffraction grating (the dispersion direction is horizontal), and the overlapping wavelength components are expanded in the horizontal direction due to the diffraction effect, so a dispersion signal with a two-dimensional plane distribution can be obtained. Assuming that the grating is a +1-order blazed grating, the grating equation is:

[0155] d[sin(θ x,i +β)+sinβ]=λ i (2);

[0156] Where β is the incident angle of the signal light and d is the grating constant.

[0157] Therefore, for a certain wavelength λ i , the lateral dispersion angle θ can be obtained x,i The dispersion law of the virtual image phase array is:

[0158]

[0159] Where α is the virtual image phase array tilt angle, and nsinα in =sinα.

[0160] Therefore, for a certain wavelength λ i , we can get the angle of longitudinal dispersion θ y,i , the two-dimensional distribution of the signal light can be calculated by combining formulas (2) and (3).

[0161] It is worth noting that in practical applications, in addition to considering the size of the free spectrum area, the size of the tilt angle must also be considered for virtual image phase arrays. Virtual image phase arrays are usually very thin, and their incident window size is 2ndtgα. In order for the incident light beam to enter the virtual image phase array, the incident light beam waist size must meet the following conditions:

[0162] 2ω<2ndtgα (4);

[0163] Therefore, a cylindrical lens is usually placed in front of the virtual image phase array to compress the spot in the longitudinal direction. Secondly, in order to obtain greater angular dispersion and spatial resolution, too small a tilt angle should be avoided. In order to reduce loss and ensure the number of virtual images produced and increase the field of view, a large tilt angle cannot be used. Therefore, the tilt angle is generally set at around 1 to 5 degrees.

[0164] In this embodiment, the experimental device is as follows Figure 1 This solution is similar to Figure 2 The biggest difference between the wavelength selective switch device and the embodiment is that: the virtual image phase array dispersion element is introduced in this embodiment. The incident window size of the device is limited, thereby limiting the longitudinal control range of the input and output ports;

[0165] Therefore, the number of ports in the y direction should not be too many. The collimating fiber array in this embodiment is arranged one-dimensionally in the x direction, so the deflection direction of the light beam by the silicon-based liquid crystal optical switch is in the x-axis direction. From the perspective of the optical path structure, in addition to the introduction of the virtual image phase array and the cylindrical mirror, the other components are the same as Figure 2 The placement positions are similar. The distance between the Fourier lens and the first spherical mirror is the sum of their focal lengths. The first spherical mirror and the second spherical mirror form a 4f system. The grating is placed on the confocal plane of the 4f system. The silicon-based liquid crystal optical switch is placed on the back focal plane of the 4f system. The distance between the virtual image phase array and the cylindrical mirror is determined according to the actual required beam waist size.

[0166] From the perspective of optical path analysis, the optical path principle in this embodiment is as follows:

[0167] First, the composite light at the input port is incident from the collimating fiber array and shaped by the cylindrical lens. After the shaped signal light enters the virtual image phase array, it is linearly dispersed along the y-axis at the output surface.

[0168] Secondly, the linearly dispersed signal light passes through a Fourier lens to convert the distance from the optical axis in the x-direction into an angle, and then passes through the first spherical mirror to convert it into an x-direction displacement and imaged on the grating. After undergoing diffraction and splitting, it is dispersed in the x-axis direction, thus forming plane dispersion.

[0169] Furthermore, the plane-dispersed light signal passes through the second spherical mirror and is incident on the silicon-based liquid crystal optical switch. The PC controls different pixels of the silicon-based liquid crystal optical switch to load different phases, so that light with different wavelength components is selectively deflected and reflected in the x-axis direction.

[0170] Finally, the light with different reflection angles is converted into displacement in the x-direction through the 4f system and the Fourier lens, and then output in reverse through the virtual image phase array and selectively enters the collimating fiber array.

[0171] It's worth noting that the two-dimensional dispersion plane isn't rectangular; it has a slope in the vertical direction, which increases monotonically with the number of wavelength components covered. Furthermore, in practical applications, system aberrations and errors also affect the distribution of the light spot. Therefore, applying phase shift to the pixel introduces unnecessary insertion loss and crosstalk into the wavelength selective switch. To achieve precise beam deflection, the position of the light spot distribution for different wavelength components on the liquid crystal on silicon optical switch must be calibrated.

[0172] In one implementation of this embodiment, the parameters required for the wavelength selective switch based on two-dimensional dispersion are selected as follows:

[0173] In this embodiment, the main parameters affecting the performance of the wavelength selective switch are the size and free spectral range of the virtual image phase array, the waist size of the light beam, the tilt angle of the two-dimensional dispersion element, the focal length of the 4f system, and the number and pixel size of the silicon-based liquid crystal optical switch.

[0174] First, the size of the incident window of the virtual image phase array determines the number of incident and outgoing beams, which directly affects the number of ports of the wavelength selective switch.

[0175] Secondly, under the condition that the tilt angle of the virtual image phase array is determined, its length in the y direction determines the number of virtual images that can be produced. The more virtual images there are, the smaller the leakage loss of light emitted from the top; therefore, the size of the virtual image phase array should be as large as possible; the size of the free spectrum area directly affects the coverage bandwidth and channel spacing of the wavelength selective switch. A larger free spectrum area can cover a wider wavelength range, while a smaller free spectrum area can support a smaller grid size.

[0176] That is, in this embodiment, the steps before step S100 include:

[0177] Step S001, determining the tilt angle and incident window size of the virtual image phase array;

[0178] Step S002: determining the free spectrum range of the virtual image phase array according to the tilt angle.

[0179] In one implementation of this embodiment, the spot divergence angle directly affects the spectral resolution and spatial resolution. In the application of wavelength selective switches, the smaller the divergence angle, the more advantages it has. The two-dimensional dispersion field distribution of the signal light at the grating output is as follows: Figure 6 As shown, δθ x and δθ y The divergence angle of the light spot in the xy plane is expressed as:

[0180]

[0181]

[0182] Where, d is the grating constant;

[0183] β is the angle between the grating and the x-axis;

[0184] θ x is the field of view angle in the x direction;

[0185] ω is the beam waist;

[0186] α is the angle between the virtual image phase array and the y-axis;

[0187] n is the refractive index of the medium inside the virtual image phase array;

[0188] R1 is the reflectivity of the first reflective film of the virtual image phase array;

[0189] R2 is the reflectivity of the second reflective film of the virtual image phase array.

[0190] When the dispersion element parameters are determined, it can be known from formula (5) that the divergence angle δθ in the x direction is x It is mainly affected by the grating angle β and the incident beam waist, and there is an optimal solution;

[0191] From formula (6), we can know that the divergence angle δθ in the y direction is y The main influence is the tilt angle α of the virtual image phase array. As α increases, the divergence angle gradually converges. Therefore, the optimal incident beam waist and the tilt angle of the dispersion element can be determined by calculation.

[0192] The focal length of the 4f system affects the size of the image on the dispersion plane. If the area of the image on the silicon liquid crystal optical switch is too large, signal loss will occur, and if the image is too small, the flexibility of the adjustable grid will be reduced. Therefore, the focal length of the spherical mirror needs to be reasonably selected.

[0193] That is, in this embodiment, the steps before step S100 include:

[0194] Step S003: determining the two-dimensional dispersion field distribution δθ of the diffraction grating according to the tilt angle and the incident beam waist. x and δθ y .

[0195] In this embodiment, the parameters of the silicon liquid crystal optical switch are crucial to the performance of the wavelength selective switch. The smaller the size of a single pixel, the finer the adjustable light beam unit, that is, the higher the grid flexibility. Currently, the pixel size of most commercial silicon liquid crystal optical switches is around 8μm. The area of the silicon liquid crystal optical switch is determined by the pixel size and number. The larger the area of the silicon liquid crystal optical switch, the wider the bandwidth that the wavelength selective switch can cover and the greater the number of ports that can be supported. Currently, most commercial silicon liquid crystal optical switches have a pixel size of 2k, and a few can reach 4k. Therefore, the technology of silicon liquid crystal optical switches can be further developed, and the performance of wavelength selective switches based on silicon liquid crystal optical switches will also be further improved.

[0196] This embodiment achieves the following technical effects through the above technical solution:

[0197] In this embodiment, the virtual image phase array provides relatively large angular dispersion. The introduction of a two-dimensional disperser effectively improves the spectral and spatial resolution of wavelength components, reducing channel crosstalk in the wavelength selective switch while maintaining the other architectures of the switch. Furthermore, two-dimensional dispersion fully utilizes the pixel area of the liquid crystal on silicon optical switch for phase modulation, significantly increasing the number of controllable beams and enabling the wavelength selective switch to support a larger number of ports. Furthermore, the dispersion changes from linear to planar. While maintaining the same channel spacing, the wavelength selective switch can support a wider coverage bandwidth, effectively increasing the transmission capacity of exchanges at all-optical network nodes. Finally, the dispersion capability of the two-dimensional disperser can be enhanced by controlling parameters such as the free spectral range, tilt angle, thickness, and grating constant of the virtual image phase array. This allows the phase loaded by the liquid crystal on silicon optical switch to manipulate more detailed wavelength components and achieve narrower channel spacing, thus providing the wavelength selective switch with a more flexible grating spacing.

[0198] Those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing related hardware through a computer program. The computer program can be stored in a non-volatile storage medium. When executed, the computer program can include the processes in the above-described method embodiments. Any reference to memory, storage, database, or other media used in the various embodiments provided herein may include non-volatile and / or volatile memory.

[0199] In summary, the present invention provides a wavelength selective switch and method based on two-dimensional dispersion, comprising: a collimating fiber array arranged in a horizontal one-dimensional form; a virtual image phase array disposed behind the collimating fiber array; a Fourier lens disposed behind the virtual image phase array; an optical lens assembly disposed behind the Fourier lens, the optical lens assembly and the Fourier lens being coaxially located; and a liquid crystal on silicon optical switch disposed behind the optical lens assembly, the end face of the liquid crystal on silicon optical switch being arranged opposite the mirror surface of the optical lens assembly. The present invention utilizes a virtual image phase array with two-dimensional dispersion characteristics to replace a one-dimensional dispersion device, allowing the wavelength signal to be spread out in a two-dimensional plane, thereby improving the performance of the wavelength selection device.

[0200] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A wavelength selective switch based on two-dimensional dispersion, characterized in that: The wavelength selective switch based on two-dimensional dispersion includes: a collimating optical fiber array, wherein the collimating optical fiber array is arranged in a transverse one-dimensional form; A virtual image phase array, the virtual image phase array being arranged behind the collimating optical fiber array; A Fourier lens, the Fourier lens being arranged behind the virtual image phase array; an optical lens group, wherein the optical lens group is disposed behind the Fourier lens, and the optical lens group and the Fourier lens are located on the same optical axis; and a liquid crystal on silicon optical switch, wherein the liquid crystal on silicon optical switch is arranged behind the optical lens group, and an end face of the liquid crystal on silicon optical switch is arranged opposite to the mirror surface of the optical lens group; After passing through the virtual image phase array, the composite light inputted from the collimating fiber array is linearly dispersed in the longitudinal direction and then passes through the Fourier lens and the optical lens group to form a plane dispersion, so as to be selectively reflected on the liquid crystal on silicon optical switch and enter the output end of the collimating fiber array; The wavelength selective switch based on two-dimensional dispersion further includes: a diffraction grating, the diffraction grating being disposed between the lenses of the optical lens group, and the diffraction grating being located on the same optical axis as the Fourier lens and the optical lens group; The optical lens assembly includes: a first spherical mirror and a second spherical mirror; The first spherical mirror is arranged in front of the diffraction grating, and the second spherical mirror is arranged behind the diffraction grating; the first spherical mirror, the diffraction grating and the second spherical mirror are located on the same optical axis; The linearly dispersed signal light passes through the Fourier lens to convert the lateral distance between the signal light and the optical axis into a lateral angle, which is then converted into a lateral displacement by the first spherical mirror and imaged on the diffraction grating. The diffraction grating then undergoes diffraction and spectral splitting to form the image on the lateral dispersion, forming the plane dispersion. The plane dispersion light signal then passes through the second spherical mirror and is incident on the silicon-based liquid crystal optical switch, so that light of different wavelength components is Selective deflection and reflection are performed in the axial direction.

2. The wavelength selective switch based on two-dimensional dispersion according to claim 1, characterized in that: The wavelength selective switch based on two-dimensional dispersion further includes: A cylindrical lens is provided between the collimating fiber array and the virtual image phase array. The composite light emitted from the collimating fiber array is subjected to beam waist shaping by the cylindrical lens, and the shaped signal light enters the virtual image phase array.

3. The wavelength selective switch based on two-dimensional dispersion according to claim 1, characterized in that: The virtual image phase array is tilted backward at a certain angle in the longitudinal direction to form a free spectrum area in the virtual image phase array.

4. The wavelength selective switch based on two-dimensional dispersion according to claim 2, characterized in that: The virtual image phase array includes: an incident surface and an exit surface; The incident surface is coated with a first reflective film, and the exit surface is coated with a second reflective film; the composite light emitted by the collimating fiber array and the cylindrical lens is reflected multiple times by the first reflective film and the second reflective film, and is spread out in linear dispersion on the exit surface.

5. The wavelength selective switch based on two-dimensional dispersion according to claim 4, characterized in that: The collimating optical fiber array includes: an input end and an output end; After being collimated by the input end, the composite light enters the cylindrical lens and the virtual image phase array; the optical signal reflected by the silicon-based liquid crystal optical switch passes through the virtual image phase array and the cylindrical lens and is output from the output end to the signal receiving end.

6. A wavelength selection method based on two-dimensional dispersion, characterized in that: The wavelength selection method based on two-dimensional dispersion includes: Determine the tilt angle and incident window size of the virtual image phase array; wherein the tilt angle is 1~5°, and the incident window size is ; Determine the free spectrum area of the virtual image phase array according to the tilt angle: ； in, 、 are the refractive index and thickness of the virtual image phase array respectively; is the tilt angle of the virtual image phase array; is a constant; The composite light at the optical signal input end is incident from the collimating optical fiber array, and the composite light is subjected to beam waist shaping by a cylindrical lens to obtain a shaped signal light; The shaped signal light is reflected multiple times by the virtual image phase array, and a signal light with linear dispersion along the longitudinal direction is formed on the output surface of the virtual image phase array; The lateral distance between the expanded signal light and the optical axis is converted into a lateral angle by a Fourier lens, and then converted into a lateral displacement by a first spherical mirror to form an image on the diffraction grating; The image is dispersed in the lateral direction by utilizing the diffraction and spectral splitting effect of the diffraction grating to form a plane dispersion in the lateral direction; The plane dispersion is incident on a liquid crystal on silicon optical switch through a second spherical mirror, and the liquid crystal on silicon optical switch is controlled to load a preset phase on a corresponding pixel so that light signals with different wavelength components are selectively reflected in the horizontal direction; The reflected signal light is converted into a lateral displacement through the second spherical mirror, the diffraction grating, the first spherical mirror, the Fourier lens and the virtual image phase array, and is selectively output to the output end of the collimating fiber array via the virtual image phase array.

Images