Optical diffraction device, wavelength selective switch and optical equipment
By designing optical diffraction devices with higher degrees of freedom in the wavelength selection switch, the specific arrangement of the surface profile structure compensates for aberration, the aberration problem in the wavelength selection switch is solved and optical performance is improved.
Patent Information
- Application Number
- CN202311177361.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-12
- Publication Date
- 2025-03-14
AI Technical Summary
There is a beam propagation in the wavelength selection switch that deviates from the optical axis, resulting in aberration problems, such as spherical aberration, intelligent aberration and field curve, which affects optical performance.
An optical diffraction device is designed, and its surface profile structure includes surface etching lines, which are arranged at equal intervals along the X-axis or Y-axis direction, and the length of the surface profile structure along the Z-axis direction varies along the X-axis or Y-axis direction, and has a higher degree of freedom for compensating for aberration.
Through this optical diffraction device, it is possible to effectively compensate for the aberration problems in the wavelength selection switching system, improve optical performance, and reduce the impact of beam deviation and higher-order diffraction light.
Smart Images
Figure CN119620269A_ABST
Abstract
Description
Technical Field
[0001] The embodiments of the present application relate to the field of optical technology, and specifically to an optical diffraction device, a wavelength selective switch and an optical device. Background Art
[0002] The filters used in optical communication systems have evolved from the original fixed wavelength filters to the current wavelength selective switches (WSS).
[0003] The optical communication system uses devices such as WSS to realize the functions of upper and lower wavelengths and arbitrary wavelength scheduling in the local dimension. Specifically, after the light beam is input into the WSS, the light beams of different wavelengths diffracted by the grating are incident on different positions on the liquid crystal on silicon (LCOS). LCOS applies voltage to the pixel points at the positions covered by the light beams of different wavelengths to change the phase of the liquid crystal, so that the input light beam is deflected in the direction that needs to be switched, and the deflected light beam returns to the corresponding port for output.
[0004] However, in WSS, the light beam will deviate from the optical axis, which will lead to aberration problems such as spherical aberration, coma and field curvature. Summary of the invention
[0005] The embodiment of the present application provides an optical diffraction device for compensating for the aberration of a wavelength selective switch system and improving the optical performance of the wavelength selective switch. The embodiment of the present application also provides a corresponding wavelength selective switch and an optical device.
[0006] In a first aspect, the present application provides an optical diffraction device, which includes a first plane, on which a surface profile structure is loaded, the surface profile structure including surface lines; in a three-dimensional coordinate system of the surface profile structure, the surface lines are arranged at intervals along the X-axis direction or the Y-axis direction; a first length of the surface profile structure along the Z-axis direction changes at preset distances along the X-axis direction and / or the Y-axis direction.
[0007] In the present application, the optical diffraction device is used to receive an incident Gaussian light beam and split the Gaussian light beam, and can be specifically applied to a wavelength selective switch.
[0008] In the present application, the first plane is any plane of the optical diffraction device, and a surface contour structure is loaded on the first plane, and the loading method includes but is not limited to scratching, etching or polymerization.
[0009] In the present application, in order to better describe the surface profile structure, a three-dimensional coordinate system of the surface profile structure is established.
[0010] Among them, the surface lines are used to realize the basic functions of the optical diffraction device, such as dispersion and phase modulation. The surface lines are arranged at intervals along the X-axis direction or the Y-axis direction. The specific arrangement method can be parallel arrangement, arrangement according to a preset curvature, equal interval arrangement, or unequal interval arrangement.
[0011] The first length of the surface contour structure along the Z-axis direction varies at preset intervals along the X-axis direction and / or the Y-axis direction, that is, the height of the surface hub structure fluctuates, and the change can be continuous, discontinuous, approximately continuous or discrete.
[0012] In the first aspect, the optical diffraction device includes a first plane, on which a surface contour structure is loaded, the surface contour structure includes surface lines, in the three-dimensional coordinate system of the surface contour structure, the surface lines are arranged at equal intervals along the X-axis direction or the Y-axis direction, the first length of the surface contour structure along the Z-axis direction varies at preset distances along the X-axis direction and / or the Y-axis direction, so the height of the surface contour structure fluctuates, has a higher degree of freedom, can compensate for the part of the WSS system with aberrations, and improve the optical performance of the WSS.
[0013] In a possible implementation manner of the first aspect, the surface profile structure includes at least two dispersion regions separated from each other, and the at least two dispersion regions are used to receive different incident light beams.
[0014] In this possible implementation, the surface profile structure can also be designed in different areas to receive different incident light beams. When the wavelength selective switch may be applied to different incident light beams, the dimension of the incident light beam will also change accordingly. The regional design can make the surface profile structure suitable for wavelength selective switches of different dimensions, thereby improving the adaptability of the optical diffraction device.
[0015] In a possible implementation manner of the first aspect, the change amount of the first length and / or the preset distance of the first length change interval in at least two dispersion regions are different.
[0016] In this possible implementation, the surface profile structures of different regions are different to adapt to different incident light beams, further improving the adaptability of the optical diffraction device.
[0017] In a possible implementation manner of the first aspect, at least two dispersion regions are arranged along the X-axis direction and / or the Y-axis direction.
[0018] In this possible implementation, the partition design can be arranged in different directions, which improves the feasibility of the solution.
[0019] In a possible implementation manner of the first aspect, areas of at least two dispersion regions are equal.
[0020] In this possible implementation, the areas of different regions are equal, which reduces the difficulty of the manufacturing process.
[0021] In a possible implementation manner of the first aspect, the preset distance is zero.
[0022] In this possible implementation, the height variation of the surface profile structure is continuous, which reduces the difficulty of the manufacturing process and improves the feasibility of the solution.
[0023] In a possible implementation manner of the first aspect, a change in the first length is determined based on a constraint function, where the constraint function is used to evaluate a spot characteristic of an outgoing light beam of the optical diffraction device.
[0024] In this possible implementation, the change in the first length can be determined based on the constraint function, and then the specific structure of the surface profile structure can be determined, and the beam requirements can be met, thereby improving the feasibility of the solution.
[0025] In a possible implementation manner of the first aspect, the spot characteristic includes a spot quality of the outgoing light beam and / or an angle between a spot pattern of the outgoing light beam and a Y-axis direction.
[0026] In this possible implementation, the beam requirement is specifically reflected in the spot quality or angle of the beam, thereby satisfying the degree of freedom or integrating the angle compensation function, thereby improving the feasibility of the solution.
[0027] In a possible implementation manner of the first aspect, an expression of the first length along the X-axis direction or the Y-axis direction is a sine function or a cosine function.
[0028] In this possible implementation, the expression of the surface profile structure can be a sine function or a cosine function, which meets the functional requirements of loading the modulation phase and improves the feasibility of the solution.
[0029] In a possible implementation manner of the first aspect, expressions of the first length along the X-axis direction and the Y-axis direction are Fourier expansion polynomials or aspherical polynomials.
[0030] In this possible implementation, the expression of the surface profile structure can be expressed by Fourier expansion polynomials or aspheric polynomials, which improves the feasibility of the solution.
[0031] In a possible implementation manner of the first aspect, the optical diffraction device is a grating or a prism.
[0032] A second aspect of the present application provides a wavelength selective switch, which includes an optical diffraction device according to the first aspect or any possible implementation of the first aspect.
[0033] A third aspect of the present application provides an optical device, which includes an optical diffraction device as described in the first aspect or any possible implementation of the first aspect.
[0034] In an embodiment of the present application, the optical diffraction device includes a first plane, on which a surface contour structure is loaded, the surface contour structure includes surface lines, and in a three-dimensional coordinate system of the surface contour structure, the surface lines are arranged at equal intervals along the X-axis direction or the Y-axis direction, and the first length of the surface contour structure along the Z-axis direction varies at preset distances along the X-axis direction and / or the Y-axis direction, so that the height of the surface contour structure fluctuates, has a higher degree of freedom, can compensate for the part of the WSS system with aberrations, and improve the optical performance of the WSS. BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Figure 1 A schematic diagram of the architecture of a wavelength selective switch;
[0036] Figure 2 A schematic diagram of an embodiment of an optical diffraction device provided in an embodiment of the present application;
[0037] Figure 3 A schematic diagram of another embodiment of an optical diffraction device provided in an embodiment of the present application;
[0038] Figure 4A A schematic diagram of another embodiment of an optical diffraction device provided in an embodiment of the present application;
[0039] Figure 4B and Figure 4C A schematic diagram of an embodiment of a surface profile structure provided in an embodiment of the present application;
[0040] Figure 5A A schematic diagram of another embodiment of an optical diffraction device provided in an embodiment of the present application;
[0041] Figure 5B-5E A schematic diagram of an embodiment of a surface profile structure provided in an embodiment of the present application;
[0042] Figure 6A-6C A schematic diagram of another embodiment of an optical diffraction device provided in an embodiment of the present application;
[0043] Figure 7 A schematic diagram of an embodiment of a method for determining a surface profile structure provided in an embodiment of the present application;
[0044] Fig. 8A Schematic diagram of Gaussian beam energy distribution provided in an embodiment of the present application;
[0045] Figure 8B A schematic diagram of another embodiment of the surface profile structure provided in the embodiment of the present application;
[0046] Figure 8C Another schematic diagram of Gaussian beam energy distribution provided in an embodiment of the present application;
[0047] Fig.8D Schematic diagram of filtering spectrum provided in the embodiment of the present application;
[0048] Fig.9A and Fig. 9B A schematic diagram of a Gaussian beam spot pattern provided in an embodiment of the present application;
[0049] Fig. 9C Another schematic diagram of the filtering spectrum provided in an embodiment of the present application;
[0050] Figure 10A-10C A schematic diagram of conical diffraction provided in an embodiment of the present application;
[0051] Fig.11 A schematic diagram of another embodiment of the method for determining a surface profile structure provided in an embodiment of the present application;
[0052] Figure 12A-12C A schematic diagram of high-order diffraction provided in an embodiment of the present application;
[0053] Fig.13 A schematic diagram of another embodiment of the surface profile structure provided in an embodiment of the present application. DETAILED DESCRIPTION
[0054] The following describes the embodiments of the present application in conjunction with the accompanying drawings. Obviously, the described embodiments are only embodiments of a part of the present application, rather than all embodiments. It is known to those skilled in the art that with the development of technology and the emergence of new scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.
[0055] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.
[0056] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.
[0057] In addition, in order to better illustrate the present application, numerous specific details are given in the following specific embodiments. It should be understood by those skilled in the art that the present application can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present application.
[0058] The following is an example of the application scenario involved in the embodiments of the present application.
[0059] Filters used in optical communication systems have evolved from fixed wavelength filters in the 20th century to selective wavelength blockers (WB), planar lightwave circuits (PLC) and wavelength selective switches (WSS).
[0060] Reconfigurable optical add-drop multiplexer (ROADM) stations use WSS and other devices to achieve the functions of adding and dropping wavelengths in the local dimension and scheduling any wavelength, that is, the characteristics of wavelength selection and scheduling. In particular, the wide and flat passband provided by WSS provides good cascading characteristics and realizes lossless signal penetration.
[0061] Specifically, after the light beam is input into the WSS, the light beams of different wavelengths are diffracted by the grating and are incident on different positions on the liquid crystal on silicon (LCOS). The LCOS applies voltage to the pixel points at the positions covered by the light beams of different wavelengths to change the phase of the liquid crystal, causing the input light beam to deflect in the direction that needs to be switched. The deflected light beam returns to the corresponding port for output.
[0062] In wavelength selective switches, considering the impact of device functions and cost, the following problems exist:
[0063] First, in the actual optical path system of WSS, there is a light beam that deviates from the optical axis and propagates. The Snell relationship in paraxial optics no longer fits perfectly, and aberration problems such as spherical aberration, coma, and field curvature will occur. In general, aberrations in paraxial optics can be approximately ignored. When silicon-based liquid crystal is used as one of the engines for wavelength selection / switching, the light spot on it has the characteristics of a long and narrow shape. The purpose of the long and narrow light spot is to arrange more wavelength channels on a switching unit of limited size, and to increase the passband bandwidth of the filter. However, correspondingly, the long and narrow shape means that the light spot is highly asymmetric, and more aberrations will be experienced in the optical system.
[0064] Secondly, when the WSS based on LCOS realizes beam deflection, the principle is that LCOS is composed of countless pixels, and different voltage controls can be loaded for each pixel. The birefringence effect of the liquid crystal is different under different voltages, and different phase delays are introduced. In port switching, LCOS provides a structure similar to a blazed grating (the diffraction energy is concentrated in a certain order), controls the voltage distribution on the LCOS, provides a specific diffraction angle for the incident light beam, and realizes the coupling of the light beam to the target port. In practical applications, due to the LCOS edge field effect, pixel size, device flatness problems, etc., the incident light beam will have high-order diffraction orders after holographic diffraction. During the beam deflection process, part of the energy will be coupled into the non-target port, affecting the insertion loss and port isolation of the coupling port, and finally the transmission performance of the system will be degraded.
[0065] Third, in the optical path layout of WSS based on LCOS, LCOS adopts single-sided or double-sided diffraction schemes according to the port arrangement method. The light beam is obliquely incident on the grating of the diffraction element, which will introduce the "conical diffraction" effect of the diffraction element. In the WSS wave combining scenario, the light beams from each wave port will be incident on the diffraction element at different angles. Conical diffraction causes the frequency deviation of the wavelength of light incident on different ports, introducing frequency deviation. At the same time, conical diffraction causes coupling mismatch with the fiber array in the dispersion direction, resulting in increased insertion loss and polarization dependent loss (PDL). In the wave splitting scenario, conical diffraction causes the tilt of the LCOS plane spot, resulting in a decrease in the filtering bandwidth.
[0066] In the future, the requirements for integration of ROADM stations will increase, and the size of each component module will need to be continuously reduced. At this time, the impact of aberration on highly asymmetric light is further aggravated, and the high-order diffraction light caused by the large diffraction angle provided by LCOS is becoming more and more serious.
[0067] In order to improve the integration of wavelength selective switches, simplification of optical path layout and reduction of the number of components have become one of the inevitable trends. In the off-axis reflective structure of the wavelength selective switch, the use of reflectors allows the Gaussian beam to pass back and forth multiple times, which can bring advantages such as simplifying the volume of the optical path space and saving the number of components. But at the same time, the impact of aberrations on the performance of the optical system will be amplified. Under the action of spherical aberration, the setting of the optimal receiving plane (focal plane) position for the light beam deviating from the optical axis and the light beam near the optical axis is worth exploring. In addition, the impact of optical aberrations such as coma and astigmatism cannot be ignored. In addition, with the improvement of integration, that is, after the length of the WSS module is extremely compressed, the aberration is less likely to be compensated.
[0068] Based on this, the embodiment of the present application provides an optical diffraction device for compensating for the aberration of the wavelength selective switch system and improving the optical performance of the wavelength selective switch. The embodiment of the present application also provides a corresponding wavelength selective switch and an optical device. The following are detailed descriptions.
[0069] like Figure 1 As shown, the optical diffraction device provided in the embodiment of the present application can be applied to a wavelength selective switch, which is configured with a fiber array consisting of a wave-adding port (Port-1 / 2 / 3) to a wave-combining port (Port-4). The WSS can realize the reconstruction and multiplexing function of any wavelength. In the wave-adding scenario, the crossover from Port-3 to the wave-combining port Port-4 is configured as an example.
[0070] The light beam enters the WSS optical system through the fiber array unit (the propagation path is shown in the figure), and the symmetry of the light beam changes after passing through the beam shaping element (not shown in the figure). When passing through the polarization diversity optics, its function is as follows: The wavelength selective switch based on LCOS is polarization sensitive, and a polarization diversity optics needs to be arranged in the optical architecture to achieve a single polarization state before the light beam reaches the LCOS.
[0071] When the light beam reaches the optical diffraction device (such as a grating), it splits each wavelength and separates it at different angles. After passing through the focusing lens (reflector), each wavelength is neatly arranged on the LCOS plane. According to the networking application and cross-configuration, wavelength 1 passes through the spatial modulator LCOS to provide a certain diffraction angle, returns according to the dotted line in the figure, passes through the collimation of the cylindrical mirror in front of the optical diffraction device, and returns to port Port-4.
[0072] Among them, the optical diffraction device can be a grating, or a combination of a grating and a prism, and the direction in which each wavelength is dispersed can be called a dispersion direction. On LCOS, the wavelengths are neatly arranged along the X-axis direction. The direction perpendicular to the wavelength dispersion is the switching direction. LCOS provides the diffraction angle of the light beam in the switching direction with the help of a phase grating. Generally, the position of the light beam on the optical diffraction device after port switching is different from that before switching in the switching direction.
[0073] The above wavelength selective switch architecture is an off-axis reflective type, and the light beam passes through the reflector multiple times, which introduces additional aberrations.
[0074] In terms of switching direction, a 2F architecture or a multi-F architecture can be used. Taking 2F as an example (the distance between the front focal plane and the back focal plane is 1F, totaling 2F, called a 2F architecture, the same applies to multi-F architecture), the light beam will be incident on the optical diffraction device at specific azimuth angles before and after reaching the LCOS, and a certain displacement difference will be introduced in the dispersion direction due to the conical diffraction phenomenon.
[0075] When LCOS provides a large diffraction switching angle, due to the influence of intrinsic factors such as fringe field effects and phase discretization, high-order diffraction terms and insertion loss degradation occur, and the high-order diffraction beam is coupled to other non-target ports through the system.
[0076] For the above example scenario, the optical diffraction device provided by the embodiment of the present application can provide not only the dispersion splitting capability, but also partial aberration correction for each wavelength (in the X-axis direction); different additional angles are provided according to the different port positions (in the Y direction) to compensate for the function of additionally introducing specific aberrations (in the Y direction) in the switching direction (in the Y direction) or at specific positions (high-order diffraction term paths), etc. In addition, it can also replace the role of cylindrical mirrors and simplify the function of the optical system.
[0077] The optical diffraction device provided in the embodiment of the present application is described below in conjunction with the above application scenarios.
[0078] like Figure 2 As shown, an embodiment of the present application provides an optical diffraction device, and an embodiment of the optical diffraction device includes a first plane 100.
[0079] The first plane 100 is loaded with a surface profile structure 200, and the surface profile structure 200 includes surface lines ( Figure 2 In the three-dimensional coordinate system of the surface profile structure 200, the surface lines are arranged at intervals along the X-axis direction or the Y-axis direction. The first length of the surface profile structure 200 along the Z-axis direction varies along the X-axis direction and / or the Y-axis direction at intervals of a preset distance.
[0080] Specifically, the main body of the optical diffraction device is a grating or a prism, etc., and the embodiment of the present application is illustrated by taking the optical diffraction device as a prism. The prism includes a prism 300 part and a grating 400 part. The grating 400 is located on any plane of the prism 300, and the plane corresponding to the grating 400 is the first plane 100 of the optical diffraction device. The surface profile structure 200 is loaded on the first plane 100 of the grating 400, that is, on the surface of the substrate, and the loading method includes but is not limited to scratching, etching or polymerization, etc. The embodiment of the present application does not limit the loading method of the surface hub structure 200.
[0081] It should be understood that if the optical diffraction device is a grating, the first plane is any plane of the grating, and the surface hub structure is loaded on this plane.
[0082] like Figure 3 As shown, in order to better describe the surface profile structure 200, a three-dimensional coordinate system of the surface profile structure 200 is established. The surface hub structure 200 includes surface scribed lines 210 to realize the basic functions of the optical diffraction device, such as dispersion and phase modulation. The surface scribed lines 210 are arranged at intervals along the X-axis direction or the Y-axis direction ( Figure 3 The specific arrangement method may be parallel arrangement, arrangement according to a preset curvature, arrangement at equal intervals, or arrangement at unequal intervals. The embodiment of the present application does not limit the arrangement method of the surface lines 210.
[0083] In addition, the first length of the surface profile structure 200 along the Z-axis direction varies along the X-axis direction and / or the Y-axis direction at a preset distance ( Figure 3 In the embodiment of the present invention, the height of the hub structure on the surface fluctuates, and the change can be continuous (i.e., the preset distance of the interval is zero), or discontinuous, approximately continuous or discrete (i.e., the preset distance of the interval is greater than zero, and the preset distances of the intervals may be different). Figure 3 shown).
[0084] Optionally, the surface profile structure may also be designed in different regions to receive different incident light beams.
[0085] Specifically, the surface profile structure includes at least two dispersion regions separated from each other, wherein the variation of the first length and / or the preset distance of the first length variation interval in the at least two dispersion regions are different, and the at least two dispersion regions are arranged along the X-axis direction and / or the Y-axis direction, and the areas of the at least two dispersion regions are equal.
[0086] For example, Figure 4A As shown ( Figure 4A The surface hub structure includes two mutually separated dispersion regions, wherein the two dispersion regions are arranged along the X-axis direction and have equal areas, such as Figure 4B and Figure 4C As shown, the variation amounts of the first lengths of dispersion region 1 and dispersion region 2 are different.
[0087] like Figure 5A As shown ( Figure 5AThe surface hub structure includes four mutually separated dispersion regions, wherein the four dispersion regions are arranged along the X-axis direction and the Y-axis direction, respectively, and the areas are equal, such as Figure 5B , Figure 5C , Figure 5D and Figure 5E As shown, the change amounts of the first lengths of dispersion region 1, dispersion region 2, dispersion region 3 and dispersion region 4 are all different, and the change directions are also different. For example, dispersion region 1 and dispersion region 2 change along the Y-axis direction, and dispersion region 3 and dispersion region 4 change along the X-axis direction.
[0088] It should be understood that in other embodiments, the change amount of the first length in each dispersion region and / or the preset distance of the first length change interval may be the same. In addition, the surface profile structure may change along the X-axis direction and the Y-axis direction at the same time, the area of each dispersion region may also be different, and the first length of each dispersion region may also change at intervals of a preset distance, that is, the preset distance of the first length change interval in each dispersion region is different, for example, zero or greater than zero, and the embodiments of the present application will not be repeated.
[0089] It should be noted that the setting of the dispersion region can be determined based on the type of wavelength selective switch. For example, the number of dispersion regions increases with the dimension of the wavelength selective switch (referring to the maximum number of connection directions that the ROADM node can provide, which can also be understood as the number of output ports of the wavelength selective switch). When the wavelength selective switch may be applied to different incident light beams, the dimension of the incident light beam will also change accordingly. The sub-region design can make the surface profile structure suitable for wavelength selective switches of different dimensions, thereby improving the adaptability of the optical diffraction device.
[0090] Exemplarily, as the incident light beam changes, when the dimension of the wavelength selective switch is 9, one dispersion region is set, that is, the entire first plane is not partitioned, when the dimension of the wavelength selective switch is 20, two dispersion regions are set, respectively for splitting light beams of 10 wavelengths, and when the dimension of the wavelength selective switch is 58, more than two dispersion regions are set. The embodiment of the present application does not limit the number of dispersion regions and partition conditions.
[0091] In addition, the surface profile structure of the optical diffraction device can also converge and / or diverge the light beam, realize the spot transformation of the Gaussian beam, for example, realize the collimation function, and can replace the lens in the WSS optical system. There is no need to set up additional lenses in the WSS, which simplifies the function of the optical system and realizes the small integration of the WSS.
[0092] The optical diffraction device provided in the embodiments of the present application is described in detail below in combination with the optical problems solved by the optical diffraction device provided in the embodiments of the present application.
[0093] 1. Optical Aberrations
[0094] In the off-axis reflective structure of the wavelength selective switch, the aberrations in the optical system will affect the quality of the light spot, which can be manifested in the form of sudden changes in the wavefront phase and the deviation of the Gaussian beam energy distribution from the ideal state.
[0095] For example, Fig. 6A The figure shows a schematic diagram of paraxial optical imaging. When a light beam deviates from the optical axis in the optical path system, it may cause the following Figure 6B The spherical aberration shown and Figure 6C Coma shown.
[0096] In order to compensate for the influence of optical aberration on the spot quality of the beam, the following can be performed: Figure 7 The method flow is shown.
[0097] Specifically, an optical model of a wavelength selective switch of 1×N or M×N (where 1 and M are the number of input ports, and N is the number of output ports, i.e., the dimension) is initialized, and the spot characteristics of each wavelength of the outgoing light beam on the imaging surface LCOS are calculated by optical software, such as M for indicating the spot quality of the outgoing light beam. 2 factor, and initialize the parameters of the surface profile structure of the optical diffraction device (such as the variation of the first length), and then set the constraint function related to the parameter, which is used to evaluate the spot characteristics of the output light beam of the optical diffraction device, and the spot characteristics are the spot quality M 2 Factor, constraining the spot quality M 2 The factor approaches 1, thus determining the parameters of the surface hub structure.
[0098] Among them, M 2 is the ratio of the product of the beam parameters to the product of the beam parameters of the fundamental mode Gaussian beam, which can be expressed as:
[0099]
[0100] Among them, the beam parameter product (BPP) is W×θ, θ0 is the far-field divergence half angle of the Gaussian beam, θ0=λ / πW0, W0 is the waist radius of the Gaussian beam, and λ is the beam wavelength.
[0101] Before using the optical diffraction device provided in the embodiment of the present application for compensation, the light spot is affected by the system aberration, such as Fig. 8A As shown in the figure (the horizontal axis is the Y-axis coordinate value, and the vertical axis is the radiation energy), the energy distribution of the Gaussian beam in the Y-axis direction is measured, and side spots can be observed at the edge of the spot energy distribution. Figure 8B After the surface profile structure shown is compensated, the surface hub structure realizes the correction of some aberrations in the system, such as Figure 8C As shown in the figure (the horizontal axis is the Y-axis coordinate value, and the vertical axis is the radiation energy), the side spots at the edge of the spot energy are suppressed, and accordingly, the bandwidth performance of the wavelength selective switch is improved. In addition, Fig.8D As shown (the horizontal axis is the frequency offset, and the vertical axis is the insertion loss), the rectangularity of the optimized filter spectrum (solid line) is also improved compared with the filter spectrum before optimization (dashed line).
[0102] The optical diffraction device provided by the embodiment of the present application has the ability to disperse each wavelength and can compensate for the optical aberrations existing in the WSS. The surface profile structure has a higher degree of freedom and can integrate and compensate for the opposite parts of different aberrations existing in the WSS system. The positions of light beams of different paths based on different polarization states / same polarization states incident on the optical diffraction device are different. A highly undulating surface profile structure with continuity / discretization is selected at different positions in the diffraction direction (X-axis direction). The dispersion ability is achieved through surface engraving, and the phase control ability is achieved through the change of the first length. There is no or very little possibility of mutual influence, and optical aberrations such as spherical aberration, coma and field curvature can be partially compensated.
[0103] 2. Conical Diffraction
[0104] The wavelength selective switch can adopt the same or different schemes in the dispersion switching direction, that is, 2F or 4F scheme. When the switching direction adopts the 2F scheme, the Gaussian beam obliquely enters the diffraction element, which will introduce the conical diffraction phenomenon, resulting in the tilt and offset of the light spot on the LCOS.
[0105] Specifically, the optical diffraction device in the wavelength selective switch is responsible for dispersing each wavelength on the spatial modulator LCOS. In the wave adding (combining) scenario, the same wavelength enters the WSS optical path system from different ports, and the azimuth angles incident on the optical diffraction device are different. The same wavelength spot has different inclinations on the LCOS, thus generating different frequency deviations. This type of frequency deviation is port-dependent. In general, the wave adding port farthest from the combining port has the largest spot offset. Fig.9A The following is the spot pattern under ideal conditions on LCOS. Fig. 9B As shown in the figure, the spot pattern is tilted and shifted, and the shift is Δf, as shown in Fig. 9C As shown (the horizontal axis is frequency, the vertical axis is insertion loss), the inclination of the light spot causes the light spot to expand along the X-axis direction, the rectangularity of the filter spectrum deteriorates, and the bandwidth deteriorates.
[0106] like Fig. 10AAs shown in the figure, when the Gaussian beam propagates to the optical diffraction device, the main beam is incident at an angle of φ0 in the plane of the y-axis direction-z-axis direction. Due to the divergence characteristics of the Gaussian beam, the angles of its edge light incident on the grating surface are φ1 and φ2 respectively. According to the conical diffraction equation, it is expressed as follows:
[0107]
[0108] Where the incident angle is α, φ is the incident color and the azimuth of the element, the diffraction angle is β, m is the color and order, d is the surface line spacing, and λ is the incident wavelength. Fig. 10B As shown, in the plane of the X-axis direction-Z-axis direction, the light beams L0, L1, and L2 are incident on the optical diffraction device at almost the same angle α. Due to the different azimuth angles φ0, φ1, and φ2, according to the formula, the light beams L0, L1, and L2 are emitted from the optical diffraction device at different dispersion angles β0, β1, and β2. Finally, as shown in Fig. 10C As shown, in the dispersion direction (the plane of the X-axis direction - the Z-axis direction), conical diffraction causes different light rays of the same light beam to have different exit angles from the grating, resulting in a tilted and offset light spot on the LCOS plane.
[0109] In order to avoid the tilt and offset of the light spot on the LCOS and determine the angle compensation, the following can be performed: Fig.11 The method flow is shown.
[0110] Specifically, the optical model of the 1×N or M×N wavelength selective switch is initialized. The optical model can be expressed by the following formula:
[0111]
[0112] Among them, c x represents the curvature in the X-axis direction, c y represents the curvature in the Y-axis direction, κ x represents the cone parameter in the X-axis direction, κ y It represents the cone parameter in the Y-axis direction. When the value of κ is different, the surface shape is different. For example, when κ=-1, the surface shape is parabolic. When κ<-1, the surface shape is hyperbolic. a is the aspheric coefficient.
[0113] After determining the optical model, the spot pattern of the Gaussian beam from each upstream port on the spatial modulator LCOS is obtained, and the geometric characteristics (main light, edge light position / angle, etc.) and physical characteristics (spot waist size, etc.) of the spot of the Gaussian beam are determined, and the parameters of the surface profile structure of the optical diffraction device are initialized. Then, a constraint function related to the parameter is set. The constraint function is used to evaluate the spot characteristics of the output light beam of the optical diffraction device. The spot characteristic is the angle between the spot pattern of the output light beam and the Y-axis direction (switching direction). After keeping the waist position of the Gaussian spot falling on the LCOS, the angle between the narrow and long Gaussian spot pattern and the switching direction is constrained to be minimized as the best optimization goal, and the above steps are repeated for each port, so as to determine the parameters of the surface hub structure to optimize the degree of spot inclination corresponding to each upstream port.
[0114] Optionally, an expression for the surface hub structure can be determined based on the parameters of the surface hub structure, that is, the expression of the first length along the X-axis direction or the Y-axis direction. The surface hub structure integrates an angle compensation function, and the expression is generally a first-order linear polynomial. For all upper wave ports, the surface hub structure is composed of multiple segmented first-order polynomials.
[0115] Furthermore, the surface structure expression is a two-dimensional multi-order combination expression (an expression of the first length along the X-axis and the Y-axis), including general polynomials (Extended Polynomials), Fourier extension polynomials (FourierExtension) or aspheric polynomials (Forbes Aspheres), etc.
[0116] The optical diffraction device provided by the embodiment of the present application can be similarly integrated with an angle compensation function to pre-compensate the angle of the light beam incident on the optical diffraction device and correct the azimuth angle of the light beam incident on the optical diffraction device, thereby reducing the degree of light spot tilt. The positions of the Gaussian beams incident on the optical diffraction device from different ports through different paths are different. The surface profile structure with a continuous / discrete height difference is selected at different positions in the switching direction (Y-axis direction), which can partially compensate for the azimuth angle of the incident optical diffraction device.
[0117] 3. High-order diffraction deviation
[0118] In the application of high-dimensional wavelength selection switches, when LCOS is used as a switching unit, it provides large-angle diffraction, the phase is discretized, and the number of pixels in the phase grating period provided by it is reduced. Secondly, due to its own structural characteristics, such as the edge field effect of the LCOS intrinsic device, that is, the transverse electric field between pixels causes the corresponding phases to change slowly, and the phase grating has a fly back area. In the direction of port switching, the optical path can be simplified to a 2F system. The LCOS plane is located on the focal plane. The high-order diffracted light beam on the source focal plane will be coupled into the non-target port, that is, the light beam incident on the LCOS will deviate from the main order by a certain angle after diffraction. It can also be understood that the phase grating provided by the LCOS deviates greatly from the ideal blazed grating structure, introducing some energy into the non-main signal diffraction order, increasing the energy of the crosstalk signal, and affecting indicators such as port isolation.
[0119] Among them, the exit angle of the high-order diffraction term can be calculated by the grating formula. Therefore, at a fixed position in the switching direction, by loading a specific one-dimensional or two-dimensional modulation phase on the optical diffraction device, the high-order diffraction order can be caused to have the following phenomenon in the dispersion or switching direction: Fig. 12A As shown in FIG. 1 , increasing the aberration defocus (Defocus, which means the focus is away from the best receiving surface along the best optical axis) will cause displacement from the non-coupled port, that is, the best coupling plane is misplaced; as shown in FIG. Fig. 12B As shown in FIG. 1 , increasing the tilt (Tilt, which refers to the deviation of the light beam in the propagation direction) causes the non-coupled port angle to deviate, that is, the best receiving plane and the light beam angle are mismatched; as shown in FIG. Fig. 12C As shown, the aberration defocus and tilt are increased at the same time, resulting in displacement and angle deviation from the non-coupled port, that is, the optimal receiving plane is mismatched with the beam position and angle at the same time. In summary, the newly added modulation phase is not limited to the above optical aberration expression form.
[0120] like Fig.13 As shown, in the surface profile structure, the expression of the first length along the X-axis direction or the Y-axis direction is a sine function or a cosine function, so that the optical diffraction device integrates a sine or cosine modulation phase to achieve a deviation in the optimal coupling position, reduce the crosstalk light coupled into the non-target port, and improve the isolation index of the wavelength selection switch.
[0121] It should be understood that as the structural complexity of the surface profile structure increases, the position and angle deviations in the dispersion / switching direction increase simultaneously, and the energy of the high-order diffracted light leaking into the uncoupled port will continue to decrease, further improving the effect.
[0122] The optical diffraction device provided by the embodiment of the present application can be loaded with a modulated phase similar to the surface of an integrated diffractive optical element (DOE), adding new optical aberrations, so that the high-order diffracted light deviates from the non-target port. After the light beam is switched by LCOS, the high-order diffracted light generated when different ports are switched has different positions on the optical diffraction device. A surface profile structure with a continuous / discrete height difference is selected in the switching direction (Y-axis direction), and a new phase is added to the wavefront of different high-order diffracted light beams to achieve the light beam deviating from the non-target port.
[0123] Summarizing the above embodiments, it can be seen that the beneficial effects brought by the optical diffraction device provided in the embodiments of the present application include but are not limited to the following four points:
[0124] (1) The surface profile structure has a higher degree of freedom and can be integrated to compensate for the opposite parts of different aberrations in the WSS system, solving the problem of large optical aberrations caused by off-axis systems in WSS;
[0125] (2) The surface profile structure integrates an angle compensation function, which pre-compensates the angle of the light beam incident on the optical diffraction device and corrects the azimuth angle of the light beam incident on the optical diffraction device, reduces the degree of light spot tilt, and solves the problem of light spot tilt caused by conical diffraction;
[0126] (3) The surface contour structure loads the modulation phase and adds new optical aberrations, causing the high-order diffracted light to deviate from the non-target port, thus solving the problem of the interference of the high-order diffracted light of the spatial phase modulator on the system performance in WSS.
[0127] (4) The surface profile structure can replace the lens, simplify the WSS optical system, and achieve the miniaturization of WSS.
[0128] In another embodiment of the present application, a wavelength selective switch is further provided. The wavelength selective switch includes the optical diffraction device described in the above embodiment. The wavelength selective switch can be Figure 1 The wavelength selective switch shown.
[0129] In another embodiment of the present application, an optical device is provided, which includes the optical diffraction device described in the above embodiment. Specifically, the optical device is a laser radar, which can be installed in a vehicle or aircraft, or the optical device is an optical communication device for realizing wireless optical communication.
[0130] In the several embodiments provided in the present application, it should be understood that the disclosed structure can be implemented in other ways. For example, the embodiments described above are merely illustrative, and for example, the division of the structure can be divided in other ways in actual implementation, such as multiple units or components can be combined or integrated into another structure, or some features can be ignored. Some or all of the structures can be selected according to actual needs to achieve the purpose of the present embodiment.
[0131] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.
Claims
1. An optical diffraction device, characterized in that: It includes a first plane, on which a surface profile structure is loaded, and the surface profile structure includes surface lines; In the three-dimensional coordinate system of the surface profile structure, the surface lines are arranged at intervals along the X-axis direction or the Y-axis direction; The first length of the surface profile structure along the Z-axis direction varies at preset intervals along the X-axis direction and / or the Y-axis direction.
2. The device according to claim 1, characterized in that The surface profile structure includes at least two dispersion regions separated from each other, and the at least two dispersion regions are used to receive different incident light beams.
3. The device according to claim 2, characterized in that The change amount of the first length and / or the preset distance of the first length change interval in the at least two dispersion regions are different.
4. The device according to claim 2 or 3, characterized in that The at least two dispersion regions are arranged along the X-axis direction and / or the Y-axis direction.
5. The device according to any one of claims 2 to 4, characterized in that The at least two dispersion regions have equal areas.
6. The device according to any one of claims 1 to 5, characterized in that The preset distance is zero.
7. The device according to any one of claims 1 to 6, characterized in that The variation of the first length is determined based on a constraint function, and the constraint function is used to evaluate the spot characteristics of the output light beam of the optical diffraction device.
8. The device according to claim 7, characterized in that The light spot characteristic includes the light spot quality of the outgoing light beam and / or the angle between the light spot pattern of the outgoing light beam and the Y-axis direction.
9. The device according to any one of claims 1 to 8, characterized in that The expression of the first length along the X-axis direction or the Y-axis direction is a sine function or a cosine function.
10. The device according to any one of claims 1 to 9, characterized in that The expressions of the first length along the X-axis direction and the Y-axis direction are Fourier expansion polynomials or aspherical polynomials.
11. The device according to any one of claims 1 to 10, characterized in that The optical diffraction device is a grating or a prism.
12. A wavelength selective switch, characterized in that: Comprising the optical diffraction device as described in any one of claims 1-11.
13. An optical device, characterized in that: Comprising the optical diffraction device as described in any one of claims 1-11.