A multi-plane optical conversion device on chip and an optimization design method thereof

Abstract

The application relates to the technical field of multi-plane light converters, and more particularly to an on-chip multi-plane light conversion device and an optimization design method thereof. A grating coupling unit, a multi-plane phase sheet and a mirror are integrated on the same glass substrate, three-dimensional monolithic integration of input coupling, light path folding and light field transformation functions is realized, precise mechanical alignment requirements among discrete components are completely eliminated, the integration degree is high, high-precision alignment is avoided, stability is improved, and the volume is reduced to a certain extent. The application realizes efficient conversion of a light field between an on-chip waveguide and free space through the grating coupling unit, and performs arbitrary unitary transformation in the free space by using an MPLC composed of the multi-plane phase sheet and the mirror, the two work cooperatively, the high mode capacity and low crosstalk advantages of the MPLC are combined with the on-chip integration advantages of the grating coupling unit, and high-performance and small-volume light field transformation can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of multi-plane light converter, more particularly, to a multi-plane light conversion device on a chip and an optimization design method thereof. BACKGROUND

[0002] With the capacity of fiber communication approaching the Shannon limit of single-mode fiber, space division multiplexing (SDM) technology becomes the key path to break the bottleneck. Among them, mode division multiplexing (MDM) improves the capacity through parallel transmission of orthogonal space modes in few-mode fiber, and its core relies on high-performance mode multiplexer / demultiplexer. Multi-plane light converter (MPLC) is considered as an ideal solution because it can theoretically realize arbitrary unitary transformation and support low-crosstalk and low-loss mode conversion. In the existing MPLC technology, the traditional MPLC is composed of free-space phase mask, mirror and fiber coupler, which has the problem of large volume caused by the discrete structure. At the same time, due to the need for high-precision alignment in discrete assembly, the stability of the device is also reduced, and it is highly sensitive to the environment, and temperature or vibration can easily cause optical path deviation, reducing the mode conversion efficiency. The existing integration scheme only integrates the phase mask, and does not solve the integration of input coupling and optical path folding, which requires external fiber or collimator input, increasing the volume. SUMMARY

[0003] The purpose of the present application is to overcome the problems of large volume, poor stability and difficult alignment of the prior art MPLC, and to provide a multi-plane light conversion device on a chip and an optimization design method thereof, which has high integration, avoids high-precision alignment, improves stability, and reduces volume to some extent.

[0004] To solve the above technical problems, the technical scheme adopted by the present application is:

[0005] Provided is a multi-plane light conversion device on a chip, comprising:

[0006] a glass substrate having a front surface and a back surface arranged oppositely;

[0007] a grating coupling unit arranged on the back surface region and / or the front surface region of the glass substrate, for coupling the free-space optical field inside the glass substrate to the optical field propagating in the waveguide, or diffracting the optical field propagating in the waveguide to the free-space optical field inside the glass substrate;

[0008] a multi-plane phase mask comprising N phase transformation regions arranged at intervals on the back surface region of the glass substrate, or respectively located on the front surface and the back surface region; for realizing phase modulation on the optical field propagating in the free space;

[0009] a mirror for folding the light path, so that the light field propagates in turn by reflection between the phase transformation regions, arranged in the front region and / or the back region of the glass substrate.

[0010] The on-chip multi-plane optical conversion device integrates the grating coupling unit, the multi-plane phase sheet and the mirror on the same glass substrate, realizes three-dimensional monolithic integration of input coupling, light path folding and light field transformation functions (such as mode conversion), completely eliminates the precise mechanical alignment requirement between discrete components, has high integration, avoids high-precision alignment, improves stability, and also reduces the volume to a certain extent. The grating coupling unit realizes efficient conversion of the light field between the on-chip waveguide and the free space, and the MPLC composed of the multi-plane phase sheet and the mirror performs arbitrary unitary transformation in the free space, and the two work together to combine the high mode capacity and low crosstalk advantage of the MPLC with the on-chip integration advantage of the grating coupling unit, so as to realize high-performance and small-volume light field transformation (including mode multiplexing / demultiplexing).

[0011] Further, the grating coupling unit includes at least two grating couplers and is spaced on the same side of the glass substrate.

[0012] Further, the grating coupler includes a focusing grating coupler or a two-dimensional grating coupler.

[0013] Further, the grating coupler is a polarization beam splitter grating coupler.

[0014] Further, the phase transformation region includes a reflective metasurface or a reflective diffractive optical phase sheet, which can realize polarization-independent or polarization-separated phase modulation.

[0015] Further, the glass substrate is further provided with a light transmission hole for outputting the modulated light field to the outside of the glass substrate or receiving the light field to be processed into the glass substrate.

[0016] Further, the grating coupling unit, the multi-plane phase sheet and the mirror are arranged on the same glass substrate; or the grating coupling unit is arranged on a first glass substrate, and the multi-plane phase sheet and the mirror are arranged on a second glass substrate, and the first glass substrate and the second glass substrate are aligned and integrated by a bonding process.

[0017] The application further provides an on-chip multi-plane optical conversion method, which uses the above-mentioned on-chip multi-plane optical conversion device to realize mode multiplexing / demultiplexing, and specifically includes:

[0018] The single-mode light is transmitted from the on-chip waveguide to the grating coupling unit, the grating coupling unit diffracts the waveguide light into spatial light, and the spatial light is emitted at a set angle in the glass substrate, and the light propagating in the glass substrate is repeatedly reflected and phase-modulated between the mirror and the multi-plane phase plate, and finally emitted from the glass substrate; wherein the grating coupler is provided with M, M is greater than or equal to 2, and the M grating couplers are regularly arranged, the M grating couplers output M spatially separated single-mode Gaussian lights, and the M single-mode Gaussian lights are converted into M coaxial and mutually orthogonal spatial mode lights after the multi-plane phase plate and the mirror, so that single-mode to few-mode multiplexing is realized;

[0019] The M spatial modes are emitted into the glass substrate at a set angle, and after the reflection and phase modulation of the multi-plane phase plate and the mirror, the M coaxial and mutually orthogonal spatial mode lights are converted into M spatially separated single-mode Gaussian lights, and the M spatially separated single-mode Gaussian lights are coupled into the on-chip waveguide through the M grating couplers respectively, so that few-mode to single-mode demultiplexing is realized.

[0020] Further, by using a polarization splitting grating coupler, polarization demultiplexing is realized while mode multiplexing / demultiplexing is realized; wherein after the reflection and phase modulation of the multi-plane phase plate and the mirror, the M coaxial and mutually orthogonal spatial mode lights are converted into M spatially separated single-mode Gaussian lights, the single-mode Gaussian light contains TE and TM polarization states, and after the single-mode Gaussian light is incident on the polarization splitting grating coupler, the polarization splitting grating coupler couples the TE polarized light into the first output waveguide and couples the TM polarized light into the second output waveguide.

[0021] The application also provides an optimization design method of the above-mentioned on-chip multi-plane optical conversion device, comprising the following steps:

[0022] S1. Parameter initialization: including determining the thickness of the glass substrate, the number of phase transformation regions, the size of the phase transformation region, the spacing value between each grating coupler in the grating coupling unit; defining the range of the working wavelength, setting the maximum value i of the outer loop Max , the maximum value j of the inner loop Max ; setting the target performance index, including coupling efficiency, crosstalk, bandwidth;

[0023] S2. Outer loop optimization:

[0024] S21. Generating / Updating the structure parameters of the grating coupler, taking the initial set of fundamental mode light field distribution or the fundamental mode light field distribution generated after the demultiplexing of the multi-plane optical conversion device as the target light field, and optimizing the structure parameters of the grating coupler according to the optimization algorithm;

[0025] S22. Electromagnetic simulation is performed on the currently generated / updated grating coupler structure, and the complete information of the grating coupler output light field is extracted from the simulation result; it is judged whether the loop number j is less than or equal to j Max, if no, go to step S23, if yes, go to step S3;

[0026] S23. Calculate the performance of the multi-plane light conversion device, using the result parameters of the current grating coupler and the optimized phase distribution, calculate the performance of the multi-plane light conversion device in the whole working wavelength range, including the total loss, crosstalk, bandwidth; record the performance of this iteration; judge whether the loop number j is greater than or equal to i Max or whether the target performance is reached, if no, go to step S21, if yes, go to step S4;

[0027] S3. Inner layer optimization loop:

[0028] S31. MPLC forward propagation calculation, take the output light field of the grating coupler obtained in step S22 as the input light field of the multi-plane light conversion MPLC light field propagation, calculate the light field forward propagated to the phase transformation area, modulate after passing through the phase transformation area, and then propagate to the next phase transformation area, and sequentially propagate until the output surface, record the light field propagated to each phase transformation area;

[0029] S32. Calculate the mode matching degree of the output light field and the target light field, compare the output light field obtained by forward propagation with the target light field;

[0030] S33. MPLC reverse propagation calculation, reverse propagate the target light field to the last phase transformation area, modulate after the phase transformation area, and then propagate to the previous phase transformation area, and sequentially propagate until the output surface, record the light field propagated to each phase transformation area;

[0031] S34. Update the phase sheet distribution of the phase transformation area, update the phase distribution of the phase transformation area by the forward propagation light field and the reverse propagation light field obtained by S31, S32, S33, and the calculated mode matching degree, using gradient descent method or wavefront matching method;

[0032] S35. Judge whether the loop number j is less than or equal to j Max , if yes, go to step S31; if no, go to step S23;

[0033] S4. Output the optimal design parameters, select a set of parameters with the optimal performance in the above loop optimization process.

[0034] Further, in step S31, the light field forward propagated to the phase transformation area is calculated by the offset angle spectrum method, and then propagated to the next phase transformation area by the offset angle spectrum method after modulation by the phase transformation area; in step S33, the target light field is reverse propagated to the last phase transformation area by the offset angle spectrum method, and then propagated to the previous phase transformation area by the offset angle spectrum method after modulation by the phase transformation area.

[0035] Further, the optimization algorithm includes a particle swarm optimization algorithm, a genetic algorithm, a gradient descent algorithm, and a wavefront matching algorithm.

[0036] Further, in step S32, a loss function is also defined, which can be defined as the square of the absolute value of the mode overlap integral.

[0037] Compared with the prior art, the present application has the following advantages:

[0038] 1. The on-chip multi-plane optical conversion device and method greatly improves the compactness of the device by reducing the size of the entire device to millimeter level through monolithic integration of the grating coupling unit, multi-plane phase sheet and mirror on the same glass substrate and folding the optical path inside the glass substrate, laying a foundation for future applications in board-level optical interconnection, co-packaged optics and other scenarios.

[0039] 2. The on-chip multi-plane optical conversion device and method eliminates most of the free space interfaces and alignment steps between discrete elements by implementing all key optical functional elements through monolithic integration, making the device less sensitive to temperature and mechanical vibration and having higher long-term stability and environmental robustness.

[0040] 3. The on-chip multi-plane optical conversion device and method can convert M-channel single-mode input light into mode multiplexed light of a few-mode fiber, or demultiplex mode multiplexed light of a few-mode fiber into M-channel single-mode output light, and can also realize polarization demultiplexing while realizing mode multiplexing / demultiplexing.

[0041] 4. The optimization design method of the on-chip multi-plane optical conversion device uses a hierarchical optimization strategy of outer light field matching optimization and inner phase distribution optimization to cooperatively optimize the structural parameters of the grating coupler and the phase distribution of the multi-plane phase sheet, realizing efficient integrated design of the grating coupler and the multi-plane optical conversion. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 It is a first perspective structural schematic diagram of the on-chip multi-plane optical conversion device of the present application.

[0043] Figure 2 It is a first perspective structural schematic diagram of the on-chip multi-plane optical conversion device of the present application.

[0044] Figure 3 It is a schematic diagram of the on-chip multi-plane optical conversion device of the present application using a bonding method.

[0045] Figure 4 It is a schematic diagram of the on-chip multi-plane optical conversion device of the present application using a bonding method.

[0046] Figure 5 The structure schematic diagram of the polarization beam splitter grating coupler of the application;

[0047] Figure 6 The flowchart of the optimization design method of the on-chip multi-plane optical conversion device of the application.

[0048] In the drawings: 1, glass substrate; 11, second glass substrate; 12, first glass substrate; 2, grating coupling unit; 21, grating coupler; 211, first output waveguide; 212, second output waveguide; 3, phase transformation area; 4, mirror; 5, light hole. DETAILED DESCRIPTION

[0049] The application will be further described below in conjunction with the specific embodiments. In the drawings, only the schematic diagram is shown, not the actual figure, and it cannot be understood as a limitation to the application; in order to better illustrate the embodiments of the application, some components in the drawings may be omitted, enlarged or reduced, and they do not represent the actual size of the product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0050] The same or similar reference numerals in the drawings of the embodiments of the application correspond to the same or similar components; in the description of the application, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for illustrative purposes, and cannot be understood as a limitation to the application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0051] Embodiment one

[0052] The first embodiment of the on-chip multi-plane optical conversion device is shown in the drawings, which comprises:

[0053] The glass substrate 1 has a front surface and a back surface arranged oppositely; the material is fused quartz, and the thickness is 0.5-3mm (ordinary fused quartz wafer thickness);

[0054] A grating coupling unit 2 is arranged on the back surface area or / and the front surface area of the glass substrate 1, and is used to couple the free-space optical field inside the glass substrate 1 to the optical field propagating in the waveguide, or to diffract the optical field propagating in the waveguide to the free-space optical field inside the glass substrate 1; the grating coupling unit 2 is used for input or output optical field coupling, the exit angle is the same as the incidence angle of the multi-plane phase plate, and can be a focusing grating coupler 21 or a two-dimensional grating coupler 21 to realize different requirements and support bidirectional optical coupling function; the grating coupling unit 2 includes at least two grating couplers 21 and is arranged at the same side of the glass substrate 1.

[0055] The multi-plane phase plate includes N phase transformation regions 3, and the phase transformation is realized by using a super surface or a phase plate; the phase plate and the super surface are integrated on a reflective film, are reflective, include different etching depths or periodic micro-nano structures, and perform polarization-independent or polarization-separated phase modulation on the optical field. The N phase transformation regions 3 are arranged at the back surface area of the glass substrate 1 or are arranged at the front surface area and the back surface area respectively; and are used to perform phase modulation on the optical field propagating in the free space.

[0056] The mirror 4 is used to fold the optical path, and is arranged on the front surface area and / or the back surface area of the glass substrate 1. The mirror 4 is made of gold film, silver film or dielectric film.

[0057] The glass substrate 1 is also provided with a light transmission hole 5 for outputting the multi-plane converted optical field, and the diameter of the light transmission hole 5 is 20 um to the same size as the phase transformation region 3, which is used to match the mode field diameter of the few-mode optical fiber or directly output to the free space, and is processed on the front surface or the back surface of the glass substrate 1.

[0058] In the embodiment, the grating coupling unit 2, the multi-plane phase plate and the mirror 4 are arranged on the same glass substrate 1; or the grating coupling unit 2 is arranged on the first glass substrate 12, the multi-plane phase plate and the mirror 4 are arranged on the second glass substrate 11, and the first glass substrate 12 and the second glass substrate 11 are aligned and integrated through a bonding process, as shown in FIG. 8, so that integration in different material systems can be realized and the application space is improved. Figure 3

[0059] ​Optical path principle: the optical path is coupled by the grating coupling unit 2, is reflected and modulated back and forth by the mirror 4 and the phase transformation area 3, and is finally output through the light hole 5. Specifically, the grating coupling unit 2 exits the incident light at a certain angle, propagates in the glass substrate 1 to the back mirror 4 or the phase transformation area 3, the phase transformation area 3 modulates the phase of the received input light field, and reflects the modulated light field to the mirror 4 or the next phase transformation area 3, and repeats the phase modulation and reflection process, so that the N phase transformation areas 3 complete the phase modulation of the input light field in turn, and then the light hole 5 is output. N phase transformation areas 3 can be located on the front surface (the same surface as the grating coupler 21) of the glass substrate 1, the back surface (different surface from the grating coupler 21) of the glass substrate 1 or both surfaces.

[0060] The on-chip multi-plane optical conversion device provided by the embodiment has the following outstanding advantages, characteristics and positive effects:

[0061] 1. Miniaturization and high integration, realizing millimeter-level packaging

[0062] Compared with the prior art: the traditional discrete MPLC is mechanically stacked by multiple free-space optical elements (phase sheet, mirror 4, fiber array, etc.), and the volume is usually centimeter level.

[0063] Effect of the application: by monolithically integrating the grating coupler 21, the multi-plane phase sheet and the mirror 4 on the same glass substrate 1, and folding the optical path inside the glass substrate 1, the size of the entire device is reduced to millimeter level, which greatly improves the compactness of the system and lays a foundation for future applications in board-level optical interconnection, co-packaged optics and other scenarios.

[0064] 2. High stability and environmental robustness

[0065] Compared with the prior art: the stability of the discrete MPLC depends on the mechanical alignment of multiple elements, which is extremely sensitive to temperature changes and vibration, and is easy to cause optical path deviation and performance degradation.

[0066] Effect of the application: since all key optical functional elements are realized by monolithic micro-nano structures, most of the free-space interfaces and alignment links between discrete elements are eliminated; therefore, the device is not sensitive to temperature and mechanical vibration, and has higher long-term stability and environmental robustness.

[0067] 3. Greatly reduce assembly complexity and cost

[0068] Compared with the prior art: the discrete MPLC requires high-precision active or passive alignment, and the assembly process is complicated, time-consuming and costly.

[0069] The application effect: the grating coupler 21 and the input / output port of the MPLC are self-aligned during the manufacturing process. Whether it is a monolithic integration scheme or a heterogeneous integration scheme through a bonding process, the complex three-dimensional spatial alignment is converted into wafer-level lithography alignment, which is more accurate, has better repeatability, and significantly reduces assembly cost and difficulty.

[0070] 4. Excellent performance and high scalability

[0071] Comparison with prior art: the mode capacity of the traditional multi-mode grating coupler 21 is limited (usually 2-3 modes), and further increasing the mode will make the design problem highly complex and cause mode crosstalk difficult to effectively control.

[0072] The application effect:

[0073] High performance: inherits the advantage of MPLC that can theoretically realize any unitary transformation, and can realize low crosstalk and low loss multi-mode conversion.

[0074] High scalability: expanding the mode capacity becomes direct. To support the M+1th mode, only one output channel needs to be added in the MPLC design and the M+1th grating coupler 21 needs to be integrated, and the design complexity increases linearly rather than exponentially, providing a clear technical path for future higher-dimensional space division multiplexing systems.

[0075] 5. Support wafer-level manufacturing and testing, and have excellent mass production

[0076] Comparison with prior art: discrete MPLC is difficult to mass-produce, and has poor performance consistency.

[0077] The application effect: the core structure of the device can be mass-produced on a glass wafer using standard micro-nano processing technology (such as ultraviolet lithography, electron beam lithography, and reactive ion etching), supporting wafer-level automated testing and screening, ensuring the consistency and reliability of device performance, and making low-cost, large-scale production possible.

[0078] 6. Functional diversification and flexibility

[0079] Comparison with prior art: traditional schemes have single functions and are difficult to implement complex functions on the same platform.

[0080] The application effect: by selecting different types of grating couplers 21 (such as focusing gratings and polarization beam splitting gratings), and combining with the flexible phase control of the MPLC, a variety of functional devices can be derived. For example, polarization diversity reception can be realized simultaneously while completing mode demultiplexing, which is a complex function that traditional single technology path cannot achieve.

[0081] Example two

[0082] The embodiment is an embodiment of a multi-plane light conversion method on chip. The embodiment uses the multi-plane light conversion device provided in Embodiment 1 to realize mode multiplexing / demultiplexing, and the working waveband is located in the optical fiber communication waveband, taking the C waveband as an example.

[0083] In the embodiment, the multi-plane light conversion device includes a grating coupling unit 2, N phase conversion regions, a mirror 4, a glass substrate 1, and a light transmission hole 5 provided on the glass substrate 1. The grating coupler 21 has a bidirectional function, supporting coupling of light in the waveguide to spatial light and coupling of spatial light to the optical waveguide. The specific working process is as follows: 1550 nm single-mode light is transmitted from the on-chip optical waveguide to the grating coupling unit 2, the grating coupling unit 2 diffracts the waveguide light into spatial light, which is reflected back and forth in the glass substrate 1 at a certain angle. The calculation method of the angle is atan (phase conversion region 3 interval / (2 * glass substrate 1 thickness)). The N phase conversion regions 3 are processed on the same surface (front surface) of the grating coupling unit 2, and the implementation is a metasurface. The reflective film is a gold film, which is processed on the glass substrate 1. The grating coupler 21 unit includes M grating couplers 21 and is regularly arranged.

[0084] Mode multiplexing: the optical waveguide transmits 1550 nm single-mode light to the grating coupling unit 2, the grating coupling unit 2 diffracts the waveguide light into spatial light, which is emitted at a certain angle in the glass substrate 1, propagates in the glass substrate 1 to the back mirror 4, and is reflected to the front first phase conversion region 3. The first phase conversion region 3 modulates the phase of the received input light field and reflects the modulated light field to the mirror 4, which is reflected to the next phase conversion region 3. The phase modulation and reflection process is repeated, so that the N phase conversion regions 3 sequentially complete the phase modulation of the input light field, and then the light is emitted through the light transmission hole 5. M grating couplers 21 output M spatially separated TM / TE polarized single-mode Gaussian light, which is converted into M coaxial and mutually orthogonal spatial mode light after passing through the multi-plane phase sheet and the mirror 4, realizing single-mode to few-mode multiplexing. The TM / TE light output by the same grating coupler 21 is converted into the same mode in the corresponding polarization state after passing through the MPLC.

[0085] Demultiplexing: M spatial modes are input into the integrated multi-plane light conversion device through the light transmission hole 5, and M coaxial and mutually orthogonal spatial mode light is converted into M spatially separated single-mode Gaussian light through the phase conversion region 3 and the reflective film, and then coupled into the optical waveguide through the grating coupler 21. Few-mode to single-mode demultiplexing is realized.

[0086] Polarization demultiplexing is realized at the same time as demultiplexing.

[0087] By adopting the polarization splitting grating coupler 21, polarization demultiplexing is realized while mode multiplexing / demultiplexing is realized; wherein after reflection and phase modulation of the multi-plane phase sheet and the mirror 4, M coaxial mutually orthogonal spatial mode lights are converted into M spatially separated single-mode Gaussian lights, the single-mode Gaussian light contains TE and TM polarization states, after the single-mode Gaussian light is incident on the polarization splitting grating coupler 21, the polarization splitting grating coupler 21 couples the TE polarized light into the first output waveguide 211 and couples the TM polarized light into the second output waveguide 212, two polarization states of one mode are separated into two different single-mode waveguides, and mode polarization diversity reception is realized.

[0088] Embodiment three

[0089] The embodiment is an embodiment of an optimal design method of a multi-plane optical conversion device on a chip, and is used for realizing optimal design of the multi-plane optical conversion device on a chip provided in embodiment one, as shown in the figure, and includes the following steps.

[0090] Step S1. Parameter initialization: including determining the thickness of the glass substrate 1 (0.5-3 millimeters), the number of phase transformation zones 3 (the specific number is adjusted according to the mode complexity), the size of the phase transformation zone 3 (greater than 300 microns to ensure sufficient working area), the spacing value between each grating coupler 21 in the grating coupling unit 2 (more than 30 microns), defining the range of working wavelengths (determine the working wavelength according to specific requirements), setting the maximum value i Max of the outer loop and the maximum value j Max of the inner loop; setting the target performance indicators, including coupling efficiency, crosstalk, and bandwidth.

[0091] Step S2. Outer loop optimization-light field matching optimization: the outer loop focuses on realizing light field matching between the multi-plane system and the grating coupler 21 and updating the structure parameters of the grating coupler 21.

[0092] Step S21. Generating / updating the structure parameters of the grating coupler 21, taking the initial set of fundamental mode light field distribution or the fundamental mode light field distribution generated after demultiplexing of the multi-plane optical conversion device as the target light field, and optimizing the structure parameters of the grating coupler 21 according to the optimization algorithm; the optimization algorithm can adopt optimization methods such as particle swarm optimization, genetic algorithm, gradient descent, and wavefront matching.

[0093] Step S22. Electromagnetic simulation is performed on the currently generated / updated grating coupler 21 structure, and complete information of the output light field of the grating coupler 21 is extracted from the simulation results; it is judged whether the loop number j is less than or equal to j Max , if not, step S23 is entered, and if yes, step S3 is entered;

[0094] Step S23. Calculate the performance of the multi-plane light conversion device, using the result parameters of the current grating coupler 21 and the optimized phase distribution, calculate the performance of the multi-plane light conversion device in the entire working wavelength range, including total loss, crosstalk, bandwidth; evaluate the overall performance of the current grating-phase sheet combination, record the performance of this iteration; judge whether the number of cycles j is greater than or equal to i Max or whether the target performance is reached, if not, go to step S21, if yes, go to step S4;

[0095] Step S3. Inner loop optimization: take the output light field of the grating coupler 21 obtained in the outer loop optimization as the input light field of the MPLC, and the inner loop is responsible for fine adjustment of the multi-plane phase distribution.

[0096] Step S31. MPLC forward propagation calculation, take the output light field of the grating coupler 21 obtained in step S22 as the input light field of the multi-plane light conversion MPLC light field propagation, calculate the forward propagation to the phase transformation area 3 by the shift angle spectrum method, and then propagate to the next phase transformation area 3 after modulation by the phase transformation area 3, and then propagate to the output surface, and record the light field propagated to each phase transformation area 3;

[0097] Step S32. Calculate the mode matching degree of the output light field and the target light field, which is used to quantify the difference between the current system output and the expected target; compare the output light field obtained by forward propagation with the target light field, for example, compare the mode field of a certain mode in the few-mode fiber. The loss function can be defined as the absolute value square of the mode overlap integral, and the loss function can be modified according to the specific situation.

[0098] Step S33. MPLC backward propagation calculation, the target light field is backward propagated to the last phase transformation area 3 by the shift angle spectrum method, and then propagated to the previous phase transformation area 3 by the shift angle spectrum method after modulation by the phase transformation area 3, and then propagated to the output surface, and the light field propagated to each phase transformation area 3 is recorded;

[0099] Step S34. Update the phase sheet distribution of the phase transformation area 3, update the phase distribution of the phase transformation area 3 by the forward propagation light field and the backward propagation light field obtained by S31, S32, S33, and the calculated mode matching degree, using gradient descent method or wavefront matching method;

[0100] Step S35. Judge whether the number of cycles j is less than or equal to j Max , if yes, go to step S31; if not, go to step S23;

[0101] Step S4. Output the optimal design parameters, select a set of parameters with the best performance in the above-mentioned cyclic optimization process, including the structural parameters (period, etching depth, duty cycle, etc.) of the grating coupler 21 and the phase distribution (which can be a discretized phase value matrix) of each phase transformation region 3.

[0102] In the specific content of the foregoing detailed description, each technical feature can be combined arbitrarily without contradiction. In order to make the description simple, all possible combinations of the foregoing technical features are not described, but as long as the combination of the technical features does not exist contradiction, it should be considered as the scope of the present disclosure.

[0103] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the implementation manners of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and also impossible to exhaust all the implementation manners. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. An optimized design method for an on-chip multi-planar optical conversion device, characterized in that, Multi-plane optical conversion devices include: A glass substrate (1) has a front side and a back side arranged opposite to each other; A grating coupling unit (2) is disposed on the back side region and / or the front side region of the glass substrate (1) to couple the free space light field inside the glass substrate (1) to the light field propagating in the waveguide, or to diffract the light field propagating in the waveguide to propagate in the free space inside the glass substrate (1). A multi-planar phase plate comprising N phase transformation regions (3), wherein the N phase transformation regions (3) are spaced apart on the back side of the glass substrate (1), or located on the front and back sides respectively; used to achieve phase modulation of the light field propagating in free space; A reflector (4) is used to fold the light path so that the light field is reflected and propagated sequentially between the phase transformation regions (3), and is disposed in the front and / or back regions of the glass substrate (1). The optimization design method includes the following steps: S1. Parameter initialization: This includes determining the thickness of the glass substrate (1), the number of phase transformation regions (3), the size of the phase transformation regions (3), and the spacing between each grating coupler (21) in the grating coupling unit (2); defining the range of the working wavelength, and setting the maximum value of the outer loop i. Max The maximum value of the inner loop, j Max Set target performance metrics, including coupling efficiency, crosstalk, and bandwidth. S2. Outer loop optimization: S21. Generate / update the structural parameters of the grating coupler (21), using the initially set fundamental mode optical field distribution or the fundamental mode optical field distribution generated after demultiplexing of the multi-plane optical conversion device as the target optical field, and optimize the structural parameters of the grating coupler (21) according to the optimization algorithm; S22. Perform electromagnetic simulation on the currently generated / updated grating coupler (21) structure, and extract complete information of the output light field of the grating coupler (21) from the simulation results; determine whether the loop count j is less than or equal to j Max If not, proceed to step S23; if yes, proceed to step S3. S23. Calculate the performance of the multi-plane optical converter. Using the resulting parameters of the current grating coupler (21) and the optimized phase distribution, calculate the performance of the multi-plane optical converter over the entire operating wavelength range, including total loss, crosstalk, and bandwidth; record the performance of this iteration; determine whether the loop number j is greater than or equal to i. Max Or whether the target performance has been achieved. If not, proceed to step S21; if yes, proceed to step S4. S3. Inner loop optimization: S31. MPLC forward propagation calculation: The output light field of the grating coupler (21) obtained in step S22 is used as the input light field for the propagation of the MPLC light field of the multi-plane light conversion. The light field propagating forward to the phase transformation region (3) is calculated. After being modulated by the phase transformation region (3), it propagates to the next phase transformation region (3) and so on until it propagates to the output surface. The light field when propagating to each phase transformation region (3) is recorded. S32. Calculate the mode matching degree between the output light field and the target light field, and compare the output light field obtained from forward propagation with the target light field; S33. MPLC back propagation calculation: the target light field is propagated back to the last phase transformation region (3), the phase transformation region (3) is modulated and then propagated to the previous phase transformation region (3), and so on until it is propagated to the output surface. The light field when it is propagated to each phase transformation region (3) is recorded. S34. Update the phase plate distribution of the phase transformation region (3). Using the forward propagation light field and backward propagation light field obtained from S31, S32, and S33, as well as the calculated mode matching degree, update the phase distribution of the phase transformation region (3) using the gradient descent method or wavefront matching method. S35. Determine if the loop count j is less than or equal to j Max If yes, proceed to step S31; otherwise, proceed to step S23. S4. Output the optimal design parameters, selecting the set of parameters with the best performance from the above steps.

2. The optimized design method for on-chip multi-planar optical conversion devices according to claim 1, characterized in that, In step S31, the light field propagating forward to the phase transformation region (3) is calculated by the offset angle spectrum method. After being modulated by the phase transformation region (3), it is propagated to the next phase transformation region (3) by the offset angle spectrum method. In step S33, the target light field is propagated backward to the last phase transformation region (3) by the offset angle spectrum method. After being modulated by the phase transformation region (3), it is propagated to the previous phase transformation region (3) by the offset angle spectrum method.

3. The optimized design method for on-chip multi-plane optical conversion devices according to claim 1, characterized in that, The optimization algorithm includes particle swarm optimization, genetic algorithm, gradient descent algorithm, or wavefront matching algorithm.

4. The optimized design method for on-chip multi-planar optical conversion devices according to claim 1, characterized in that, The grating coupling unit (2) includes at least two grating couplers (21) and is spaced apart on the same side of the glass substrate (1).

5. The optimized design method for on-chip multi-plane optical conversion devices according to claim 4, characterized in that, The grating coupler (21) is a polarization beam splitting grating coupler.

6. The optimized design method for on-chip multi-plane optical conversion devices according to claim 4, characterized in that, The phase transformation region (3) includes a reflective metasurface or a reflective diffractive optical phase plate, which can achieve polarization-independent or polarization-separated phase modulation.

7. The optimized design method for on-chip multi-plane optical conversion devices according to any one of claims 4 to 6, characterized in that, The glass substrate (1) is also provided with a light-transmitting hole (5) for outputting the modulated light field to the outside of the glass substrate (1) or receiving the light field to be processed into the inside of the glass substrate (1); the grating coupling unit (2), the multi-plane phase plate and the reflector (4) are all disposed on the same glass substrate (1); or, the grating coupling unit (2) is disposed on the first glass substrate (12), the multi-plane phase plate and the reflector (4) are disposed on the second glass substrate (11), and the first glass substrate (12) and the second glass substrate (11) are aligned and integrated by bonding process.

8. An on-chip multi-plane light conversion method, characterized in that, The on-chip multi-plane optical converter designed using the optimization design method of any one of claims 1 to 7 is used to realize mode multiplexing / demultiplexing, specifically including: Single-mode light is transmitted from the on-chip waveguide to the grating coupling unit (2). The grating coupling unit (2) diffracts the waveguide light into spatial light and exits the glass substrate (1) at a set angle. The light propagating in the glass substrate (1) undergoes repeated reflection and phase modulation between the mirror (4) and the multi-plane phase plate, and finally exits the glass substrate (1). Among them, there are M grating couplers (21), M≥2, which are arranged regularly. The M grating couplers (21) output M spatially separated single-mode Gaussian light. After passing through the multi-plane phase plate and the mirror (4), the M single-mode Gaussian light is converted into M coaxial mutually orthogonal spatial mode light, realizing the multiplexing from single-mode to few-mode. M spatial modes are incident on a glass substrate (1) at a set angle. After reflection and phase modulation by a multi-plane phase plate and a mirror (4), the M coaxial orthogonal spatial mode lights are converted into M spatially separated single-mode Gaussian lights, which are then coupled to the on-chip waveguide through M grating couplers (21) to achieve demultiplexing from few modes to single modes.

9. The on-chip multi-plane optical conversion method according to claim 8, characterized in that, By employing a polarization beam splitter coupler (21), polarization demultiplexing is achieved while mode multiplexing / demultiplexing is realized. After reflection and phase modulation by a multi-plane phase plate and a mirror (4), M coaxial mutually orthogonal spatial mode lights are converted into M spatially separated single-mode Gaussian lights. The single-mode Gaussian light contains TE and TM polarization states. After the single-mode Gaussian light is incident on the polarization beam splitter coupler (21), the polarization beam splitter coupler (21) couples the TE polarized light to the first output waveguide (211) and the TM polarized light to the second output waveguide (212).

Images