On-chip integrated computing spectrometer based on multimode interference coupling and ring feedback regulation

Abstract

The present application relates to the technical fields of integrated photonic devices, and proposes an on-chip integrated computing spectrometer based on multi-mode interference coupling and ring feedback regulation, comprising an input coupling and signal injection unit, a multi-mode interference coupler, a ring feedback loop, a signal output and collection unit, and an FPGA control unit; the multi-mode interference coupler is used for guiding optical signals to N output ports; the ring feedback loop is used for receiving optical signals of N-1 output ports, generating wavelength-related complex spectral coding through phase modulation, delay regulation and path feedback interference; the signal output and collection unit is used for receiving complex spectral coding, guiding coded optical signals to a photoelectric detection module for data collection and conversion into analog electrical signals; the FPGA control unit is used for converting analog electrical signals output by the photoelectric detection module into digital signals through an ADC module, and converting digital signals into analog signals through a DAC module to control voltage combinations in N-1 feedback loops. The method improves spectral reconstruction accuracy.

Description

Technical Field

[0001] This invention relates to the field of integrated photonic device technology, and in particular to an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control. Background Technology

[0002] Spectroscopic analysis, as a crucial means of acquiring the optical properties and information of materials, is widely used in fields such as communication monitoring, biomedical imaging, environmental monitoring, and industrial quality control, and plays an irreplaceable role. Traditional spectrometers typically rely on macroscopic optical components such as mechanical scanning, prisms, or diffraction gratings, resulting in large overall size and complex structures, which are not conducive to the application requirements of portable or integrated systems. With the rapid development of silicon photonics technology, miniaturized and on-chip integrated spectrometers have gradually become a research hotspot. By integrating optical path structures on silicon-based integrated photonic platforms, it is possible to significantly reduce size, cost, and power consumption while maintaining resolution and bandwidth.

[0003] In the field of on-chip integrated spectrometers, traditional solutions, represented by dispersive, filter, and Fourier transform types, still rely on long optical paths or fixed filter structures. Their resolution is limited by physical scale, they are highly sensitive to process variations, and overall debugging is complex, making it difficult to simultaneously achieve high resolution, large bandwidth, and high integration. In recent years, computational spectrometers have achieved spectral reconstruction through non-resolution structures and spectral encoding matrices, possessing the potential to obtain large bandwidth and relatively high resolution within a limited chip area.

[0004] Existing research schemes generally suffer from insufficient sensitivity of the coding structure to wavelength changes and limited coding dimensions, making it difficult to generate sufficiently complex and stable interferometric codes, thus limiting the accuracy and resolution of spectral reconstruction. Therefore, it is necessary to develop an on-chip spectrometer architecture that can provide rich spectral responses, generate a large number of effective coding channels, and possess high controllability within a compact on-chip size, and combine it with efficient reconstruction algorithms to achieve high-resolution, high-bandwidth, and stable spectral analysis capabilities. Summary of the Invention

[0005] In view of this, the present invention proposes an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, which improves the complexity of spectral coding, enhances the controllable interference capability, and achieves high-precision spectral reconstruction, thereby reducing the contradiction between resolution, bandwidth and device size in traditional integrated spectrometers.

[0006] In a first aspect, the present invention provides an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, including an input coupling and signal injection unit, a multimode interference coupler, a ring feedback loop, a signal output and acquisition unit, and an FPGA control unit; The input coupling and signal injection unit is used to receive external optical signals and inject the external optical signals into the chip through end-face coupling to obtain input optical signals. The multimode interference coupler is used to excite the multimode interference coupling effect of the input optical signal, distribute the input optical signal, and guide the optical signal to N output ports; The ring feedback loop is used to receive optical signals from N-1 output ports and generate wavelength-dependent complex spectral codes through phase modulation, delay modulation and path feedback interference. The signal output and acquisition unit is used to receive complex spectral codes, guide the encoded optical signals to the photoelectric detection module for data acquisition, and convert them into analog electrical signals; The FPGA control unit is used to convert the analog electrical signal output by the photoelectric detection module into a digital signal through the ADC module, and convert the digital signal into an analog signal through the DAC module, thereby controlling the voltage combination in N-1 feedback loops.

[0007] Based on the above technical solutions, preferably, the input coupling and signal injection unit includes an inverted conical end face coupler and an input waveguide, wherein the inverted conical end face coupler is used to reduce coupling loss and improve the quality of optical signal injection.

[0008] Based on the above technical solutions, preferably, the multimode interference coupler is an imaging interference type MMI device, and the number of ports of the multimode interference coupler is N×N.

[0009] Based on the above technical solutions, preferably, the ring feedback loop includes N-1 ring waveguide routes, each with a different total optical path length, used to construct multi-dimensional optical path difference and enhance spectral coding capability.

[0010] Based on the above technical solutions, preferably, the ring waveguide route includes a thermo-optical phase shifter and a time-delay interference structure.

[0011] Based on the above technical solutions, preferably, the thermo-optical phase shifter includes a silicon waveguide, a silicon dioxide cladding, and a TiN heating electrode, and the thermo-optical phase shifter achieves continuous and adjustable optical phase through temperature control.

[0012] Based on the above technical solutions, preferably, the delay interference structure is set in the Mach-Zehnder interferometer structure or delay waveguide structure inside the ring waveguide route, so as to introduce a controllable or fixed optical path difference inside the ring waveguide route to enhance the wavelength sensitivity of spectral coding.

[0013] Based on the above technical solutions, preferably, the signal output and acquisition unit includes an output waveguide, an end-face coupler, and a photodetector module.

[0014] Based on the above technical solutions, preferably, the optical detection module is an off-chip discrete PIN photodetector or an on-chip germanium-silicon PIN photodetector.

[0015] Based on the above technical solutions, preferably, the FPGA control unit includes an FPGA logic module, a DAC module, and an ADC module. The FPGA logic module is used to control the DAC module and the ADC module. The DAC module is used to provide a driving voltage for the thermo-optical phase shifter. The ADC module is used to convert analog signals into digital signals and send them to the FPGA logic module.

[0016] The on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control provided by this invention has the following advantages over existing technologies: (1) By combining a multimode interference coupling structure with multiple ring feedback loops with different optical paths and control functions, a large number of spectral coding channels with obvious differences can be generated efficiently, and a highly uncorrelated transmission matrix can be constructed, thereby achieving high spectral resolution within a compact chip area.

[0017] (2) By relying on thermally tuned scanning and PIN photodetector for detection, a fast data acquisition speed can be achieved while ensuring high resolution; combined with the spectral reconstruction method of elastic network constraint and convex optimization solution, stable spectral reconstruction can be completed in the range of several seconds to tens of seconds, with good response time and great practical value.

[0018] (3) The spectrometer is composed of basic integrated photonic devices such as multimode interference units, several ring feedback loops, and thermo-optical phase shifters. The structure is relatively simple, the process tolerance is large, and the chip can be fabricated on the existing silicon-based 200nm process platform. Compared with traditional spectrometers that rely on long gratings or long optical path structures, it has higher integration and mass production potential. It is compatible with communication bands and some near-infrared bands, and has strong applicability and practical value in communication monitoring, biomedical detection, and integrated optical testing. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the overall structure of an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control provided in an embodiment of the present invention; Figure 2 This is a micrograph of an example chip structure of an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, provided in an embodiment of the present invention. Figure 3 This is a flowchart of the spectral analysis workflow of an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, provided by an embodiment of the present invention. Figure 4 This is a schematic diagram of the transmission matrix of an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, provided by an embodiment of the present invention. Figure 5 This is a schematic diagram of the spectral autocorrelation function of an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, provided by an embodiment of the present invention; Figure 6 This is a flowchart of a reconstruction algorithm for an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, provided by an embodiment of the present invention. Figure 7 This is an exemplary single-peak spectrum reconstruction diagram of an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control provided in an embodiment of the present invention; Figure 8 This is an exemplary bimodal spectral reconstruction diagram of an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, provided by an embodiment of the present invention. Figure 9 This is an exemplary broadband spectral reconstruction diagram of a chip-integrated computational spectrometer based on multimode interference coupling and ring feedback control, provided by an embodiment of the present invention, for the communication band. Explanation of reference numerals in the attached figures: 1. Input coupling and signal injection unit; 2. Multimode interference coupler; 3. Loop feedback loop; 4. Signal output and acquisition unit; 5. FPGA control unit; 31. Thermo-optic phase shifter; 32. Delayed interference structure. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0022] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "connected" or "linked" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up," "down," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0023] Figure 1 This is a schematic diagram of the overall structure of an on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control, as provided in an embodiment of the present invention. Figure 1 As shown, the present invention provides an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control, including an input coupling and signal injection unit 1, a multimode interference coupler 2, a ring feedback loop 3, a signal output and acquisition unit 4, and an FPGA control unit 5; The input coupling and signal injection unit 1 is used to receive external optical signals and inject the external optical signals into the chip in an end-face coupling manner to obtain input optical signals. The multimode interference coupler 2 is used to excite the multimode interference coupling effect of the input optical signal, distribute the input optical signal, and guide the optical signal to N output ports; The ring feedback loop 3 is used to receive optical signals from N-1 output ports and generate wavelength-dependent complex spectral codes through phase modulation, delay control and path feedback interference. The signal output and acquisition unit 4 is used to receive complex spectral codes, guide the encoded optical signals to the photoelectric detection module for data acquisition, and convert them into analog electrical signals; The FPGA control unit 5 is used to convert the analog electrical signal output by the photoelectric detection module into a digital signal through the ADC module, and to convert the digital signal into an analog signal through the DAC module, thereby controlling the voltage combination of N-1 feedback loops.

[0024] In some embodiments, the input coupling and signal injection unit 1 injects the external optical signal into the chip via end-face coupling to obtain the input optical signal. The multimode interference coupler 2 excites the multimode interference coupling effect of the input optical signal, thereby obtaining a complex and rich optical field distribution at multiple output ports. The loop feedback loop 3 feeds back the MMI multi-channel output to the input end, introducing phase modulation, delay control and path feedback interference on different paths to generate wavelength-related complex spectral codes. The signal output and acquisition unit 4 guides the encoded optical signal to the photodetector module for data acquisition. The FPGA control unit 5 drives the thermo-optical phase shifter, controls the switching of the sampling channel and processes the acquired data to achieve spectral reconstruction.

[0025] In some embodiments, the input coupling and signal injection unit 1 includes an inverted conical end face coupler and an input waveguide, wherein the inverted conical end face coupler is used to reduce coupling loss and improve the quality of optical signal injection.

[0026] It is easy to understand that the input coupling and signal injection unit 1 includes an end-face coupler and a connected input waveguide, which are used to improve fiber-to-chip coupling efficiency and reduce insertion loss. The end-face coupler can adopt an inverted conical structure, a multi-tip tapered structure, a cascaded multi-conical structure, or a cantilever beam structure, etc., to improve mode matching and reduce coupling loss.

[0027] Optionally, the end face coupler can be replaced by a grating coupler, including a vertically coupled grating coupler, an oblique incident grating coupler, or a double-layer grating coupler, to achieve top-down fiber coupling and improve alignment tolerance.

[0028] In some embodiments, the multimode interference coupler 2 is an imaging interferometric MMI device, and the number of ports of the multimode interference coupler 2 is N×N.

[0029] It is easy to understand that the multimode interference coupler 2 is a general imaging interferometric MMI device with N×N ports. It distributes the input light to multiple output ports according to a preset power ratio, forming a multi-path interference light field with obvious spatial mode differences, providing multi-channel input for subsequent ring feedback. Through the multimode interference coupling effect, the input light is distributed to each output port, thereby generating a rich light field distribution at the output end, and different ring feedback loops are introduced for control.

[0030] In this embodiment, a wavelength-dependent interference field is generated within a compact chip size through multimode interference effect. The output light field has resolvable intensity and phase modulation characteristics as the wavelength changes, which can provide rich coding differences for subsequent feedback control loops.

[0031] The multimode interference coupler 2 can achieve a predetermined power distribution ratio and interference mode complexity by adjusting parameters such as the length and width of its multimode region and the shape and size of the transition waveguide, thereby improving the overall spectral coding dimension.

[0032] In some embodiments, the ring feedback loop 3 includes N-1 ring waveguide routes, each with a different total optical path length, used to construct multi-dimensional optical path difference and enhance spectral coding capability.

[0033] The ring feedback loop 3 includes N-1 ring waveguide routes, each with a different total optical path length, used to construct multi-dimensional optical path difference and enhance spectral coding capabilities.

[0034] In some embodiments, the ring waveguide route includes a thermo-optical phase shifter 31 and a time-delay interference structure 32.

[0035] In some embodiments, the thermo-optical phase shifter 31 includes a silicon waveguide, a silicon dioxide cladding, and a TiN heating electrode, and the thermo-optical phase shifter 31 achieves continuous tunability of the optical phase through temperature control.

[0036] The ring feedback loop 3 includes N-1 ring waveguide loops with different total optical path lengths. Each loop is equipped with a thermo-optical phase shifter 31 and a time-delay interference structure 32, which are used to realize the continuous adjustment of phase and the introduction of fine optical path difference, respectively.

[0037] The input ends of N-1 ring waveguide loops are connected to each output port of the multimode interference coupler (excluding the through port), allowing the spatial interference modes carried by different output ports to form further phase and amplitude codes via ring loops of varying lengths. Each input waveguide of the ring loop is directly connected to each output waveguide of the multimode interference coupler to ensure coupling efficiency and coding stability. The ring waveguide loops are arranged concentrically in a nested pattern on the chip, resulting in a sequentially increasing total optical path length for each loop, thus generating multi-order spectral codes with significant optical path differences and wavelength sensitivity.

[0038] The ring feedback loop comprises multiple ring waveguide loops with different optical path lengths. Each loop contains a thermo-optical phase shifter 31 and a time-delay interference structure 32, which are used to achieve continuous phase adjustment, fine control of optical path difference, and multi-level feedback interference, thereby generating a wavelength-sensitive, highly complex, and reconfigurable coded spectrum. The thermo-optical phase shifter 31 achieves phase adjustment by changing the local temperature of the waveguide through adjusting the driving voltage.

[0039] In some embodiments, the delay interference structure 32 is disposed in a Mach-Zehnder interferometer structure or a delay waveguide structure inside the ring waveguide route, for introducing a controllable or fixed optical path difference inside the ring waveguide route to enhance the wavelength sensitivity of the spectral encoding.

[0040] The time-delay interference structure 32 is a Mach-Zehnder interferometer (MZI) structure or a time-delay waveguide structure disposed inside each loop feedback loop. It is used to introduce a controllable or fixed optical path difference within the feedback path to enhance the wavelength sensitivity of the spectral encoding. The arm length or waveguide length of each time-delay interference structure 32 is different to improve the spectral channel discrimination and the condition number of the encoding matrix.

[0041] The time-delay interference structure 32 can be an asymmetric Mach-Zehnder interference structure, a delay waveguide segment, or, in some embodiments, the structure may be omitted.

[0042] In some embodiments, the signal output and acquisition unit 4 includes an output waveguide, an end-face coupler, and a photodetector module.

[0043] Optionally, the signal output and acquisition unit 4 includes an output waveguide and end face coupler for coupling out the encoded optical signal and transmitting it to an external optical detection module.

[0044] In some embodiments, the signal output and acquisition unit 4 includes an output waveguide, an end-face coupler, and a photodetector module, used to couple the encoded optical signal to an external indium gallium arsenide PIN photodetector for acquisition. The output end-face coupler and the photodetector module can also be directly replaced by an on-chip germanium silicon PIN photodetector, used to directly complete the photoelectric conversion on the chip.

[0045] In some embodiments, the light detection module is an off-chip discrete PIN photodetector or an on-chip germanium-silicon PIN photodetector. It is used to convert light intensity information into electrical signals.

[0046] In some embodiments, the FPGA control unit 5 includes an FPGA logic module, a DAC module, and an ADC module. The FPGA logic module is used to control the DAC module and the ADC module. The DAC module is used to provide a driving voltage for the thermo-optical phase shifter 31. The ADC module is used to convert analog signals into digital signals and send them to the FPGA logic module.

[0047] The FPGA control unit 5 includes an FPGA module, a digital-to-analog converter (DAC) module, and an analog-to-digital converter (ADC) module. It is used to apply control voltage to the thermo-optical phase shifter, control the switching of voltage combinations of different sampling channels, and convert the analog signal output by the photodetector module into a digital signal for subsequent processing and calculation.

[0048] As shown in Figure 1, the incident light is coupled into the chip via the input coupling and signal injection unit 1, and then enters the multimode interference coupler 2 through the input waveguide. The multimode interference coupler 2 is used to distribute the optical field across multiple channels. Each output channel, except the through-hole, is sequentially connected to its corresponding ring waveguide feedback loop. A thermo-optical phase shifter 31 within the ring waveguide is used for programmable control of the optical path phase. Delay interference structures 32 with different arm lengths are further introduced into the ring waveguides of each channel, thereby generating a high-dimensional, low-cross-correlation spectral response. The modulated optical signal is led out to the optical detection module through the output waveguide and output coupler to achieve encoded sampling of spectral information. The FPGA control unit 5 drives all the thermo-optical phase shifters, controls the switching of different encoding states, and acquires and processes the optical signal to complete spectral reconstruction.

[0049] In some embodiments, the input waveguide enters one port of the designed multimode interference coupler 2MMI, exciting complex mode interference within the MMI to achieve optical field distribution across multiple output ports. One output port of the MMI serves as the overall output of the spectrometer, while the remaining ports are connected to their corresponding input ports via loop waveguide feedback loops of varying lengths.

[0050] In this embodiment, the combined design of multimode interference coupling structure and ring feedback loop control significantly improves the degree of freedom of spectral measurement matrix and spectral reconstruction accuracy while maintaining device compactness, making it suitable for applications such as broadband, high-resolution spectral analysis and on-chip integrated optical sensing.

[0051] Furthermore, the transfer matrix of the spectrometer was established through experimental calibration. First, a continuous broadband light source covering the operating bandwidth was used as input, and the spectral distribution of the output ports was recorded sequentially under different thermal tuning states. Each tuning state corresponds to a row in the transfer matrix, and all tuning states are accumulated to form a complete sampling channel; each wavelength point corresponds to a column in the transfer matrix. After establishing the transfer matrix, an unknown spectrum was input, and the optical power response of all output ports under each tuning state was recorded, thus forming a set of linear equations used to solve for the original spectrum.

[0052] Furthermore, a reconstruction method based on elastic network regularization is adopted, which simultaneously introduces sparsity constraint L1 and smoothness constraint L2 to ensure the stability of the spectral solution process under different scenarios. In practical implementation, the above linear equations are solved using the CVX convex optimization tool to obtain high-precision reconstruction results of the unknown spectrum.

[0053] Furthermore, the reconstruction process is not limited to the methods described above; other algorithms for undersampled spectral reconstruction can also be employed. For example, regularization methods based on spectral priors, solution algorithms based on Lasso regression, or machine learning and deep learning models based on training data can be selected to adapt to reconstruction needs with different noise levels, different spectral types, and different system architectures.

[0054] Figure 2 is a micrograph of an example chip structure of an on-chip integrated computational spectrometer based on multimode interference coupling and ring feedback control provided in an embodiment of the present invention. Figure 2 The diagram illustrates the layout of input / output coupling units 1 and 4, the N×N multimode interference coupler 2, and multiple loop feedback loops 3. Each thermo-optical phase shifter is powered by an FPGA.

[0055] Figure 3 is a flowchart of the spectral analysis workflow of an on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control, provided by an embodiment of the present invention. Figure 3 As shown in the diagram, this flowchart presents an algorithmic framework, outlining the complete operational path of the spectrometer from startup and calibration to actual measurements.

[0056] Specifically, the spectral analysis method first enters the process initiation step, where the system determines whether pre-calibration S1 needs to be performed.

[0057] If the corresponding transmission matrix for the device has not been established before, or if the environmental conditions change significantly, such as temperature or packaging status, the result is negative, and the process enters the pre-calibration stage S2.

[0058] During the pre-calibration process, a flat spectrum is input to the chip via an external broadband ASE light source. The computer controls the FPGA to apply multiple sets of random voltage configurations, recording the spectral response of each output port, thereby constructing and storing the spectrometer's transfer matrix. This matrix describes the linear mapping relationship from the input wavelength space to the output signal space and is the basis for subsequent spectral reconstruction calculations. Once the transfer matrix has been established and the result is positive, the process proceeds to the formal measurement stage S3.

[0059] During the measurement process, the optical signal under test is input to the chip via optical fiber, while a voltage source is simultaneously applied with the voltage combination corresponding to the pre-calibration stage. The photodetector module acquires the optical power data of different spectral sampling channels at the output port in real time. Assuming the input spectrum... Through the spectral response The sampling channels, among which The wavelength is represented by 0, and the optical power response collected at the output port of the spectrometer is denoted as 0. Mathematically, this is expressed as: in, and These represent the lower and upper limits of the operating band, respectively. If we consider that the entire spectrometer system has N sampling channels with different responses, and the band is discretized into M wavelength channels, then the above equation can be further expressed in matrix form: Wherein, the power response O is an N-dimensional optical power vector, corresponding to the optical power information measured by different sampling channels under different tuning states. A is... The M-dimensional transfer matrix, whose elements are obtained through the system's pre-calibration process, is represented by S, an M-dimensional unknown spectral vector, which represents the spectral distribution across discrete wavelength channels.

[0060] In actual measurement, the optical power signal can be affected by noise interference, leading to deviations in the measured values. in, This represents the measurement error term. After acquiring the optical power, the process proceeds to the spectral reconstruction step S4.

[0061] Due to measurement noise, the reconstructed spectrum may deviate from the true spectrum. Generally, the goal of reconstruction is to solve the following optimization problem: This invention employs an Elastic Net regularized solution framework, simultaneously introducing L1 and L2 constraints to suppress noise amplification and enhance solution stability. Its reconstruction optimization problem can be expressed as: in, and This is a regularization parameter used to balance spectral sparsity and smoothness. The computer calls a pre-established transfer matrix and solves the elastic network regularization problem using the CVX method to recover and reconstruct the spectrum to be measured, and outputs the final spectral result.

[0062] Through the above process design, this invention realizes a complete working method for on-chip computational spectrometers from calibration and acquisition to reconstruction, ensuring that the system maintains stable and repeatable spectral analysis performance in multiple measurements.

[0063] Figure 4 is a schematic diagram of the transmission matrix of an on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control provided by an embodiment of the present invention. As shown in Figure 4, applying different voltages to the phase shifter can generate multiple sets of different encoding states. Figure 4 shows a schematic diagram of the analog transmission matrix obtained under different tuning states, with each row corresponding to one encoding channel and each column corresponding to one wavelength channel.

[0064] Figure 5 is a schematic diagram of the spectral autocorrelation function of an on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control provided in an embodiment of the present invention. Figure 5 As shown, the half-width at half-maximum (WHM) of the autocorrelation function represents the wavelength shift required for the correlation between adjacent channels of the spectrometer to decrease to half, and is an indicator of the resolving power of a random speckle spectrometer. The figure shows that the WHM of the autocorrelation function is approximately 0.17 nm, indicating a high degree of decorrelation of the transfer matrix.

[0065] Figure 6 is a flowchart of a reconstruction algorithm for an on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control, provided by an embodiment of the present invention. As shown in Figure 6, the present invention uses elastic network regularization combined with the CVX convex optimization framework for spectral reconstruction. By minimizing the error between the output power and the transmission matrix mapping, and applying L1 and L2 regularization constraints, noise can be effectively suppressed and overfitting of the reconstruction can be prevented. This method is applicable to various cases such as sparse narrowband spectra, dense bimodal spectra, and broadband spectra, and can also be replaced by other standard reconstruction methods.

[0066] Figure 7 is an exemplary single-peak spectral reconstruction diagram of an on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control provided by an embodiment of the present invention. As shown in Figure 7, a single narrowband unknown spectrum is reconstructed. This result is based on a pre-established transfer matrix, and the input spectrum is numerically reconstructed through a computational reconstruction algorithm, demonstrating that the present invention possesses the capability to achieve high-resolution spectral analysis at both the theoretical and algorithmic levels. To further quantify the reconstruction accuracy, a relative error ε is introduced as an evaluation index: Where S is the reconstructed spectrum. The reference spectrum is used. This index reflects the degree of fit of the reconstructed spectrum in the overall energy sense; the smaller the ε value, the higher the accuracy of the spectral reconstruction. Generally, when ε < 0.1, the reconstruction result is considered to have high accuracy. Figure 7 The ε=0.063 indicates that the reconstruction has high reliability.

[0067] Figure 8 is an exemplary schematic diagram of bimodal spectral reconstruction of an on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control, provided by an embodiment of the present invention. As shown in Figure 8, a demonstrative reconstruction of the bimodal unknown spectrum is performed, and both peaks spaced 1 nm apart can be successfully distinguished and restored. Figure 8 The result of ε=0.074 demonstrates the system's accurate reconstruction capability in bimodal spectral measurements.

[0068] Figure 9 is a schematic diagram illustrating an exemplary broadband spectral reconstruction of the communication band using an on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control, according to an embodiment of the present invention. As shown in Figure 9, the present invention demonstrates the reconstruction of the broadband spectrum in the communication band. Broadband spectral reconstruction is more challenging. Figure 9 With ε=0.081, it can be seen that the ability to reproduce the overall spectral shape can still be maintained under broadband conditions.

[0069] In summary, the on-chip computational spectrometer proposed in this invention achieves multi-dimensional, highly complex spectral modulation through a triple superposition of multimode interferometric spatial coding, annular optical path difference coding, and thermo-optical tunable coding. By pre-calibrating the transfer matrix and combining it with a reconstruction algorithm based on convex optimization, unknown spectra can be restored with high precision. This invention features a compact structure, high integration, and easy expansion, making it suitable for various scenarios such as communication, sensing, optical measurement, and on-chip analysis.

[0070] In this embodiment, a spectrometer is constructed using basic integrated photonic devices such as multimode interferometers, several ring feedback loops, and thermo-optical phase shifters. The structure is relatively simple, with a large process tolerance, and chip fabrication can be achieved using existing silicon-based 200nm processes. Compared to traditional spectrometers that rely on long gratings or long optical path structures, it offers higher integration and mass production potential. The operating wavelength covers approximately 1400–1625nm, and it is compatible with communication bands and parts of the near-infrared band, making it highly applicable and practical in communication monitoring, biomedical detection, and integrated optical testing.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control, characterized in that, It includes an input coupling and signal injection unit (1), a multimode interference coupler (2), a loop feedback loop (3), a signal output and acquisition unit (4), and an FPGA control unit (5). The input coupling and signal injection unit (1) is used to receive external optical signals and inject the external optical signals into the chip in an end-face coupling manner to obtain input optical signals; The multimode interference coupler (2) is used to excite the multimode interference coupling effect of the input optical signal, distribute the input optical signal, and guide the optical signal to N output ports; The ring feedback loop (3) is used to receive optical signals from N-1 output ports and generate wavelength-related complex spectral codes through phase modulation, delay control and path feedback interference. The signal output and acquisition unit (4) is used to receive complex spectral codes, guide the encoded optical signals to the photoelectric detection module for data acquisition, and convert them into analog electrical signals; The FPGA control unit (5) is used to convert the analog electrical signal output by the photoelectric detection module into a digital signal through the ADC module, and to convert the digital signal into an analog signal through the DAC module, thereby controlling the voltage combination in the N-1 feedback loops.

2. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in claim 1, characterized in that, The input coupling and signal injection unit (1) includes an inverted conical end face coupler and an input waveguide. The inverted conical end face coupler is used to reduce coupling loss and improve the quality of optical signal injection.

3. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in claim 2, characterized in that, The multimode interference coupler (2) is an imaging interference type MMI device, and the number of ports of the multimode interference coupler (2) is N×N.

4. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in claim 3, characterized in that, The ring feedback loop (3) includes N-1 ring waveguide routes, each with a different total optical path length, used to construct multi-dimensional optical path difference and enhance spectral coding capability.

5. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in claim 4, characterized in that, The ring waveguide route includes a thermo-optical phase shifter (31) and a time-delay interference structure (32).

6. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in claim 5, characterized in that, The thermo-optical phase shifter (31) includes a silicon waveguide, a silicon dioxide cladding, and a TiN heating electrode. The thermo-optical phase shifter (31) achieves continuous and adjustable optical phase through temperature control.

7. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in claim 6, characterized in that, The delay interference structure (32) is set in the Mach-Zehnder interferometer structure or delay waveguide structure inside the ring waveguide route to introduce a controllable or fixed optical path difference inside the ring waveguide route to enhance the wavelength sensitivity of the spectral encoding.

8. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in claim 7, characterized in that, The signal output and acquisition unit (4) includes an output waveguide, an end-face coupler, and a photodetector module.

9. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in any one of claims 1-8, characterized in that, The optical detection module is either an off-chip discrete PIN photodetector or an on-chip germanium-silicon PIN photodetector.

10. The on-chip integrated computational spectrometer based on multimode interferometric coupling and ring feedback control as described in any one of claims 1-9, characterized in that, The FPGA control unit (5) includes an FPGA logic module, a DAC module and an ADC module. The FPGA logic module is used to control the DAC module and the ADC module. The DAC module is used to provide a driving voltage for the thermo-optical phase shifter (31). The ADC module is used to convert analog signals into digital signals and send them to the FPGA logic module.

Images