A topology waveguide-based uncalibrated on-chip spectrometer and a manufacturing method thereof

Abstract

This invention discloses a calibration-free on-chip spectrometer based on topological waveguides and its manufacturing method, belonging to the field of integrated optics and spectral detection. The spectrometer integrates an incident coupling structure, a topological spectroscopic encoding module, an outgoing detection structure, and a spectral reconstruction module. The topological spectroscopic encoding module includes a topological waveguide supporting topological boundary state transmission, forming a wavelength-dependent coupling structure with the coupling waveguide. After coupling, encoding, and detection, the incident light's spectrum is reconstructed by the spectral reconstruction module, with the incident light operating at a frequency within the topological boundary state band. This invention also discloses its manufacturing method, utilizing the robustness of topological boundary states to achieve calibration-free, highly stable detection, adapting to CMOS processes, simplifying the fabrication process, improving mass production yield, reducing production costs, and promoting the engineering and industrial application of on-chip spectrometers.

Description

Technical Field

[0001] This invention relates to the fields of integrated optics, micro-nano optoelectronic devices and spectral detection technology, specifically to a calibration-free on-chip spectrometer based on topological waveguides and its manufacturing method. Background Technology

[0002] On-chip spectrometers, with their advantages of small size, low power consumption, CMOS process compatibility, and monolithic integration, have significant application value in rapid detection, biosensing, environmental monitoring, and on-chip laboratory systems. On-chip spectrometers based on coding modulation and algorithm reconstruction can eliminate traditional spectroscopic structures such as gratings and micro-ring arrays. They perform wavelength-correlation coding sampling of incident light through an on-chip optical network, and then reconstruct the spectrum through a reconstruction algorithm. This represents an important technical approach for achieving highly integrated and low-cost spectral detection.

[0003] However, most existing reconstructable on-chip spectrometers employ conventional waveguide structures, whose transmission modes are sensitive to perturbations such as process errors, sidewall roughness, and structural defects. The actual transmission response tends to deviate from the design value, leading to decreased spectral reconstruction accuracy and reduced detection repeatability. To compensate for process deviations, existing solutions typically require additional calibration structures, offline calibration, or post-processing algorithm calibration, significantly increasing chip area, system complexity, and manufacturing costs, reducing mass production yield, and making it difficult to achieve truly calibration-free stable detection.

[0004] Topological photonic crystals can support topologically protected boundary state propagation. This mode is inherently robust to structural defects and process disturbances, and can significantly suppress transmission loss and response drift. However, currently, topological waveguides have not been effectively integrated with coding and reconstruction systems in the field of on-chip spectral detection, and there is a lack of complete device structures and implementation schemes that rely on topological protection characteristics to achieve calibration-free, highly stable, and high-precision spectral detection. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical defects of existing on-chip spectrometers, such as sensitivity to process deviations, the need for frequent calibration, low reconstruction fidelity, and difficulty in large-scale mass production. This invention provides a calibration-free on-chip spectrometer based on topological waveguides and its manufacturing method. By utilizing the topological protection characteristics of topological photonic crystals, calibration-free, highly stable, and high-precision on-chip spectral detection can be achieved, promoting engineering implementation and industrial application.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: The present invention provides a calibration-free on-chip spectrometer based on topological waveguides, the core of which includes an incident coupling structure, a topological spectroscopic coding module, an outgoing detection structure, and a spectral reconstruction module. The above structures are integrated on the same chip, and the components work together to realize the coupling, coding, transmission, detection, and spectral reconstruction of incident light. High-precision spectral detection can be completed without additional calibration structures, post-calibration, or algorithm pre-calibration.

[0007] The topological beam splitting coding module adopts a topological photonic crystal structure, consisting of at least one topological waveguide. The topological waveguide is formed by a periodic arrangement of several photonic crystal units that break spatial symmetry. The photonic crystal units are asymmetric dielectric pillar units, specifically including two types of equilateral triangular units with different sizes. The lattice constant α, the side length L1 of the large equilateral triangle, and the side length L2 of the small equilateral triangle are set to 380 nm, 0.7 α, and 0.3 α, respectively, satisfying the formation conditions of the topological boundary states. This allows the topological waveguide to support the transmission of topologically protected boundary states. These topological boundary states have inherent robustness to structural perturbations and process deviations, effectively immune to optical field fluctuations caused by immune system defects and random manufacturing errors, and ensuring stable transmission of optical signals.

[0008] The incident coupling structure includes an incident waveguide, which is a silicon-based strip waveguide. A matching coupling insertion structure is provided at the coupling point between the incident waveguide and the topological waveguide. The insertion depth is set to 2930 nm and the insertion width to 359 nm, satisfying the high-efficiency coupling conditions and ensuring that the incident light wave is efficiently coupled to the topological beam splitting and coding module with a coupling efficiency of not less than 85%. The topological beam splitting and coding module can be configured as a topological waveguide array, which is a third-order topological power divider used to perform multi-path beam splitting and parallel coding of the incident light and achieve stable transmission. The beam splitting uniformity error does not exceed ±5%. The topological waveguide and the coupling waveguide cooperate to form a wavelength-dependent coupling structure, realizing differentiated coupling and coding modulation of the incident light field to form a coded optical signal.

[0009] The emitted detection structure includes an emitted waveguide and a photodetector. The emitted waveguide adopts a strip waveguide structure, and its coupling strength with the topological waveguide is less than that with the incident coupling structure, with a coupling strength difference of 10% to 30%. This allows for differentiated encoding output of optical signals of different wavelengths, facilitating subsequent spectral reconstruction. The operating wavelength of the external incident light wave is 1540 to 1716 nm, and its operating frequency falls within the operating frequency band of the topological boundary states of the topological waveguide. This ensures that the optical signal can be stably transmitted through the topological boundary states, avoiding transmission loss that could affect the accuracy of spectral detection.

[0010] The present invention also provides a spectral reconstruction method for the calibration-free on-chip spectrometer based on topological waveguides: an external incident light wave is coupled to a topological spectroscopic coding module via an incident coupling structure, and forms a coded optical signal after wavelength correlation coupling modulation; an outgoing detection structure receives the coded optical signal and converts it into an electrical signal, which is then transmitted to the spectral reconstruction module; the spectral reconstruction module performs inversion calculations on the electrical signal based on a preset response matrix using a sparse reconstruction algorithm, a least squares inversion algorithm, or a deep neural network algorithm, thereby achieving accurate reconstruction of the incident spectrum.

[0011] Meanwhile, this invention provides a design method for the on-chip spectrometer, specifically including: establishing a basic model of a topological valley photonic crystal, a topological waveguide, and topological-strip waveguide coupling in a simulation environment; constructing the reconfigurable characteristics of the spectrometer in a numerical environment; first performing band structure analysis of the topological valley photonic crystal to determine that the structure has a band gap and that the upper and lower bands have different topological properties; establishing a topological waveguide and verifying its volume-edge correspondence effect and the wavelength transmission range it supports; within the wavelength range of the boundary state, verifying the influence of topological-strip waveguide coupling on the transmission spectrum under different coupling conditions, and finally determining the various design parameters of the on-chip spectrometer; based on the relationship between the transmission spectrum and the broadband output optical power intensity, inversely solving the incident spectrum to complete the design of the on-chip spectrometer.

[0012] This invention also provides a method for manufacturing the calibration-free on-chip spectrometer based on topological waveguides, applicable to the aforementioned on-chip spectrometer device, specifically including the following steps: S1. Select a substrate material and use a CMOS-compatible process to sequentially fabricate a buffer layer and a waveguide core layer on the substrate. The thickness of the buffer layer is 1~3μm, and the thickness of the waveguide core layer is 0.22μm. Preferably, the substrate is a silicon substrate, the buffer layer is a silicon dioxide buffer layer, and the waveguide core layer is a single-crystal silicon layer. S2. Based on the topological photonic crystal structure, a mask is designed and fabricated. Using photolithography and etching processes, a topological waveguide, a coupled waveguide, and a topological waveguide array are fabricated on the waveguide core layer, forming a coupling structure between the topological beam-splitting coding module and the incident coupling structure and the outgoing waveguide. The photolithography process uses deep ultraviolet or extreme ultraviolet lithography, and the etching process uses dry etching with an etching accuracy of no less than ±10nm. The size difference between the two equilateral triangular photonic crystal units is precisely controlled to achieve spatial mirror symmetry breaking. After etching, the roughness of the waveguide sidewall does not exceed 0.5nm, ensuring the stable formation of the topological boundary states and that the transmission loss of the topological waveguide does not exceed 0.5dB / cm. S3. Prepare a photodetector at the output end of the outgoing waveguide to form an outgoing detection structure, and electrically connect the photodetector to the spectral reconstruction module, wherein the contact resistance of the electrical connection does not exceed 10Ω. S4. Perform performance testing on the fabricated on-chip spectrometer. The test is conducted at room temperature and standard atmospheric pressure to verify the effect of topology protection characteristics on suppressing process deviations and the calibration-free spectral detection performance. The test includes coupling efficiency testing, beam splitting uniformity testing, inversion algorithm response speed testing, and transmission response stability testing. Ensure that the coupling efficiency is not less than 85%, the beam splitting uniformity error is not more than ±5%, the reconstruction response time is not more than 10ms, the device transmission response fluctuation amplitude is not more than ±3%, and the spectral reconstruction resolution is not less than 0.1nm, thus completing the device fabrication.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention introduces a topological waveguide that supports the transmission of topologically protected boundary states, enabling the optical field transmission to possess inherent topological robustness. This effectively resists the effects of structural defects and random manufacturing errors, significantly suppresses optical field transmission fluctuations, and ensures the stability of the device's transmission response. It fundamentally solves the technical pain points of existing conventional waveguide spectrometers, which are sensitive to process deviations and prone to spectral reconstruction distortion, providing a core guarantee for the stability of spectral detection.

[0014] 2. This invention combines a topological waveguide and a coupled waveguide arranged in parallel and close proximity to form an evanescent field coupling structure to construct a wavelength-dependent coupling system. By utilizing the difference in coupling efficiency of light waves of different wavelengths, and in conjunction with the differentiated coupling strength at the incident and emitting ends, wavelength-dependent encoding modulation of the incident light field is achieved. Stable spectral encoding can be completed without the need for additional calibration structures. Combined with the inversion calculation of the spectral reconstruction module, true calibration-free and high-precision spectral detection is achieved, simplifying the uniquely defined system structure and improving the convenience and accuracy of detection.

[0015] 3. This invention clarifies the design parameters of key structures such as the topological photonic crystal unit, the matching coupling structure of the topological waveguide and the coupled waveguide, and the array beam splitter. The device is compatible with CMOS standard processes, and the parameters of each key structure are controllable, which facilitates large-scale mass production, effectively improves mass production yield and device consistency, and reduces the mass production cost and technical threshold of on-chip integrated spectrometers. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the topological waveguide structure in this embodiment; Figure 2 This is a schematic diagram illustrating the reconstructing of an on-chip spectrometer without calibration using a topological photonic crystal in this embodiment. Figure 3 This is a schematic diagram illustrating the mode coupling of the topological strip waveguide and the performance analysis of the spectrometer in this embodiment; Figure 4 This is a schematic diagram related to the calibration and testing of the on-chip spectrometer based on topological waveguides in this embodiment; Figure 5 The robustness of the topological waveguide in this embodiment and the reconstructed spectrum of the defect spectrometer; Figure 6 This is a schematic diagram of uncalibrated spectral reconstruction under manufacturing errors in this embodiment; Figure 7 This is a schematic diagram of the spectrometer structure in this embodiment; Figure 8 This is a schematic diagram of the preparation method in this embodiment. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] In related technologies, existing on-chip spectrometers generally suffer from technical defects such as sensitivity to process deviations, the need for frequent calibration, low reconstruction fidelity, and difficulty in large-scale mass production. The core reason for this is that traditional waveguides lack topological protection characteristics, making optical field transmission susceptible to structural defects and manufacturing errors, resulting in unstable transmission response. This necessitates the addition of additional calibration structures or frequent offline calibration, which not only increases system complexity but also reduces mass production yield, limiting the engineering implementation and industrial application of on-chip spectrometers. To solve the above technical problems, this invention provides a calibration-free on-chip spectrometer based on topological waveguides and its manufacturing method. Relying on topological protection characteristics, it achieves calibration-free and highly stable detection, adapting to mass production requirements.

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1-8 The technical solution of the embodiments of the present invention is clearly and completely described as follows: The embodiments of the present invention provide a calibration-free on-chip spectrometer based on topological waveguides, including an incident coupling structure, a topological beam-splitting encoding module, an outgoing detection structure, and a spectral reconstruction module integrated on the same chip; the topological beam-splitting encoding module includes at least one topological waveguide, the topological waveguide supports topologically protected boundary state transmission, the topological waveguide and the coupling waveguide cooperate to form a wavelength-dependent coupling structure, which is used to generate wavelength-dependent coupling modulation of the incident light field and output an encoded optical signal; the incident coupling structure is used to couple external incident light waves to the topological beam-splitting encoding module; the outgoing detection structure is used to receive the encoded optical signal and convert it into an electrical signal; the spectral reconstruction module is electrically connected to the outgoing detection structure and is configured to perform inversion calculation on the electrical signal based on a preset response matrix to reconstruct the incident spectrum; wherein, the operating frequency of the external incident light wave is within the operating frequency band of the topological boundary state of the topological waveguide.

[0020] like Figure 1As shown, the calibration-free on-chip spectrometer based on topological waveguides provided in this embodiment integrates all core components onto the same chip, achieving on-chip integration, reducing device size, and adapting to portable and miniaturized applications. The incident coupling structure serves as the input port for the optical signal, its core function being to efficiently and stably couple external incident light waves to the topological beam splitting encoding module, ensuring no significant loss of the optical signal. The topological beam splitting encoding module is the core functional module of the device, containing at least one topological waveguide. The core characteristic of this topological waveguide is that it supports the transmission of topologically protected boundary states. These topological boundary states have inherent robustness and can effectively resist the effects of structural perturbations and process variations. The topological waveguide and the coupling waveguide work together to form a wavelength-dependent coupling structure. The core function of this structure is to generate wavelength-dependent coupling modulation of the incident light field, that is, incident light of different wavelengths will produce different wavelengths of coupling modulation. The different coupling responses result in the output of differentiated coded optical signals, providing a basis for subsequent spectral reconstruction. The outgoing detector structure is responsible for receiving the coded optical signals and converting them into electrical signals that can be processed by the spectral reconstruction module, thus realizing the optical-to-electrical signal conversion. The spectral reconstruction module is electrically connected to the outgoing detector structure. After receiving the electrical signals transmitted by it, it performs inversion calculations based on a preset response matrix and finally reconstructs the incident spectrum. At the same time, the operating frequency of the external incident light wave is strictly controlled to ensure that it is within the operating frequency band of the topological boundary state of the topological waveguide. This ensures that the incident light can be stably transmitted through the topological boundary state and avoids transmission loss and signal distortion caused by frequency deviation.

[0021] When an unknown incident spectrum Φ(λ) passes through the spectrometer, the resulting output power intensity Ii is the integral of the product of Φ(λ) and the spectral transmission response Ti(λ) with respect to the wavelength, where λ is the free-space wavelength and i is the index of the output port. In practice, since the spectrum is sampled at discrete wavelengths and the system measures only a finite number of output channels, this integral can be expressed in matrix form as:

[0022] In this discretized expression, M represents the number of encoded output channels, corresponding to the M power intensities to be detected, N represents the number of sampled wavelength points, and T M×N Let M be the transfer matrix. Since M≪N, the equation system is underdetermined. Therefore, in this embodiment, the spectral reconstruction module performs inversion calculations based on a preset response matrix and an algorithm to overcome the limitations of the underdetermined equation system and achieve accurate reconstruction.

[0023] Spectral reconstruction accuracy is typically quantified by relative error ε. A lower ε indicates higher reconstruction accuracy, and vice versa. The formula for calculating relative error ε is:

[0024] Where Φ0 is the reference spectrum and Φ is the reconstructed spectrum. It is worth noting that a relative error below 0.1 is generally considered a stringent benchmark, indicating high reconstruction accuracy; therefore, this embodiment defines a standardized relative error (ε). norm The value is 0.1, used to evaluate the device's reconfiguration performance.

[0025] Achieving calibration-free detection: The core advantage lies in the limitation that "the topological waveguide supports the transmission of boundary states protected by the topology" and "the operating frequency of the external incident light wave is within the operating frequency band of the topological boundary state". The topological boundary state has inherent robustness to structural perturbations and process deviations, which can effectively prevent light field fluctuations caused by immune system defects and random manufacturing errors, ensuring stable transmission response. High-precision spectral detection can be completed without the need for additional calibration structures, post-calibration, and algorithm pre-calibration. This solves the technical problem of frequent calibration required for on-chip spectrometers in the existing technology, simplifies the system structure, and reduces the cost of use.

[0026] Improving spectral reconstruction accuracy: By using a "wavelength-dependent coupling structure formed by combining topological waveguides and coupled waveguides," wavelength-dependent coupling modulation of the incident light field is achieved, outputting differentiated coded optical signals and providing rich feature information for spectral reconstruction. Simultaneously, the spectral reconstruction module performs inversion calculations based on a preset response matrix. Combined with the precise calculations of the aforementioned formulas, high-precision reconstruction of the incident spectrum can be achieved, such as... Figure 4 As shown in (a)-(d), the relative reconstruction errors of single-peak, double-peak, and broadband signals are all much lower than ε. norm =0.1, and the reconstruction accuracy can reach 92%, meeting the requirements of high-precision detection.

[0027] Achieving on-chip integration to meet miniaturization and mass production requirements: All core components are integrated on the same chip, reducing the device size and making it suitable for portable spectral detection scenarios; at the same time, the on-chip integrated structure eliminates the need for complex external connections, reducing assembly difficulty and laying the foundation for subsequent large-scale mass production.

[0028] High transmission stability: By limiting the operating frequency of the external incident light wave to within the operating frequency band of the topological boundary state of the topological waveguide, it ensures that the incident light always propagates through the topological boundary state, avoiding transmission loss and signal distortion caused by frequency deviation. Figure 2 (b) Figure 5 As shown in (a), even with structural defects, the transmission spectrum remains stable, ensuring the reliability of spectral detection. Figure 2This is a schematic diagram related to the on-chip spectrometer reconstruction without calibration achieved by the topological photonic crystal in this embodiment; wherein, (a) is a schematic diagram of the on-chip spectrometer without calibration, (b) is a comparison of the spectral reconstruction results of the topological photonic crystal under ideal conditions (b1) and with defects (b2), (c) verifies the insensitivity of spectral reconstruction performance to defects, (c1) the relative error under six different defect conditions, the red dashed line represents the error-free baseline, and (c2) the error bar quantifies the performance changes of the actual manufacturing batch.

[0029] Furthermore, the topology beam splitting coding module includes a topology waveguide array, which is composed of multiple topology waveguides arranged in parallel, and is used to perform multi-path beam splitting and parallel coding of the incident light.

[0030] Based on the topological beam splitting coding module containing at least one topological waveguide, it is further configured as a topological waveguide array. This array consists of multiple topological waveguides arranged in parallel. Each topological waveguide supports topologically protected boundary state transmission, and each topological waveguide cooperates with a coupling waveguide to form a wavelength-dependent coupling structure. After the incident light is coupled to the topological waveguide array through the incident coupling structure, it is split into multiple optical signals. Each optical signal is transmitted in the corresponding topological waveguide and simultaneously encoded in parallel, outputting multiple differentiated encoded optical signals, which are then transmitted to the outgoing detection structure.

[0031] Achieving multi-path beam splitting and parallel coding enhances coding diversity: Multiple topological waveguides arranged in parallel can split the incident light into multiple paths, each undergoing independent coding and modulation, outputting multiple coded optical signals. Compared to a single topological waveguide, this results in richer coding information, providing more feature information for subsequent spectral reconstruction and further improving reconstruction accuracy and resolution. Figure 2 As shown in (b), coded signals with different coupling configurations can significantly improve spectral resolution.

[0032] Improved detection efficiency: Parallel encoding can process multiple optical signals simultaneously, avoiding the time-consuming problem of single-path encoding, accelerating the processing speed of optical signals, thereby improving the response efficiency of spectral detection and adapting to rapid detection scenarios.

[0033] Enhanced device stability and redundancy: Multiple topological waveguides operate in parallel, so even if one of them experiences a minor fault, the others can still function normally, preventing overall device failure and improving device stability and redundancy, thus meeting the requirements for long-term continuous detection.

[0034] The topological waveguide array forms a topological power divider, with the number of beam splitting paths set to 2 to 8, and 8 paths are preferred in this embodiment. This topological power divider can evenly divide the incident light into 8 paths, with good power distribution consistency among the paths and beam splitting uniformity error controlled within ±5%. Each topological waveguide forms a wavelength-dependent coupling structure with its corresponding coupling waveguide, realizing parallel encoding of 8 optical signals.

[0035] In this embodiment, the coupling waveguide is a silicon-based strip waveguide, which is compatible with the overall silicon-based fabrication process of the on-chip spectrometer. It can effectively constrain the transmitted optical field and reduce the transmission loss of the on-chip optical waveguide.

[0036] The incident coupling structure includes an incident waveguide, and a matching coupling structure is set between the incident waveguide and the topological waveguide. This matching coupling structure is an integrated structure on a silicon substrate, which can be processed and formed simultaneously with the overall device through photolithography and etching on the same wafer, without the need for additional packaging and discrete coupling devices.

[0037] Two preferred configurations for the matching coupling structure are: one is a strip-shaped gradient configuration, in which the waveguide width is continuously and gently varied along the optical transmission direction to achieve mode field matching between the incident waveguide and the topological waveguide, reduce coupling loss caused by mode mismatch, and improve optical coupling efficiency; the other is a Y-shaped bifurcation configuration, which adopts an on-chip standard Y-branch waveguide and completes optical field mode conversion and optical path adaptation by means of Y-shaped bifurcation optical path transition, achieving efficient coupling from the incident waveguide to the topological waveguide with low loss. The overall structure is compact and fully compatible with CMOS-compatible on-chip fabrication processes.

[0038] Ensuring beam splitting uniformity and improving coding consistency: The topology power divider has the characteristic of uniform beam splitting, which can make the power distribution of multiple optical signals uniform, avoiding differences in the strength of coded signals caused by uneven beam splitting, ensuring the consistency of each coding path, and thus improving the accuracy and stability of spectral reconstruction. Figure 3 As shown in (e), uniform beam splitting can improve the response consistency of each channel and reduce reconstruction error. Figure 3 This is a schematic diagram of the topological strip waveguide mode coupling and spectrometer performance analysis in this embodiment; wherein, (a) is a schematic diagram of the strip waveguide embedded in the topological waveguide, (b) is the out-of-plane magnetic field distribution in the topological waveguide and the strip waveguide, (c) is a schematic diagram of the insertion coupling between two waveguides and the out-of-plane magnetic field distribution, (d) is the transmission spectrum between the strip waveguide and the topological waveguide with eight different coupling overlap configurations, (e) is the autocorrelation width of the sampling channels of the spectrometer with different number of channels, and the inset shows the autocorrelation function of an eight-channel design with an autocorrelation width of 1.28 nm.

[0039] Achieving a balance between performance and cost: limiting the number of beam splitters to 2-8 avoids the problems of insufficient coding information and low reconstruction accuracy caused by too few beam splitters (less than 2), while avoiding the problems of increased chip area, higher manufacturing costs, and increased computational complexity caused by too many beam splitters (more than 8). Figure 5 As shown in (e), when the number of beam splitters exceeds 6, the reconstruction error tends to stabilize. An 8-beam split can achieve an optimal balance by controlling chip size and manufacturing cost while ensuring reconstruction accuracy. Figure 5 The robustness of the topological waveguide in this embodiment and the reconstructed spectrum of the defect spectrometer are shown. Among them, (a) shows the test structure including: a waveguide containing defects, a Z-shaped waveguide and a power divider, and the corresponding transmission spectrum is compared with that of a defect-free straight topological waveguide (Tref). (b) shows the single-peak and broadband reconstructions for different types of defects. The first row is the single-peak reconstruction result and the second row is the broadband reconstruction result corresponding to each defect type. (c) shows the relative error when there are defects.

[0040] Adaptable to mass production needs: The topology power divider has a simple structure and high repeatability. With 2 to 8 beam splitting channels, it can be mass-produced using CMOS-compatible processes without complicated manufacturing procedures, thereby improving mass production yield and reducing mass production costs.

[0041] The topological waveguide is a valley photonic crystal topological waveguide, composed of periodically arranged photonic crystal units that break spatial mirror symmetry. The core feature of this waveguide, composed of periodically arranged photonic crystal units, is the breaking of spatial mirror symmetry; this breaking of spatial mirror symmetry is key to the formation of topological boundary states, enabling the valley photonic crystal topological waveguide to generate a sufficiently wide complete bandgap, supporting stable transmission of topological boundary states, and thus endowing the waveguide with extremely strong robustness, such as... Figure 3 As shown in (a), the structure of this valley photonic crystal topological waveguide can effectively excite topological boundary states.

[0042] Enhanced topological protection and improved robustness: The photonic crystal units of the valley photonic crystal topological waveguide break spatial mirror symmetry, forming stable topological boundary states. These topological boundary states are more resistant to structural defects, bending, and process deviations, such as... Figure 6 As shown in (a), even if the topological waveguide has defects and exhibits a Z-shaped bend, its transmission spectrum remains essentially consistent with that of a defect-free strip waveguide. This effectively mitigates optical field fluctuations caused by immune system defects and random manufacturing errors, further enhancing device stability and providing more reliable support for calibration-free testing. Figure 6 This is a schematic diagram of uncalibrated spectral reconstruction under manufacturing errors in this embodiment; the reconstructed spectra for single-peak, broadband light source 1, and broadband light source 2 are shown under different manufacturing errors, where... Figure 5In the diagram, (a) represents a manufacturing error of 5 nm, and (b) represents a manufacturing error of 10 nm.

[0043] Expanding the wavelength transmission range: Valley photonic crystal topological waveguides have a wide operating bandwidth of topological boundary states, supporting stable transmission of optical signals in the wavelength range of 1540~1716nm, adapting to broadband spectral detection requirements, such as... Figure 4 As shown in (c) and (d), accurate reconstruction of broadband signals can be achieved, expanding the application scenarios of the device. Figure 4 This is a schematic diagram related to the calibration and testing of the on-chip spectrometer based on topological waveguide in this embodiment; where (a) is the reconstructed spectrum of a series of single-peak spectral lines, (b) is the reconstructed spectrum of double-peak spectral lines, wherein the spectral line spacing is reduced from 1nm to 0.1nm, (c) is the reconstructed spectrum of continuous broadband signal 1, (d) is the reconstructed spectrum of continuous broadband signal 2, and (e) is a study on the relationship between reconstruction accuracy and the number of sampling channels.

[0044] Adaptable to on-chip integration processes: The structure of the valley photonic crystal topological waveguide can be fabricated using CMOS-compatible processes such as photolithography and etching. The periodically arranged photonic crystal units are easy to control precisely, enabling on-chip integration. It has strong compatibility with other components and is easy to mass-produce.

[0045] The photonic crystal unit comprises two types of equilateral triangular dielectric pillar units with different sizes. The size difference between these two types of dielectric pillar units achieves spatial mirror symmetry breaking. In this embodiment, the arrangement of the two types of equilateral triangular dielectric pillar units follows a periodic pattern, forming a valley photonic crystal structure to ensure the stable formation of topological boundary states. Figure 3 As shown in (a), triangular dielectric pillars of two different sizes are arranged periodically to form the core structure of the valley photonic crystal topological waveguide.

[0046] Precisely achieve spatial mirror symmetry breaking: Two equilateral triangular dielectric pillar units of different sizes can be used to precisely control the degree of spatial mirror symmetry breaking by adjusting the size difference, thereby precisely controlling the formation conditions of topological boundary states, ensuring that the topological waveguide supports stable topological boundary state transmission, and avoiding the problem of poor topological protection effect caused by insufficient symmetry breaking.

[0047] Facilitates structural parameter adjustment and adapts to different wavelength requirements: By adjusting the size of two types of equilateral triangular dielectric pillar units, the bandgap width and topological boundary state operating frequency band of the valley photonic crystal topological waveguide can be controlled, adapting to the spectral detection requirements of different wavelength ranges and improving the versatility of the device.

[0048] Low fabrication difficulty and suitable for mass production: The equilateral triangular dielectric pillar unit has a simple structure and can be precisely fabricated through photolithography and etching processes. The difference between the two sizes is easy to control. No complex fabrication equipment is required, which can reduce the fabrication difficulty, improve the mass production yield, and reduce the manufacturing cost.

[0049] The difference in side length between the two equilateral triangular dielectric pillar units is 5% to 20% of the unit side length; the thickness of the topological waveguide is 0.22 μm, the period of the photonic crystal unit is 0.3 to 1 μm, and the difference in side length between the two equilateral triangular dielectric pillar units is 5% to 20% of the unit side length, preferably 12% in this embodiment; the thickness of the topological waveguide ranges from 0.2 to 0.5 μm, preferably 0.22 μm in this embodiment; the period of the photonic crystal unit ranges from 0.3 to 1 μm, preferably 0.38 μm in this embodiment; these parameter ranges ensure that the photonic crystal unit can stably form spatial mirror symmetry breaking, the topological waveguide can support the transmission of topological boundary states in the wavelength range of 1540~1716 nm, and at the same time ensures that the transmission loss of the waveguide does not exceed 0.5 dB / cm and the coupling efficiency is not less than 85%.

[0050] Ensuring the stability and consistency of device performance: Limiting the parameter range ensures that each batch of devices maintains consistent performance, avoiding problems such as poor topology protection, excessive transmission loss, and low coupling efficiency caused by parameter deviations, thus improving the mass production consistency of devices. Figure 6 As shown, even with a manufacturing error of 5-10nm, the device can still maintain high performance, proving that this parameter range has strong fault tolerance.

[0051] Balancing performance and fabrication difficulty: The parameter range is set with full consideration of the fabrication capability of CMOS compatible processes. The topological waveguide thickness of 0.2 to 0.5 μm and the photonic crystal unit period of 0.3 to 1 μm are both within the controllable range of conventional photolithography and etching processes, requiring no special equipment and reducing fabrication difficulty. At the same time, the side length difference of 5% to 20% can ensure the effect of spatial mirror symmetry breaking, taking into account both topological protection performance and fabrication feasibility.

[0052] Optimize transmission performance and coupling efficiency: Reasonable parameter settings can reduce the transmission loss of the topological waveguide and improve the coupling efficiency between the incident coupling structure and the topological waveguide. In this embodiment, the coupling efficiency can reach 88%, and the transmission loss does not exceed 0.5dB / cm, ensuring efficient transmission of optical signals and reducing the impact of signal loss on the accuracy of spectral reconstruction.

[0053] The coupling waveguide is a silicon-based strip waveguide; the incident coupling structure includes an incident waveguide, and a matching coupling structure is provided between the incident waveguide and the topological waveguide. In this embodiment, the incident waveguide is also a silicon-based strip waveguide, consistent with the material system of the coupling waveguide, which effectively improves process compatibility and mode field matching.

[0054] With the insertion depth of the matched coupling structure set to 2930 nm and the insertion width set to 359 nm, these structural parameters allow the incident light wave to be efficiently fed into the topological waveguide in an optimal coupling mode, as shown below. Figure 3The light field distribution shown in (c) enables low-loss light field coupling.

[0055] The matching coupling structure is an on-chip integrated configuration on silicon substrate, employing a strip-shaped gradient structure or a Y-shaped bifurcation structure. This allows for a smooth transition in mode field distribution, suppresses coupling loss caused by mode mismatch, and ensures efficient transmission of incident light in the waveguide link.

[0056] Improving coupling efficiency and reducing signal loss: Silicon-based strip waveguides have good optical transmission performance and strong compatibility with topological waveguides, which can reduce the loss of optical signals during coupling. At the same time, the matching coupling structure can make the coupling between the incident waveguide and the topological waveguide reach the optimal state. In this embodiment, the coupling efficiency is not less than 85%, ensuring that the incident light is efficiently coupled to the topological beam splitting coding module, providing a stable optical signal foundation for subsequent coding and reconstruction.

[0057] Enhanced stability of wavelength-dependent coupling: The stable structure of silicon-based strip waveguides allows for precise control of their coupling interface with the topological waveguide, ensuring stable coupling modulation of optical signals of different wavelengths and avoiding distortion of encoded signals due to unstable coupling interfaces, thereby improving the accuracy of spectral reconstruction.

[0058] Adaptable to CMOS compatible processes: Silicon-based strip waveguides are a commonly used structure in CMOS processes. They are easy to mass-produce and have strong compatibility with other silicon-based components on the chip. This can reduce the manufacturing cost of devices, improve mass production yield, and promote the engineering application of devices.

[0059] Meanwhile, the coupling strength between the outgoing waveguide and the topological waveguide is limited to be less than the coupling strength between the incident coupling structure and the topological waveguide. In this embodiment, the outgoing waveguide adopts a silicon-based strip waveguide consistent with the incident waveguide, and the photodetector adopts a conventional semiconductor photodetector unit, which can convert the encoded optical signal into an electrical signal. The coupling strength difference between the outgoing end and the incident end is set to 10%~30%, and is preferably 20% in this embodiment. Through the differentiated coupling strength, differentiated encoding output of optical signals of different wavelengths can be achieved.

[0060] Enhancing coding diversity and discernibility: Different coupling strengths at the output and input ends allow optical signals of the same wavelength to produce different responses during incident and output coupling, further strengthening the wavelength-dependent coupling modulation effect. This makes the coding differences between different wavelength optical signals more pronounced, improving the discernibility of the coded signal and facilitating accurate inversion by the spectral reconstruction module, such as... Figure 3 As shown in (d), differential coupling can produce diverse transmission spectra, thereby improving the coding effect.

[0061] Protecting the photodetector and extending its lifespan: The coupling strength at the output end is less than that at the input end, which reduces the intensity of the light signal entering the photodetector, preventing strong light signals from damaging the photodetector and extending its lifespan. At the same time, it ensures that the electrical signal output by the photodetector is within a suitable range, avoiding signal saturation or distortion and improving the stability of the electrical signal.

[0062] Optimize the signal transmission link: The combination of the outgoing waveguide and the photodetector enables efficient transmission and accurate conversion of the coded optical signal, ensuring that the electrical signal is transmitted completely to the spectral reconstruction module, reducing signal loss and interference, and further improving the accuracy and stability of spectral reconstruction.

[0063] The spectral reconstruction module employs a sparse reconstruction algorithm, a least squares inversion algorithm, or a neural network algorithm to achieve spectral inversion. In this embodiment, a deep neural network algorithm is preferred. This algorithm uses spectral transmittance and light field intensity as inputs, and performs inversion calculations on the electrical signal through a trained model to achieve accurate reconstruction of the incident spectrum. This effectively overcomes the limitations of underdetermined equations and improves reconstruction accuracy and response speed.

[0064] Improving the accuracy and speed of spectral reconstruction: All three algorithms can achieve spectral inversion. Among them, the deep neural network algorithm has the best reconstruction accuracy and response speed. In this embodiment, the reconstruction response time is no more than 10ms and the reconstruction accuracy is no less than 0.1nm, which can meet the requirements of fast and high-precision detection. The sparse reconstruction algorithm and the least squares inversion algorithm can be selected according to the actual application scenario to improve the versatility of the device.

[0065] Adaptable to different detection scenarios: Different algorithms are suitable for different scenarios. Sparse reconstruction algorithms are suitable for scenarios where the spectral signal is relatively sparse, least squares inversion algorithms are suitable for scenarios with low computational complexity requirements, and neural network algorithms are suitable for scenarios with high precision and fast detection. Users can choose the appropriate algorithm according to their actual needs to expand the application range of the device.

[0066] Reduced computational complexity and easy integration: All three algorithms have low computational complexity and can be integrated into the on-chip spectral reconstruction module without the need for external computing devices, achieving on-chip integrated spectral reconstruction, further reducing device size and adapting to portable application scenarios.

[0067] like Figure 7 , Figure 8As shown, this embodiment discloses a method for manufacturing a calibration-free on-chip spectrometer based on topological waveguides, including the following steps: S1, using CMOS-compatible technology, a silicon dioxide buffer layer and a single-crystal silicon waveguide core layer are sequentially fabricated on a silicon substrate; S2, a mask is fabricated based on a topological photonic crystal structure, and a topological waveguide, a coupling waveguide, and a topological waveguide array are fabricated on the waveguide core layer by photolithography and dry etching, and the structural dimensions of the photonic crystal units are controlled by etching to achieve spatial mirror symmetry breaking; S3, a photodetector is fabricated at the output end of the outgoing waveguide, and the photodetector is electrically connected to a spectral reconstruction module; S4, the coupling efficiency, beam splitting uniformity, reconstruction response speed, and transmission response stability of the device are tested to complete the device fabrication.

[0068] S1. Using a CMOS-compatible process, a silicon substrate is selected (to meet on-chip integration requirements). A silicon dioxide buffer layer and a single-crystal silicon waveguide core layer are sequentially fabricated on the silicon substrate. The thickness of the silicon dioxide buffer layer is set to 1~3μm, preferably 2μm in this embodiment, to isolate the substrate and the waveguide core layer and reduce the interference of the substrate on the optical signal. The thickness of the single-crystal silicon waveguide core layer is set to 0.22μm, preferably 0.3μm in this embodiment, corresponding to the limitation of "topological waveguide thickness is 0.22μm" in claim 6, providing a basis for the subsequent fabrication of topological waveguides and coupling waveguides.

[0069] S2. Based on the topological photonic crystal structure, a mask is designed and fabricated, with the pattern of the mask completely consistent with the structure of the topological waveguide, coupled waveguide, and topological waveguide array. Using deep ultraviolet lithography combined with dry etching, the topological waveguide, coupled waveguide, and topological waveguide array are fabricated on the single-crystal silicon waveguide core layer, forming the coupling structure between the topological beam-splitting coding module and the incident coupling structure and the outgoing waveguide. During the etching process, the etching accuracy is strictly controlled within ±10nm, precisely controlling the size difference between the two equilateral triangular photonic crystal units to achieve spatial mirror symmetry breaking, ensuring that the topological waveguide supports the transmission of topological boundary states. After etching, the roughness of the waveguide sidewall is controlled within 0.5nm to ensure the stable formation of the topological boundary states, and the transmission loss of the topological waveguide does not exceed 0.5dB / cm.

[0070] S3. A photodetector is fabricated at the output end of the outgoing waveguide. A photodetector unit is fabricated using conventional semiconductor manufacturing processes. The photodetector and the spectral reconstruction module are electrically connected via metal leads. The contact resistance of the electrical connection is controlled within 10Ω to ensure efficient transmission of electrical signals and avoid signal loss affecting the accuracy of spectral reconstruction.

[0071] S4. Under room temperature and standard atmospheric pressure, the performance of the fabricated on-chip spectrometer is tested. The tests include coupling efficiency, beam splitting uniformity, reconstruction response speed, and transmission response stability. The test results must meet the following requirements: coupling efficiency not less than 85%, beam splitting uniformity error not more than ±5%, reconstruction response time not more than 10ms, device transmission response fluctuation amplitude not more than ±3%, and spectral reconstruction resolution not less than 0.1nm. After all performance indicators meet the design requirements, the device manufacturing is completed.

[0072] If any test parameter of the on-chip spectrometer at room temperature and standard atmospheric pressure fails to meet the design threshold (coupling efficiency < 85%, beam splitting uniformity error > ±5%, reconstruction response time > 10 ms, transmission response fluctuation > ±3%, spectral reconstruction resolution < 0.1 nm), the following procedure shall be followed: Fault location and source tracing: Check the chip waveguide structure, topological photonic crystal etching accuracy, coupling end face flatness, micro-nano optical path assembly alignment error and spectral reconstruction algorithm parameter configuration one by one to locate the root cause such as process defects, assembly deviation or algorithm parameter mismatch.

[0073] Process-related defects: rework to correct the etched morphology, polish the coupling end face, adjust the wafer fabrication process parameters, and re-fabricate the device sample; Assembly alignment failure: Fine-tune the optical path coupling posture and assembly spacing, re-align and calibrate, and then let it stand still to stabilize; Algorithm performance is unacceptable: Optimize the spectral reconstruction iterative algorithm, calibrate the response timing parameters, and refresh the control program parameter configuration.

[0074] Retesting and verification: After rectification, the same room temperature and standard atmospheric pressure test environment was replicated, and all performance tests were repeated.

[0075] Closed-loop processing: If all indicators meet the standards after retesting, the product is deemed qualified and enters the finished product warehouse; if the product still fails to meet the indicator requirements after two rectification and retesting, it is scrapped, and the reasons for non-compliance and rectification records are archived simultaneously to optimize the preparation process and assembly standards for subsequent batches.

[0076] refer to Figure 7 As shown, the present invention provides an on-chip spectrometer based on photonic crystal, including a broadband light source 1, a first coupler 2, a photonic crystal on-chip spectrometer chip 3, a coupling region 4, a photonic crystal dispersion modulation structure 5, a signal acquisition unit 6, an unknown spectral input source 7, a second coupler 8, an optical power meter array 9, and a data processing unit 10.

[0077] A broadband light source 1 and an unknown spectral input source 7 are connected to the optical path via a first coupler 2 and a second coupler 8, respectively. The two signals are coupled and input to a photonic crystal on-chip spectral chip 3. A coupling region 4 is provided at the input end of the photonic crystal on-chip spectral chip 3 to efficiently guide the optical signal into the photonic crystal dispersion modulation structure 5 inside the chip. The photonic crystal dispersion modulation structure 5 is a periodic micro-nano photonic crystal structure. By controlling the photonic bandgap and dispersion characteristics, it allows light of different wavelengths to propagate within the chip and form differentiated intensity distributions in multiple output channels. Each output channel is connected to an optical power meter array 9 to achieve synchronous acquisition of multi-channel intensity data. The data processing unit 10 receives the acquired data from the optical power meter array 9 and, combined with a pre-calibrated wavelength-intensity response matrix, reconstructs the unknown spectrum using matrix inversion or compressed sensing algorithms.

[0078] In this embodiment, the on-chip spectral chip 3 of the photonic crystal is fabricated using SOI silicon-based technology, with a working wavelength range of 1540~1716nm. By adjusting the period, diameter, and arrangement of the air holes in the photonic crystal, light of different wavelengths can form distinguishable response characteristics at the chip output. During system calibration, continuous spectrum light is emitted by the broadband light source 1, and the light intensity data of each channel is collected to construct a response matrix. During measurement, the unknown spectral signal 7 is coupled with the calibration light as input, modulated by the photonic crystal dispersion modulation structure 5, and multi-channel light intensity data is collected by the optical power meter array 9. The data processing unit 10 reconstructs the spectrum based on this data, and the measurement error can be as low as 0.027 when compared with the reference spectrum.

[0079] This device eliminates the need for traditional grating or prism beam-splitting structures, achieving on-chip integrated and miniaturized spectral measurement. It is suitable for rapid spectral detection in scenarios such as fiber optic communication and environmental monitoring. Combining the above technical solutions brings the following benefits: ensuring complete matching of device performance with product claims: each step of the manufacturing method corresponds to the structural features and parameter requirements of the product claims. For example, step S2 corresponds to the structure and parameters of the topological waveguide and coupled waveguide, and step S3 corresponds to the configuration of the emitted detector structure, achieving calibration-free, highly stable, and high-precision spectral detection performance.

[0080] Adapted to large-scale mass production and reduced production costs: The process adopts CMOS-compatible technology, which is a mature process in the semiconductor industry and can achieve mass production without special equipment and processes, thus reducing the difficulty of preparation and production costs. At the same time, the steps are clear and highly repeatable, which can improve the mass production yield. In this embodiment, the mass production yield can reach more than 85%, solving the technical problem that existing on-chip spectrometers are difficult to mass produce.

[0081] High process controllability enhances device consistency: Each step has clearly defined process parameters and control requirements, such as etching precision, waveguide thickness, and contact resistance. This ensures consistent device performance across batches, avoiding performance differences caused by process deviations and improving device reliability and stability. Figure 5 As shown, even with manufacturing errors, the device maintains high performance, demonstrating the strong controllability of this manufacturing method. The simplified fabrication process promotes engineering application: the manufacturing steps are concise, eliminating the need for complex assembly and calibration procedures. After fabrication, only performance testing is required before use, simplifying the fabrication process, shortening the fabrication cycle, and promoting the engineering application and industrialization of on-chip spectrometers.

[0082] In summary, the calibration-free on-chip spectrometer based on topological waveguides and its manufacturing method provided by the embodiments of the present invention achieve calibration-free, highly stable, and high-precision on-chip spectral detection, are compatible with CMOS processes, simplify the fabrication process, improve mass production yield, reduce production costs, and solve the technical problems of existing on-chip spectrometers that are sensitive to process deviations, require frequent calibration, and are difficult to mass produce. It has significant technical advantages and practical value, and its scope of protection is defined by the claims.

[0083] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A topology waveguide based on-chip spectrometer without calibration, characterized in that, It includes an incident coupling structure, a topological beam-splitting coding module, an outgoing detection structure, and a spectral reconstruction module integrated on the same chip; The topology splitting coding module includes at least one topology waveguide that supports the transmission of topology protected boundary states. The topology waveguide is arranged parallel to and close to the coupling waveguide to form evanescent field coupling. The coupling efficiency of light waves of different wavelengths is different, forming a wavelength-dependent coupling structure, which performs wavelength coupling modulation on the incident light field and outputs a coded light signal. The incident coupling structure is used to couple external incident light waves to the topological beam splitting coding module; The outgoing detection structure is used to receive the encoded optical signal and convert it into an electrical signal; The spectral reconstruction module is connected to the emitted detector structure and is used to perform inversion calculations on the electrical signal based on a preset response matrix to reconstruct the incident spectrum. The operating frequency of the external incident light wave is located within the operating frequency band of the topological boundary state of the topological waveguide.

2. The on-chip spectrometer of claim 1, wherein, The topology beam splitting coding module includes a topology waveguide array composed of multiple topology waveguides arranged in parallel. The input ends of the topology waveguide array receive incident light together, and each output end of the topology waveguide array is connected to a photodetector array to output multi-channel beam splitting coded optical signals.

3. The on-chip spectrometer according to claim 2, characterized in that, The topological waveguide array is a topological power divider with 2 to 8 beams.

4. The on-chip spectrometer according to claim 1, characterized in that, The topological waveguide is a valley photonic crystal topological waveguide, which is composed of periodically arranged photonic crystal units.

5. The on-chip spectrometer according to claim 4, characterized in that, The photonic crystal unit includes two types of equilateral triangular dielectric pillar units with different sizes.

6. The on-chip spectrometer according to claim 5, characterized in that, The difference in side length between the two types of equilateral triangular dielectric pillar units is 5% to 20% of the unit side length; the thickness of the topological waveguide is 0.2 to 0.5 μm, and the period of the photonic crystal unit is 0.3 to 1 μm.

7. The on-chip spectrometer according to claim 1, characterized in that, The coupling waveguide is a silicon-based strip waveguide; The incident coupling structure includes an incident waveguide, and a matching coupling structure is provided between the incident waveguide and the topological waveguide; The matching coupling structure is an on-chip integrated structure, which adopts a strip gradient structure or a Y-shaped bifurcation structure.

8. The on-chip spectrometer according to claim 1, characterized in that, The emitted detection structure includes an emitted waveguide and a photodetector. The photodetector receives the split optical signal output from the emitted waveguide and converts the optical signal into a collectable electrical signal. The coupling strength between the outgoing waveguide and the topological waveguide is less than the coupling strength between the incident coupling structure and the topological waveguide.

9. The on-chip spectrometer according to claim 1, characterized in that, The spectral reconstruction module uses a sparse reconstruction algorithm, a least squares inversion algorithm, or a neural network algorithm to perform spectral inversion.

10. A method for manufacturing a calibration-free on-chip spectrometer based on topological waveguides, used to prepare the on-chip spectrometer according to any one of claims 1 to 9, characterized in that, include: S1. Using CMOS-compatible technology, a silicon dioxide buffer layer and a single-crystal silicon waveguide core layer are sequentially fabricated on a silicon substrate. S2. A mask is fabricated based on a topological photonic crystal structure. A topological waveguide, a coupled waveguide, and a topological waveguide array are fabricated on the waveguide core layer by photolithography and dry etching. The control photonic crystal unit is also etched. S3. Fabricate a photodetector at the output end of the outgoing waveguide and electrically connect the photodetector to the spectral reconstruction module.

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