A computing spectrometer based on a random multimode waveguide grating and a spectrum reconstruction method

Abstract

The application discloses a kind of computing spectrometer and spectral reconstruction method based on random multimode waveguide grating.It includes silicon substrate layer, silicon dioxide buried oxygen layer, lithium niobate waveguide layer, silicon dioxide coating layer and interdigital electrode arranged in turn from bottom to top.The lithium niobate waveguide layer is formed with mode multiplexer, multimode waveguide spiral and multimode waveguide grating, the mode multiplexer and multimode waveguide spiral are communicated, the multimode waveguide spiral includes at least one multimode straight waveguide, and the multimode straight waveguide is provided with a plurality of non-periodically distributed multimode waveguide gratings, each multimode waveguide grating unit adopts Bragg grating structure, and each multimode waveguide grating unit includes two groups of grating tooth structures located on both sides of the multimode straight waveguide.The application can simplify the electrical control logic, and the unordered resonance of different modes in the spiral can provide high spectral reconstruction resolution, and lithium niobate electro-optic modulation can realize fast and low-power measurement channel scanning.

Description

Technical Field

[0001] This invention relates to the field of spectrometer technology, specifically to a computational spectrometer and spectral reconstruction method based on a random multimode waveguide grating. Background Technology

[0002] Spectroscopic analysis plays a crucial role in chemical industrial testing, medical diagnostics, and materials characterization. Compared to bulky and expensive benchtop spectrometers, integrated spectrometers offer advantages in size, cost, scalability, and energy consumption, better meeting the needs of portable spectroscopic analysis. Integrated spectrometers are mainly classified into four categories based on their operating principles: dispersive spectrometers, narrowband filtered spectrometers, Fourier transform spectrometers, and computational spectrometers. Among these, the bandwidth resolution of integrated dispersive spectrometers is limited by spatial size, and dispersive spectral detection degrades the signal-to-noise ratio of the incident spectrum. Narrowband filtered spectrometers typically rely on microring resonators, whose manufacturing errors affect the uniform channel spacing in the filter, while high-quality microring filtering increases scan time and power consumption. The resolution of Fourier transform spectrometers depends on the maximum optical path difference, making it challenging to achieve pm-level resolution spectral measurements with limited power consumption or drive voltage.

[0003] Computational spectrometers can achieve high bandwidth-to-resolution ratios within a limited footprint and power consumption by spatially or temporally mapping and encoding the spectrum of each wavelength. Researchers have achieved good spectral reconstruction using passive structures such as light scattering in disordered media, reverse-designed optical networks, or multimode helical waveguides. However, limited spatial sampling cannot achieve broadband spectral measurements while ensuring high resolution. To address this, researchers have introduced a time-coding scheme of thermo-optical modulation into computational spectrometers, achieving spectral reconstructions with bandwidth-to-resolution ratios greater than 10,000. However, complex electrical logic control limits the scanning speed of the sampling process and increases power consumption. Furthermore, fields such as atmospheric monitoring require spectral resolutions of 1 pm, and currently demonstrated on-chip computational spectrometers still struggle to achieve such high resolutions. Summary of the Invention

[0004] To address the problems in the background technology, this invention provides a computational spectrometer based on a random multimode waveguide grating, which can effectively improve the disorder of reflected light and solve the problem of limited resolution in existing computational spectrometers. It utilizes a low-power electro-optical scan controlled by a single electrode to complete the sampling of the detection channel, thus solving the problems of slow scanning speed and complex electrical control logic in thermo-optical modulation spectrometers.

[0005] The technical solution adopted in this invention is:

[0006] This invention comprises, from bottom to top, a silicon substrate, a silicon dioxide buried oxide layer, a lithium niobate waveguide layer, a silicon dioxide cladding layer, and interdigitated electrodes. A mode multiplexer, a multimode waveguide spiral, and a multimode waveguide grating unit are formed on the lithium niobate waveguide layer. The first port of the mode multiplexer serves as an input port to receive incident light, the second port of the mode multiplexer serves as an output port to output outgoing light, and the third port of the mode multiplexer is connected to one end of the multimode waveguide spiral, while the other end of the multimode waveguide spiral serves as a monitoring port.

[0007] The multimode waveguide helix includes at least one multimode straight waveguide. Each multimode straight waveguide is provided with several non-periodicly distributed multimode waveguide grating units. Each multimode waveguide grating unit adopts a Bragg grating structure. Each multimode waveguide grating unit includes two sets of grating tooth structures located on both sides of the multimode straight waveguide, and the two sets of grating tooth structures are offset by half a grating period along the extension direction of the multimode straight waveguide.

[0008] The grating tooth structure is integrated with the multimode straight waveguide. Each multimode waveguide grating unit and a section of multimode straight waveguide between the two sets of grating tooth structures in the multimode waveguide grating unit together constitute a mode coupling region.

[0009] The mode multiplexer receives TE0 mode light from the input port as incident light. The TE0 mode light is kept in TE0 mode by the mode multiplexer and enters the multimode waveguide spiral. After entering the multimode waveguide spiral, the TE0 mode light is coupled through the mode coupling region to form forward-propagating TE0 mode light and reverse-propagating TE1 mode light. A resonant cavity structure is formed between each two adjacent mode coupling regions. The resonant cavity structures of different lengths have different reflection spectra. The incident light propagates along the multimode waveguide spiral and forms a disordered reflection spectrum and transmission spectrum after passing through several resonant cavity structures of different lengths. The forward-propagating TE0 mode light is output from the monitoring port along the multimode waveguide spiral, and the reverse-propagating TE1 mode light enters the mode multiplexer from the multimode waveguide spiral. In the mode multiplexer, it is coupled and converted into TE0 mode light as output light and output from the output port.

[0010] The multimode waveguide helix is ​​a racetrack-shaped structure with an octagonal shape at its center. The multimode waveguide helix includes two helical waveguides and one S-shaped waveguide. The two helical waveguides are arranged in a generally helical shape along the plane and are arranged alternately inside and outside to form a planar double helix shape. The inner ends of the two helical waveguides are connected by an S-shaped waveguide. One end of the outer end of the two helical waveguides serves as a monitoring port, and the other end is connected to the third port of the mode multiplexer.

[0011] Both helical waveguides are mainly composed of several alternating multimode straight waveguides and a first multimode bent waveguide. The waveguides at both ends of the two helical waveguides are multimode straight waveguides. The S-shaped waveguide is mainly composed of a second multimode bent waveguide, a multimode straight waveguide, and a second multimode bent waveguide connected in sequence, generally arranged in an S-shape. All multimode straight waveguides in the helical waveguides and S-shaped waveguides are arranged in parallel and on the straight section of the racetrack-shaped structure. The second multimode bent waveguide and the first multimode bent waveguide are both Euler bent structures.

[0012] The ends of the two multimode straight waveguides at the inner ends of the two helical waveguides are respectively connected to the outer ends of the two second multimode bent waveguides in the S-shaped waveguide. One end of the outer end of the two multimode straight waveguides at the outer ends of the two helical waveguides serves as a monitoring port, and the other end is connected to one end of the mode multiplexer.

[0013] Each grating tooth structure includes multiple grating teeth arranged at equal intervals along the extension direction of the multimode straight waveguide, and the number of grating teeth in each grating tooth structure is no more than 20.

[0014] The sum of the lengths of the multimode straight waveguides in the multimode waveguide helix is ​​not less than 5cm.

[0015] The mode multiplexer includes a first adiabatic tapered waveguide and a second adiabatic tapered waveguide, which are arranged at intervals and coupled together to realize the mutual conversion between TE0 and TE1 modes during optical signal transmission.

[0016] One end of the first adiabatic tapered waveguide serves as the first port, and the other end serves as the third port and is connected to the multimode waveguide helix. In the second adiabatic tapered waveguide, the end furthest from the multimode waveguide helix serves as the second port, and the other end is suspended.

[0017] The interdigitated electrode comprises two sets of electrode units. Each set of electrode units includes interdigitated fingers, electrode wires, and electrode plates. The interdigitated fingers are arranged parallel to each other above both sides of the multimode straight waveguide. The interdigitated fingers are connected to the electrode plates through electrode wires. The interdigitated fingers of the two sets of electrode units are arranged in an alternating manner to form at least one pair of positive and negative electrodes. Each multimode straight waveguide has a pair of positive and negative electrodes arranged above it, with the positive and negative electrodes of the pair respectively positioned above both sides of the multimode straight waveguide to apply an electric field to the multimode straight waveguide.

[0018] The interdigitated fingers, electrode wires, and electrode plates are made of titanium, the silicon substrate is made of silicon, the silicon dioxide buried oxide layer is made of silicon dioxide, the lithium niobate waveguide layer is made of lithium niobate, and the silicon dioxide cladding layer is made of silicon dioxide.

[0019] A method for spectral reconstruction using a computational spectrometer includes the following steps:

[0020] S1. Pre-calibration stage: A set of TE0 mode optical signals with different wavelengths and known spectra are sequentially input as incident light to the input port. Under each wavelength of incident light, a set of preset voltages V1, V2...V are applied. N All electrode pairs applied sequentially to the interdigitated electrodes are recorded, and the corresponding interference light intensities output from the output port under different preset voltages for incident light of different wavelengths are recorded respectively, thereby constructing the relationship matrix A;

[0021] S2, Measurement Stage: Input the optical signal to be measured to the input port, and use the same set of preset voltages V1, V2...V1 as in the pre-calibration stage in step S1. N The interference light intensity of the optical signal under test is recorded at the output port under different preset voltages, and the output light intensity vector is obtained.

[0022] S3. Spectral Reconstruction Stage: The relationship function between the output light intensity vector, the light signal to be measured, and the relation matrix is ​​set according to the following formula, and the spectrum to be measured is reconstructed using a convex optimization algorithm:

[0023] Y = A × X

[0024] Where Y represents the output light intensity vector of the light signal to be measured, X represents the spectral intensity vector of the light signal to be measured, and A represents the relation matrix.

[0025] The beneficial effects of this invention are:

[0026] Combining the lithium niobate platform enables low-power electro-optic scanning controlled by a single electrode; the random multimode waveguide grating resonance of the spiral can maximize the disorder of the reflected spectrum detected at the output port, solving the problems of limited resolution, slow scanning speed and complex electrical control logic of existing computational spectrometers. Attached Figure Description

[0027] Figure 1 This is a top view schematic diagram of the random multimode waveguide grating electro-optic modulation computational spectrometer of this embodiment;

[0028] Figure 2 This is a three-dimensional schematic diagram of the random multimode waveguide grating electro-optic modulation computational spectrometer of this embodiment;

[0029] Figure 3 This is a schematic diagram of the mode multiplexer of the random multimode waveguide grating electro-optic modulation computational spectrometer of the present invention;

[0030] Figure 4 This is a schematic diagram of the multimode waveguide grating unit of the random multimode waveguide grating electro-optic modulation computational spectrometer of the present invention;

[0031] Figure 5This is a graph showing the changes in voltage and reflected light output intensity over time for the random multimode waveguide grating electro-optic modulation computational spectrometer in this embodiment under a 1547nm wavelength laser input.

[0032] Figure 6 This is the test speckle pattern of the random multimode waveguide grating electro-optic modulation computational spectrometer in this embodiment;

[0033] Figure 7 This is a graph of the spectral correlation function of the random multimode waveguide grating electro-optic modulation computational spectrometer in this embodiment;

[0034] Figure 8 This is the spectral reconstruction diagram of the random multimode waveguide grating electro-optic modulation computational spectrometer in this embodiment;

[0035] In the figure, 1-input port, 2-first adiabatic conical waveguide, 3-second adiabatic conical waveguide, 4-output port, 5-random multimode waveguide grating unit, 6-second multimode bent waveguide, 7-first multimode bent waveguide, 8-monitoring port, 9-interdigital, 10-electrode wire, 11-electrode plate. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0037] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0038] like Figure 1 and Figure 2 As shown, this embodiment includes a silicon substrate layer, a silicon dioxide buried oxide layer, a lithium niobate waveguide layer, a silicon dioxide cladding layer, and interdigitated electrodes stacked sequentially from bottom to top; a mode multiplexer, a multimode waveguide spiral, and a multimode waveguide grating unit 5 are formed on the lithium niobate waveguide layer; the first port of the mode multiplexer serves as the input port 1 to receive incident light, the second port of the mode multiplexer serves as the output port 4 to output outgoing light, the third port of the mode multiplexer is connected to one end of the multimode waveguide spiral, and the other end of the multimode waveguide spiral serves as the monitoring port 8;

[0039] like Figure 3 As shown, the mode multiplexer includes a first adiabatic conical waveguide 2 and a second adiabatic conical waveguide 3 with equal spacing.

[0040] The multimode waveguide helix includes at least one multimode straight waveguide. Each multimode straight waveguide has several aperiodically distributed multimode waveguide grating units 5. Each multimode waveguide grating unit 5 employs a Bragg grating structure. Each multimode waveguide grating unit 5 includes two sets of identical grating tooth structures arranged opposite each other on both sides of the multimode straight waveguide. The two sets of grating tooth structures have a relative offset distance of half a grating period along the extension direction of the multimode straight waveguide. Figure 4 As shown.

[0041] The grating tooth structure is integrated with the multimode straight waveguide, meaning they are connected and have the same etching depth. Each multimode waveguide grating unit 5 and the section of multimode straight waveguide between the two sets of grating tooth structures in the multimode waveguide grating unit 5 together constitute a mode coupling region. Each grating tooth structure includes multiple grating teeth arranged at equal intervals along the extension direction of the multimode straight waveguide. The distance between the centers of every two adjacent grating teeth is one grating period. The grating teeth on both sides of the multimode straight waveguide are integrated with the multimode straight waveguide and are all lithium niobate protrusions. The starting position of the section of multimode straight waveguide between the two sets of grating tooth structures is the incident edge of the first grating tooth encountered along the light propagation direction, and the ending position is the exit edge of the last grating tooth in the other set of grating tooth structures.

[0042] The non-periodic distribution of the multimode waveguide grating units 5 specifically means that the multimode waveguide grating units 5 on the same multimode straight waveguide are not set at the same spacing, that is, the spacing between different adjacent multimode waveguide grating units 5 is different and randomly set. The "random" in the computational spectrometer based on random multimode waveguide gratings refers to the fact that the positions of the multimode waveguide grating units 5 on the multimode straight waveguide are random and non-periodic.

[0043] The mode multiplexer receives TE0 mode light from input port 1 as incident light. The TE0 mode light, after being kept in TE0 mode by the mode multiplexer, enters the multimode waveguide spiral. After entering the multimode waveguide spiral, the TE0 mode light passes through the mode coupling region to form forward-propagating TE0 mode light and reverse-propagating TE1 mode light. A resonant cavity structure is formed between each pair of adjacent mode coupling regions. The reflection spectrum of the resonant cavity is mainly determined by the physical distance between the two adjacent mode coupling regions and the refractive index of the waveguide. Since the multimode waveguide grating units 5 are aperiodically distributed on the multimode straight waveguide, the reflection spectra of resonant cavity structures of different lengths are different. The incident light propagates along the multimode waveguide spiral and, after passing through several resonant cavity structures of different lengths, forms a disordered reflection and transmission spectrum. The reverse-propagating light always maintains the TE1 mode, while the forward-propagating light always maintains the TE0 mode. In the transmission of TE0 mode light, whenever it encounters a mode coupling region, a portion of the forward-propagating TE0 mode light is converted into the reverse-propagating TE1 mode light, and a portion of the reverse-propagating TE1 mode light is converted into the forward-propagating TE0 mode light. The reflection spectra of several resonant cavities superimpose to form a complex and unpredictable random spectrum. The forward-propagating TE0 mode light is output from monitoring port 8 along the multimode waveguide spiral, while the reverse-propagating TE1 mode light is reverse-propagating and enters the mode multiplexer from the multimode waveguide spiral. In the mode multiplexer, it is coupled and converted into TE0 mode light, which is then output from output port 4. Monitoring port 8 is used to monitor the sum of the light field intensity of the incident light before resonance and the light field intensity of the forward-propagating TE0 mode light after resonance. When the light field intensity output from monitoring port 8 is close to that of output port 4, it indicates that most of the incident light has undergone reflection and resonance during transmission.

[0044] Reflectance spectrum refers to the relationship between the intensity of light reflected by a material or structure at different wavelengths and the wavelength. Forward transmission refers to the optical signal that enters the multimode waveguide spiral through the mode multiplexer and propagates along the direction of the multimode waveguide spiral. Reverse transmission refers to the optical signal that propagates along the direction of the multimode waveguide spiral entering the mode multiplexer.

[0045] In summary, the incident light is coupled into the mode multiplexer from input port 1, maintaining the TE0 mode and entering the multimode waveguide spiral. Each mode coupling region converts a small portion of the forward-propagating TE0 mode light into the reverse-propagating TE1 mode light, and simultaneously converts a small portion of the reverse-propagating TE1 mode light into the forward-propagating TE0 mode light. The randomly distributed multimode waveguide gratings create complex resonances within the spiral. All reverse-propagating TE1 mode light is demultiplexed by the mode multiplexer and converted back into TE0 mode light, which is then coupled out from output port 4. All forward-propagating TE0 mode light is coupled out from monitoring port 8. The TE0 mode optical signal achieves mutual conversion between TE0 and TE1 modes and forms resonance and interference through the multimode waveguide grating 5. The reverse TE1 mode light is demultiplexed by the mode multiplexer and converted back into TE0 mode light, resulting in a spectral interference pattern.

[0046] The random multimode waveguide grating 5 is specifically designed with a low number of periods and low reflection efficiency, so that only a small portion of the light is reflected back after passing through each grating. The purpose of the low number of periods in the random multimode waveguide grating is to minimize the reflection loss of the incident light after passing through each set of gratings, ensuring that the incident light can propagate in a sufficiently long spiral to achieve complex disordered resonance.

[0047] The main body of the multimode waveguide helix is ​​a racetrack-shaped structure with an octagonal shape at the center. The multimode waveguide helix has a centrally symmetrical structure. The multimode waveguide helix includes two centrally symmetrically arranged helical waveguides and one S-shaped waveguide. The two helical waveguides are arranged in a generally helical shape along the plane and are arranged alternately inside and outside to form a planar double helix shape. The inner ends of the two helical waveguides are connected by an S-shaped waveguide. One end of the outer end of the two helical waveguides serves as monitoring port 8, and the other end is connected to the third port of the mode multiplexer.

[0048] Both helical waveguides are mainly composed of several alternating multimode straight waveguides and a first multimode bent waveguide 7. The waveguides at the inner and outer ends of both helical waveguides are multimode straight waveguides. One S-shaped waveguide is mainly composed of a second multimode bent waveguide 6, a multimode straight waveguide, and a second multimode bent waveguide 6 connected in sequence, roughly in an S-shape. All multimode straight waveguides in the helical waveguides and S-shaped waveguides are arranged in parallel and on the straight section of the racetrack-shaped structure. The second multimode bent waveguide 6 and the first multimode bent waveguide 7 are both Euler bending structures with gradually changing curvature.

[0049] Specifically, the ends of the two multimode straight waveguides at the inner ends of the two helical waveguides are respectively connected to the outer ends of the two second multimode bent waveguides 6 in the S-shaped waveguide. One end of the outer end of the two multimode straight waveguides at the outer ends of the two helical waveguides serves as a monitoring port 8, and the other end is connected to one end of the mode multiplexer.

[0050] All multimode straight waveguides in helical waveguides and S-shaped waveguides have the same length and the same structure.

[0051] Each grating tooth structure includes multiple grating teeth arranged at equal intervals along the extension direction of the multimode straight waveguide, and the number of grating teeth in each grating tooth structure is no more than 20.

[0052] The sum of the lengths of the multimode straight waveguides in the multimode waveguide helix shall not be less than 5cm.

[0053] The mode multiplexer includes a first adiabatic tapered waveguide 2 and a second adiabatic tapered waveguide 3, which are arranged at intervals and coupled together to realize the mutual conversion between TE0 and TE1 modes during the transmission of optical signals.

[0054] The first adiabatic conical waveguide 2 has one end away from the multimode waveguide helix as the first port, i.e., input port 1, and the other end as the third port and connected to the multimode waveguide helix. One end of the second adiabatic conical waveguide 3 is suspended, and the other end, i.e., the end away from the multimode waveguide helix, is the second port, i.e., output port 4.

[0055] The interdigitated electrode comprises two sets of electrode units. Each set of electrode units includes interdigitated fingers 9, electrode wires 10, and electrode plates 11. The interdigitated fingers 9 are arranged in parallel above both sides of the multimode straight waveguide. The interdigitated fingers 9 are connected to the electrode plates 11 through the electrode wires 10. The interdigitated fingers 9 of the two sets of electrode units are arranged alternately to form at least one set of positive and negative electrode pairs. The number of positive and negative electrode pairs is the same as the number of multimode straight waveguides and corresponds one-to-one. A set of positive and negative electrode pairs is arranged above each multimode straight waveguide, and the positive and negative electrodes of the positive and negative electrode pairs are respectively arranged above both sides of the corresponding multimode straight waveguide. A set of positive and negative electrode pairs covers the modulation region of a corresponding multimode straight waveguide. All the positive and negative electrode pairs above the multimode straight waveguides constitute the interdigitated electrode, which is used to apply an electric field to the multimode straight waveguide.

[0056] The modulation region of a multimode straight waveguide is the area in the multimode straight waveguide where the refractive index is adjusted by applying an electric field or other external control methods. The modulation of this region causes an interference pattern to form at the output port.

[0057] In this embodiment, the speckle sampling function is achieved by replacing the thermo-optic modulation of the traditional on-chip computational spectrometer with thin-film lithium niobate electro-optic modulation.

[0058] In x-cut lithium niobate waveguides, birefringence leads to mode hybridization of polarized light, where different modes of light convert to each other during transmission, introducing losses. In this embodiment, both the inner and outer bends of the multimode waveguide helix are Euler bends with gradually varying curvature, ensuring that the forward-propagating TE0 mode light and the reverse-propagating TE1 mode light do not undergo mode hybridization within the entire lithium niobate waveguide helix, thus reducing transmission losses.

[0059] The interdigitated fingers 9, electrode wires 10, and electrode plates 11 are made of titanium gold, the silicon substrate is made of silicon, the silicon dioxide buried oxide layer is made of silicon dioxide, the lithium niobate waveguide layer is made of lithium niobate, and the silicon dioxide cladding layer is made of silicon dioxide.

[0060] A spectral reconstruction method based on a random multimode waveguide grating computational spectrometer includes the following steps:

[0061] S1. Pre-calibration stage: A set of TE0 mode optical signals with different wavelengths and known spectra are input as incident light to input port 1. The TE0 mode is maintained by a mode multiplexer and enters the multimode waveguide spiral. After passing through several non-periodic distributed multimode waveguide gratings 5, a disordered resonance is formed. Under each wavelength of incident light, a set of preset voltages V1, V2...V... are applied. N All electrode pairs applied sequentially to the interdigitated electrodes are recorded, and the corresponding interference light intensities output from output port 4 under different preset voltages for incident light of different wavelengths are recorded respectively, thereby constructing the relationship matrix A;

[0062] S2, Measurement Stage: Input the optical signal to be measured to input port 1, and use the same set of preset voltages V1, V2...V1 as in the pre-calibration stage in step S1. N The interference light intensity of the light signal to be measured is recorded at the output port (4) under different preset voltages, and the output light intensity vector is obtained.

[0063] S3. Spectral Reconstruction Stage: The relationship function between the output light intensity vector, the light signal to be measured, and the relation matrix is ​​set according to the following formula, and the spectrum to be measured is reconstructed using a convex optimization algorithm:

[0064] Y = A × X

[0065] Where Y represents the output light intensity vector of the light signal to be measured, X represents the spectral intensity vector of the light signal to be measured, and A represents the relation matrix.

[0066] The relationship matrix A, which is constructed by incident light wavelength, preset voltage and interference light intensity, is specifically an N×M two-dimensional matrix, where N is the number of applied voltage data points on electrode plate 11 and M is the number of response spectrum data points.

[0067] In this embodiment, the spectral reconstruction method of the random multimode waveguide grating electro-optic modulation computational spectrometer includes the following steps:

[0068] 1) Pre-calibration: Narrowband lasers with wavelengths from 1545nm to 1550nm are sequentially input into a random multimode waveguide grating electro-optic modulation computational spectrometer. A rapidly scanning voltage is applied to the electrode plate 11, and an electric field is applied to the modulation region of the multimode waveguide spiral straight waveguide through the electrode wire 10 and the electro-optic modulation interdigital electrode 9. The response light intensity of each wavelength laser under different voltage driving conditions is detected at the output port 4, and the relationship matrix A between the incident light wavelength, the preset voltage, and the interference light intensity is constructed.

[0069] 2) Input the spectrum to be measured X into the random multimode waveguide grating electro-optic modulation computational spectrometer, apply a rapidly scanning voltage to the electrode plate 11, and apply an electric field to the modulation region of the multimode waveguide spiral straight waveguide through the electrode wire 10 and the electro-optic modulation interdigital electrode 9. Detect the output light intensity vector Y under different voltage driving conditions at the output port 4, and construct the relationship function Y = A × X between the output light intensity vector Y, the spectrum to be measured X, and the relationship matrix A.

[0070] 3) Based on the relationship function between the output light intensity vector Y, the spectrum to be measured X and the relation matrix A, and combined with the convex optimization algorithm, the spectrum to be measured X is reconstructed.

[0071] The relationship matrix A between incident light wavelength, preset voltage, and interference light intensity is specifically an N×M two-dimensional matrix, where N is the number of applied voltage data points on electrode plate 11, and M is the number of response spectrum data points.

[0072] like Figure 5 The figure shows the relationship between scanning voltage and response light intensity over time under a 1547nm wavelength laser input and a 100kHz sinusoidal voltage scan, with the voltage scan range from -70V to 70V. The fast electro-optic response of lithium niobate enables the measurement channel scan time to be less than 10μs.

[0073] like Figure 6 The figure shows the output speckle pattern of the 1545nm to 1550nm band under a sinusoidal voltage scan from -70V to 70V. The horizontal axis represents the wavelength channels, and the vertical axis represents the interference light intensity measurement channels under different voltages. The output light intensity is normalized. 998 measurement channels are sampled for each wavelength, with a wavelength scan interval of 1 pm. Under voltage scanning, the refractive index of the resonant cavity between the multimode waveguide gratings changes, and the reflected output light achieves different modulation effects under different voltages. This speckle pattern is directly related to the performance of the spectrometer. According to the spectral correlation function C(Δλ)=<(<I(λ,k)I(λ+Δλ,k)> λ ) / (<I(λ,k)> λ <I(λ+Δλ,k)> λ )-1> k It is possible to plot the spectral correlation function curve of the spectrometer, such as... Figure 7 As shown.

[0074] like Figure 7 As shown, C(Δλ) represents the spectral correlation, Δλ represents the wavelength interval, k represents the sampling and detection channels, and I(λ,k) represents the optical power when the wavelength channel is λ and the detection channel is k. λ Take the sign of the average wavelength, <…> k The average sign of the detection channels is taken. The resolution of the spectrometer can be estimated by the full width at half maximum (FWHM) of the spectral correlation function, which represents the minimum wavelength separation required to reduce the correlation by half. As shown in the figure, the theoretical prediction of the spectral resolution of this device is 0.0061 nm.

[0075] The resolution of a computational spectrometer is determined by many factors, including the number of sampling channels, algorithm performance, and signal-to-noise ratio. When there are enough sampling channels, the actual resolution of a computational spectrometer may exceed the full width at half maximum (FWHM) of the spectral correlation function.

[0076] like Figure 8 As shown, the spectral reconstruction was tested for narrowband double-peak incident and broadband incident light. A compressed sensing algorithm based on a convex optimization function was used to reconstruct the input spectral signal. The tests were conducted on a narrowband double-peak signal with a working bandwidth of 5 nm and wavelengths of (1547.32, 1547.321) nm and a continuous broadband signal with a bandwidth of approximately 1 nm. The test results show that the reconstructed spectrum is in good agreement with the input spectrum, and the spectral resolution can reach 1 pm. The spectral reconstruction diagram of the random multimode waveguide grating electro-optic modulation computational spectrometer in this embodiment is shown below. Figure 8 As shown.

[0077] The innovation of this invention lies in:

[0078] 1. This invention employs a random multimode waveguide grating design, in which multiple grating units are non-periodically distributed along a multimode straight waveguide. This maximizes the degree of disorder in the reflected light detected at the output port. Each grating constitutes a low-reflectivity structure, which can induce complex random resonances in the waveguide. Subsequently, by applying different voltages through electrodes, the refractive index distribution within the waveguide is modulated, thereby altering the interference behavior of light in the waveguide. This causes a change in the response of the output light intensity to the input spectrum, thus establishing a mapping relationship between different wavelengths of light under voltage scanning and the output light intensity (interference pattern). This enables spectral encoding. This encoding method differs from existing spectral encoding technologies, solving the problems of limited resolution, slow scanning speed, and complex electrical control logic in existing computational spectrometers.

[0079] 2. By employing two centrally symmetrically arranged helical waveguides and a multimode straight waveguide connecting their inner ends, a long-path propagation structure is constructed within a limited chip area, thereby improving the resonance complexity and spectral resolution of the reflected light.

[0080] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A computational spectrometer based on a random multimode waveguide grating, characterized in that: The structure includes a silicon substrate, a silicon dioxide buried oxide layer, a lithium niobate waveguide layer, a silicon dioxide cladding layer, and interdigitated electrodes arranged sequentially from bottom to top. A mode multiplexer, a multimode waveguide spiral, and a multimode waveguide grating unit (5) are formed on the lithium niobate waveguide layer. The first port of the mode multiplexer serves as the input port (1) to receive incident light, the second port of the mode multiplexer serves as the output port (4) to output outgoing light, and the third port of the mode multiplexer is connected to one end of the multimode waveguide spiral. The other end of the multimode waveguide spiral serves as the monitoring port (8). The multimode waveguide helix includes at least one multimode straight waveguide. Each multimode straight waveguide is provided with several randomly distributed multimode waveguide grating units (5). Each multimode waveguide grating unit (5) adopts a Bragg grating structure. Each multimode waveguide grating unit (5) includes two sets of grating tooth structures located on both sides of the multimode straight waveguide. The two sets of grating tooth structures have an offset distance of half a grating period between them along the extension direction of the multimode straight waveguide. The grating tooth structure is integrated with the multimode straight waveguide. Each multimode waveguide grating unit (5) and a section of multimode straight waveguide between the two sets of grating tooth structures in the multimode waveguide grating unit (5) together constitute a mode coupling region. The mode multiplexer receives TE0 mode light from the input port (1) as incident light. The TE0 mode light is kept in TE0 mode by the mode multiplexer and enters the multimode waveguide spiral. After entering the multimode waveguide spiral, the TE0 mode light is coupled through the mode coupling region to form forward-propagating TE0 mode light and reverse-propagating TE1 mode light. A resonant cavity structure is formed between each two adjacent mode coupling regions. The resonant cavity structures of different lengths have different reflection spectra. The incident light is propagated along the multimode waveguide spiral and forms a disordered reflection spectrum and transmission spectrum after passing through several resonant cavity structures of different lengths. The forward-propagating TE0 mode light is output from the monitoring port (8) along the multimode waveguide spiral. The reverse-propagating TE1 mode light enters the mode multiplexer from the multimode waveguide spiral and is coupled and converted into TE0 mode light in the mode multiplexer as output light and output from the output port (4). The multimode waveguide helix is ​​a racetrack-shaped structure with an octagonal shape at the center. The multimode waveguide helix includes two helical waveguides and one S-shaped waveguide. The two helical waveguides are arranged in a generally spiral shape along the plane and are arranged alternately inside and outside to form a planar double helix shape. The inner ends of the two helical waveguides are connected by an S-shaped waveguide. One end of the outer end of the two helical waveguides serves as a monitoring port (8), and the other end is connected to the third port of the mode multiplexer. Both spiral waveguides are composed of several alternating multimode straight waveguides and a first multimode bent waveguide (7). The waveguides at both ends of the two spiral waveguides are multimode straight waveguides. The S-shaped waveguide is composed of a second multimode bent waveguide (6), a multimode straight waveguide, and a second multimode bent waveguide (6) connected in sequence, generally arranged in an S-shape. All multimode straight waveguides in the spiral waveguide and the S-shaped waveguide are arranged in parallel and on the straight section of the racetrack-shaped structure. The second multimode bent waveguide (6) and the first multimode bent waveguide (7) are both Euler bent structures. The ends of the two multimode straight waveguides at the inner ends of the two helical waveguides are respectively connected to the outer ends of the two second multimode bent waveguides (6) in the S-shaped waveguide; Each of the grating tooth structures includes a plurality of grating teeth arranged at equal intervals along the extension direction of the multimode straight waveguide, and the number of grating teeth in each grating tooth structure is no more than 20; The sum of the lengths of the multimode straight waveguides in the multimode waveguide helix is ​​not less than 5cm.

2. A computational spectrometer based on a random multimode waveguide grating according to claim 1, characterized in that: The mode multiplexer includes a first adiabatic conical waveguide (2) and a second adiabatic conical waveguide (3). The first adiabatic conical waveguide (2) and the second adiabatic conical waveguide (3) are arranged at intervals and coupled together, and are used to realize the mutual conversion between TE0 and TE1 modes during the transmission of optical signals. One end of the first adiabatic conical waveguide (2) serves as the first port, and the other end serves as the third port and is connected to the multimode waveguide helix. The end of the second adiabatic conical waveguide (3) that is far from the multimode waveguide helix serves as the second port, and the other end is suspended.

3. A computational spectrometer based on a random multimode waveguide grating according to claim 1, characterized in that: The interdigitated electrode includes two sets of electrode units. Each set of electrode units includes interdigitated fingers (9), electrode wires (10), and electrode plates (11). The interdigitated fingers (9) are arranged in parallel above both sides of the multimode straight waveguide. The interdigitated fingers (9) are connected to the electrode plates (11) through the electrode wires (10). The interdigitated fingers (9) of the two sets of electrode units are arranged in an alternating manner to form at least one pair of positive and negative electrodes. Each multimode straight waveguide has a pair of positive and negative electrodes arranged above it, and the positive and negative electrodes of the pair are respectively arranged above both sides of the multimode straight waveguide to apply an electric field to the multimode straight waveguide.

4. A computational spectrometer based on a random multimode waveguide grating according to claim 3, characterized in that: The interdigitated fingers (9), electrode wires (10) and electrode plates (11) are made of titanium gold, the silicon substrate is made of silicon, the silicon dioxide buried oxide layer is made of silicon dioxide, the lithium niobate waveguide layer is made of lithium niobate, and the silicon dioxide cladding layer is made of silicon dioxide.

5. A spectral reconstruction method applied to a computational spectrometer based on a random multimode waveguide grating as described in any one of claims 1-4, characterized in that, The method includes the following steps: S1, Pre-calibration stage: A set of TEO mode optical signals with different wavelengths and known spectra are sequentially input as incident light to the input port (1). Under each wavelength of incident light, a set of preset voltages V1, V2...V are applied. N All electrode pairs applied sequentially to the interdigitated electrodes are recorded, and the corresponding interference light intensity output from the output port (4) of different wavelength incident light under different preset voltages is recorded, thereby constructing the relationship matrix A; S2, Measurement Stage: Input the optical signal to be measured to the input port (1), and use the same set of preset voltages V1, V2...V1 as in the pre-calibration stage in step S1. N The interference light intensity of the light signal to be measured is recorded at the output port (4) under different preset voltages, and the output light intensity vector is obtained. S3. Spectral Reconstruction Stage: The relationship function between the output light intensity vector, the light signal to be measured, and the relation matrix is ​​set according to the following formula, and the spectrum to be measured is reconstructed using a convex optimization algorithm: Y = A × X Where Y represents the output light intensity vector of the light signal to be measured, X represents the spectral intensity vector of the light signal to be measured, and A represents the relation matrix.

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