A microchip spectrometer with large bandwidth and adjustable resolution

Abstract

A microchip spectrometer with large bandwidth and adjustable resolution comprises a spectrum coarse segmentation unit A, a tunable annular filter B, a sampling spectrum recording and restoration unit C and a reference unit D, wherein the upper output end of the coarse segmentation unit A is connected to the input end of the tunable annular filter B, the lower output end of the coarse segmentation unit A is connected to the reference unit D, and the output end of the tunable annular filter B is connected to the sampling spectrum recording and restoration unit C via a 1×2 beam splitter. The present invention has large bandwidth, adjustable resolution, low power consumption and is applicable to various material platforms.

Description

Technical Field

[0001] The invention relates to a chip spectrometer, in particular to a micro chip spectrometer with large bandwidth and adjustable resolution. Background Art

[0002] Spectrometers provide important information about samples by analyzing their spectra, and are widely used in environmental protection, biological and chemical testing, industrial and agricultural production, medical diagnosis, and astronomical exploration. Photon integrated spectrometers have the advantages of small size, low cost, good stability, and low power consumption, and have very important application prospects in miniaturized and portable spectral analysis instruments. There are currently three main types of chip spectrometers. The first type is the Fourier transform spectrometer (FPS) based on an on-chip Mach-Zehnder interferometer (MZI) array (reference [1] Przemek J. Bock, et al, "High-resolution Fourier-transform spectrometer chip with microphotonic silicon spiral waveguides," Opt. Lett. 38, 706-708 (2013); reference [2] Mario CMM Souza, et al, "Fourier transform spectrometer on silicon with thermo-optic non-linearity and dispersion correction", Nature Comm. 9, 665 (2018)). It has the advantages of high signal-to-noise ratio and large light flux, but there is a trade-off between its spectral bandwidth and resolution, that is, a higher resolution corresponds to a smaller spectral bandwidth, and vice versa. The second category is the dispersion device based on optical waveguide, such as arrayed waveguide grating (reference [3] P. Cheben, et al., "A high-resolution silicon-on-insulator arrayed waveguide grating microspectrometer with sub-micrometer aperture waveguides," Opt. Express 15, 2299-2306 (2007);

[0003] Document [4] J.Zou, et al, "Ultracompact silicon-on-insulator-based reflective arrayed waveguide gratings for spectroscopic applications," Appl. Opt.55, 3531-3536 (2016).), etched diffraction grating (Document [5] P. Pottier, et al, "Integrated Microspectrometer with Elliptical Bragg Mirror Enhanced Diffraction Gratingon Silicon on Insulator" ACS Photonics 1,430-436 (2014); Document [6] Bernardo B.C. Kyotoku, et al, "Sub-nm resolution cavity enhanced micro-spectrometer," Opt.Express 18,102-107(2010)), etc. The problem they face is that as the resolution of the spectrometer increases, the size of the device will increase greatly. At the same time, it is difficult to produce an on-chip spectrometer with good performance and sub-nanometer resolution using the existing process level; the third type is to use cascaded microring arrays (reference [7] Z.Xia, et al, "High resolution on-chip spectroscopy based on miniaturized microdonut resonators," Opt.Express19,12356-12364(2011)), but due to the high Q value of the microring, it is very sensitive to process deviations and it is also difficult to produce a spectrometer with good performance.

[0004] Therefore, a chip spectrometer that can solve the problems of the above three types of spectrometers at the same time becomes particularly important, especially with the development of portable sensors and on-chip miniaturized detection systems in recent years, such chip spectrometers are in urgent need. At the same time, if the resolution of the chip spectrometer is adjustable, it will have greater application potential. Summary of the invention

[0005] In order to overcome the constraints between resolution and bandwidth, the constraints between chip size and resolution, and the influence of process deviation in traditional chip spectrometers, the present invention proposes a microchip spectrometer with large bandwidth and adjustable resolution.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A microchip spectrometer with large bandwidth and adjustable resolution comprises a spectrum coarse segmentation unit A, a tunable annular filter B, a sampling spectrum recording and restoration unit C and a reference unit D, wherein the upper output end of the coarse segmentation unit A is connected to the input end of the tunable annular filter B, the lower output end of the coarse segmentation unit A is connected to the reference unit D, and the output end of the tunable annular filter B is connected to the sampling spectrum recording and restoration unit C via a 1×2 beam splitter.

[0008] Furthermore, the spectrum coarse segmentation unit A includes a 1×M optical switch, an M×2 wavelength division multiplexer, and a 2×2 3dB coupler, and the M output ports of the 1×M optical switch are respectively connected to the M input ports of the M×2 wavelength division multiplexer, and the two output ports of the M×2 wavelength division multiplexer are respectively connected to the two input ports of the 2×2 3dB coupler.

[0009] Furthermore, the resonant wavelength position of the tunable ring filter B is tuned by a heater above the waveguide, and the tuning region of the tunable ring filter B includes one ring or multiple cascaded rings.

[0010] Furthermore, the sampling spectrum recording and restoration unit C comprises a 1×N power divider, N 1×1 MZIs, and N detectors, wherein adjacent MZIs have a fixed length difference ΔL. The N detectors may also be a camera that can receive the output light of all MZI arrays.

[0011] Furthermore, the reference unit D comprises a detector.

[0012] Furthermore, the minimum resolution value Δλ of the microchip spectrometer with large bandwidth and adjustable resolution is R_min The 3dB bandwidth Δλ of the micro-ring in the tunable ring filter B is 3dB Determine the actual resolution value Δλ used R Determined by the tuning step size of the heater, between Δλ 3dB and the free spectral range of the microring Δλ FSR Between, that is, Δλ 3dB ≤Δλ R <Δλ FSR .

[0013] The beneficial effects of the present invention are mainly manifested in: 1. large bandwidth; 2. adjustable resolution; 3. low power consumption; 4. applicable to various material platforms, such as silicon nitride (Si3N4), silicon (Si) and GeSi and other material platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1It is a schematic diagram of a microchip spectrometer with large bandwidth and adjustable resolution proposed by the present invention;

[0015] Figure 2 yes Figure 1 An implementation example of the mid-spectrum coarse segmentation unit A;

[0016] Figure 3 yes Figure 2 An implementation example of a 2×2 3dB coupler;

[0017] Figure 4 yes Figure 2 Layout example and operation diagram of M×2 wavelength division multiplexer, where M=4;

[0018] Figure 5 yes Figure 1 A design example of tunable ring filter B in ;

[0019] Figure 6 yes Figure 1 A design example of a 1×2 beam splitter;

[0020] Figure 7 yes Figure 1 A design example of a medium sampling spectrum recording and restoration unit C, where N = 16;

[0021] Figure 8 is to use Figure 1 Schematic diagram of the workflow for realizing input unknown spectrum restoration.

[0022] In the figure: 1, input end of the spectrometer, 2, spectrum coarse segmentation unit A, 3, tunable ring filter B, 4, sampling spectrum recording and restoration unit C, 5, reference unit D, 6, 1×2 beam splitter, 7, lower output end of 6, 8, input spectrum to be detected, 9, 1×M optical switch, 10, M×2 wavelength division multiplexer, 11, 2×2 3dB coupler, 12, 1×2MZI with electrical tuning, 13, electrical tuning area of ​​12, 14, each output port I in the upper part of 9 u , 15, 9, the lower half of each output port I d , 16, 10 upper output port O d , 17, 10 lower output port O u , 18, upper output port of 11, 19, lower output port of 11, 20, electrically tunable heater above the microring in 3, 21, output end of 3, 22, upper output end of 6, 23, 1×N beam splitter, 24, N MZI arrays with fixed length difference, 25, detector array. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Reference Figures 1 to 8 A microchip spectrometer with large bandwidth and adjustable resolution comprises a spectrum coarse segmentation unit A2, a tunable ring filter B3, a sampling spectrum recording and restoration unit C4 and a reference unit D5, wherein an upper output end 18 of the spectrum coarse segmentation unit A2 is connected to an input end 18 of the tunable ring filter B3, a lower output end 19 of the spectrum coarse segmentation unit A2 is connected to the reference unit D5, and an output end 21 of the tunable ring filter B3 is connected to an input end 22 of the sampling spectrum recording and restoration unit C4 via a 1×2 beam splitter 6.

[0025] The spectrum coarse segmentation unit A2 includes a 1×M optical switch 9, an M×2 wavelength division multiplexer 10, and a 2×2 3dB coupler 11. The M output ports of the 1×M optical switch 9 are respectively connected to the M input ports of the M×2 wavelength division multiplexer 10, and the two output ports 16 and 17 of the M×2 wavelength division multiplexer 10 are respectively connected to the two input ports of the 2×2 3dB coupler 11.

[0026] The resonant wavelength position of the tunable ring filter B3 is tuned by the heater 20 above the waveguide, and the tuning region of the tunable ring filter B3 includes one ring or multiple cascaded rings.

[0027] The sampling spectrum recording and restoration unit C4 comprises a 1×N power divider 23, N 1×1 MZIs 24, and N detectors 25, wherein adjacent MZIs have a fixed length difference ΔL. The N detectors can also be a camera that can receive the output light of all MZI arrays.

[0028] The reference unit D5 comprises a detector.

[0029] The minimum resolution of the spectrometer is Δλ R_min The 3dB bandwidth Δλ of the micro-ring in the tunable ring filter B3 is 3dB Determine the actual resolution value Δλ used R Determined by the tuning step size of the heater 20, between Δλ 3dB and the free spectral range of the microring Δλ FSR Between, that is, Δλ 3dB ≤Δλ R <Δλ FSR .

[0030] Figure 1 It is the overall framework diagram of the present invention.

[0031] Figure 2 It is for Figure 1In the embodiment of the spectrum rough segmentation unit A2, it is assumed that M=4. The 1×4 optical switch 9 is realized by cascading three 1×2 symmetrical MZIs 12; the 4×2 wavelength division multiplexer 10 is realized by a bidirectional array waveguide grating AWG, and the two input waveguides I u The light in the AWG is transmitted and then output from the output waveguide 17 below it. Similarly, the two input waveguides I below it are d After transmission through the AWG, it is output from the output waveguide 16 above it; the two output ends 16 and 17 of the AWG are connected to a 2×2 3dB coupler 11, and the equally divided power after passing through the 3dB coupler is output from its output ends 18 and 19 respectively. In the optical switch 9, a metal heater 13 is placed on one arm of each MZI 12, and one of the two output ends of the MZI can be selected by adjusting the voltage on the metal heater 13. Appropriate adjustment of the heating voltage on each MZI can select a certain output of the 1×4 optical switch 9, and then activate the input port corresponding to the output end in the 4×2 wavelength division multiplexer 10. Changing the heating voltage of each MZI in the optical switch can realize the light output of another output port and activate another input end of the 4×2 wavelength division multiplexer 10. When the input light with spectrum 8 enters the spectrum coarse segmentation unit A2 from input port 1, the output of the 1×4 optical switch is adjusted to select one of the output ports to output light and activate the corresponding port of the 4×2 wavelength division multiplexer 10 connected thereto. u The incoming light will be output from the lower output port O u 17 output, similarly, from port I d The incoming light will be output from the upper output port O u 16 outputs, and after passing through the 2×2 3dB coupler 11, one light is output from the output port 18 to the next stage tunable ring filter B3 of the cascade, and the other light is output from the output port 19 to the reference unit D5 for monitoring as a reference.

[0032] Figure 3 Given Figure 2 There are two embodiments of the 2×2 3dB coupler 11, which can be made of Figure 3 (a) is realized by the multi-mode interferometer MMI, or by Figure 3 The directional coupler of (b) can be used to realize the 2×2 3dB coupler, and other structures can also be used to realize the 2×2 3dB coupler, such as sub-wavelength grating.

[0033] Figure 4 yes Figure 2 The 4×2 wavelength division multiplexer 10 is shown in FIG. 4. The 4 input waveguides are divided into two groups, namely the upper two input waveguides 14I u1 and I u2, the following two input waveguides 15I d1 and I d2 , and the intervals between the corresponding 4 channel center wavelengths are as follows Figure 4 When light is input from the upper waveguide 14, it will be output from the lower output waveguide 17; when light is input from the lower waveguide 15, it will be output from the upper output waveguide 16.

[0034] Figure 5 Given Figure 1 An embodiment of the tunable ring filter B3 is shown in the figure. It is composed of an add-drop type micro-ring, on which a metal waveguide electric tuning heater 20 is added. The resonant wavelength position of the micro-ring can be tuned by changing the applied voltage on the metal waveguide. When a sub-band divided by the spectrum coarse division unit A2 is input to the micro-ring, a group of discrete resonance peaks will be generated in the micro-ring output waveguide 21, and the interval between adjacent peaks is the free spectrum range FSR of the micro-ring; by changing the heating voltage on the micro-ring, another group of discrete resonance peaks will be generated in the output waveguide 21.

[0035] Figure 6 Given Figure 1 An embodiment of the 1×2 beam splitter 6, one of its output terminals 22 is connected to the input terminal of the sampling spectrum recording and restoration unit C 4, and the other output terminal 7 serves as a reference terminal of the tunable ring filter B 3. The power splitting ratio of the beam splitter 6 can be equal or unequal.

[0036] Figure 7 An embodiment of the sampling spectrum recording and restoration unit C 4 is given, which is composed of 16 MZIs 24, the length difference between adjacent MZIs is ΔL, and the 1:16 beam splitter 23 can be composed of 1:16 MMIs or composed of units Figure 6 The detector array 25 can also be replaced by a camera that can receive the output light of all MZI arrays. Figure 7 The main function of the MZI array is to record the information of the sampled spectrum B(σ) from the tunable ring filter B 3 and restore it. Figure 7 The optical power received by the detector array 25 can be calculated by combining Fourier transform to obtain the spectrum input to the sampling spectrum recording and restoration unit C4:

[0037]

[0038] Where σ = 1 / λ is the wave number, N is the number of MZI arrays, here N = 16, Υ i is the optical power received by the i-th detector, and the delay line length difference of each array waveguide is ΔL i =ng ×[ΔL0+(i-1)×ΔL], ΔL0 is the length difference between the two arms in the first MZI, n g =n eff -λ×dn eff / dλ and n eff They are the group refractive index and effective refractive index of the two-arm waveguides, where ΔL0 = 0, ΔL max =15×n g ×ΔL. The resolution and free spectral range of the MZI array are

[0039]

[0040]

[0041] Here, λ0 is the central wavelength of the restored spectrum. In order to ensure that the MZI array can completely restore the sampled spectrum B(σ) from the tunable ring filter B 3, the resolution δλ should satisfy δλ <FSR MRR , FSR MRR is the wavelength difference between two adjacent resonance peaks of the microring in the tunable ring filter B 3. At the same time, the free spectral range FSR of the MZI array FT Should be greater than the wavelength range of the sampling spectrum B(σ), i.e. FSR FT >λ B(σ) Since the actual detection spectrum is relative to the free spectral range (FSR) of the MZI FT The spectrum rough segmentation unit A2 is used to segment the detection spectrum first so that the segmented sub-spectra can be detected and restored by the sampling spectrum recording and restoration unit C4, thereby greatly improving the working bandwidth of the chip spectrometer.

[0042] Figure 8 It is for Figure 1The structure of FIG. 1 is used to implement a schematic process diagram of restoring an input spectrum, where M=4. The input light is first coupled to the input terminal 1 of the spectrometer and enters the spectrum coarse segmentation unit A2, which controls the output of the 1×4 optical switch 9 so that the input light is output from one of the output channels each time and coupled to the corresponding input terminal of the 4×2 wavelength division multiplexer 10. After passing through the 4×2 wavelength division multiplexer 10, a segmented sub-spectrum I is obtained. After the sub-spectrum I is transmitted to the 2×2 3dB coupler 11, one end is output to the reference unit D5 for monitoring, and the other end enters the tunable ring filter B3 to be sampled by the micro-ring resonator therein and output a group of discrete resonance peaks. This group of discrete resonance peaks then enters the sampling spectrum recording and restoration unit C4 and is received by the detector array. Finally, the input spectrum input to the sampling spectrum recording and restoration unit C4 can be restored using formula (1-3). The heater above the microring resonator in the tunable ring filter B3 is adjusted to tune the position of the microring resonance peak to obtain another set of discrete resonance peaks, which are input to the sampling spectrum recording and restoration unit C4. The same data processing can be used to restore the input resonance peaks at this time. Similarly, the heater above the microring is tuned again until the microring is tuned within a free spectrum range. Each tuned spectrum is recorded and restored by the sampling spectrum recording and restoration unit C4. In this way, an output sub-spectrum of the spectrum coarse segmentation unit A2 can be restored. The restored spectrum is I'. Assuming that the tuning step of the microring is Δλ step , then the number of tunings required to restore a sub-spectrum is N t =FSR MRR / Δλ step . Then, the 1×4 optical switch 9 in the spectrum coarse segmentation unit A2 is changed to output another sub-spectrum II, and the same method is used to restore it, and then the sub-spectra III and IV are output and restored. After all the sub-spectra are restored, the restored spectra I', II', III', and IV' are combined to obtain a complete restored spectrum. Change the tuning step Δλ of the microring resonator in the tunable ring filter B3 step The resolution Δλ of the restored spectrum can be changed R , the minimum spectral resolution Δλ Rmin The full width at half maximum of the microring resonance peak Δλ 3dB So the resolution range of the spectrometer is Δλ 3dB ≤Δλ R <Δλ FSR Generally speaking, the Q value of microrings is relatively high, and their full width at half maximum is less than 0.5nm, so the resolution of the spectrometer can be <0.5nm. In actual detection, the appropriate resolution can be selected as needed to meet different application requirements.

[0043] exist Figure 1In the embodiment, the reference unit 5 is used in combination with a known light source to turn the spectrometer into a spectrometer for measuring the absorption spectrum of a substance. The operation method is as follows: First, the known spectrum is directly input into the spectrometer to calibrate the reduced spectrum and obtain the transmission curve of the spectrometer. The reference unit 5 is used as a reference end to monitor the intensity change of a specific sub-spectrum output from the spectrum coarse segmentation unit A2. Using the known input light source spectrum, the substance to be detected is placed between the input light source and the spectrometer chip to obtain the input spectrum after being absorbed by the substance, which is input into the chip spectrometer proposed by the present invention, and the spectrum rough segmentation unit A2 is adjusted to output a sub-spectrum, and the light power received by the detector in the reference unit 5 and the corresponding light power change when no detection substance is connected are observed. If there is no change, it means that there is no light absorption in the sub-spectrum area, and then the spectrum rough segmentation unit A2 is adjusted to output another sub-spectrum, and the light power change in the reference unit 5 is continued to be observed. If there is a power change, it means that there is light absorption in the sub-spectrum, and then the tunable ring filter B3 is used to sample the sub-spectrum to obtain a series of resonance peaks, and these resonance peaks are input into the sampling spectrum recording and restoration unit C4 for analysis and processing, and finally compared with the normalized transmission curve of the spectrometer to obtain the restored spectrum. In turn, another sub-spectrum is detected, the reference unit 5 is observed, and the same operation is performed to obtain the restored spectrum of all sub-spectra. Finally, these restored sub-spectra are combined and compared with the known light source spectrum to obtain the absorption spectrum of the substance to be detected.

[0044] In addition, although the present invention proposes a microchip spectrometer with large bandwidth and adjustable resolution, and provides some embodiments of key components, other designs and modifications of key components therein belong to the scope of the present invention, including but not limited to: using an off-chip optical switch, a different type of M×2 wavelength division multiplexer such as based on an etched diffraction grating, an MZI cascade array, a thin film filter, etc., using a novel 2×2 coupler and beam splitter, using a different number of 1×1MZI arrays or a novel Fourier spectrum conversion unit. The functions they ultimately achieve are consistent, so they all belong to the scope of the present invention.

Claims

1. A microchip spectrometer with large bandwidth and adjustable resolution, characterized in that: The microchip spectrometer comprises a spectrum coarse segmentation unit A, a tunable annular filter B, a sampling spectrum recording and restoration unit C and a reference unit D, wherein the upper output end of the coarse segmentation unit A is connected to the input end of the tunable annular filter B, the lower output end of the coarse segmentation unit A is connected to the reference unit D, and the output end of the tunable annular filter B and the sampling spectrum recording and restoration unit C are connected via a 1×2 beam splitter; The spectrum coarse segmentation unit A comprises a 1×M optical switch, an M×2 wavelength division multiplexer, and a 2×2 3dB coupler, wherein the M output ports of the 1×M optical switch are respectively connected to the M input ports of the M×2 wavelength division multiplexer, and the two output ports of the M×2 wavelength division multiplexer are respectively connected to the two input ports of the 2×2 3dB coupler; The resonant wavelength position of the tunable ring filter B is tuned by a heater above the waveguide, and the tuning region of the tunable ring filter B includes one ring or multiple cascaded rings; Minimum resolution Δ λ R_min The 3dB bandwidth Δ of the micro-ring in the tunable ring filter B is λ 3dB Determine the actual resolution value Δ λ R Determined by the tuning step size of the heater, between Δ λ 3dB and the free spectral range of the microring Δ λ FSR Between, that is, Δ λ 3dB ≤ Δ λ R < Δ λ FSR .

2. The microchip spectrometer with large bandwidth and adjustable resolution as claimed in claim 1, characterized in that: The sampling spectrum recording and restoration unit C comprises a 1×N power divider, N 1×1 MZIs, and N detectors, wherein adjacent MZIs have a fixed length difference Δ L .

3. The microchip spectrometer with large bandwidth and adjustable resolution as claimed in claim 1, characterized in that: The sampling spectrum recording and restoration unit C comprises a 1×N power divider, N 1×1 MZIs and a camera capable of receiving the output light of all MZI arrays, wherein there is a fixed length difference Δ between adjacent MZIs. L .

4. The microchip spectrometer with large bandwidth and adjustable resolution as claimed in claim 1, characterized in that: The reference unit D comprises a detector.

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