Spectrometry device and method based on all-fiber cascaded mach-zehnder interferometer

Abstract

The application discloses a spectrum measuring device and method based on an all-fiber cascaded Mach-Zehnder interferometer, which comprises a broadband light source module, a fiber polarizer connected with the broadband light source module, an output end of the fiber polarizer connected with an input end of an optical convolution kernel module, and an output end of the optical convolution kernel module connected with an input end of a photoelectric detection module; the optical convolution kernel module comprises a plurality of cascaded Mach-Zehnder interferometers, a stress phase tuning unit comprises a plurality of lead zirconate titanate piezoelectric ceramic rings corresponding to the plurality of cascaded Mach-Zehnder interferometers, the middle fiber sections of the Mach-Zehnder interferometers are respectively wound on the corresponding lead zirconate titanate piezoelectric ceramic rings, the control ends of the lead zirconate titanate piezoelectric ceramic rings are connected with the output end of a multi-channel DAC driving module, and the input end of the driving module and the output end of the photoelectric detection module are connected with a data processing unit. The device has the capability of flexible and configurable working waveband and is suitable for different application scene requirements.

Description

Technical Field

[0001] This invention relates to the field of optical spectral measurement and analysis technology, specifically to a spectral measurement device and method based on an all-fiber cascaded Mach-Zehnder interferometer. Background Technology

[0002] Spectrometers are core instruments for material composition analysis and biochemical sensing, and are widely used in industrial testing, food safety, environmental monitoring, and healthcare. Traditional spectrometer architectures are mainly divided into three categories: dispersive, narrowband filtering, and Fourier transform.

[0003] In recent years, advancements in integrated photonics have driven research into on-chip spectrometers. For example, existing technologies have developed cascaded nonequilibrium Mach-Zehnder interferometers based on silicon nitride (SiN) platforms, coupled with thermo-optical phase shifters, enabling a novel spectrometer based on the optical convolution theorem. This spectrometer utilizes the convolution theorem as its mathematical foundation, performing spectral domain waveform shifting through thermo-optical proportional phase scanning, cyclically convolving the measured spectrum with the system response in the time domain, and finally recovering the original spectrum through a fast Fourier transform.

[0004] However, relying on specialized wafer fabrication services on silicon nitride photonic integration platforms, the cost of a single multi-project wafer fabrication can reach hundreds of thousands of yuan, with design iteration cycles lasting several months to half a year, which is difficult for ordinary laboratories to afford. Mode field mismatch exists between the on-chip waveguide and single-mode fiber, with end-face coupling losses typically exceeding 2-3 dB / end-face, and multiple couplings in cascaded systems significantly reduce signal strength. Planar waveguide devices have strict requirements on the polarization state of the input light, requiring additional polarization controllers or polarization-maintaining fiber coupling, increasing system complexity. Furthermore, detectors are expensive; indium gallium arsenide photodetectors must be used in the near-infrared band, whose cost is significantly higher than the silicon photodetectors commonly used in the visible light band.

[0005] In the field of fiber optics, the Mach-Zehnder interferometer (MZI) is a well-known fundamental component, typically constructed by fusion splicing a section of fiber between two fiber couplers. However, this discrete component splicing scheme has multiple physical fusion points, leading to problems such as high insertion loss, parasitic interference caused by parasitic reflections at the fusion points, and poor structural stability due to segmented fixing of multiple components.

[0006] Furthermore, existing technologies include single-cone fiber interferometers, which generate a conical region through a single tapering process and utilize the interference between the core mode and the cladding mode. However, the spectral response generated by the single-cone structure is a chaotic signal resulting from the simultaneous superposition of multiple modes, lacking a single periodicity. Its splitting ratio is uncontrollable, and the mode purity is low, making it unsuitable for cascaded spectral measurement systems requiring precise and stable periodic responses. More importantly, the single-cone structure is even less stable in the visible light band because shorter wavelengths excite more cladding modes, leading to a more chaotic interference signal. Summary of the Invention

[0007] In order to solve the above-mentioned technical problems, this application proposes the following technical solution: In a first aspect, embodiments of this application provide a spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer, comprising: A broadband light source module, an optical fiber polarizer connected to the output end of the broadband light source module, the output end of the optical fiber polarizer connected to the input end of an optical convolution kernel module, and the output end of the optical convolution kernel module connected to the input end of a photoelectric detection module; The optical convolution kernel module includes a multi-stage cascaded Mach-Zehnder interferometer sequentially fabricated on a continuous single-mode fiber. Each stage of the Mach-Zehnder interferometer includes a pair of tapered regions and an intermediate fiber segment located between the tapered regions. The stress phase tuning unit includes multiple lead zirconate titanate piezoelectric ceramic rings corresponding one-to-one with the multi-stage cascaded Mach-Zehnder interferometers. The intermediate fiber segments of each stage of the Mach-Zehnder interferometer are wound and fixed on the corresponding lead zirconate titanate piezoelectric ceramic rings. The control terminal of the lead zirconate titanate piezoelectric ceramic ring is connected to the output terminal of the multi-channel DAC drive module. The input terminal of the multi-channel DAC drive module and the output terminal of the photoelectric detection module are both connected to the data processing unit. The free spectral range of each stage of the Mach-Zehnder interferometer satisfies a preset proportional relationship. The multi-channel DAC drive module outputs a driving voltage according to the reciprocal ratio of the free spectral range of each stage, causing the lead zirconate titanate piezoelectric ceramic rings of each stage to produce a corresponding proportional phase change.

[0008] In one possible implementation, the data processing unit includes a microcontroller and an analog-to-digital converter (ADC). The input of the ADC is connected to the output of the photoelectric detection module. The ADC is communicatively connected to the microcontroller, and the microcontroller is communicatively connected to the multi-channel DAC driver module.

[0009] In one possible implementation, the photodetector module includes a single-point photodetector and a transimpedance amplifier. The input of the single-point photodetector is connected to the output of the optical convolution kernel module, the output of the single-point photodetector is connected to the input of the transimpedance amplifier, and the output of the transimpedance amplifier is connected to the input of the analog-to-digital converter.

[0010] In one possible implementation, an optical switch or combiner is provided between the output of the broadband light source module and the fiber polarizer.

[0011] In one possible implementation, the multi-stage cascaded Mach-Zehnder interferometer sequentially fabricated on a continuous single-mode fiber includes: Take a section of standard single-mode optical fiber, use fiber strippers to remove the acrylate coating in the middle section, then wipe the bare fiber section along the fiber axis in one direction with a non-woven cloth soaked in anhydrous ethanol, then wipe it with deionized water, and finally blow it dry with high-purity nitrogen. Immediately after drying, perform tapering operation, use a fiber optic cleaver to cut flat end faces at both ends of the fiber, and inspect the end face quality under a microscope to confirm that there are no chipped edges or cracks. During the fabrication process, the output end of the optical fiber is connected to a spectrometer, and a broadband light source is incident from the input end. The transmission spectrum is monitored in real time by the spectrometer. The pre-treated optical fiber is fixed on the two displacement stages of the tapering machine, the bare optical fiber segment is centered, and the optical fiber is kept in a horizontal tension state. After aligning the center of the hydrogen flame nozzle with the first preparation position, the hydrogen flame heating is turned on. After the temperature stabilizes, the stretching program is started, and the transmission spectrum displayed by the spectrometer is monitored in real time. When the fiber diameter gradually decreases to the target value, sinusoidal interference fringes appear in the transmission spectrum. Transmission spectra are continuously acquired by a spectrometer at a preset integration time. Real-time fast Fourier transform is performed on the acquired transmission spectra to calculate the free spectral range of the current interference fringes. When the free spectral range is close to the target value and the fringe contrast is greater than the first target value, the stretching is stopped immediately and the flame is turned off. After a preset time period of natural cooling, a miniature fan is used to blow cold air to accelerate cooling to room temperature, forming the first pair of tapered areas and the first intermediate fiber segment; After the first-stage Mach-Zehnder interferometer is prepared, the displacement stage clamp is released, the optical fiber is moved axially so that the second position is aligned with the center of the flame, and a heat dissipation copper block or thermal conductive silicone grease is wrapped around the preset position behind the first-stage cone region. Using the same heating and stretching procedure and spectral monitoring process as the first stage, when the free spectral range reaches the second target value, the stretching is immediately stopped and the flame is turned off. After cooling, the second pair of tapered regions and the second intermediate fiber segment are formed. The optical fibers were sequentially moved to the preset preparation positions to prepare multi-stage Mach-Zehnder interferometers. After all preparations were completed, the optical fibers were not cut, and the spectrometer and light source were kept connected at both ends. The transmission spectrum of the entire multi-stage cascaded Mach-Zehnder interferometer was measured. The interference frequencies of each stage were separated by Fourier transform, and the deviation between the measured values ​​and the target values ​​of the free spectral range of each stage was confirmed to be within the allowable range. Low-refractive-index UV-curable adhesive is applied to all cone regions and the middle fiber segment and cured by UV irradiation. The fiber is then coiled and fixed onto the substrate. Connectors are fused to both ends of the fiber, and the fusion joints are reinforced with heat-shrink tubing.

[0012] Secondly, embodiments of this application provide a spectral measurement method based on an all-fiber cascaded Mach-Zehnder interferometer, including: Pre-calibrate the spectral measurement device based on the all-fiber cascaded Mach-Zehnder interferometer by lighting only one light source in the broadband light source module or using a calibration monochromatic light source, and send a slow sawtooth wave from 0V to full drive voltage only to the output channel of the lead zirconate titanate piezoelectric ceramic ring corresponding to the first-stage Mach-Zehnder interferometer, while recording the change in the output light intensity of the photoelectric detection module. When the voltage scan covers the entire phase range, the DAC encoding-phase shift lookup table of the first-stage Mach-Zehnder interferometer is established using the parameters of the sinusoidal signal. The Mach-Zehnder interferometers at each level were calibrated sequentially, resulting in multiple independent lookup tables; Calculate the voltage ratio based on the actual free spectral range of each Mach-Zehnder interferometer and generate a synchronous drive sequence list; Input a standard light source with a known flat spectrum, perform a complete scale scan, and acquire the time-series power signal. Store the time-series power signal as a system response function in the data processing unit. After precalibration is completed, select and light a suitable broadband light source according to the target working band. After preheating for a preset time period, ensure that the output spectrum of the light source is stable and then determine the working status of the fiber polarizer. Under conditions of no light input, the dark current output of the photoelectric detection module is recorded, and the dark current output is used as the reference for subsequent signal subtraction. The optical signal of the spectrum to be measured is connected to the input end of the spectral measurement device based on the all-fiber cascaded Mach-Zehnder interferometer through an optical fiber. The proportional voltage is synchronously output to multiple lead zirconate titanate piezoelectric ceramic rings according to the synchronous drive sequence list. After each output, the lead zirconate titanate piezoelectric ceramic rings are waited for to stabilize before the analog-to-digital converter is triggered to read the light intensity value of the photoelectric detection module. The collected light intensity value is associated with the current step number and stored as a time sequence signal; The time-series signal and the system response function are subjected to Fast Fourier Transform (FFT) respectively, deconvolution is performed in the frequency domain to recover the signal, and then inverse Fast Fourier Transform is performed to recover the spectrum to be measured. The recovered spectrum is filtered and then output to the user interface or stored in local memory in graphical or text form.

[0013] In one possible implementation, the formula for calculating the voltage ratio based on the actual free spectral range of each Mach-Zehnder interferometer is as follows: in, This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the first-stage Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the second-order Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the third-order Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the fourth-order Mach-Zehnder interferometer. This represents the free spectral range of the first-order Mach-Zehnder interferometer. The free spectral range of the second-order Mach-Zehnder interferometer. The free spectral range of the third-order Mach-Zehnder interferometer. This represents the free spectral range of the fourth-order Mach-Zehnder interferometer.

[0014] In one possible implementation, the formulas for calculating the Fast Fourier Transform of the time-series signal and the system response function are as follows: in, For Fast Fourier Transform, The acquired time-series optical power signal, Let be the system response function. For the frequency domain components of the time-series signal, The frequency domain component of the system response function, n This is the scan step number. K For frequency indexing.

[0015] In one possible implementation, the formula for deconvolution recovery in the frequency domain is: in, The spectral frequency domain result obtained by deconvolution recovery. The complex conjugate of the system response spectrum, This is the regularization parameter.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: The entire optical convolution kernel module of this application is fabricated by tapering on ordinary single-mode fiber, without the need for photonic integrated fabrication such as silicon nitride or silicon-on-insulator. It can be fabricated using existing fiber tapering equipment, and the additional loss of a single-stage tapered MZI can be controlled within 0.3 dB, and the total loss of four-stage cascade is less than 2 dB, which is far superior to discrete coupler splicing schemes and on-chip waveguide schemes.

[0017] This application utilizes a multi-stage unbalanced Mach-Zehnder interferometer continuously drawn on a single optical fiber as the core optical element, and achieves spectral recovery through proportional stress phase tuning, forming an all-fiber spectral measurement device. The applicable operating band covers the visible to near-infrared range, and broadband light source modules and photoelectric detection modules can be flexibly configured according to target application requirements. Attached Figure Description

[0018] Figure 1 A schematic diagram of a spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer provided for an embodiment of this application; Figure 2 A connection diagram of a spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer provided for embodiments of this application; Figure 3 A schematic diagram of the structure of a single tapered optical fiber MZI provided in an embodiment of this application; Figure 4 This is a schematic diagram illustrating the principle of waveform translation achieved by proportional phase tuning in an embodiment of this application. Detailed Implementation

[0019] The present solution will now be described in conjunction with the accompanying drawings and specific embodiments.

[0020] Figure 1 This is a schematic diagram of a spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer, provided as an embodiment of this application. In this embodiment, "all-fiber" means that throughout the entire optical path from the output end of the broadband light source module to the input end of the single-point photodetector, the optical signal is always confined within the optical fiber or the tapered-air waveguide structure formed by the fiber tapering, and is not exported as a free-space beam or coupled to a waveguide of other material platforms at any stage. The core optical functions, including beam splitting, beam combining, optical path difference accumulation, and interference, are all realized by the structure of the optical fiber itself. There are no fusion splices, fiber connectors, or free-space optical coupling devices between the stages within the optical convolution kernel module.

[0021] See Figure 1 and Figure 2 This embodiment provides a spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer, comprising: The system includes a broadband light source module, an optical fiber polarizer connected to the output of the broadband light source module, an output of the optical fiber polarizer connected to the input of an optical convolution kernel module, and an output of the optical convolution kernel module connected to the input of a photodetector module. In this embodiment, the optical convolution kernel module comprises a multi-stage cascaded Mach-Zehnder interferometer sequentially fabricated on a continuous single-mode fiber. Each stage of the Mach-Zehnder interferometer includes a pair of tapered regions and an intermediate fiber segment located between the tapered regions. The stress phase tuning unit includes multiple lead zirconate titanate piezoelectric ceramic rings corresponding one-to-one with the multi-stage cascaded Mach-Zehnder interferometers. The intermediate fiber segments of each stage of the Mach-Zehnder interferometer are wound and fixed onto the corresponding lead zirconate titanate piezoelectric ceramic rings to achieve proportional stress phase tuning. The control end of the lead zirconate titanate piezoelectric ceramic ring is connected to the output of a multi-channel DAC driver module. The input of the multi-channel DAC driver module and the output of the photodetector module are both connected to a data processing unit.

[0022] In this embodiment, the broadband light source module consists of multiple light sources, covering the target measurement range from the visible light to the near-infrared band. Depending on the different target measurement bands, the broadband light source module can employ one or a combination of the following schemes: Near-infrared band (1200-1700 nm): Composed of multiple superluminescent light-emitting diodes (SLDs) and optical switches. The center wavelengths of each SLD are staggered, and the total width of their output spectrum covers the near-infrared band. Each SLD is connected to the system in a time-division manner via an optical switch, with only one SLD lit at a time.

[0023] Visible-near infrared band 400-1100 nm: Composed of multiple white light-emitting diodes (LEDs) or broadband halogen lamps. The LEDs in the white light LED array have different color temperatures, and their output spectra are superimposed to cover the visible to near infrared band. A single halogen lamp light source can cover the entire 400-1700 nm band, with high output power and a flat spectrum.

[0024] Broad spectrum 400-1700 nm: Employs a supercontinuum light source, a single light source can cover the entire spectrum from visible light to near-infrared.

[0025] The total width of the output spectrum of the broadband light source module is not less than the composite free spectrum range of the optical convolution kernel module.

[0026] The fiber polarizer is an in-line fused fiber polarizer used to convert input light into linearly polarized light, improving the visibility of interference fringes and the measurement accuracy of the system. An optical switch or combiner is installed between the output end of the broadband light source module and the fiber polarizer.

[0027] See further Figure 2In this embodiment, the data processing unit includes a microcontroller and an analog-to-digital converter (ADC). The input terminal of the ADC is connected to the output terminal of the photodetector module. The ADC is communicatively connected to the microcontroller, and the microcontroller is communicatively connected to the multi-channel DAC driver module. The photodetector module includes a single-point photodetector and a transimpedance amplifier. The input terminal of the single-point photodetector is connected to the output terminal of the optical convolution kernel module, the output terminal of the single-point photodetector is connected to the input terminal of the transimpedance amplifier, and the output terminal of the transimpedance amplifier is connected to the input terminal of the ADC.

[0028] In this embodiment, the photodetector module can select different types of photodetectors according to the target operating wavelength, and its sensing wavelength matches the output spectrum of the broadband light source module. When the operating wavelength is near-infrared (1200-1700 nm), an indium gallium arsenide (IGaAs) photodiode is used; when the operating wavelength is visible-near-infrared (400-1100 nm), a silicon PIN photodiode is used, which costs only a fraction of the cost of an IGaAs detector and has lower dark current. When the operating wavelength covers the full spectrum (400-1700 nm), a combination of silicon and IGaAs detectors can be used, or other wide-response photodetectors can be used. The detection signal is amplified by a transimpedance amplifier, acquired by an analog-to-digital converter, and stored in the data processing unit.

[0029] The optical convolution kernel module is the core of this device. It consists of four pairs of tapered regions sequentially fabricated on a continuous standard single-mode fiber using a localized heating and stretching method. Each pair of tapered regions forms a non-equilibrium Mach-Zehnder interferometer, creating a four-stage cascaded structure. The length of the intermediate fiber segment of each MZI, i.e., the distance between two tapered regions, is precisely controlled to ensure the free spectral range of each MZI stage (…). () represents the selected distinct values ​​that are not multiples of each other by a lower order integer, for example: 84, 60, 32.3, 24.7 This enables subsequent proportional phase tuning.

[0030] In this embodiment, the preparation process includes taking a standard single-mode optical fiber approximately 50 cm long and using fiber strippers to remove the acrylate coating layer for about 30 cm of the middle section. Stripping should be done at a uniform speed and evenly to avoid scratching the surface of the bare fiber. The bare fiber section is then wiped unidirectionally along the fiber axis with a non-woven cloth soaked in anhydrous ethanol, followed by wiping with deionized water, and finally dried with high-purity nitrogen. Immediately after cleaning, a tapering operation should be performed to prevent dust adhesion. Both ends of the fiber are cut with a fiber optic cleaver to create flat end faces, which are then inspected under a microscope to confirm the absence of chipped edges or cracks.

[0031] The pretreated optical fiber is fixed on the two displacement stages of the tapering machine, centered, and ensured to be horizontally tensioned. The center of the hydrogen flame nozzle is aligned with the first preparation position, typically about 10 cm from the fiber input end. A broadband light source, such as a superluminescent diode or halogen lamp, is connected to the fiber input end via a polarizer. The fiber output end is connected to a spectrometer, which is connected to a computer via USB or Ethernet. The integration time is set to less than or equal to 100 ms, and transmission spectra are continuously acquired. Parameters such as the stretching speed (e.g., 150 μm / s), heating time, and displacement stage distance are set in the tapering machine control software. The flame temperature is adjusted by the hydrogen flow rate to preheat to a stable state.

[0032] The hydrogen flame was ignited, and after the temperature stabilized, the stretching program was initiated. Two displacement stages moved synchronously in opposite directions at a speed of 150 μm / s, gradually thinning the heated area of ​​the optical fiber. The transmission spectrum displayed on the spectrometer was observed in real time. When the fiber diameter gradually decreased from 125 μm to approximately 5–8 μm (near-infrared band) or 2–5 μm (visible band), sinusoidal interference fringes began to appear in the spectrum, indicating that the first pair of cone regions had formed and the two modes had been successfully excited and interfered.

[0033] The computer performs a Fast Fourier Transform (FFT) on the transmission spectrum acquired by the spectrometer or directly measures the wavenumber interval between adjacent interference peaks / valleys to calculate the current free spectral range. When the FSR value approaches the target value of 84... At that time, slow down the stretching speed to make fine adjustments. Accuracy reached 84 When the stripe contrast is greater than or equal to 15 dB, immediately stop the displacement stage and shut off the hydrogen flame. Record the actual value at this point. The value is stored in the parameter table. After natural cooling for 10 seconds, a miniature fan is used to blow cold air to accelerate cooling to room temperature. At this point, the first-stage MZI fabrication is complete, and the length of the fiber segment between its two cone regions is L1, which is approximately 4.0 cm in actual measurement.

[0034] The second-stage MZI was then prepared, with the target... For 60 Release the stage clamps and carefully translate the optical fiber axially until the second preparation position, i.e., the starting point of the second set of cone regions, is aligned with the flame center. The translation distance is determined based on the target middle section length L2, i.e., moving 5.7 cm backward from the end of the first-stage second cone region. To prevent the heat from the subsequent stage flame from affecting the cone regions already prepared in the previous stage, a heat-dissipating copper block or thermal grease can be wrapped around the cone regions of the previous stage approximately 1 cm behind them. Use the same heating and stretching procedure as the first stage, but the target... For 60 Real-time monitoring of the spectrum, when Reaching 60 Stop at this time. Record the actual level of MZI. And the length of the middle section L2.

[0035] The third-stage MZI was prepared with a target FSR of 32.3. The fiber was moved and positioned again, aligning the third preparation position with the center of the flame. The target middle section length L3 was 10.3 cm. The stretching speed was set slightly slower because the longer middle section required more precise control. Real-time monitoring was performed. It reached 32.3. Stop at this time. Record the actual value of the third-level MZI. And the length of the middle section L3.

[0036] Preparation of fourth-stage MZI, with the objective of It is 24.7 The fiber was translated, with a target mid-section length L4 of 13.7 cm. A stretching speed of 120 μm / s was also used for monitoring. Reached 24.7 Stop at this point. Record the actual FSR of the fourth-level MZI and the intermediate segment length L4.

[0037] After all four levels of the cone region are fabricated, the optical fiber is not cut; both ends remain connected to the spectrometer and the light source. The transmission spectrum of the entire device is measured, which should present a complex pattern of multi-level interference superposition. The interference frequencies of each level are separated using Fourier transform to verify the results. The deviation between the measured value and the target value is less than or equal to ±2%. If the deviation at any level is too large, the device is deemed unqualified and needs to be remade.

[0038] A low-refractive-index UV-curable adhesive (refractive index less than 1.35) is applied to the entire conical region and the middle fiber segment, and cured by UV light. This protective layer prevents external refractive index changes from affecting interference conditions while enhancing mechanical strength. The fiber is carefully coiled into a V-groove on a ceramic or metal substrate and secured with silicone rubber, ensuring the fiber bending radius is greater than or equal to 3 cm to avoid additional loss. FC / APC or FC / PC connectors are fused to both ends of the fiber, and the fusion splices are reinforced with heat-shrink tubing.

[0039] The specific structure of the optical convolution kernel module is as follows: Along the optical transmission direction, the first tapered region and the second tapered region form the first set of tapered pairs. A section of normal fiber between them is the first intermediate segment with a length of L1. This pair of tapered regions and the first intermediate segment together constitute the first-stage MZI. After the second tapered region is a section of normal fiber, followed by the third and fourth tapered regions forming the second set of tapered pairs. The normal fiber section in between is the second intermediate segment with a length of L2. Together, they constitute the second-stage MZI. This process continues, forming a total of four sets of tapered pairs, corresponding to four stages of MZI. The four stages of MZI are connected in series along the same fiber. The working principle of each MZI is described in [link to relevant documentation]. Figure 3 A single tapered fiber MZI is constructed by creating a pair of identical tapered regions on a continuous single-mode fiber through two localized heating and stretching processes. In the first tapered region, as the fiber diameter is gradually thinned to the micrometer level, the core-cladding waveguide structure of the standard single-mode fiber evolves into a tapered-air waveguide structure. Through adiabatic graded-change design, the fundamental mode is smoothly decomposed into two modes, A and B, with different effective refractive indices, achieving beam splitting. The two modes propagate in parallel in the intermediate normal fiber segment L, accumulating optical path difference due to the difference in effective refractive index. In tapered region B, the morphology is identical to the first tapered region. The two modes undergo a reverse adiabatic graded-change, recouple back to the fundamental mode, and interfere, completing the beam combining function. The transmission spectrum of a single-stage MZI is a standard sinusoidal periodic function, with a free spectral range of... The free spectral range of a single-stage Mach-Zehnder interferometer is uniquely determined by the optical path difference (OPD). The relationship between the effective optical path difference between the two interference modes is related to the optical path difference between them, and can be expressed as: ,in, The free spectral range is given, OPD is the optical path difference between the two modes, and Δn is the optical path difference between the two modes. eff Let Δn be the effective refractive index difference between the two interference modes, and L be the length of the intermediate fiber segment between the two tapered regions. Under the same tapering process conditions, the geometric parameters of each tapered region are basically the same, therefore Δn eff It remains approximately constant. At this point, the MZI at each level... It is mainly determined by the length L of the intermediate fiber segment. As L increases, OPD increases and FSR decreases; as L decreases, OPD decreases. This application increases the MZI by designing different intermediate fiber segment lengths L1 to L4, so that the corresponding MZI levels obtain different results and there is no low-order integer multiple relationship between them. The value is thus determined to meet the requirements of proportional phase tuning and spectral recovery. In the actual preparation process, the value is obtained by real-time measurement using a spectrometer. The value serves as the final control basis.

[0040] The diameter of the finest part of the cone region is determined according to the working wavelength: when the working wavelength is near-infrared, i.e., 1200-1700 nm, the diameter of the finest part of the cone region is about 5-8 μm; when the working wavelength includes visible light, i.e., 400-1100 nm, the diameter of the finest part of the cone region is about 2-5 μm, so as to ensure effective excitation of dual modes at shorter wavelengths and maintain a controllable splitting ratio.

[0041] The intermediate fiber segment lengths L1 to L4 of the four-level MZI are designed separately, so that the corresponding MZI levels... The selected values ​​are distinct and do not have any low-order integer multiples of each other. During the preparation process, the transmission spectrum is monitored in real time using a spectrometer. When the interference fringes... Stop stretching immediately when the target value is reached. (Actual) The measured values ​​recorded by the spectrometer are used as the standard and are then entered into the subsequent data processing algorithm.

[0042] The stress phase tuning unit consists of four independent lead zirconate titanate (DZI) piezoelectric ceramic rings. The intermediate fiber segments of each MZI are tightly and uniformly wound around their respective DZI rings and fixed with UV-curable adhesive to ensure uniform stress transmission. When a driving voltage is applied, the DZI rings undergo radial expansion and contraction, causing axial strain in the wound fiber segments. This alters the refractive index and physical length of the fiber through the elasto-optic effect, thereby changing the optical path difference between the two modes and achieving phase modulation. When the phase change of each stage is related to its... When the ratio is inversely proportional, the composite spectral response waveform of the entire cascade system retains its shape and undergoes an overall translation. This translation is equivalent in the time domain to the circular convolution of the measured spectrum and the system response function, and therefore the spectrum can be recovered by deconvolution.

[0043] See Figure 4 To achieve distortion-free translation of the overall spectral response waveform of the cascaded system, the phase change of each stage is related to... Inversely proportional, after calibration and conversion to the corresponding driving voltage, the ratio of the voltage changes at each stage is equal to its... The inverse of. The smallest MZI-4 requires the largest drive voltage change. The maximum MZI-1 requires the minimum driving voltage change. By synchronously outputting a proportional voltage sequence through a multi-channel DAC, the system waveform undergoes a uniform step-wise overall translation on the wavenumber axis, thus completing the cyclic convolution sampling of the measured spectrum in the time domain. The physical essence of the proportional relationship is: Smaller MZIs have longer intermediate fiber segments and correspondingly larger optical path differences. To achieve the same spectral shift step size as other MZIs, a larger optical path change is required, thus necessitating a larger expansion and contraction of the lead zirconate titanate piezoelectric ceramic ring. By synchronously outputting this proportional voltage sequence through a multi-channel high-precision digital-to-analog converter, the system's spectral response waveform undergoes a consistent cyclic shift along the wavenumber axis under the drive of each MZI.

[0044] Corresponding to the spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer provided in the above embodiments, this application also provides a spectral measurement method based on an all-fiber cascaded Mach-Zehnder interferometer. The entire measurement process is divided into three stages: system pre-calibration stage, formal measurement stage, and spectral recovery stage.

[0045] First, perform system pre-calibration. Upon first use or when environmental conditions change significantly, the following calibration steps must be performed: Illuminate only one light source in the broadband light source module or use a calibration monochromatic light source. Turn off or keep the drive voltage of the other three MZI stages constant. Send a slow sawtooth or triangular wave from 0V to full drive voltage only to the output channel of the lead zirconate titanate piezoelectric ring corresponding to the first-stage MZI. Simultaneously record the change in the output light intensity of the photodetector. When the voltage scan covers the entire 2π phase range, the detector light intensity will exhibit a complete cycle of sinusoidal oscillation. Using the parameters of this sinusoidal signal, establish a DAC encoding-phase offset lookup table for this stage of the MZI. Using this method, calibrate all four stages of the MZI, obtaining four independent lookup tables.

[0046] The voltage ratio is calculated based on the actual free spectral range of each Mach-Zehnder interferometer, and a synchronous drive sequence list is generated. The formula for calculating the voltage ratio is: in, This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the first-stage Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the second-order Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the third-order Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the fourth-order Mach-Zehnder interferometer. This represents the free spectral range of the first-order Mach-Zehnder interferometer. The free spectral range of the second-order Mach-Zehnder interferometer. The free spectral range of the third-order Mach-Zehnder interferometer. This represents the free spectral range of the fourth-order Mach-Zehnder interferometer.

[0047] Determine the total number of steps N for a complete scan, such as 256, 512, or 1024 steps, and the phase increment for each step. Based on the established lookup table, convert the required phase step amount for each stage into the corresponding DAC step increment, generating a four-stage synchronous drive sequence table. This table describes the encoded values ​​that the four DAC channels should output at each step from step 0 to step N-1.

[0048] Then, a standard light source with a known flat spectrum is input, a complete scale scan is performed, using the same drive sequence list as the formal measurement, and the time-series power signal is acquired. The time-series power signal is stored in the data processing unit as the system response function. If the system has nonlinearity or polarization dependence, the measurement can be repeated and averaged, or the system can be calibrated separately for different light sources.

[0049] After pre-calibration, select and illuminate a suitable broadband light source according to the target operating wavelength. In the near-infrared band, illuminate the corresponding SLD (Light Detector Lighting Unit), switching between them via an optical switch, with only one light illuminating at a time. In the visible-near-infrared band, illuminate a white LED array or halogen lamp, and in the full-spectrum band, illuminate a supercontinuum light source.

[0050] After preheating for 5-10 minutes to ensure the stable output spectrum of the light source, determine the working state of the fiber polarizer. Under no light input conditions, record the dark current output of the photoelectric detection module and use the dark current output as the reference for subsequent signal subtraction.

[0051] During the formal measurement phase, the optical signal of the spectrum to be measured is connected to the input end of the spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer via optical fiber, located between the broadband light source and the polarizer, or at a position that replaces the calibration light source. Care should be taken to maintain a stable optical path connection and avoid vibration.

[0052] The microcontroller reads a pre-generated four-level synchronous drive sequence list from memory and, through a multi-channel DAC drive module, synchronously outputs the voltage combination of the current step to four lead zirconate titanate (LZT) piezoelectric ceramic rings according to the sequence list. Each LZT piezoelectric ceramic ring expands or contracts according to the drive voltage, changing the optical path difference of the corresponding MZI and achieving an overall translation of the system's spectral response waveform. After each output step, a 10-20 ms wait is performed to ensure the LZT piezoelectric ceramic ring response is complete and the optical path difference is stable. After the stabilization wait, the analog-to-digital converter is triggered to read the output light intensity value of the photodetector module. The acquired light intensity value is associated with the current step number and stored as a timing signal p[n], where n = 0, 1, ..., N-1 is the step number. The above steps are repeated until all N steps are completed. The typical total acquisition time is approximately 2-4 seconds, calculated with N = 256 and 15 ms per step.

[0053] If the system uses multiple SLDs to cover a wide spectral band, such as near-infrared 1200-1700 nm, the optical switch is switched to the first SLD, the above steps are performed, and the sub-time sequence signal p1[n] is acquired. Then, the system is switched to the second SLD, and the above steps are repeated to obtain p2[n]. The measurement of all SLDs is completed in sequence to obtain multiple sub-time sequences.

[0054] In the spectral reconstruction stage, fast Fourier transforms are performed on the time-series signal and the system response function, respectively. The calculation formula is as follows: , in, For Fast Fourier Transform, The acquired time-series optical power signal, Let be the system response function. For the frequency domain components of the time-series signal, The frequency domain component of the system response function, n This is the scan step number. K For frequency indexing.

[0055] To enhance numerical stability, a regularized form is used for deconvolution recovery in the frequency domain. The calculation formula is as follows: in, The spectral frequency domain result obtained by deconvolution recovery. The complex conjugate of the system response spectrum, This is the regularization parameter.

[0056] Finally, after inverse fast Fourier transform, the real part is taken to obtain the recovered spectral intensity sequence. A low-pass filter is applied to the spectral intensity sequence to suppress high-frequency noise. According to the pre-calibrated dispersion correction factor, that is, the relationship between effective refractive index and wavelength, the wavenumber axis is mapped to the wavelength axis, and nonlinear distortion is compensated and zero-frequency background caused by dark current or ambient light is subtracted.

[0057] For each SLD subband, frequency domain deconvolution recovery and post-processing are repeated to obtain sub-spectral segments. Weighted average stitching is performed in the overlapping regions of adjacent subbands. Overall normalization is then performed to generate a continuous, seamless, complete spectrum. The recovered spectral data is output to the user interface in graphical or text format or stored in local memory.

[0058] This embodiment employs six superluminescent diodes (SLEDs) with center wavelengths of 1200 nm, 1280 nm, 1360 nm, 1450 nm, 1550 nm, and 1650 nm, respectively, switched via a 1×6 fiber optic switch. It also includes an in-line fused-in fiber polarizer, a section of pre-fabricated quadrature taper MZI single-mode fiber, four lead zirconate titanate piezoelectric ceramic rings with an outer diameter of approximately 3 cm, an indium gallium arsenide photodetector and transimpedance amplifier, an STM32 microcontroller, a 14-bit precision 4-channel digital-to-analog converter and its driving circuit, and a 12-bit precision analog-to-digital converter for signal acquisition.

[0059] The middle fiber segment of the four-stage MZI was wound onto four lead zirconate titanate (LZT) piezoelectric ceramic rings, each segment approximately 10 to 15 turns, with the turns tightly fitted but not overlapping. After winding, UV-curing adhesive was uniformly applied and cured, fixing the fiber and LZT piezoelectric ceramic rings as a single unit. The LZT piezoelectric ceramic rings were installed in a thermally insulated enclosure, with leads connected to the output of the drive circuit. First, the voltage-phase response of each MZI was calibrated. A slow sawtooth wave from 0V to full drive voltage was sent along the output channel of the LZT piezoelectric ceramic ring corresponding to the first-stage MZI, while simultaneously recording the change in the output light intensity of the photodetector. When the voltage scan covered the entire 2π phase range, the detector light intensity exhibited a complete sinusoidal oscillation cycle. A DAC encoding-phase offset lookup table was established using the parameters of this sinusoidal signal. All four-stage MZIs were calibrated accordingly.

[0060] Then, the proportional drive parameters are set. According to each level... The required phase step for each stage is calculated based on the proportional relationship. The corresponding DAC step increment for each stage is then calculated using the lookup tables to form a four-stage synchronous drive sequence table.

[0061] Start the broadband light source module according to the configuration and preheat for 5–10 minutes to ensure stable output spectrum. For multi-SLD systems, switch the optical switch channels sequentially to ensure that each sub-light source is lit independently, avoiding interference artifacts caused by spectral superposition. Confirm that the online fiber polarizer is undamaged and that the polarization extinction ratio is normal. Under no-light input conditions, record the dark current output of the photodetector as a reference for subsequent signal subtraction.

[0062] The target free spectral range of the four-stage MZI, measured during the actual preparation process, is loaded from system storage. The normalized voltage ratio is calculated using a formula, and a four-stage synchronous driving voltage sequence is generated using a lead zirconate titanate piezoelectric ceramic ring calibration lookup table. The number of steps within a complete scan cycle is set, for example, 256, 512, or 1024 steps, with each step corresponding to a voltage combination, ensuring uniform sampling along the wavenumber axis.

[0063] Upon initiating the scan, the microcontroller synchronously outputs the voltage combination of the current step to four lead zirconate titanate (LZT) piezoelectric ceramic rings via a multi-channel DAC driver module, driving the intermediate fiber segments of each stage of the MZI to generate axial strain. After each output step, a 10–20 ms wait is allowed to ensure stable response of the LZT piezoelectric ceramic rings and completion of the optical path difference change. After the wait period, the ADC is triggered to read the output light intensity value of the photodetector module. The acquired light intensity value is associated with the current step number and stored as a timing signal p[t], where t is the scan step number. This process is repeated until all preset scan steps are completed, forming a complete timing power sequence.

[0064] Before formal measurement, the system response function is obtained by balancing a field filter using a known standard light source, such as a xenon lamp or halogen lamp, and stored in the data processing unit. A Fast Fourier Transform (FFT) is performed on the acquired time-series signal to obtain the frequency domain component sequence P[k]. An FFT of the same length is then performed on the system response function to obtain... Conjugate processing is performed to match the division direction. Regularization is applied to components close to zero to avoid numerical instability. Finally, an inverse FFT is performed to obtain the recovered original spectrum. A digital low-pass filter is applied to remove high-frequency noise, and wavelength axis mapping is performed according to pre-calibrated dispersion correction coefficients to output the final spectral curve. For multiple SLDs covering a wide near-infrared spectral band, the above scanning process is performed separately to obtain each sub-spectral segment. Based on the center wavelength and spectral overlap region of each SLD, weighted splicing and normalization are performed to generate a continuous, seamless, complete spectrum. The recovered spectral data is output to the user interface or storage medium in graphical or textual form. The DAC output is reset to zero, and the lead zirconate titanate piezoelectric ring returns to its initial state, awaiting the next measurement command.

[0065] In this embodiment, within the near-infrared band of 1200 to 1700 nm, the single scan time is approximately 3 seconds, and the spectral resolution is approximately 5.4. Insertion loss is less than 4 dB including polarizer loss. All components are standardized and readily available, requiring no special or custom-made parts.

[0066] In this embodiment, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, the simultaneous existence of A and B, or the existence of B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0067] The above description is merely a specific embodiment of this application. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application. The protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer, characterized in that, include: A broadband light source module, an optical fiber polarizer connected to the output end of the broadband light source module, the output end of the optical fiber polarizer connected to the input end of an optical convolution kernel module, and the output end of the optical convolution kernel module connected to the input end of a photoelectric detection module; The optical convolution kernel module includes a multi-stage cascaded Mach-Zehnder interferometer sequentially fabricated on a continuous single-mode fiber. Each stage of the Mach-Zehnder interferometer includes a pair of tapered regions and an intermediate fiber segment located between the tapered regions. The stress phase tuning unit includes multiple lead zirconate titanate piezoelectric ceramic rings corresponding one-to-one with the multi-stage cascaded Mach-Zehnder interferometers. The intermediate fiber segments of each stage of the Mach-Zehnder interferometer are wound and fixed on the corresponding lead zirconate titanate piezoelectric ceramic rings. The control terminal of the lead zirconate titanate piezoelectric ceramic ring is connected to the output terminal of the multi-channel DAC drive module. The input terminal of the multi-channel DAC drive module and the output terminal of the photoelectric detection module are both connected to the data processing unit. The free spectral range of each stage of the Mach-Zehnder interferometer satisfies a preset proportional relationship. The multi-channel DAC drive module outputs a driving voltage according to the reciprocal ratio of the free spectral range of each stage, causing the lead zirconate titanate piezoelectric ceramic rings of each stage to produce a corresponding proportional phase change.

2. The spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer according to claim 1, characterized in that, The data processing unit includes a microcontroller and an analog-to-digital converter (ADC). The input terminal of the ADC is connected to the output terminal of the photoelectric detection module. The ADC is communicatively connected to the microcontroller, and the microcontroller is communicatively connected to the multi-channel DAC driver module.

3. The spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer according to claim 2, characterized in that, The photoelectric detection module includes a single-point photodetector and a transimpedance amplifier. The input end of the single-point photodetector is connected to the output end of the optical convolution kernel module, the output end of the single-point photodetector is connected to the input end of the transimpedance amplifier, and the output end of the transimpedance amplifier is connected to the input end of the analog-to-digital converter.

4. The spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer according to claim 1, characterized in that, An optical switch or combiner is provided between the output end of the broadband light source module and the optical fiber polarizer.

5. The spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer according to claim 1, characterized in that, The multi-stage cascaded Mach-Zehnder interferometer, sequentially fabricated on a continuous single-mode fiber, includes: Take a section of standard single-mode optical fiber, use fiber strippers to remove the acrylate coating in the middle section, then wipe the bare fiber section along the fiber axis in one direction with a non-woven cloth soaked in anhydrous ethanol, then wipe it with deionized water, and finally blow it dry with high-purity nitrogen. Immediately after drying, perform tapering operation, use a fiber optic cleaver to cut flat end faces at both ends of the fiber, place it under a microscope to check the quality of the end faces, and confirm that there are no chipped edges or cracks. During the fabrication process, the output end of the optical fiber is connected to a spectrometer, and a broadband light source is incident from the input end. The transmission spectrum is monitored in real time by the spectrometer. The pre-treated optical fiber is fixed on the two displacement stages of the tapering machine, the bare optical fiber segment is centered, and the optical fiber is kept in a horizontal tension state. After aligning the center of the hydrogen flame nozzle with the first preparation position, the hydrogen flame heating is turned on. After the temperature stabilizes, start the stretching program and monitor the transmission spectrum displayed by the spectrometer in real time. When the fiber diameter gradually decreases to the target value, sinusoidal interference fringes appear in the transmission spectrum. Transmission spectra are continuously acquired by a spectrometer at a preset integration time. Real-time fast Fourier transform is performed on the acquired transmission spectra to calculate the free spectral range of the current interference fringes. When the free spectral range is close to the target value and the fringe contrast is greater than the first target value, the stretching is stopped immediately and the flame is turned off. After a preset time period of natural cooling, a miniature fan is used to blow cold air to accelerate cooling to room temperature, forming the first pair of tapered areas and the first intermediate fiber segment; After the first-stage Mach-Zehnder interferometer is prepared, the displacement stage clamp is released, the optical fiber is moved axially so that the second position is aligned with the center of the flame, and a heat dissipation copper block or thermal conductive silicone grease is wrapped around the preset position behind the first-stage cone region. Using the same heating and stretching procedure and spectral monitoring process as the first stage, when the free spectral range reaches the second target value, the stretching is immediately stopped and the flame is turned off. After cooling, the second pair of tapered regions and the second intermediate fiber segment are formed. The optical fibers were sequentially moved to the preset preparation positions to prepare multi-stage Mach-Zehnder interferometers. After all preparations were completed, the optical fibers were not cut, and the spectrometer and light source were kept connected at both ends. The transmission spectrum of the entire multi-stage cascaded Mach-Zehnder interferometer was measured. The interference frequencies of each stage were separated by Fourier transform, and the deviation between the measured values ​​and the target values ​​of the free spectral range of each stage was confirmed to be within the allowable range. Low-refractive-index UV-curable adhesive is applied to all cone regions and the middle fiber segment and cured by UV irradiation. The fiber is then coiled and fixed onto the substrate. Connectors are fused to both ends of the fiber, and the fusion joints are reinforced with heat-shrink tubing.

6. A spectral measurement method based on an all-fiber cascaded Mach-Zehnder interferometer, employing the spectral measurement device based on an all-fiber cascaded Mach-Zehnder interferometer as described in any one of claims 1-5, characterized in that, include: Pre-calibrate the spectral measurement device based on the all-fiber cascaded Mach-Zehnder interferometer by lighting only one light source in the broadband light source module or using a calibration monochromatic light source, and send a slow sawtooth wave from 0V to full drive voltage only to the output channel of the lead zirconate titanate piezoelectric ceramic ring corresponding to the first-stage Mach-Zehnder interferometer, while recording the change in the output light intensity of the photoelectric detection module. When the voltage scan covers the entire phase range, the DAC encoding-phase shift lookup table of the first-stage Mach-Zehnder interferometer is established using the parameters of the sinusoidal signal. The Mach-Zehnder interferometers at each level were calibrated sequentially, resulting in multiple independent lookup tables; Calculate the voltage ratio based on the actual free spectral range of each Mach-Zehnder interferometer and generate a synchronous drive sequence list; Input a standard light source with a known flat spectrum, perform a complete scale scan, and acquire the time-series power signal. Store the time-series power signal as a system response function in the data processing unit. After precalibration is completed, select and light a suitable broadband light source according to the target working band. After preheating for a preset time period, ensure that the output spectrum of the light source is stable and then determine the working status of the fiber polarizer. Under conditions of no light input, the dark current output of the photoelectric detection module is recorded, and the dark current output is used as the reference for subsequent signal subtraction. The optical signal of the spectrum to be measured is connected to the input end of the spectral measurement device based on the all-fiber cascaded Mach-Zehnder interferometer through an optical fiber. The proportional voltage is synchronously output to multiple lead zirconate titanate piezoelectric ceramic rings according to the synchronous drive sequence list. After each output, the lead zirconate titanate piezoelectric ceramic rings are waited for to stabilize before the analog-to-digital converter is triggered to read the light intensity value of the photoelectric detection module. The collected light intensity value is associated with the current step number and stored as a time sequence signal; The time-series signal and the system response function are subjected to Fast Fourier Transform (FFT) respectively, deconvolution is performed in the frequency domain to recover the signal, and then inverse Fast Fourier Transform is performed to recover the spectrum to be measured. The recovered spectrum is filtered and then output to the user interface or stored in local memory in graphical or text form.

7. The spectral measurement method based on an all-fiber cascaded Mach-Zehnder interferometer according to claim 6, characterized in that, The formula for calculating the voltage ratio based on the actual free spectral range of each Mach-Zehnder interferometer is as follows: in, This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the first-stage Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the second-order Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the third-order Mach-Zehnder interferometer. This represents the driving voltage of the lead zirconate titanate piezoelectric ceramic ring corresponding to the fourth-order Mach-Zehnder interferometer. This represents the free spectral range of the first-order Mach-Zehnder interferometer. The free spectral range of the second-order Mach-Zehnder interferometer. The free spectral range of the third-order Mach-Zehnder interferometer. This represents the free spectral range of the fourth-order Mach-Zehnder interferometer.

8. The spectral measurement method based on an all-fiber cascaded Mach-Zehnder interferometer according to claim 6, characterized in that, The formulas for calculating the Fast Fourier Transform of the time-series signal and the system response function are as follows: in, For Fast Fourier Transform, The acquired time-series optical power signal, Let be the system response function. For the frequency domain components of the time-series signal, The frequency domain component of the system response function, n This is the scan step number. K For frequency indexing.

9. The spectral measurement method based on an all-fiber cascaded Mach-Zehnder interferometer according to claim 6, characterized in that, The formula for deconvolution recovery in the frequency domain is: in, The spectral frequency domain result obtained by deconvolution recovery. The complex conjugate of the system response spectrum, This is the regularization parameter.

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