Folding miniaturized fiber bragg grating demodulation system

Abstract

The invention provides a folding type miniaturized fiber bragg grating demodulation system, and relates to the technical field of miniature fiber bragg grating demodulation systems.The folding type miniaturized fiber bragg grating demodulation system is constructed, the optical design theory, the grating diffraction principle and the high-performance detection technology are fused, and a compact and efficient optical path structure is achieved; accurate grating parameter calculation and spatial dispersion mapping methods are utilized to ensure accurate positioning of spatial distribution of diffracted light, and the resolution and stability of wavelength demodulation are improved; by combining the comprehensive design of the diffraction limit resolution and the pixel limit resolution, parameters of an optical element and a detector are scientifically matched, and high sensitivity and high precision of the system are ensured; the optical path parameters are iteratively optimized through a simulation optimization algorithm, the imaging quality and the system stability are improved, miniaturization and integration of the optical system are achieved, and the system is more suitable for scenes such as laboratory development and teaching experiments.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of small fiber grating demodulation system, in particular to a folding small fiber grating demodulation system. BACKGROUND

[0002] In industrial production and infrastructure construction, the fiber grating demodulator can monitor the temperature, strain and other parameters of the equipment in real time, provide high-precision data feedback, help engineers quickly identify the running status and structural changes of the equipment, and thus take necessary measures to ensure safe operation. Compared with traditional monitoring technology, the fiber grating demodulator is widely used because of its fast response speed, high precision, strong reliability, simple operation, high measurement accuracy and other advantages. The working principle of the fiber grating demodulator is that the light signal reflected or transmitted by the fiber grating is spectrally split by a spectrometer, and the light intensity distribution is collected by a detector (such as a CCD or a photodiode array), and the wavelength corresponding to the light intensity peak is analyzed by a computer or upper computer program, so as to quickly obtain the change of the grating center wavelength, and realize high-precision monitoring of temperature, strain and other physical quantities.

[0003] In the prior art, the demodulator on the market usually uses optical fiber for signal transmission, and the applicable center wavelength is generally around 1310nm and 1550nm. In the 850nm±50nm band, the optical fiber has high loss and high noise, making signal detection difficult and the signal-to-noise ratio low, so that no commercial demodulator suitable for this band has been launched on the market, and it is still in the development stage. For use scenarios with small cost budget and not strict precision requirements, if you want to demodulate this band, you can only purchase this special customized equipment, which will undoubtedly greatly increase the cost of the equipment, resulting in an overall budget exceeding the standard. Therefore, the applicability of the demodulator in the prior art in this use scenario is greatly reduced, and a low-cost demodulation system that can demodulate the 850nm±50nm band without causing the cost of the equipment to exceed the standard is urgently needed.

[0004] The above information disclosed in the background section is only used to strengthen the understanding of the background of the present disclosure, and therefore it can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0005] The purpose of the present application is to provide a folding small fiber grating demodulation system to solve the problems raised in the background.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: A folding small fiber grating demodulation system, specifically comprising: a three-terminal ring-shaped unit, used for emitting the received incident light to the sensing array unit, receiving the reflected light returned by the sensing array unit, and emitting the reflected light to a converging unit; a sensing array unit, used for reflecting the incident light meeting the Bragg condition back; a converging unit, which is a plano-convex lens, used for converging the reflected light and emitting the converged reflected light to a converting unit; a converting unit, which is a collimating mirror, used for converting the converged reflected light into parallel light and emitting the parallel light to a grating unit; a grating unit, which is a plane reflective grating, used for diffracting the parallel light to achieve wavelength separation and emitting the diffracted light to a focusing unit; a focusing unit, which is a focusing mirror, used for converging the diffracted light and emitting the converged diffracted light to a collecting unit; a collecting unit, including a photosensitive element, a digital-to-analog conversion element, and a signal processing element, used for converting the optical signal of the diffracted light into an electrical signal, obtaining corresponding spectral data, and sending the spectral data after digital-to-analog conversion to an upper computer.

[0007] Preferably, the spatial distribution of the diffracted light is determined by the plane reflective grating, and the logic for obtaining the spatial distribution of the diffracted light is as follows: collecting physical parameters of the plane reflective grating, including but not limited to groove spacing, diffraction order, and light source incidence angle; determining the central wavelength according to the sensing array unit, and substituting the central wavelength, groove spacing, diffraction order, and light source incidence angle into the grating equation to obtain the diffraction angle of the diffracted light; determining the spatial distribution of the diffracted light in the optical path according to the diffraction angle.

[0008] Preferably, the focal length of the focusing mirror is obtained based on the diffraction angle, and the logic for obtaining the focal length is as follows: firstly, obtaining the effective photosensitive length of the photosensitive element in the collecting unit and the spectral band range in the spectral data; calculating the focal length of the focusing mirror based on the spatial dispersion mapping principle of the Czerny-Turner optical path structure, and the calculation formula is as follows: In the formula, focal length of the focusing mirror, , upper and lower limits of the spectral band range, effective photosensitive length of the photosensitive element, groove spacing of the plane reflective grating, diffraction angle of the diffracted light.

[0009] Preferably, the system resolution of the demodulation system is determined by a diffraction limit resolution and a pixel limit resolution, wherein the diffraction limit resolution is calculated by a point spread function and a Rayleigh criterion, the pixel limit resolution is calculated by a pixel size of the photosensitive element and a dispersion rate of the demodulation system, the system resolution is the maximum of the diffraction limit resolution and the pixel limit resolution, and is less than a preset target resolution.

[0010] Preferably, the acquisition logic of the diffraction limit resolution and the pixel limit resolution is as follows: Firstly, based on the Rayleigh criterion, the Airy disk radius corresponding to the central wavelength is obtained as the minimum imaging displacement difference of the demodulation system; Then, based on the effective photosensitive length of the photosensitive element and the spectral band range in the spectral data, the dispersion rate of the demodulation system is calculated, and the calculation method is as follows: In the formula, D represents the dispersion rate, Next, the diffraction limit resolution is calculated according to the dispersion rate and the minimum imaging displacement difference, and the calculation method is as follows: In the formula, R represents the diffraction limit resolution, Again, the pixel limit resolution is calculated according to the pixel size of the photosensitive element and the dispersion rate, and the calculation method is as follows: In the formula, P represents the pixel limit resolution,

[0011] Preferably, the minimum focal length of the collimating mirror is obtained based on the target resolution, and the calculation method is as follows: In the formula, F represents the minimum focal length of the collimating mirror,

[0012] Preferably, the collimating mirror and the focusing mirror are both spherical mirrors, and the spherical aberration of both is not more than one fourth of the central wavelength.

[0013] ​​​​​​​​​Preferably, the demodulation system verifies the performance of the optical path structure in a simulation mode, and optimizes the design parameters of the optical path structure through an optimization algorithm, the design parameters including but not limited to the spatial distance between units, the tilt angle of the collimating mirror, the tilt angle of the focusing mirror, and the tilt angle of the collection unit.

[0014] Compared with the prior art, the present application has the following advantages: The present application realizes a compact and efficient optical path structure by constructing a folding miniaturized fiber grating demodulation system, combining optical design theory, grating diffraction principle and high-performance detection technology; signal transmission is realized by using the optical path structure, avoiding the poor transmission performance of optical fiber at 850nm±50nm; precise grating parameter calculation and spatial dispersion mapping method are used to ensure accurate positioning of the spatial distribution of diffracted light, improving the resolution and stability of wavelength demodulation; the comprehensive design of diffraction limit resolution and pixel limit resolution is combined to scientifically match the parameters of optical elements and detectors, ensuring high sensitivity and high precision of the system; the imaging quality and system stability are improved by iteratively optimizing the optical path parameters through a simulation optimization algorithm, realizing the miniaturization and integration of the optical system; the overall scheme not only can demodulate the 850nm±50nm band, but also has lower cost, and is more suitable for use in scenarios with small cost budget and less stringent accuracy requirements. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Figure 1 is a schematic diagram of the module structure of the present application; Figure 2 Figure 2 is a schematic diagram of the optical path structure of the present application; Figure 3 Figure 3 is a schematic diagram of the point spread function when the diffraction limit resolution is involved; Figure 4 Figure 4 is a schematic diagram of the point spread function when the pixel limit resolution is involved. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to specific embodiments.

[0017] It should be noted that the technical terms or scientific terms used in the present application shall be the usual meanings understood by those skilled in the art to which the present application belongs, unless otherwise defined. The terms "first", "second", and similar words used in the present application do not represent any order, number or importance, but are only used to distinguish different components. The terms "include" or "contain" and similar words mean that the elements or objects appearing before the words include the elements or objects listed after the words and their equivalents, without excluding other elements or objects. The terms "connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms "upper", "lower", "left", "right" and the like are only used to represent relative positional relationships, which may change accordingly when the absolute positions of the described objects change.

[0018] Embodiments: Please refer to Figures 1-4 The present application provides a technical solution: A folding miniaturized fiber grating demodulation system, specifically comprising: a three-port ring unit 2, a sensing array unit 3, a converging unit 4, a conversion unit 5, a grating unit 6, a focusing unit 7, a collection unit 8, and in addition, a light source 1 for emitting incident light and an upper computer 9 for data processing.

[0019] The three-port ring unit is used to emit the received incident light to the sensing array unit, while receiving the reflected light returned by the sensing array unit and emitting the reflected light to the converging unit; The three-port ring unit can adopt a three-port fiber ring, which is used for light path distribution and isolation, realizes efficient switching of incident light and reflected light, can accurately guide broadband incident light to the sensing array, and guide the array reflected light to the subsequent optical system, thereby simplifying the optical path structure, avoiding straight-through and reflection path cross interference, improving signal quality, and also improving reflected light capture efficiency, reducing light loss, and improving overall system sensitivity.

[0020] The sensing array unit is used to reflect the incident light that meets the Bragg condition back; The sensing array unit is composed of a plurality of FBGs (Fiber Bragg Gratings), which correspond to different Bragg wavelengths respectively, can realize wavelength encoding reflection of multiple physical quantities (such as strain, temperature, etc.) of incident light, thereby realizing multi-point, multi-parameter distributed measurement and improving system information capacity. When light waves of a certain wavelength meet the Bragg reflection condition of the FBG, strong reflection occurs, and other wavelengths of light pass through the grating or weak reflection. Therefore, based on the required center wavelength (i.e. the wavelength that meets the Bragg reflection condition), the corresponding FBG can be selected, and the position of the center wavelength is directly related to the grating period of the FBG and the effective refractive index of the fiber material.

[0021] The converging unit is a plano-convex lens, configured to converge the reflected light and emit the converged reflected light to the converting unit; By setting the plano-convex lens as the converging unit, the reflected light can be preliminarily converged, the light spot divergence is reduced, and the light efficiency of the subsequent optical system is improved. In this way, not only the light flux of the subsequent optical system is improved, and the signal strength is enhanced, but also the space utilization is improved, and the miniaturization design is supported.

[0022] The converting unit is a collimating mirror, configured to convert the converged reflected light into parallel light and emit the parallel light to the grating unit; The parallel light incident on the grating can obtain higher dispersion rate and wavelength resolution, and the wavelength separation function of the subsequent grating element can be easily played, so as to reduce the system volume.

[0023] The grating unit is a plane reflective grating, configured to diffract the parallel light to realize wavelength separation and emit the diffracted light to the focusing unit; The plane reflective grating is configured to diffract the incident parallel light to realize spatial separation of different wavelength lights, so as to form a dispersed spectrum.

[0024] The focusing unit is a focusing mirror, configured to converge the diffracted light and emit the converged diffracted light to the collecting unit; The focusing mirror can converge the dispersed light after diffraction, focus the light of different wavelengths to different spatial positions of the collecting unit, so as to realize accurate mapping of the spectrum to the spatial position, facilitate subsequent photoelectric signal collection and processing, and the focal length of the focusing mirror is adjustable, so as to flexibly adapt to different detector and system resolution requirements.

[0025] The collecting unit includes a photosensitive element, a digital-to-analog conversion element, and a signal processing element, configured to convert the light signal of the diffracted light into an electric signal, obtain corresponding spectrum data, and send the spectrum data to an upper computer after digital-to-analog conversion.

[0026] The photosensitive element in the collecting unit can adopt a CCD or a CMOS, which can convert the focused light signal into an electric signal. The digital-to-analog conversion element can adopt an A / D chip, so as to convert the analog electric signal into a digital signal. The signal processing element can adopt a micro-processing chip with a USB / IO interface, which is configured to analyze and demodulate the digital signal and output to the upper computer (such as a PC computer) through the USB / IO interface.

[0027] The spatial distribution of the diffracted light is determined by the plane reflective grating, and the logic for obtaining the spatial distribution of the diffracted light is as follows: The physical parameters of the plane reflective grating are collected, including but not limited to groove distance, diffraction order, and light source incident angle. The center wavelength is determined according to the sensing array unit, and the center wavelength, the groove spacing, the diffraction order, and the light source incident angle are substituted into the grating equation to obtain the diffraction angle of the diffracted light, and the calculation formula is: In the formula, the groove spacing of the plane reflection grating is represented, the diffraction angle is represented, the incident angle is represented, the diffraction order is represented, and the center wavelength is represented.

[0028] The spatial distribution of the diffracted light in the optical path is determined according to the diffraction angle.

[0029] In this embodiment, the center wavelength is set to 850 nm, the groove spacing of the plane reflection grating is set to 1 / 1200 mm, the diffraction order is 1, and the incident angle is set to 40°. Therefore, the diffraction angle of the center wavelength is 22.161°.

[0030] It can be understood that the accurate determination of the spatial distribution of the diffracted light is the basis for the high-efficiency demodulation of the entire fiber grating demodulation system, which ensures that the subsequent focusing and acquisition unit can accurately locate and capture the signal, and improves the overall demodulation accuracy. By accurately calculating the diffraction angle, the optical path folding path can be reasonably designed, the placement position and angle of the optical element can be optimized, the system volume can be reduced, miniaturization and integration can be realized, and the optical element space distance, inclination angle, etc. Design can be used for optical path simulation and optimization algorithm input to guide the design of the optical element, to achieve the best spectral resolution and imaging effect.

[0031] The focal length of the focusing mirror is obtained based on the diffraction angle, and the obtaining logic is as follows: First, the effective photosensitive length of the photosensitive element in the acquisition unit and the spectral band range in the spectral data are obtained; The focal length of the focusing mirror is calculated based on the spatial dispersion mapping principle of the Czerny-Turner optical path structure, and the calculation formula is as follows: In the formula, the focal length of the focusing mirror is represented, , the upper and lower limits of the spectral band range are represented, and the effective photosensitive length of the photosensitive element is represented.

[0032] In this embodiment, the center wavelength is 850 nm, the upper and lower limits of the spectral band range are 900 nm and 800 nm, and the collection unit selects a linear array CCD collection module of the TCD1304 series, the size of which is 29.184 mm x 0.2 mm (the pixel size is 8 pm x 200 pm, and the number of pixels is 3684), that is, the effective photosensitive length of the photosensitive element in the collection unit is 29.184 mm. Then, by substituting each parameter into the formula, the ideal focal length of the focusing mirror is 225.234 mm, and the model selection can be based on this parameter (for example, a concave mirror of the CM508-200-E03 series).

[0033] Through reasonable design of spatial dispersion mapping and reasonable control of focal length, the long focal length is avoided to cause long optical path, so that the entire optical system is compact and easy to fold and arrange, thereby reducing the straight-line distance between optical elements, and based on the light tracing theory, while ensuring the effective optical path length unchanged, the system space occupation can be greatly reduced, which is more suitable for the application environment of laboratory with small space. Moreover, the focal length of the focusing mirror promotes the effective expansion and imaging of the dispersed spectrum, which can directly enhance the wavelength resolution and final demodulation accuracy of the system, so as to ensure that the dispersed light can accurately fall on the effective photosensitive area of the collection unit after focusing, avoid signal truncation or space waste, and improve the collection efficiency and data quality. Further, the position and angle of the optical element can be further adjusted by cooperating with the simulation software and optimization algorithm, so as to improve the overall optical path performance and system stability.

[0034] The system resolution of the demodulation system is determined by the diffraction limit resolution and the pixel limit resolution, wherein the diffraction limit resolution is calculated by the point spread function and the Rayleigh criterion, the pixel limit resolution is calculated by the pixel size of the photosensitive element and the dispersion rate of the demodulation system, the system resolution is the maximum value of the diffraction limit resolution and the pixel limit resolution, and is less than the preset target resolution.

[0035] In this step, by considering the joint influence of the diffraction limit and the pixel limit, the performance bottleneck caused by the mismatch between the optical design and the detector selection can be effectively avoided, thereby improving the system stability.

[0036] The acquisition logic of the diffraction limit resolution and the pixel limit resolution is as follows: Firstly, the Rayleigh criterion indicates that when the center distance of two point light sources is equal to or greater than the radius of an Airy disk of a point light source, they are considered to be just distinguishable in imaging. Based on this, the corresponding Airy disk radius is obtained based on the center wavelength, and it is taken as the minimum imaging displacement difference of the demodulation system; Then, based on the effective photosensitive length of the photosensitive element and the spectral band range in the spectral data, the dispersion rate of the demodulation system is calculated, and the calculation method is as follows: wherein represents the dispersion rate; Then, the diffraction-limited resolution is calculated according to the dispersion rate and the minimum imaging displacement difference, and the calculation method is as follows: wherein represents the diffraction-limited resolution, represents the Airy disk radius; At the same time, the pixel-limited resolution is also a factor limiting the resolution, that is, when the resolution of the imaging system is limited by the pixel size of the detector, the minimum resolution that can be achieved is limited. When the spot or spectral line is imaged on the detector, if the change range is less than one pixel, the detector cannot distinguish it; usually, more than two pixels are needed to cover one minimum distinguishable spectral interval.

[0037] Therefore, based on the above reasons, the pixel-limited resolution is calculated according to the pixel size of the photosensitive element and the dispersion rate, and the calculation method is as follows: wherein represents the pixel-limited resolution, represents the pixel size of the photosensitive element, which is equivalent to the is calculated as the minimum imaging displacement difference.

[0038] In this embodiment, the upper and lower limits of the spectral band range are 900 nm and 800 nm, so the designed bandwidth is 100 nm, the overall dispersion rate of the system is 291.84 pm / nm, and the Airy disk radius corresponding to the center wavelength 850 nm is 8.911 pm. Substituted into the formula, the diffraction-limited resolution is about 30 pm. Substituted into the Zemax software, it is confirmed by the point spread function simulation that the imaging of the two extremely close wavelengths 850 nm and 850.03 nm forms two distinguishable peaks on the image plane (see Figure 3 ), so it is considered that the system can distinguish the two extremely close wavelength signals in space, and the diffraction-limited resolution of the system is 30 pm. At the same time, the pixel size of the photosensitive element is substituted into the calculation formula, and the pixel-limited resolution is about 55 pm. Similarly, substituted into the Zemax software, it is confirmed by the point spread function simulation that the imaging of the two extremely close wavelengths 850 nm and 850.055 nm forms two distinguishable peaks on the image plane (see Figure 4 ), so it is considered that the system can distinguish the two extremely close wavelength signals in space, and the diffraction-limited resolution of the system is 55 pm. The resolution of the system takes the maximum value of the two, that is, 55 pm. In this embodiment, the target resolution is set to 0.2 nm, which is much larger than the system resolution, so it meets the requirements, and it is proved that the selected elements are reasonable.

[0039] In this step, by combining the classical Rayleigh criterion with the Airy disc theory, the formula is used to calculate the diffraction limit resolution and pixel limit resolution, and at the same time, the existence of two peaks in the point spread function (PSF) is verified by Zemax optical simulation, which ensures that the theory is consistent with the actual imaging effect, and ensures that the focal length, dispersion rate, pixel size and other parameters of the focusing lens are matched within a reasonable range, so as to improve the credibility and scientificity of the scheme.

[0040] The minimum focal length of the collimating lens is based on the target resolution, and the calculation method is as follows: In the formula, d represents the preset target resolution, s represents the slit width, and f represents the minimum focal length of the collimating lens.

[0041] In this embodiment, the target resolution is 0.2 nm, and the slit width is approximately 40 μm. By substituting the above formula, it can be calculated that the minimum focal length of the collimating lens is about 166.67 mm. The specific model of the collimating lens can be selected according to this parameter.

[0042] The collimating lens and the focusing lens are both spherical lenses, and the spherical aberration of both is not more than one fourth of the central wavelength. This is because the wavefront error not exceeding 1 / 4 of the wavelength (i.e. one fourth wavelength) is recognized as the standard for an optical element to achieve "diffraction limit" performance. The wavefront error of one fourth wavelength corresponds to a slight expansion of the imaging point spread function (PSF) spot size and ideal diffraction limit spot, which can still maintain high resolution. That is, the spherical aberration error within one fourth wavelength will not significantly reduce the resolution and contrast of the system. By controlling the spherical aberration of the collimating lens and the focusing lens within this range, it can not only avoid excessive aberration to cause spot expansion, ensure the collimation and focusing quality of the light beam after the slit, but also increase the selection range, so as to balance the manufacturing difficulty and cost under the premise of ensuring high performance.

[0043] ​​​The demodulation system verifies the performance of the optical path structure in a simulation mode, and optimizes the design parameters of the optical path structure through an optimization algorithm. Specifically, the performance to be verified includes, but is not limited to, wavefront error, which is generally detected by detecting the wavefront error (RMS and peak-to-valley value) introduced by each optical element of the system, ensuring that the overall wavefront error is controlled within the design target (such as within one quarter of the central wavelength), and ensuring near-diffraction-limited imaging quality; point spread function simulation, which is to simulate the imaging spot of a monochromatic point source after passing through the optical system, analyze the spot size and shape, and confirm the focusing effect and spatial resolution; dispersion curve simulation, which is to calculate the image plane position corresponding to different wavelengths, confirm that the dispersion rate is consistent with the design calculation, and ensure that the spectral band is completely and uniformly mapped to the photosensitive element. The design parameters include, but are not limited to: the spatial distance between each unit, the tilt angle of the collimating mirror, the tilt angle of the focusing mirror, and the tilt angle of the acquisition unit. The spatial distance between each unit can ensure that the focal position matches the spectral mapping; the tilt angle of the collimating mirror can avoid non-ideal angle of the incident light with the grating, focusing mirror and other elements to introduce additional aberration; the tilt angle of the focusing mirror can optimize the spot shape and position, and improve the accuracy of spatial dispersion mapping; the tilt angle of the acquisition unit can ensure that the spectral line is accurately projected onto the detector image plane, avoiding distortion and signal loss.

[0044] Specifically, the optimization algorithm can use genetic algorithm, gradient descent method, particle swarm optimization, etc. First, an optical design software (such as Zemax, Code V, etc.) is used to build an optical path structure model, then the design target and constraints are defined, the design target can be set as: the system resolution reaches or is better than the preset target (such as 0.2 nm); the optical system spherical aberration is less than one quarter of the wavelength; the maximum light flux and signal-to-noise ratio are maximized; the system volume and weight requirements, etc.; the constraint parameters include element physical size, mechanical installation space range, optical element incidence angle range and manufacturing tolerance, etc. After setting, the design parameters (i.e. optimization variables) to be optimized are determined, and the wavefront error (RMS or P-V), the focusing spot size (PSF), the diffraction limit achievement degree, the dispersion rate uniformity, and the spectral resolution are used as indicators to construct the objective function in a weighted manner, and the optical software is run for ray tracing and wavefront analysis to obtain the point spread function (PSF), wavefront error distribution, dispersion relationship and imaging position, etc. to verify whether the design meets the spherical aberration control within one quarter of the wavelength, and whether the imaging spot size meets the expectation. Finally, a suitable optimization algorithm is selected to automatically search and iteratively adjust the design parameters, and the design parameters are output after convergence.

[0045] In this step, by scientifically establishing a model, reasonably selecting a parameter range, using advanced optical simulation and automatic optimization algorithm, combining experience fine-tuning and verification, a high-performance design of the optical path of the folded fiber grating demodulation system is realized, which can not only effectively improve the imaging quality and stability of the system, but also realize the miniaturization and cost control.

[0046] The above formulas are dimensionless values calculated, the formula is obtained by collecting a large amount of data to simulate the most recent real situation, and the preset parameters in the formula are set by a person skilled in the art according to the actual situation.

[0047] The above embodiments can be realized wholly or partially by software, hardware, firmware or any combination thereof. When realized by software, the above embodiments can be realized wholly or partially in the form of a computer program product. Those skilled in the art can realize that the units and algorithm steps of the examples described in conjunction with the embodiments disclosed herein can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are executed in hardware or software methods depends on the specific application and design constraints of the technical solutions.

[0048] The units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, which can be located in one place or distributed on multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0049] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered within the protection scope of the present application.

Claims

1. A foldable miniaturized fiber Bragg grating demodulation system, characterized in that, Specifically, it includes: The three-terminal ring unit is used to output the received incident light to the sensing array unit, receive the reflected light returned by the sensing array unit, and output the reflected light to the converging unit. A sensing array unit is used to reflect and transmit incident light that satisfies the Bragg condition, and the center wavelength of the incident light that satisfies the Bragg condition is 850nm±50nm. A converging unit, which is a plano-convex lens, is used to converge the reflected light and then send the converged reflected light to the conversion unit. The conversion unit, which is a collimating lens, is used to convert the converging reflected light into parallel light and then output the parallel light to the grating unit. A grating unit, wherein the grating unit is a planar reflection grating, is used to diffract parallel light to achieve wavelength separation and to output the diffracted light to a focusing unit; A focusing unit, which is a focusing lens, is used to converge the diffracted light and then emit the converged diffracted light to the acquisition unit. The acquisition unit includes a photosensitive element, a digital-to-analog converter, and a signal processing element, which is used to convert the optical signal of the diffracted light into an electrical signal to obtain the corresponding spectral data, and send the spectral data to the host computer after digital-to-analog conversion. The demodulation system uses simulation to verify the performance of its optical path structure, and optimizes the design parameters of the optical path structure through optimization algorithms. The design parameters include, but are not limited to: the spatial distance between each unit, the tilt angle of the collimating lens, the tilt angle of the focusing lens, and the tilt angle of the acquisition unit.

2. The foldable miniaturized fiber Bragg grating demodulation system according to claim 1, characterized in that: The spatial distribution of the diffracted light is determined by a planar reflection grating, and the logic for obtaining the spatial distribution of the diffracted light is as follows: Collect the physical parameters of the planar reflection grating, including but not limited to the slot pitch, diffraction order, and incident angle of the light source; The center wavelength is determined based on the sensor array unit, and the center wavelength, slot pitch, diffraction order, and incident angle of the light source are substituted into the grating equation to solve for the diffraction angle of the diffracted light. The spatial distribution of diffracted light in the optical path is determined based on the diffraction angle.

3. The foldable miniaturized fiber Bragg grating demodulation system according to claim 2, characterized in that: The focal length of the focusing lens is obtained based on the diffraction angle, and the logic for obtaining it is as follows: First, obtain the effective photosensitive length of the photosensitive element in the acquisition unit, as well as the spectral band range in the spectral data; The focal length of the focusing lens is calculated based on the spatial dispersion mapping principle of the Czerny–Turner optical path structure. The formula is as follows: In the formula This indicates the focal length of the focusing lens. , These represent the upper and lower limits of the spectral band range, respectively. Indicates the effective photosensitive length of the photosensitive element. The slot pitch of a planar reflection grating is indicated. This indicates the diffraction angle of the diffracted light.

4. The foldable miniaturized fiber Bragg grating demodulation system according to claim 3, characterized in that: The system resolution of the demodulation system is determined by the diffraction-limited resolution and the pixel-limited resolution. The diffraction-limited resolution is calculated by the point spread function and the Rayleigh criterion, while the pixel-limited resolution is calculated by the pixel size of the photosensitive element and the dispersion rate of the demodulation system. The system resolution is the maximum value of the diffraction-limited resolution and the pixel-limited resolution, and is less than the preset target resolution.

5. The foldable miniaturized fiber Bragg grating demodulation system according to claim 4, characterized in that: The logic for obtaining the diffraction-limited resolution and pixel-limited resolution is as follows: First, based on the Rayleigh criterion, the corresponding Airy disk radius is obtained through the center wavelength and used as the minimum imaging displacement difference of the demodulation system. Then, based on the effective photosensitive length of the photosensitive element and the spectral band range in the spectral data, the dispersion rate of the demodulation system is calculated as follows: In the formula Indicates the dispersion rate; Next, the diffraction-limited resolution is calculated based on the dispersion rate and the minimum imaging shift difference. The calculation method is as follows: In the formula Indicates the diffraction-limited resolution. Indicates the radius of the Airy disk; Then, the pixel limit resolution is calculated based on the pixel size and dispersion rate of the image sensor. The calculation method is as follows: In the formula Indicates the maximum resolution per pixel. This indicates the pixel size of the photosensitive element.

6. The foldable miniaturized fiber Bragg grating demodulation system according to claim 4, characterized in that: The minimum focal length of the collimating lens is obtained based on the target resolution, and it is calculated as follows: In the formula This indicates the preset target resolution. Indicates the slit width. Indicates the diffraction order. This indicates the minimum focal length of the collimating lens.

7. The foldable miniaturized fiber Bragg grating demodulation system according to claim 1, characterized in that: Both the collimating lens and the focusing lens are spherical mirrors, and their spherical aberration does not exceed one-quarter of the center wavelength.

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