Fiber bragg grating demodulation system and demodulation method based on polarization measurement technology, and corresponding grating weighing sensor

Abstract

The invention discloses a fiber grating demodulation system and demodulation method based on a polarization measurement technology, and a corresponding grating weighing sensor, and belongs to the technical field of optical fiber sensing. The system comprises a broadband light source, a circulator, a grating weighing sensor, a polarizer, an optical fiber delayer, a polarization beam splitter, a first photoelectric detector, a second photoelectric detector, a data acquisition card and a demodulation module. According to the method, reflected light of the sensor is changed into linearly polarized light through the polarizer, the linearly polarized light is delayed and then divided into two paths of orthogonal components through the polarization beam splitter, the two paths of orthogonal components are converted into voltage signals, the demodulation module processes the two paths of signals through a differential balance algorithm, a phase delay angle related to wavelength change is extracted, and then the weight is calculated. The invention further provides a grating weighing sensor adopting the left-handed and right-handed fixing bolt and reinforcing bolt structure, and the grating weighing sensor is used for applying and keeping constant pretension force. According to the method, the problems of low precision and poor anti-interference performance of a traditional demodulation method are solved, and the accuracy and the stability of fiber grating weighing measurement are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a fiber optic grating demodulation system and demodulation method based on polarization measurement technology, and a corresponding grating weighing sensor. Background Technology

[0002] Fiber Bragg gratings (FBGs), as important fiber optic sensor devices, possess outstanding advantages such as resistance to electromagnetic interference, corrosion resistance, and distributed measurement capabilities, and have been widely used in structural health monitoring, temperature measurement, and pressure sensing. Traditional FBG demodulation methods mainly rely on intensity demodulation or wavelength demodulation techniques. While these methods can achieve basic sensing functions in many scenarios, they still have significant shortcomings in practical applications: limited demodulation accuracy, poor stability, and susceptibility to interference from environmental factors such as temperature fluctuations, light source power drift, and fiber bending, leading to measurement errors, especially in long-term monitoring and high-precision measurement applications.

[0003] In the field of weighing, extremely high requirements are placed on measurement accuracy, stability, and reliability. Traditional resistance strain gauge load cells are susceptible to electromagnetic interference and have limited long-term stability, thus limiting their application in special environments such as flammable and explosive, highly corrosive, and high-electromagnetic-interference conditions. Fiber Bragg grating (FBG) sensors, due to their inherent safety and strong anti-interference capabilities, are considered a highly promising alternative. However, achieving high-precision and high-stability FBG weighing measurements remains a significant technical challenge in this field. Existing demodulation techniques often struggle to balance high resolution and strong anti-interference capabilities, especially under complex operating conditions, where signal drift and noise significantly impact performance, hindering the widespread adoption and application of FBGs in precision weighing.

[0004] Therefore, there is an urgent need to develop a new demodulation system and method that can enhance the ability to suppress environmental interference while ensuring high accuracy, thereby improving the practicality and reliability of fiber Bragg gratings in weighing and other high-requirement sensing scenarios. Summary of the Invention

[0005] The purpose of this invention is to provide a fiber optic grating demodulation system based on polarization measurement technology to improve the accuracy and stability of weighing.

[0006] The second objective of this invention is to provide a fiber Bragg grating demodulation method based on polarization measurement technology, implemented using the aforementioned fiber Bragg grating demodulation system based on polarization measurement technology. This method achieves high-precision fiber Bragg grating demodulation through fine-tuning and demodulation of the polarization state, combined with differential balance algorithm processing. Simultaneously, a high-precision grating weighing sensor is proposed, applying fiber Bragg grating demodulation technology to the weighing field, significantly improving the accuracy and stability of weighing.

[0007] The third objective of this invention is to provide a grating weighing sensor.

[0008] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0009] A fiber grating demodulation system based on polarization measurement technology includes:

[0010] Broadband light source, used as the light source required by the output grating demodulation system;

[0011] The circulator has a circulator a port, a circulator b port and a circulator c port, wherein the circulator a port is connected to the broadband light source;

[0012] A grating load cell is connected to port b of the circulator and is used to sense external weight signals.

[0013] The polarizer has a first polarizer port and a second polarizer port. The first polarizer port is connected to the circulator port c and is used to convert the specific wavelength light reflected by the grating load cell into polarized light.

[0014] The fiber optic delay device has a first fiber optic delay port and a second fiber optic delay port. The first fiber optic delay port is connected to the second polarizer port and is used to change the fiber delay time. ;

[0015] A polarization beam splitter is provided with a polarization beam splitter a port, a polarization beam splitter b port and a polarization beam splitter c port. The polarization beam splitter a port is connected to the second port of the fiber delayer and is used to split the optical signal into two orthogonal linear polarization components to obtain a first optical signal and a second optical signal, respectively.

[0016] A first photodetector is connected to port b of the polarization beam splitter and is used to convert a first optical signal from that port into a first voltage signal.

[0017] The second photodetector is connected to port c of the polarization beam splitter and is used to convert the second optical signal from the port into a second voltage signal.

[0018] A data acquisition card is connected to the first photodetector and the second photodetector and is used to acquire the first voltage signal and the second voltage signal;

[0019] The demodulation module, connected to the data acquisition card, is used to demodulate the measured weight of the grating weighing sensor based on the first voltage signal and the second voltage signal.

[0020] By way of limitation, the fiber optic delayer is a delay fiber or a delay crystal.

[0021] A fiber grating demodulation method based on polarization measurement technology, implemented using the aforementioned fiber grating demodulation system based on polarization measurement technology, includes the following steps:

[0022] S1. Acquire the first voltage signal and the second voltage signal;

[0023] S2. Signal processing yields the phase delay angle. information

[0024] S21. Digital Filtering: Perform digital filtering on the two voltage signals to suppress high-frequency noise;

[0025] S22. Balancing and obtaining the sum and difference signals: using pre-calibrated balance coefficients The two filtered signals are balanced and corrected, and their sum and difference signals are calculated.

[0026] S23. Normalize the obtained sum and difference signals to extract the phase delay angle that is only related to the change in fiber grating wavelength. information;

[0027] S3: Calculate the measured weight of the grating weighing sensor based on the phase delay angle information.

[0028] As a limitation, step S1 includes the following process: Light emitted from the broadband light source enters the circulator through port a and is output to the grating weighing sensor through port b. The grating weighing sensor reflects a specific wavelength light signal, which is then input into the circulator through port b. The specific wavelength light signal is further output from port c and enters the polarizer, where it is polarized into linearly polarized light. After entering the fiber delay unit and polarization beam splitter, the specific wavelength light signal is split into two orthogonal linearly polarized components, resulting in a first light signal and a second light signal. The first light signal is converted into a first voltage signal after passing through the first photodetector. The second optical signal is converted into a second voltage signal after passing through the second photodetector. .

[0029] As a further limitation, the balance coefficient The following calibration steps are predetermined: a tunable light source is selected instead of a broadband light source and a grating load cell as the system input; a phase delay angle is induced by periodic wavelength sweeping. The change; at this time, the voltage signals output by the first photodetector and the second photodetector are respectively... and Their expressions are as follows: , ,in, , These represent the transmission loss coefficients of the two optical path systems, The photoelectric conversion gain of the first photodetector. The photoelectric conversion gain of the second photodetector; summation using the definition of variance. and To achieve balance, determine the balance coefficient when the AC component reaches its minimum value. .

[0030] As a further limitation, in real-time measurements, a balance coefficient is used. Calculate the first voltage signal after passing through the weighing sensor. Second voltage signal The balancing results; and the signal: , poor signal: ;

[0031] Extract the phase delay angle that is only related to the wavelength variation of the fiber grating. information: .

[0032] As a further limitation, the phase delay angle The specific relationship with the change in grating wavelength is as follows:

[0033]

[0034] in, The delay time generated by the fiber optic delayer. At the speed of light, This represents the change in the center wavelength of the grating load cell. The center wavelength, This refers to the change in optical frequency caused by the change in wavelength.

[0035] By calibrating the weight factor The weight measured by the grating load cell is obtained. : .

[0036] A grating load cell is applicable to the fiber grating demodulation system based on polarization measurement technology described above. The grating load cell includes: an elastic component, a first grating fixing component, a second grating fixing component, a base shell, a fiber grating, and bolts.

[0037] The elastic component is cylindrical in shape, with a weighing contact surface at the top, grating fiber outlets on both sides, a first grating fixing component and a second grating fixing component inside, and a threaded hole at the bottom;

[0038] The first grating fixing assembly and the second grating fixing assembly each include a pair of fixing bolts and a pair of reinforcing bolts; the fixing bolts of the first grating fixing assembly are left-hand bolts, and the fixing bolts of the second grating fixing assembly are right-hand bolts;

[0039] The bottom shell is provided with a threaded hole corresponding to the bottom threaded hole of the elastic component, and is fixed to the elastic component by the bolt;

[0040] The two ends of the fiber optic grating are respectively fixed between the fixing bolts of the first grating fixing assembly and the fixing bolts of the second grating fixing assembly.

[0041] As a limitation, the planes where the fixing bolt and the reinforcing bolt are located are perpendicular to each other, and the fixing bolt and the fiber outlet of the grating of the elastic component are on the same plane.

[0042] As a second limitation, the fixing bolt is used to generate a preload on the fiber Bragg grating, and the reinforcing bolt is used to maintain a constant preload on the fiber Bragg grating by the fixing bolt.

[0043] The present invention, by adopting the above-described technical solution, achieves the following technical advancements compared to existing technologies:

[0044] (1) Achieved high-precision and high-stability fiber optic grating demodulation and weighing measurement: This invention introduces polarization measurement technology to convert the wavelength change information of the fiber optic grating into the phase delay information of polarized light for demodulation. This avoids the shortcomings of traditional intensity demodulation, which is susceptible to light source fluctuations and link loss interference, and also avoids the high dependence and high cost of direct wavelength demodulation on spectral analysis equipment. Combined with the subsequent differential balancing algorithm, common-mode noise can be effectively suppressed, significantly improving the measurement accuracy and long-term stability of the system. Specific experimental data show that within the 5-25Kg range, the relative measurement error of the system can be controlled within ±3%, verifying its high-precision characteristics.

[0045] (2) Significantly improved anti-interference capability and environmental adaptability of the system: The system of the present invention adopts dual-path differential detection and balancing algorithm, which can automatically compensate for systematic errors introduced by small loss changes of devices in the optical path (such as connectors, optical fibers themselves), power drift of the light source, and inherent performance differences (such as different responsivity) between the two photodetectors. This ability to actively eliminate common-mode interference enables the system of the present invention to maintain reliable measurement performance in complex industrial environments or in situations with weak disturbances, solving the technical problem of traditional methods being susceptible to environmental interference.

[0046] (3) A highly efficient and novel signal processing mechanism is provided: The signal processing flow of "balance adjustment-summation-difference-normalization" proposed in this invention is based on the principle of minimizing variance to dynamically determine the balance coefficient of the two voltage signals. This method can adaptively calibrate the asymmetry between the two signals, thereby accurately extracting the phase delay angle contributed solely by the change in fiber grating wavelength. This algorithm is computationally efficient and easy to implement in embedded systems or host computers, providing a feasible software solution for achieving real-time, online, and accurate demodulation.

[0047] (4) A high-precision fiber optic load cell with an ingenious structure and stable preload was designed: In this invention, the elastic component inside the sensor works in concert with the dual fixing components (left-hand and right-hand bolts), which can not only efficiently convert the external weight into the axial strain of the fiber optic grating, but also ensure that a constant and symmetrical preload is applied to and maintained on the fiber optic grating during fastening and long-term use. This avoids measurement nonlinearity, hysteresis or zero-point drift caused by preload relaxation or asymmetry, and ensures the consistency and reliability of the measurement from the source of sensing.

[0048] (5) Promoting the practical application of fiber Bragg grating technology in the field of precision weighing: This invention combines polarization demodulation, a highly sensitive optical measurement method, with a mechanical structure (sensor) optimized for weighing, forming a complete solution. This system inherits the advantages of fiber optic sensors, such as resistance to electromagnetic interference, corrosion resistance, and intrinsic safety, while achieving accuracy and stability comparable to or even superior to some traditional electrical weighing technologies. It provides a new technical path for high-precision weighing requirements in special environments (such as flammable and explosive environments, strong electromagnetic fields, and corrosive media), and expands the application boundaries of fiber Bragg gratings.

[0049] In summary, this invention has made systematic innovations in sensing mechanism, demodulation system, signal processing algorithm and sensor structure, effectively overcoming the shortcomings of existing technologies and providing a practical technical solution for achieving high-precision, high-stability and high-environmental-resistance fiber optic grating weighing measurement. Attached Figure Description

[0050] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0051] In the attached diagram:

[0052] Figure 1 This is a schematic diagram of the fiber grating demodulation system based on polarization measurement technology provided in Embodiment 1 of the present invention;

[0053] Figure 2 for Figure 1 The diagram shows the port definition of the circulator shown.

[0054] Figure 3 for Figure 1 A schematic diagram of the port definition of the polarization beam splitter shown in the figure;

[0055] Figure 4This is a schematic diagram of the front structure of the grating weighing sensor provided in Embodiment 3 of the present invention;

[0056] Figure 5 for Figure 4 The diagram shows the reverse side structure of the grating weighing sensor.

[0057] Figure 6 for Figure 4 A cross-sectional view of the internal structure of the grating load cell shown.

[0058] Figure 7 This is an experimental verification curve showing the relationship between the weight measured using the system, method, and sensor of this invention and the actual weight.

[0059] In the diagram: 1. Broadband light source; 2. Circulator; 3. Grating load cell; 4. Polarizer; 5. Fiber optic delayer; 6. Polarization beam splitter; 7. First photodetector; 8. Second photodetector; 9. Data acquisition card; 10. Demodulation module; 301. Elastic component; 302. Weighing contact surface; 303. Grating fiber outlet; 304. Bottom shell; 305. Bolt; 306. First grating fixing component; 307. Second grating fixing component; 308. Left-hand fixing bolt; 309. Right-hand fixing bolt; 3010. Reinforcing bolt; 3011. Fiber grating. Detailed Implementation

[0060] The preferred embodiments of the present invention will now be described with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0061] Example 1

[0062] This embodiment provides a complete fiber optic grating demodulation system based on polarization measurement technology, the structure of which is as follows: Figure 1 As shown.

[0063] The demodulation system in this embodiment mainly includes the following components: broadband light source 1, circulator 2, grating weighing sensor 3, polarizer 4, fiber optic delayer 5, polarization beam splitter 6, first photodetector 7, second photodetector 8, data acquisition card 9, and demodulation module 10. The following provides a detailed description of each component.

[0064] Broadband light source 1: Amplified spontaneous emission (ASE) light source with a center wavelength of 1550nm is used to provide broadband light for the entire system.

[0065] Circulator 2: such as Figure 2 As shown, it is a three-port optical circulator, defined with circulator port a, circulator port b, and circulator port c. Circulator port a is connected to the output of broadband light source 1 via a single-mode optical fiber.

[0066] Grating load cell 3: Used to sense external weight and convert it into wavelength shift of the fiber optic grating. Its input / output fiber optic cable is connected to port b of the circulator.

[0067] Polarizer 4: This is an online fiber optic polarizer with a first polarizer port and a second polarizer port. The first polarizer port is connected to port c of the circulator via a single-mode fiber and is used to convert the narrowband light reflected back from the grating load cell 3 into linearly polarized light.

[0068] Fiber optic delayer 5: In this embodiment, a section of polarization-maintaining fiber with precisely controlled length is used as the delay fiber, which generates a delay time. It is a fixed value. The fiber optic delayer 5 has a first fiber optic delayer port and a second fiber optic delayer port, wherein the first fiber optic delayer port is connected to the second polarizer port.

[0069] Polarization beam splitter 6: such as Figure 3 As shown, it is an optical fiber polarization beamsplitter, equipped with polarization beamsplitter port a, polarization beamsplitter port b, and polarization beamsplitter port c. Polarization beamsplitter port a is connected to the second port of the optical fiber delayer and is used to decompose the delayed linearly polarized light into two orthogonal linearly polarized components, namely the first optical signal and the second optical signal, which are output from polarization beamsplitter port b and polarization beamsplitter port c, respectively.

[0070] Both the first photodetector 7 and the second photodetector 8 are InGaAs photodiodes, with a response wavelength covering 1550nm. The photosensitive surface of the first photodetector 7 is aligned with port b of the polarization beam splitter via an optical fiber jumper, used to receive the first optical signal and convert it into a first voltage signal. The second photodetector 8 is aligned with port c of the polarization beam splitter in the same manner to generate the second voltage signal. .

[0071] Data acquisition card 9: Employs a high-speed, high-precision analog-to-digital converter card. Its two analog input channels are electrically connected to the output terminals of the first photodetector 7 and the second photodetector 8, respectively, to synchronously acquire two voltage signals. and .

[0072] Demodulation module 10: This is a computer or embedded processor equipped with a dedicated demodulation algorithm. The demodulation module 10 communicates with the data acquisition card 9 via a bus, receives the acquired voltage signal data, and performs subsequent signal processing and weight calculation.

[0073] The working principle of this embodiment is briefly described as follows: Light emitted from the broadband light source 1 is guided by the circulator 2 into the grating weighing sensor 3. The specific wavelength light reflected back from the sensor is guided by the circulator 2 to the polarizer 4 and converted into linearly polarized light. After being introduced with a fixed delay by the fiber optic delayer 5, it is split into two orthogonally polarized beams by the polarization beam splitter 6 and received by two photodetectors respectively. Finally, the two electrical signals containing wavelength-phase information are sent to the demodulation module 10 for processing, thereby obtaining a high-precision weight measurement value.

[0074] Example 2

[0075] This embodiment provides a fiber optic grating demodulation method based on polarization measurement technology, implemented using Embodiment 1, specifically including steps S1 to S3. Each step will be described in detail below.

[0076] S1. Obtain the first voltage signal Second voltage signal

[0077] The broadband light source 1 is activated, and the light it emits enters through port a of the circulator, exits through port b of the circulator, and is transmitted to the grating load cell 3. The fiber grating inside the grating load cell 3 reflects the light signal near its center wavelength. This reflected light signal returns along the original path, enters through port b of the circulator, and exits through port c of the circulator. This light signal of a specific wavelength then enters the polarizer 4, where it is polarized into a single linearly polarized light. This linearly polarized light enters the fiber optic delayer 5 and undergoes a fixed time delay. Subsequently, the optical signal enters the polarization beam splitter 6, where it is decomposed into two linearly polarized components with mutually orthogonal vibration directions, namely the first optical signal and the second optical signal. These are received by the first photodetector 7 and the second photodetector 8, respectively, and converted into the first voltage signal. Second voltage signal Data acquisition card 9 synchronously acquires these two voltage signals and transmits them to demodulation module 10.

[0078] S2. Signal processing yields the phase delay angle. information

[0079] The demodulation module 10 first processes the acquired first voltage signal. Second voltage signal Preprocessing mainly includes the following two steps:

[0080] S21. Digital Filtering: Perform digital filtering on the two voltage signals to suppress high-frequency noise.

[0081] S22. Balancing and obtaining the sum and difference signals: using pre-calibrated balancing coefficients The two filtered signals are balanced and corrected, and their sum and difference signals are calculated.

[0082] Balance coefficient The following calibration steps are predetermined: a tunable light source is selected to replace broadband light source 1 and grating load cell 3 as system input, and a phase delay angle is induced by periodic wavelength sweeping. The change. At this time, the voltage signals output by the first photodetector 7 and the second photodetector 8 are respectively... and Their expressions are as follows: , ,in, , These represent the transmission loss coefficients of the two optical path systems, The photoelectric conversion gain of the first photodetector 7, Let be the photoelectric conversion gain of the second photodetector 8. Summation is performed using the definition of variance. and To achieve balance, determine the balance coefficient when the AC component reaches its minimum value. .

[0083] In real-time measurements, this balance coefficient is used. Calculate the first voltage signal after passing through the weighing sensor. Second voltage signal The balancing result. And the signal: , poor signal: .

[0084] This step aims to compensate for the difference in responsivity between the two photodetectors and the asymmetric loss of the optical path, and to separate the phase term containing sensing information into the difference signal, while the sum signal mainly reflects the common change in light intensity.

[0085] S23. Calculate the phase delay angle

[0086] By normalizing the sum and difference signals obtained from the preprocessing, the phase delay angle, which is only related to the wavelength variation of the fiber grating, can be extracted. information: This operation eliminates common-mode interference such as light intensity fluctuations.

[0087] S3, based on the phase delay angle Calculate and measure weight

[0088] Because the grating weighing sensor 3 is affected by changes in weight, causing changes in the grating wavelength, its phase delay angle... The specific relationship with the grating wavelength is as follows: ,in, The delay time generated by the fiber optic delayer. At the speed of light, This represents the change in the center wavelength of the grating load cell 3. The center wavelength, This refers to the change in optical frequency caused by the change in wavelength. This is due to the change in the center wavelength of the grating load cell 3. The phase retardation angle is proportional to the strain (i.e., weight) applied to it, therefore... It is also directly proportional to weight. Through preliminary calibration experiments, a weight coefficient can be determined. This makes it possible to measure weight It can be simply calculated as follows: .

[0089] Example 3

[0090] This embodiment describes in detail the specific structure of a high-precision grating weighing sensor 3 applicable to Embodiment 1, such as... Figure 4 , Figure 5 and Figure 6 As shown.

[0091] The grating load cell 3 mainly includes: an elastic component 301, a first grating fixing component 306, a second grating fixing component 307, a fiber optic grating 3011, a base shell 304, and bolts 305.

[0092] Elastic component 301: Made of alloy steel, with an overall cylindrical structure. Its top is the weighing contact surface 302, used to support the object being measured. Optical fiber outlets 303 are located on both sides of the cylinder for inserting and withdrawing optical fibers; an internal cavity is provided to accommodate the fixing components; and threaded holes are machined at the bottom.

[0093] The first grating fixing assembly 306 and the second grating fixing assembly 307 are symmetrically arranged at both ends of the cavity inside the elastic assembly 301. Each fixing assembly includes a pair of fixing bolts and a pair of reinforcing bolts 3010. Crucially, the fixing bolts of the first grating fixing assembly 306 are left-handed fixing bolts 308, while the fixing bolts of the second grating fixing assembly 307 are right-handed fixing bolts 309. The axes of the left-handed fixing bolts 308 and the right-handed fixing bolts 309 are on the same horizontal plane as the axis of the grating fiber outlet 303. The axes of the pair of reinforcing bolts 3010 are perpendicular to the plane containing the axes of the pair of fixing bolts.

[0094] Fiber Bragg grating 3011: A fiber Bragg grating with a center wavelength of 1550nm and a grating length of 10mm is selected. After the coating is stripped from both ends, it is fixed to the left-hand fixing bolt 308 and the right-hand fixing bolt 309 by high-strength adhesive and a winding method.

[0095] Bottom shell 304 and bolt 305: The bottom shell 304 is provided with a through hole. The bolt 305 is engaged with the threaded hole at the bottom of the elastic component 301 to seal the entire sensor base, which plays a role in protecting the internal structure and isolating the environment.

[0096] The assembly and working principle of the grating load cell 3 in this embodiment are as follows:

[0097] First, one end of the fiber Bragg grating 3011 is fixed to the left-hand fixing bolt 308. Then, the right-hand fixing bolt 309 is rotated to apply axial preload to the fiber Bragg grating. Because the bolts at both ends rotate in opposite directions, the fiber Bragg grating is uniformly tightened without twisting during tightening. Once the preload reaches the set value, the reinforcing bolts 3010 on both sides are tightened, their ends pressing against the sides of the fixing bolts to prevent loosening, thus ensuring a constant preload on the fiber Bragg grating. This design ensures the long-term stability of the preload. Finally, the bottom shell 304 is placed on top and secured with bolts 305.

[0098] When weight is applied to the weighing contact surface 302, the elastic component 301 undergoes slight deformation. This deformation is transmitted to the fiber optic grating 3011 through the fixing components at both ends, causing axial strain and resulting in a drift of its reflection center wavelength. By demodulating this wavelength drift using the system and method described in Examples 1 and 2, high-precision and high-stability weight measurement can be achieved.

[0099] The following experimental test results demonstrate the accuracy of the demodulation system, demodulation method, and grating weighing sensor 3 of this invention.

[0100] A fiber grating 3011 with a center wavelength of 1550±0.3nm, bandwidth of 0.2nm, grating length of 10mm, and reflectivity of 90% was selected and fixed between the elastic component 301 and the fixing component of the grating load cell 3, thus completing the overall assembly of the grating load cell 3. The grating load cell 3 was connected to the demodulation system and kept at a constant room temperature. Different weights of 5-25kg were applied to the grating load cell 3 at 5kg intervals three times. After processing the two detected signals, the change in optical frequency phase caused by the center wavelength of the fiber grating 3011 under different weights was obtained. After calibration, the following relationship was obtained:

[0101]

[0102] After completing the system weighing calibration according to the above formula, apply different weights of 5-25 kg to the grating weighing sensor 3 three times at 5 kg intervals. The measured weight of the system and the actual weight of the weight are as follows: Figure 7As shown in the figure, the measured weight is in good agreement with the actual weight. The calculated relative errors are -1.15%, 2.82%, 2.64%, 0.76%, and 1.70%, respectively, which verifies the accuracy of the system method and the grating weighing sensor 3.

Claims

1. A fiber optic grating demodulation system based on polarization measurement technology, characterized in that, include: Broadband light source, used as the light source required by the output grating demodulation system; The circulator has a circulator a port, a circulator b port and a circulator c port, wherein the circulator a port is connected to the broadband light source; A grating load cell is connected to port b of the circulator and is used to sense external weight signals. The polarizer has a first polarizer port and a second polarizer port. The first polarizer port is connected to the circulator port c and is used to convert the specific wavelength light reflected by the grating load cell into polarized light. The fiber optic delay device has a first fiber optic delay port and a second fiber optic delay port. The first fiber optic delay port is connected to the second polarizer port and is used to change the fiber delay time. ; A polarization beam splitter is provided with a polarization beam splitter a port, a polarization beam splitter b port and a polarization beam splitter c port. The polarization beam splitter a port is connected to the second port of the fiber delayer and is used to split the optical signal into two orthogonal linear polarization components to obtain a first optical signal and a second optical signal, respectively. A first photodetector is connected to port b of the polarization beam splitter and is used to convert a first optical signal from that port into a first voltage signal. The second photodetector is connected to port c of the polarization beam splitter and is used to convert the second optical signal from the port into a second voltage signal. A data acquisition card is connected to the first photodetector and the second photodetector and is used to acquire the first voltage signal and the second voltage signal; The demodulation module, connected to the data acquisition card, is used to demodulate the measured weight of the grating weighing sensor based on the first voltage signal and the second voltage signal.

2. The fiber optic grating demodulation system based on polarization measurement technology according to claim 1, characterized in that, The fiber delayer is a delay fiber or a delay crystal.

3. A fiber optic grating demodulation method based on polarization measurement technology, implemented using the fiber optic grating demodulation system based on polarization measurement technology as described in claim 1 or 2, characterized in that... The method includes the following steps: S1. Acquire the first voltage signal and the second voltage signal; S2. Signal processing yields the phase delay angle. information S21. Digital Filtering: Perform digital filtering on the two voltage signals to suppress high-frequency noise; S22. Balancing and obtaining the sum and difference signals: using pre-calibrated balance coefficients The two filtered signals are balanced and corrected, and their sum and difference signals are calculated. S23. Normalize the obtained sum and difference signals to extract the phase delay angle that is only related to the change in fiber grating wavelength. information; S3: Calculate the measured weight of the grating weighing sensor based on the phase delay angle information.

4. The fiber optic grating demodulation method based on polarization measurement technology according to claim 3, characterized in that, Step S1 includes the following process: Light emitted from the broadband light source enters the circulator through port a and is output to the grating load cell through port b. The grating load cell reflects a specific wavelength light signal, which is then input into the circulator through port b. The specific wavelength light signal is further output from port c and enters the polarizer, where it is polarized into linearly polarized light. After entering the fiber delay unit and polarization beam splitter, the specific wavelength light signal is split into two orthogonal linearly polarized components, resulting in a first optical signal and a second optical signal. The first optical signal is converted into a first voltage signal after passing through the first photodetector. The second optical signal is converted into a second voltage signal after passing through the second photodetector. .

5. The fiber optic grating demodulation method based on polarization measurement technology according to claim 4, characterized in that, Balance coefficient The following calibration steps are predetermined: a tunable light source is selected instead of a broadband light source and a grating load cell as the system input; a phase delay angle is induced by periodic wavelength sweeping. The change; at this time, the voltage signals output by the first photodetector and the second photodetector are respectively... and Their expressions are as follows: , ,in, , These represent the transmission loss coefficients of the two optical path systems, The photoelectric conversion gain of the first photodetector. The photoelectric conversion gain of the second photodetector; summation using the definition of variance. and To achieve balance, determine the balance coefficient when the AC component reaches its minimum value. .

6. The fiber optic grating demodulation method based on polarization measurement technology according to claim 5, characterized in that, In real-time measurements, the balance coefficient is used. Calculate the first voltage signal after passing through the weighing sensor. Second voltage signal The balancing results; and the signal: , poor signal: ; Extract the phase delay angle that is only related to the wavelength variation of the fiber grating. information: .

7. The fiber optic grating demodulation method based on polarization measurement technology according to claim 6, characterized in that, Phase delay angle The specific relationship with the change in grating wavelength is as follows: in, The delay time generated by the fiber optic delayer. At the speed of light, This represents the change in the center wavelength of the grating load cell. The center wavelength, This refers to the change in optical frequency caused by the change in wavelength. By calibrating the weight factor The weight measured by the grating load cell is obtained. : .

8. A grating weighing sensor, applicable to the fiber optic grating demodulation system based on polarization measurement technology as described in claim 1 or 2, characterized in that, The grating load cell includes: an elastic component, a first grating fixing component, a second grating fixing component, a base shell, a fiber optic grating, and bolts; The elastic component is cylindrical in shape, with a weighing contact surface at the top, grating fiber outlets on both sides, a first grating fixing component and a second grating fixing component inside, and a threaded hole at the bottom; The first grating fixing assembly and the second grating fixing assembly each include a pair of fixing bolts and a pair of reinforcing bolts; the fixing bolts of the first grating fixing assembly are left-hand bolts, and the fixing bolts of the second grating fixing assembly are right-hand bolts; The bottom shell is provided with a threaded hole corresponding to the bottom threaded hole of the elastic component, and is fixed to the elastic component by the bolt; The two ends of the fiber optic grating are respectively fixed between the fixing bolts of the first grating fixing assembly and the fixing bolts of the second grating fixing assembly.

9. The grating weighing sensor according to claim 8, characterized in that, The planes of the fixing bolt and the reinforcing bolt are perpendicular to each other, and the fixing bolt and the fiber outlet of the grating of the elastic component are on the same plane.

10. The grating weighing sensor according to claim 8, characterized in that, The fixing bolt is used to generate a preload on the fiber Bragg grating, and the reinforcing bolt is used to maintain a constant preload on the fiber Bragg grating by the fixing bolt.

Images