A fiber optic sensor based on laser feedback

Abstract

This invention discloses a laser feedback-based fiber optic sensor, belonging to the field of fiber optic sensing technology. It includes a dual-frequency orthogonal laser source module, a fiber optic sensing probe module, a feedback signal acquisition and processing module, and a data output and control module. The source module generates dual-frequency lasers with adjustable frequency difference and orthogonal polarization; the sensing probe module consists of multiple fiber Bragg gratings with different center wavelengths connected in series, used for reflection to form feedback light; the signal processing module employs a dual-frequency orthogonal demodulation algorithm and a multi-parameter feature extraction algorithm, combined with adaptive filtering technology, to achieve high-precision synchronous measurement and anti-interference processing of temperature, pressure, vibration, and displacement. This invention solves the cross-interference problem of traditional sensors in multi-parameter measurements and is suitable for health monitoring and physical quantity detection in complex environments such as aerospace, deep-sea oil and gas pipelines, and precision machinery.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a fiber optic sensor based on laser feedback. Background Technology

[0002] Currently, laser feedback fiber optic sensors have gained widespread attention in the field of industrial measurement due to their advantages such as high sensitivity and compact structure. However, existing technical solutions have the following limitations: Limitations of Single-Frequency Laser Feedback: Existing solutions mostly use single-frequency lasers as the light source. When external physical quantities (such as temperature, pressure, and vibration) change, measurement can only be achieved through amplitude or phase changes of a single frequency signal. This makes it impossible to distinguish the cross-interference of different physical quantities on the signal, leading to a significant decrease in accuracy when measuring multiple parameters. For example, in scenarios where temperature and pressure are measured simultaneously, the change in fiber refractive index caused by temperature changes will be superimposed on the fiber deformation signal caused by pressure, making accurate decoupling difficult.

[0003] Feedback signal processing is simple: Traditional solutions typically use simple Fourier transforms or filtering algorithms to process feedback signals, which cannot effectively extract feature information from weak signals. In harsh environments such as strong electromagnetic interference and complex vibrations, the signal-to-noise ratio is extremely low, and the lower limit of measurement is high, making it difficult to meet the requirements of high-precision measurement. For example, in the measurement of vibration of aero-engine blades, the strong electromagnetic noise generated by engine operation can mask the weak feedback signal of blade vibration, leading to distortion of measurement data.

[0004] To address the aforementioned issues, this invention proposes a fiber optic sensor based on dual-frequency orthogonal laser feedback. Through innovative light source design, signal processing algorithms, and sensor structure, it achieves high-precision synchronous measurement of multiple parameters and possesses strong anti-interference capabilities and environmental adaptability. Summary of the Invention

[0005] The purpose of this invention is to provide a fiber optic sensor based on laser feedback, which overcomes the shortcomings of traditional sensors in terms of measurement accuracy, multi-parameter compatibility, and anti-interference capability.

[0006] To achieve the above objectives, the present invention provides a fiber optic sensor based on laser feedback, comprising: Dual-frequency orthogonal laser source module, used to generate dual-frequency lasers with adjustable frequency difference and orthogonal polarization direction; The fiber optic sensing probe module includes a fiber optic coupler, a fiber Bragg grating sensing unit, and a reflective film layer. The fiber Bragg grating sensing unit is composed of multiple fiber Bragg gratings with different center wavelengths connected in series, and is used to receive the dual-frequency laser and reflect it to form feedback light. The feedback signal acquisition and processing module includes a photodetector, a high-speed data acquisition card, and a signal processing unit, which is used to convert the feedback light into an electrical signal and process it in real time to extract physical quantity measurement information. The data output and control module includes a microprocessor, a display screen, a data storage unit, and a communication interface, used to output measurement data and achieve remote control; The dual-frequency orthogonal laser source module, fiber optic sensing probe module, feedback signal acquisition and processing module, and data output and control module are connected by optical fiber or cable. The signal processing unit uses a dual-frequency orthogonal demodulation algorithm and a multi-parameter feature extraction algorithm to process the feedback signal.

[0007] Preferably, the dual-frequency orthogonal laser source module includes a dual-frequency laser based on lithium niobate crystal electro-optic modulation, which generates dual-frequency lasers with frequencies f1 and f2, the frequency difference of which is adjustable in the range of 10-100MHz, and the polarization directions are perpendicular to each other; the dual-frequency orthogonal laser source module also has a built-in temperature control unit and a current stabilization unit, with a temperature control accuracy of ±0.01℃ and a current stability of ±0.1mA.

[0008] Preferably, the center wavelengths of the multiple fiber Bragg gratings in the fiber Bragg grating sensing unit are spaced 5 nm apart in the range of 1520-1560 nm, respectively corresponding to temperature, pressure, and vibration measurements; the fiber optic sensing probe module also includes a protective shell, which is made of titanium alloy, filled with inert gas, and has heat sinks on its surface.

[0009] Preferably, the photodetector is a dual-channel balanced detector used to simultaneously receive feedback light and reference light; the high-speed data acquisition card has a resolution of 16 bits and a sampling rate adjustable from 100MS / s to 1GS / s; the signal processing unit is implemented based on FPGA; the dual-frequency quadrature demodulation algorithm includes mixing, filtering, and phase detection steps; and the multi-parameter feature extraction algorithm distinguishes different physical quantities based on the amplitude, phase, and rate of change of the frequency offset signal.

[0010] Preferably, the signal processing unit also integrates an interference suppression algorithm, which employs adaptive filtering technology to remove electromagnetic interference and environmental noise.

[0011] Preferably, the microprocessor of the data output and control module is an ARM Cortex-A9 processor with a main frequency of 1GHz; the display screen is a 7-inch touch screen with a resolution of 1280x800; the data storage unit is a 128GB SSD solid-state drive; and the communication interface includes an Ethernet interface, an RS485 interface, a USB interface, and a wireless WiFi module.

[0012] Preferably, the operating environment temperature of the fiber optic sensor is -40℃ to 85℃, the humidity is 0-95%RH, the protection level is IP67, the power supply voltage is 12-24VDC, and the power consumption is less than 10W.

[0013] Preferably, the measurement parameters of the fiber optic sensor include temperature, pressure, vibration, and displacement. The temperature measurement range is -50℃ to 200℃ with an accuracy of ±0.05℃; the pressure measurement range is 0-100MPa with an accuracy of ±0.1%FS; the vibration measurement range is 0-10kHz with an accuracy of ±0.5%FS; and the displacement measurement range is 0-10mm with an accuracy of ±10nm.

[0014] Preferably, the fiber optic sensor is also used for health monitoring of aerospace equipment, monitoring of deep-sea oil and gas pipelines, or measurement of vibration and displacement of precision machinery.

[0015] The present invention also provides a measurement method based on an optical fiber sensor, characterized by comprising the following steps: S1. Dual-frequency orthogonal laser is generated through a dual-frequency orthogonal laser source module; S2. The dual-frequency laser is divided into a probe light and a reference light. The probe light enters the fiber optic grating sensing unit and is reflected to form a feedback light. S3. Acquire the feedback light and reference light, convert them into electrical signals and perform dual-frequency quadrature demodulation to obtain the frequency offset signal; S4. Differentiate temperature, pressure, and vibration physical quantities through a multi-parameter feature extraction algorithm and output measurement data.

[0016] Therefore, the fiber optic sensor based on laser feedback using the above structure of the present invention has the following beneficial effects: (1) Multi-parameter synchronous high-precision measurement: This invention uses a combination of dual-frequency orthogonal laser light source and series FBG sensing unit to achieve synchronous measurement of temperature, pressure, vibration and displacement through multi-parameter feature extraction algorithm, which solves the problem of cross interference in multi-parameter measurement of traditional sensors.

[0017] (2) Strong anti-interference capability: The signal processing unit of the present invention integrates an adaptive filtering interference suppression algorithm, which can effectively remove electromagnetic interference and environmental noise. It can still work stably in harsh environments with a signal-to-noise ratio as low as 10dB, and the signal distortion rate is less than 1%, which meets the measurement requirements of strong interference scenarios.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a fiber optic sensor based on laser feedback according to the present invention; Figure 2This is a schematic diagram of the FPGA signal processing flow of a fiber optic sensor based on laser feedback according to the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0022] Example like Figure 1-2 As shown, the present invention provides a fiber optic sensor based on laser feedback, including a dual-frequency orthogonal laser source module, a fiber optic sensing probe module, a feedback signal acquisition and processing module, and a data output and control module.

[0023] Dual-frequency orthogonal laser source module: This module uses a dual-frequency laser based on lithium niobate (LiNbO3) crystal electro-optic modulation. Core components include: Laser diode: Outputs continuous laser light with a wavelength of 1550nm and a power of 10mW.

[0024] Electro-optic modulator: By applying an AC voltage (frequency adjustable range of 10-100MHz), the laser frequency is split to generate dual-frequency lasers with frequencies of f1 and f2, and the frequency difference Δf=|f1-f2| can be precisely adjusted by voltage.

[0025] Polarization beam splitter: ensures that the polarization directions of the dual-frequency lasers are perpendicular (orthogonal) to each other, forming an orthogonal polarization state.

[0026] Control Unit: Built-in temperature control unit (using semiconductor cooler TEC, temperature control accuracy ±0.01℃) and current stabilization unit (current stability ±0.1mA), which are adjusted in real time through PID algorithm to ensure long-term stability of laser frequency and power.

[0027] Output interface: Dual-frequency laser output is sent to the fiber optic sensing probe module via the FC / APC fiber optic connector.

[0028] Fiber optic sensing probe module: This module adopts an all-fiber structure, and its specific components are as follows: Fiber Optic Coupler: A 1×2 type coupler that splits the incident dual-frequency laser into a probe beam (80% power) and a reference beam (20% power). The laser is efficiently coupled into the sensing fiber through the fiber optic coupler, with a coupling efficiency greater than 95%, ensuring stable distribution of optical power, thereby reducing insertion loss and improving the measurement signal-to-noise ratio.

[0029] Fiber Bragg grating sensing unit: Composed of multiple fiber Bragg gratings (FBGs) connected in series, with the center wavelength of each FBG spaced 5nm apart in the range of 1520-1560nm (e.g., 1520nm corresponds to temperature measurement, 1530nm to pressure measurement, and 1540nm to vibration measurement). The FBGs are written into single-mode optical fiber using ultraviolet exposure technology, and all have a reflectivity greater than 90%.

[0030] The coupling process employs a tapered fiber design, which optimizes mode field matching, ensuring that the dual-frequency lasers maintain polarization orthogonality during transmission and avoiding signal distortion caused by modal dispersion.

[0031] Reflective film layer: A multilayer high-reflectivity TiO2 / SiO2 film (reflectivity >99%) is deposited at the end of the optical fiber to reflect the probe light and form the feedback light.

[0032] Protective shell: Made of titanium alloy TC4 material, filled with inert gas (such as argon), with aluminum heat sink on the surface, temperature range -50℃ to 200℃, protection level IP67, suitable for corrosive environments (such as deep sea or chemical scene).

[0033] Feedback signal acquisition and processing module: This module is responsible for the conversion of optical signals to electrical signals and real-time processing. Photodetector: Employs a dual-channel balanced detector (such as Thorlabs PDB450C) with a bandwidth of 1GHz, simultaneously receiving feedback light and reference light, and outputting a differential current signal to suppress common-mode noise.

[0034] High-speed data acquisition card: 16-bit resolution, with a programmable sampling rate adjustable from 100MS / s to 1GS / s, supporting simultaneous acquisition of dual-channel signals.

[0035] Signal processing unit: Implemented based on Xilinx Artix-7 series FPGA, with the following built-in algorithms: Dual-frequency quadrature demodulation algorithm: The feedback optical signal and the reference optical signal are mixed (multiplier), low-pass filtered (cutoff frequency 50MHz) and phase detected (based on CORDIC algorithm) to extract the frequency offset signals Δf1 and Δf2.

[0036] Multi-parameter feature extraction algorithm: Distinguish physical quantities based on the amplitude, phase, and rate of change of Δf1 and Δf2. For example: Temperature changes cause Δf1 and Δf2 to drift slowly in the same direction (rate of change < 1 Hz / s); Pressure changes cause Δf1 and Δf2 to change rapidly in opposite directions (rate of change > 100 Hz / s); The vibration signal is characterized by high-frequency modulation of Δf1 and Δf2 (frequency 0-10kHz).

[0037] Interference suppression algorithm: The LMS (Least Mean Square) adaptive filtering technique is used to estimate and subtract environmental noise (such as 50Hz power frequency interference and electromagnetic pulse) in real time.

[0038] Data Output and Control Module: This module integrates data processing and communication functions. Microprocessor: ARM Cortex-A9 processor, 1GHz, running Linux system, responsible for data calibration (based on polynomial fitting), trend analysis (moving average algorithm) and anomaly alarm (threshold trigger).

[0039] Display: 7-inch capacitive touchscreen with a resolution of 1280×800, displaying measurement curves and parameters (such as temperature, pressure, and vibration spectrum) in real time.

[0040] Data storage unit: 128GB SSD solid-state drive, supports data cyclic storage (up to 30 days).

[0041] Communication interface: The Ethernet interface (1000BASE-T) is used for high-speed data transmission; The RS485 interface supports the Modbus protocol for industrial fieldbus integration. The USB interface is used for data export and firmware upgrades; The WiFi module (IEEE 802.11ac) enables wireless remote monitoring.

[0042] Power management: Input voltage 12-24VDC, internal DC-DC converter, total power consumption <10W.

[0043] Working principle and detailed process Laser emission and transmission: The dual-frequency orthogonal laser source module generates dual-frequency lasers with a frequency difference of Δf, which are transmitted to the fiber coupler via optical fiber. The coupler splits the laser into probe light (80%) and reference light (20%), and the probe light enters the fiber optic grating sensing unit.

[0044] Optical feedback generation: The probe light is transmitted in the FBG sensing unit. When external physical quantities (such as temperature and pressure) change, the center wavelength of the FBG shifts (Δλ), and the phase and frequency of the reflected light are modulated, forming feedback light. The feedback light and the reference light return to the photodetector through the same optical fiber.

[0045] Signal acquisition and processing: The photodetector converts the optical signal into an electrical signal, and the high-speed data acquisition card digitizes it at a sampling rate of 1 GS / s.

[0046] FPGA performs dual-frequency quadrature demodulation: Frequency mixing: The feedback signal is multiplied by the reference signal to obtain the difference frequency signal.

[0047] Filtering: The low-pass filter extracts the frequency offset components Δf1 and Δf2.

[0048] Feature extraction: Physical quantities are distinguished based on the time-domain characteristics of Δf1 and Δf2 (such as amplitude ratio and phase difference), and frequency shifts are converted into physical quantity values ​​by a lookup table method (for example, Δf1 is linearly related to temperature, and Δf2 is related to the square of pressure).

[0049] The interference suppression algorithm optimizes filter parameters in real time, improving the signal-to-noise ratio (typical value >60dB).

[0050] Data output and control: The microprocessor performs temperature compensation and nonlinear correction on the processed data and outputs the calibrated measurement value.

[0051] Data is uploaded to the monitoring center (such as a SCADA system) via a communication interface, and is also stored and displayed locally.

[0052] Users can set parameters or trigger automatic diagnostic mode via the touchscreen.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A fiber optic sensor based on laser feedback, characterized in that, include: Dual-frequency orthogonal laser source module, used to generate dual-frequency lasers with adjustable frequency difference and orthogonal polarization direction; The fiber optic sensing probe module includes a fiber optic coupler, a fiber Bragg grating sensing unit, and a reflective film layer. The fiber Bragg grating sensing unit is composed of multiple fiber Bragg gratings with different center wavelengths connected in series, and is used to receive the dual-frequency laser and reflect it to form feedback light. The feedback signal acquisition and processing module includes a photodetector, a high-speed data acquisition card, and a signal processing unit, which is used to convert the feedback light into an electrical signal and process it in real time to extract physical quantity measurement information. The data output and control module includes a microprocessor, a display screen, a data storage unit, and a communication interface, used to output measurement data and achieve remote control; The dual-frequency orthogonal laser source module, fiber optic sensing probe module, feedback signal acquisition and processing module, and data output and control module are connected by optical fiber or cable. The signal processing unit uses a dual-frequency orthogonal demodulation algorithm and a multi-parameter feature extraction algorithm to process the feedback signal.

2. The fiber optic sensor according to claim 1, characterized in that, The dual-frequency orthogonal laser source module includes a dual-frequency laser based on lithium niobate crystal electro-optic modulation, which generates dual-frequency lasers with frequencies f1 and f2. The frequency difference is adjustable in the range of 10-100MHz, and the polarization directions are perpendicular to each other. The dual-frequency orthogonal laser source module also has a built-in temperature control unit and a current stabilization unit. The temperature control accuracy is ±0.01℃, and the current stability is ±0.1mA.

3. The fiber optic sensor according to claim 1, characterized in that, The fiber Bragg gratings in the fiber Bragg grating sensing unit have center wavelengths spaced 5 nm apart in the range of 1520-1560 nm, corresponding to temperature, pressure, and vibration measurements, respectively. The fiber optic sensing probe module also includes a protective shell made of titanium alloy, filled with inert gas, and with heat sinks on its surface.

4. The fiber optic sensor according to claim 1, characterized in that, The photodetector is a dual-channel balanced detector used to simultaneously receive feedback light and reference light; the high-speed data acquisition card has a resolution of 16 bits and a sampling rate adjustable from 100MS / s to 1GS / s; the signal processing unit is implemented based on FPGA; the dual-frequency quadrature demodulation algorithm includes mixing, filtering, and phase detection steps; and the multi-parameter feature extraction algorithm distinguishes different physical quantities based on the amplitude, phase, and rate of change of the frequency offset signal.

5. The fiber optic sensor according to claim 4, characterized in that, The signal processing unit also integrates an interference suppression algorithm, which employs adaptive filtering technology to remove electromagnetic interference and environmental noise.

6. The fiber optic sensor according to claim 1, characterized in that, The microprocessor of the data output and control module is an ARM Cortex-A9 processor with a main frequency of 1GHz; the display screen is a 7-inch touch screen with a resolution of 1280x800; the data storage unit is a 128GB SSD solid-state drive; the communication interface includes an Ethernet interface, an RS485 interface, a USB interface, and a wireless WiFi module.

7. The fiber optic sensor according to claim 1, characterized in that, The fiber optic sensor operates in an ambient temperature range of -40℃ to 85℃, with a humidity range of 0-95%RH, an IP67 protection rating, a power supply voltage of 12-24VDC, and a power consumption of less than 10W.

8. The fiber optic sensor according to claim 1, characterized in that, The fiber optic sensor measures parameters including temperature, pressure, vibration, and displacement. The temperature measurement range is -50℃ to 200℃ with an accuracy of ±0.05℃; the pressure measurement range is 0-100MPa with an accuracy of ±0.1%FS; the vibration measurement range is 0-10kHz with an accuracy of ±0.5%FS; and the displacement measurement range is 0-10mm with an accuracy of ±10nm.

9. The fiber optic sensor according to claim 1, characterized in that, The fiber optic sensor is also used for health monitoring of aerospace equipment, monitoring of deep-sea oil and gas pipelines, or measurement of vibration and displacement of precision machinery.

10. A measurement method based on the fiber optic sensor according to any one of claims 1-9, characterized in that, Including the following steps: S1. Dual-frequency orthogonal laser is generated through a dual-frequency orthogonal laser source module; S2. The dual-frequency laser is divided into a probe light and a reference light. The probe light enters the fiber optic grating sensing unit and is reflected to form a feedback light. S3. Acquire the feedback light and reference light, convert them into electrical signals and perform dual-frequency quadrature demodulation to obtain the frequency offset signal; S4. Differentiate temperature, pressure, and vibration physical quantities through a multi-parameter feature extraction algorithm and output measurement data.

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