An interferometric sensing device and demodulation system, method for multiplexing

Abstract

An interferometric sensing device, demodulation system, and method for multiplexing are disclosed. The sensing device comprises multiple interferometric sensing units connected in series. Each interferometric sensing unit has two input terminals connected to an F-P cavity fiber optic sensor and a linearly chirped fiber grating sensor, respectively, and its output terminal connected to a coupler. The reflection bandwidth of the fiber grating in the linearly chirped fiber grating sensor exactly covers one period of the F-P cavity reflection spectrum, and the reflection wavelength ranges of the fiber gratings in the multiple interferometric sensing units do not overlap. The demodulation system includes a broadband light source, an interferometric sensing device, and a signal detector. This invention enables real-time measurement of multiple sensors on a single optical fiber, improves multiplexing capacity, simplifies the structure of the detection and demodulation system, reduces the number of optical fibers required, and lowers the system complexity.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to an interferometric sensing device and demodulation system for multiplexing. Background Technology

[0002] In fields such as structural health monitoring, oil drilling, and aerospace, temperature and strain are two key detection parameters. Traditional sensing technologies struggle to meet the precise and rapid response requirements of these environments. Interferometric fiber optic sensors, with their superior resistance to electromagnetic interference, compact structure, and high resolution, have become an ideal choice for temperature and strain monitoring. By monitoring the reflection spectrum of interferometric fiber optic sensors, minute changes in temperature or strain can be accurately detected, making their application in harsh environments increasingly widespread.

[0003] However, achieving high-capacity multiplexing at a low cost remains a crucial challenge in large-scale signal detection or structural health monitoring. As the number of sensors increases, the complexity of the multiplexing scheme also rises, increasing system design and operating costs. When multiple interferometric sensors are cascaded on a single optical fiber, crosstalk occurs from reflected signals from different sensors, making demodulation difficult. Furthermore, parallel operation of multiple sensing structures typically requires multiple optical fibers, further increasing system complexity. Therefore, designing feasible multiplexing methods for interferometric sensors and researching how to minimize crosstalk in the sensing path are indispensable aspects of optimizing and improving these sensors. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a reasonable design, simple structure and high signal detection efficiency for use as an interferometric sensing device and demodulation system.

[0005] The technical solution adopted to solve the above technical problems is: an interferometric sensing device for multiplexing, which is composed of multiple interferometric sensing units connected in series. The interferometric sensing unit is: the two input ends of the circulator are connected to the FP cavity fiber optic sensor and the linear chirped fiber grating sensor respectively, and the output end is connected to the coupler. The reflection bandwidth of the fiber grating of the linear chirped fiber grating sensor exactly covers one period of the FP cavity reflection spectrum, and the reflection wavelength ranges of the fiber gratings of the multiple interferometric sensing units do not overlap.

[0006] A demodulation system for a multiplexed interferometric sensing device includes a broadband light source, the interferometric sensing device, and a signal detector. The broadband light source emits C+L band laser light to the interferometric sensing device. The interferometric sensing device is connected to the signal detector. The light signal reflected back from the interferometric sensing device carries information about the physical quantity to be measured. The signal detector detects the wavelength and intensity changes of these light signals to obtain the physical quantity measured by each FP cavity sensor.

[0007] Preferably, the signal detector includes a collimator, a volume phase grating, a focusing lens, a linear InGaAs detector, and a data processor;

[0008] The collimator converts the incident signal into parallel light so that it can illuminate the volume phase grating;

[0009] The volume phase grating is used to spatially separate optical signals of different wavelengths;

[0010] The focusing lens is used to focus the optical signal output by the volume phase grating onto the linear InGaAs detector;

[0011] On the linear InGaAs detector, each pixel detects light signals within a specific wavelength range, selects pixel units that match the center wavelengths of each interferometric sensor, and outputs the power of the reflected spectrum.

[0012] The data processor processes the power of the reflection spectrum to obtain the measured physical quantity.

[0013] A demodulation method for a demodulation system of an interferometric sensor for multiplexing includes the following steps:

[0014] Step 1. Use a broadband light source to emit light signals to the interferometric sensing unit;

[0015] Step 2. The optical signal is reflected at the FP cavity and the linear chirped fiber grating. Changes in environmental parameters will cause the FP cavity reflection spectrum to drift.

[0016] Step 3. Use the threshold method to eliminate the influence of other pixels and select the pixel unit that matches the center wavelength of the interferometric sensing unit;

[0017] Step 4. Use a linear InGaAs detector that has been calibrated for wavelength-to-pixel relationship to collect the power of the reflectance spectrum;

[0018] Step 5. Fit the wavelength and power information of the selected pixel unit using a quadratic polynomial to match the spectral characteristics of the Gaussian distribution;

[0019] Step 6. Perform a logarithmic transformation on the Gaussian spectrum to convert it into a quadratic polynomial form, perform curve fitting and solve to obtain the center wavelength, thereby obtaining the physical quantities measured by each FP cavity fiber optic sensor.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention enables real-time measurement by multiple sensors on a single optical fiber, improving multiplexing capacity, simplifying the structure of the detection and demodulation system, reducing the number of optical fibers required, and lowering the system complexity.

[0022] The linear chirped fiber grating sensor of the interferometric sensing unit of this invention has a reflection bandwidth that exactly covers one period of the FP cavity reflection spectrum, which improves the accuracy of demodulation, avoids crosstalk between signals, and improves the efficiency of signal demodulation. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the interferometric sensing device used for multiplexing according to the present invention.

[0024] Figure 2 This is a schematic diagram of the demodulation system of the multiplexed interferometric sensing device of the present invention.

[0025] Figure 3 This is a schematic diagram of the signal detector of the present invention.

[0026] Figure 4 This is the reflection spectrum of a standalone FP cavity fiber optic sensor.

[0027] Figure 5 This is the reflection spectrum of a single linear chirped fiber Bragg grating sensor.

[0028] Figure 6 This is the reflection spectrum of the interferometric sensing unit of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments.

[0030] exist Figure 1 In this embodiment, an interferometric sensing device for multiplexing is composed of multiple interferometric sensing units connected in series. The interferometric sensing unit is as follows: the two input ends of the circulator are connected to the FP cavity fiber optic sensor and the linear chirped fiber grating sensor, respectively, and the output end is connected to the coupler. The reflection bandwidth of the linear chirped fiber grating sensor exactly covers one period of the FP cavity reflection spectrum, avoiding excessive period signal overlap. In addition, the reflection wavelength ranges of the fiber gratings of the multiple interferometric sensing units do not overlap, thereby avoiding crosstalk between signals from different sensors.

[0031] exist Figure 2 In this embodiment, the demodulation system for the multiplexed interferometric sensing device includes a broadband light source, a signal detector, and an interferometric sensing device for multiplexing. The broadband light source emits C+L band laser light to the interferometric sensing device. The interferometric sensing device is connected to the signal detector. The light signal reflected back from the interferometric sensing device carries information about the physical quantity to be measured. The signal detector detects the wavelength and intensity changes of these light signals to obtain the physical quantity measured by each FP cavity sensor.

[0032] exist Figure 3 In this embodiment, the signal detector includes a collimator, a volume phase grating, a focusing lens, a linear InGaAs detector, and a data processor. The collimator converts the incident signal into parallel light so that it can illuminate the volume phase grating. The volume phase grating is used to spatially separate light signals of different wavelengths. The focusing lens is used to focus the light signal output by the volume phase grating onto the linear InGaAs detector. On the linear InGaAs detector, each pixel detects light signals within a specific wavelength range, selects pixel units that match the center wavelengths of each interferometric sensing device, and outputs the power of the reflected spectrum.

[0033] The signal detector in this embodiment includes a collimator, a volume phase grating, a focusing lens, a linear InGaAs detector, and a data processor. The collimator converts the incident signal into parallel light so that it can illuminate the volume phase grating. The volume phase grating is used to spatially separate light signals of different wavelengths. The focusing lens is used to focus the light signal output by the volume phase grating onto the linear InGaAs detector. On the linear InGaAs detector, each pixel detects light signals within a specific wavelength range and selects pixel units that match the center wavelengths of each interferometric sensing device.

[0034] The demodulation method for a multiplexed interferometric sensing device in this embodiment includes the following steps:

[0035] Step 1. Use a broadband light source to emit light signals to the interferometric sensing unit;

[0036] Step 2. The optical signal is reflected at the FP cavity and the linear chirped fiber grating. Changes in environmental parameters will cause the FP cavity reflection spectrum to drift.

[0037] Step 3. Use the threshold method to eliminate the influence of other pixels and select the pixel unit that matches the center wavelength of the interferometric sensing unit;

[0038] Step 4. Use a linear InGaAs detector that has been calibrated for wavelength-to-pixel relationship to collect the power of the reflectance spectrum;

[0039] Step 5. Fit the wavelength and power information of the selected pixel unit using a quadratic polynomial to match the spectral characteristics of the Gaussian distribution;

[0040] Step 6. Perform a logarithmic transformation on the Gaussian spectrum to convert it into a quadratic polynomial form, perform curve fitting and solve to obtain the center wavelength, thereby obtaining the physical quantities measured by each FP cavity fiber optic sensor.

[0041] To verify the beneficial effects of the present invention, the inventors conducted the following spectral comparison tests, such as... Figure 4-6 As shown in the figure, specific wavelengths in the reflection spectrum of the FP cavity in different sensing units are reflected back to the signal detector by the CFBG in the same sensing unit, thereby obtaining the changes in environmental parameters such as temperature and strain at different detection positions based on the wavelength changes of the FP cavity reflection spectrum.

Claims

1. A demodulation system for multiplexed interferometric sensing devices, characterized by: It includes a broadband light source, an interferometric sensor, and a signal detector. The broadband light source emits C+L band laser light to the interferometric sensor, which is connected to the signal detector. The light signal reflected back from the interferometric sensor carries information about the physical quantity to be measured. The signal detector detects the wavelength and intensity changes of these light signals to obtain the physical quantity measured by each FP cavity sensor. The interferometric sensing device is composed of multiple interferometric sensing units connected in series. The interferometric sensing unit is as follows: the two input ends of the circulator are connected to the FP cavity fiber optic sensor and the linear chirped fiber grating sensor, respectively, and the output end is connected to the coupler. The reflection bandwidth of the fiber grating of the linear chirped fiber grating sensor exactly covers one period of the FP cavity reflection spectrum, and the reflection wavelength ranges of the fiber gratings of the multiple interferometric sensing units do not overlap.

2. The demodulation system for multiplexed interferometric sensor devices according to claim 1, characterized in that: The signal detector includes a collimator, a volume phase grating, a focusing lens, a linear InGaAs detector, and a data processor; The collimator converts the incident signal into parallel light so that it can illuminate the volume phase grating; The volume phase grating is used to spatially separate optical signals of different wavelengths; The focusing lens is used to focus the optical signal output by the volume phase grating onto the linear InGaAs detector; On the linear InGaAs detector, each pixel detects light signals within a specific wavelength range, selects pixel units that match the center wavelengths of each interferometric sensor, and outputs the power of the reflected spectrum. The data processor processes the power of the reflection spectrum to obtain the measured physical quantity.

3. The demodulation method of the system according to claim 2, characterized in that: Includes the following steps: Step 1. Use a broadband light source to emit an optical signal to the interferometric sensing unit; Step 2. The optical signal is reflected at the FP cavity and the linear chirped fiber grating. Changes in environmental parameters will cause the FP cavity reflection spectrum to drift. Step 3. Use the threshold method to eliminate the influence of other pixels and select pixel units that match the center wavelength of the interferometric sensing unit; Step 4. Use a linear InGaAs detector that has been calibrated for wavelength-to-pixel relationship to collect the power of the reflectance spectrum; Step 5. Fit the wavelength and power information of the selected pixel unit using a quadratic polynomial to match the spectral characteristics of the Gaussian distribution; Step 6. Perform a logarithmic transformation on the Gaussian spectrum to convert it into a quadratic polynomial form, perform curve fitting and solve to obtain the center wavelength, thereby obtaining the physical quantities measured by each FP cavity fiber optic sensor.

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