Interferometric sensing device for multiplexing and demodulation system and method

Abstract

The invention relates to an interference type sensing device for multiplexing and a demodulation system and method, the sensing device is formed by sequentially connecting a plurality of interference type sensing units in series, and each interference type sensing unit is characterized in that two input ends of a circulator are respectively connected with an F-P cavity optical fiber sensor and a linear chirp fiber grating sensor, and an output end of the circulator is connected with a coupler; the reflection bandwidth of the fiber bragg grating of the linear chirped fiber bragg grating sensor just covers one period of the reflection spectrum of the F-P cavity, and the reflection wavelength ranges of the fiber bragg gratings of the plurality of interference type sensing units are not overlapped. The demodulation system comprises a broadband light source, an interference type sensing device and a signal detector. According to the invention, real-time measurement of a plurality of sensors on one optical fiber is realized, the multiplexing capacity is improved, the structure of a detection and demodulation system is simplified, the number of required optical fibers is reduced, and the complexity of the system is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to an interference sensing device and a demodulation system for multiplexing. Background Art

[0002] In the fields of structural health monitoring, oil drilling, aerospace, etc., temperature and strain are two key detection parameters. Traditional sensing technology is difficult to meet the requirements of accurate and fast response in these environments. Interferometric fiber optic sensors have become an ideal choice for temperature and strain monitoring due to their superior anti-electromagnetic interference, compact structure, high resolution, etc. By monitoring the reflection spectrum of interferometric fiber optic sensors, it is possible to accurately sense tiny changes in temperature or strain, which makes them more widely used in harsh environments.

[0003] However, in large-scale signal detection or large-scale structural health monitoring, how to perform high-capacity multiplexing at a low cost is still an extremely important issue. When the number of sensors increases, the complexity of the multiplexing scheme will also increase, and the design and operation costs of the system will increase. When multiple interferometric sensors are connected in series on an optical fiber, the reflected signals of different sensors will produce crosstalk, making signal demodulation difficult; when multiple sensing structures are connected in parallel, multiple optical fibers are usually required, which increases the complexity of the system. Therefore, designing a highly feasible multiplexing method for interferometric sensors and studying how to minimize crosstalk in the sensing path are an indispensable part of the optimization and improvement of such 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 an interference type sensing device and demodulation system for multiplexing with reasonable design, simple structure and high signal detection efficiency.

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

[0006] A demodulation system for a multiplexed interferometric sensor device comprises a broadband light source, the interferometric sensor device and a signal detector. The broadband light source emits C+L band laser to the interferometric sensor device. The interferometric sensor device is connected to the signal detector. The optical signal reflected by the interferometric sensor device carries information of a physical quantity to be measured. The signal detector detects the wavelength and intensity changes of the optical 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 array InGaAs detector, and a data processor;

[0008] The collimator converts the incident signal into parallel light so as to illuminate the volume phase grating;

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

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

[0011] On the linear array InGaAs detector, each pixel detects light signals within a specific wavelength range, selects pixel units that match the central wavelengths of the interferometric sensing device, 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 multiplexed interferometric sensor device demodulation system comprises the following steps:

[0014] Step 1. Use a broadband light source to transmit an optical signal to the interferometric sensing unit;

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

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

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

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

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

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

[0021] The present invention realizes the real-time measurement of multiple sensors on one optical fiber, improves the multiplexing capacity, simplifies the structure of the detection and demodulation system, reduces the number of required optical fibers, and reduces the complexity of the system.

[0022] The reflection bandwidth of the linear chirped fiber grating sensor of the interference sensing unit of the present invention just covers one period of the FP cavity reflection spectrum, thereby improving the accuracy of demodulation, avoiding crosstalk between signals, and improving the efficiency of signal demodulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of the interference type sensing device used for multiplexing of the present invention.

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

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

[0026] Figure 4 It is the reflection spectrum of a single FP cavity optical fiber sensor.

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

[0028] Figure 6 It is a reflection spectrum diagram of the interference sensing unit of the present invention. DETAILED DESCRIPTION

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

[0030] exist Figure 1 In this embodiment, an interference sensing device for multiplexing is composed of multiple interference sensing units connected in series in sequence. The interference sensing units are: the two input ends of the circulator are respectively connected to the FP cavity fiber sensor and the linear chirped fiber grating sensor, and the output end is connected to the coupler. The reflection bandwidth of the linear chirped fiber grating sensor just covers one period of the FP cavity reflection spectrum to avoid overlapping of too many periodic signals, and the reflection wavelength ranges of the fiber gratings of the multiple interference sensing units do not overlap, thereby avoiding crosstalk between different sensor signals.

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

[0032] exist Figure 3 In the embodiment, the signal detector includes a collimator, a volume phase grating, a focusing lens, a linear array InGaAs detector, and a data processor; the collimator converts the incident signal into parallel light so as to irradiate the volume phase grating; the volume phase grating is used to separate the light signals of different wavelengths in space; the focusing lens is used to focus the light signal output by the volume phase grating onto the linear array InGaAs detector; on the linear array InGaAs detector, each pixel detects the light signal within a specific wavelength range, selects the pixel unit matching each central wavelength of the interference sensing device, and outputs the power of the reflected spectrum.

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

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

[0035] Step 1. Use a broadband light source to transmit an optical signal to the interferometric sensing unit;

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

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

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

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

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

[0041] In order to verify the beneficial effects of the present invention, the inventors conducted the following spectral comparison tests: Figure 4-6 ,As can be seen from the figure, the specific wavelength in the reflection spectrum of the FP cavity in different ,sensing units is reflected back to the signal detector by the CFBG in the same sensing unit, ,so the changes of environmental parameters such as temperature and ,strain at different detection positions are obtained according to the wavelength changes of the FP cavity reflection ,spectrum.

Claims

1. An interferometric sensing device for multiplexing, characterized in that: The invention is composed of a plurality of interference type sensing units connected in series in sequence. The interference type sensing units are: the two input ends of the circulator are respectively connected to the FP cavity type optical fiber sensor and the linear chirped optical fiber grating sensor, and the output end is connected to the coupler. The reflection bandwidth of the optical fiber grating of the linear chirped optical fiber grating sensor just covers one cycle of the FP cavity reflection spectrum, and the reflection wavelength ranges of the optical fiber gratings of the plurality of interference type sensing units do not overlap.

2. The demodulation system of the device according to claim 1, characterized in that: It includes a broadband light source, the interference type sensor device, and a signal detector. The broadband light source emits C+L band laser to the interference type sensor device. The interference type sensor device is connected to the signal detector. The light signal reflected back by the interference type sensor device carries the information of 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.

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

4. The demodulation method of the system according to claim 3, characterized in that: The following steps are involved: Step 1. Use a broadband light source to transmit 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. The change of environmental parameters will cause the drift of the FP cavity reflection spectrum. Step 3. Use the threshold method to eliminate the influence of other pixels and select the pixel unit that matches the central wavelength of the interference sensing unit; Step 4. Use a linear array InGaAs detector that has been calibrated for wavelength and pixel relationship to collect the power of the reflection spectrum; Step 5. Fitting the wavelength and power information of the selected pixel unit according to a quadratic polynomial to match the spectral characteristics of the Gaussian distribution; Step 6. Perform logarithmic transformation on the spectrum of Gaussian distribution, convert it into a quadratic polynomial form, perform curve fitting and solve, and obtain the central wavelength, thereby obtaining the physical quantity measured by each FP cavity fiber sensor.

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