CN114777950B - Temperature strain double-parameter sensing system and method based on dual-wavelength pulse - Google Patents

Abstract

The present invention discloses a temperature-strain dual-parameter sensing system and method based on dual-wavelength pulses, and specifically relates to the field of optical fiber sensing technology. The sensing system includes a dual-wavelength pulse light source module, an optical fiber coupler, a circulator, a sensing unit module, a wavelength division multiplexer, a filtering module, an adjustable optical attenuator, and a signal detection and demodulation module; the dual-wavelength pulse light source module can output a picosecond pulse signal with adjustable central wavelength and the same intensity, which is divided into two beams by an optical fiber coupler, one of which is used as a reference beam; the other is used as a detection beam and is incident on the sensing unit module after passing through the circulator, and the generated optical fiber grating reflected light and backward Raman anti-Stokes scattered light are split by the wavelength division multiplexer and enter the signal detection and demodulation module. The present invention combines optical fiber grating sensing and distributed Raman temperature sensing, and adopts differential detection and single-photon detection methods, which can not only measure temperature and strain information simultaneously, but also has the characteristics of high system wavelength resolution and high spatial resolution, thereby meeting various needs in practical applications.

Description

A temperature-strain dual-parameter sensing system and method based on dual-wavelength pulses

Technical Field

The invention belongs to the technical field of distributed optical fiber and quasi-distributed optical fiber grating sensing, and in particular relates to a temperature-strain dual-parameter sensing system and method based on dual-wavelength pulses.

Background technique

In recent years, fiber optic sensing, as a new type of sensing technology, has attracted the attention of more and more researchers. Fiber Bragg grating sensors and distributed Raman sensors have been widely used in the field of structural safety detection because of their strong anti-electromagnetic interference ability, high sensitivity, corrosion resistance, and good electrical insulation performance. However, fiber Bragg gratings have the problem of temperature cross-sensitivity when performing strain sensing, and although distributed Raman temperature sensors are only sensitive to temperature, their spatial resolution is limited to the meter level. Therefore, it is particularly important to achieve simultaneous sensing of temperature and strain with high precision and high spatial resolution.

At present, the method of simultaneous measurement of temperature and strain based on fiber Bragg grating sensing and distributed Raman sensing has been realized, but its fiber Bragg grating still uses a single wavelength demodulation method, which cannot eliminate the error caused by the power fluctuation of the laser, thereby reducing the demodulation accuracy of the fiber Bragg grating central wavelength.

Summary of the invention

In order to solve the above problems, the present invention provides a temperature-strain dual-parameter sensing system and method based on dual-wavelength pulses, which synchronously detects the fiber grating reflected light and the backward Raman anti-Stokes scattered light, and adopts dual-wavelength pulse differential detection and single-photon detection to improve the system wavelength resolution and spatial resolution, thereby realizing simultaneous sensing of temperature-strain dual parameters with high precision and high spatial resolution.

The technical solution adopted by the present invention is as follows:

A temperature-strain dual-parameter sensing system and method based on dual-wavelength pulses, the sensing system comprising a dual-wavelength pulse light source module, a first optical fiber coupler, a second optical fiber coupler, a first circulator, a sensing unit module, a wavelength division multiplexer, a filtering module, an adjustable attenuator, and a signal detection and demodulation module; the dual-wavelength pulse light source module is connected to the first optical fiber coupler, the first optical fiber coupler is respectively connected to a port of the first circulator and a second optical fiber coupler, the second port and the third port of the first circulator are respectively connected to the sensing unit module and the com port of the wavelength division multiplexer, the signal of the 1450nm output port of the wavelength division multiplexer enters the signal detection and demodulation module via the filtering module, and the signal of the 1550nm output port of the wavelength division multiplexer enters the signal detection and demodulation module via the second optical fiber coupler and the adjustable attenuator in sequence.

The dual-wavelength pulse light source module is composed of a tunable laser, an electro-optic modulator and a pulse signal generator, and can output picosecond pulse light with adjustable wavelength, and the central wavelength of the output light is within the reflection spectrum of the fiber grating sensor;

The first optical fiber coupler and the second optical fiber coupler are used to divide the pulse signal into reference light and detection light with a power ratio of 1:99;

The first circulator and the second circulator are used to guide incident, reflected or scattered pulsed light;

The sensing unit module is a single Gaussian fiber grating, or a series or/and parallel structure consisting of multiple Gaussian fiber gratings with the same central wavelength;

The filtering module is composed of a second circulator and a high reflectivity uniform fiber Bragg grating, and is used to filter the noise signal of the fiber Bragg grating reflected light and Rayleigh scattered light that crosstalk to the 1450nm output port of the wavelength division multiplexer;

The signal detection and demodulation unit comprises a first single photon detector, a second single photon detector, a time digital converter and a host computer. The single photon detector is composed of an avalanche diode or a superconducting waveguide device, the time digital converter is composed of a single chip microcomputer and/or a programmable logic device, and/or a digital signal processing chip, and/or an embedded chip, and/or a delayed acquisition device, and the host computer contains a signal demodulation and processing program.

Furthermore, the sensing method comprises the following steps:

S1, the dual-wavelength pulse light source module outputs picosecond pulse light with central wavelengths of λ ₁ and λ ₂ respectively for the first and second times, λ ₁ and λ ₂ are both around 1550nm with a small wavelength difference, and their peak power and pulse width are the same.

S2. The pulse is divided into two beams through the first optical fiber coupler. One beam is used as detection light and enters the sensor unit module through the circulator to detect the external temperature and strain information; the other beam enters the second optical fiber coupler as reference light.

S3, the fiber Bragg grating reflected light and backward Raman anti-Stokes scattered light generated by the sensing unit module enter the wavelength division multiplexer through the second port and the third port of the circulator, and the wavelength division multiplexer divides the backward Raman Stokes scattered light and the grating reflected light into two paths. The 1450nm output end signal enters the first single-photon detector after passing through the filter module, and the 1550nm output end signal enters the second single-photon detector after passing through the second fiber coupler and the adjustable optical attenuator. The light reflected back from the fiber Bragg grating at different positions of the sensing fiber and at various locations has different energy and propagation time. After being detected by the first and second single-photon detectors, the photon coincidence count value that changes with time will be obtained on the time digital converter;

S4. The host computer can obtain the temperature and strain information of each point of the optical fiber by analyzing and processing the size of the photon coincidence count value; by analyzing the time coordinates corresponding to the photon coincidence count value and using the OTDR positioning principle, high-precision spatial positioning of the fiber grating position point can be achieved.

Furthermore, the intensity of the backward Raman anti-Stokes scattered light generated by the pulse light in step S3 varies with the external temperature, and the center wavelength drift of the grating reflected light varies with the external temperature and strain, thereby realizing sensing;

When the central wavelengths of the pulses sent by the dual-wavelength pulse light source module are λ ₁ and λ ₂ respectively, the photon coincidence count values of the reference pulse light are N ₁ (λ ₁ ) and N ₁ (λ ₂ ), which can be expressed as:

Where k ₁ is a constant with a size of Where m is the power proportion of the reference light, _P0 is the pulse peak power, η is the detection efficiency of the single-photon detector, t is the measurement time, τ is the pulse width, f is the laser repetition frequency, _α0 is the fiber attenuation constant of the incident light, and _L1 is the distance from the first coupler to the single-photon detector.

When the central wavelengths of the pulses sent by the dual-wavelength pulse light source module are λ ₁ and λ ₂ respectively, the photon coincidence count values of the pulse light reflected by the fiber grating are N ₂ (λ ₁ ) and N ₂ (λ ₂ ) respectively, which can be expressed as:

Where k ₂ is a constant with a size of (1-m) is the split power ratio of the detection light, R _max is the peak reflectivity of the fiber Bragg grating, λ _B is the central wavelength of the fiber Bragg grating, ω _B is the 3dB bandwidth of the Gaussian spectrum, L ₂ is the distance from the fiber Bragg grating to the circulator, and the drift Δλ of the central wavelength λ _B of the Gaussian spectrum changes with the temperature and strain, which can be expressed as:

Δλ＝(α+β)λ _B ΔT+(1-P _e )λ _B Δε＝Δλ _T +Δλ _ε (5)

Among them, α is the thermal expansion coefficient, β is the thermo-optic coefficient, _Pe is the effective elastic-optic coefficient, ΔT and Δε are the temperature change and axial stress change, respectively.

When the central wavelengths of the pulses sent by the dual-wavelength pulse light source module are λ ₁ and λ ₂ respectively, the photon coincidence count values of the backward Raman anti-Stokes scattering are N _AS (λ ₁ ,T) and N _AS (λ ₂ ,T) respectively, which can be expressed as:

Among them, k ₂ is a constant with a size of Where η is the detection efficiency of the single-photon detector, Δf _AS is the filter bandwidth of the 1450nm output channel of the wavelength division multiplexer, P ₀ is the pulse peak power, D is the duty cycle of the pulse, L ₃ is the distance between the position of the measured fiber point and the circulator, T is the temperature at the position of L ₃ , g _R,AS is the Raman gain coefficient, λ _AS is the Raman anti-Stokes wavelength, α _AS is the fiber attenuation constant of the Raman anti-Stokes light, B _AS is the dark count and the background photon number caused by Rayleigh backscattering and fiber Bragg grating reflected light crosstalk, N(T) is the Raman anti-Stokes temperature modulation function, and its size is/>

Furthermore, in step S4, the host computer performs differential processing on the fiber Bragg grating signal in a logarithmic manner to obtain a grating measurement signal M, which can be expressed as:

Among them, S is the sensitivity coefficient, which is λ _c is the central wavelength of two pulses of different wavelengths, and its size is/> According to formula (9), it can be concluded that the demodulated center wavelength drift Δλ changes linearly with the change ΔM of the grating measurement signal, which can be expressed as:

Furthermore, in step S4, the host computer calculates the average value of the backward Raman anti-Stokes scattered photons generated by the two wavelengths at the same temperature T ₀ , N _AS (λ ₁ , T ₀ ) and N _AS (λ ₂ , T ₀ ) As the backward Raman anti-Stokes scattered photon coincidence count value of the current temperature, when the temperature changes by ΔT, the temperature change ΔT of the optical fiber under test can be calculated according to the change in the backward Raman anti-Stokes scattered photon coincidence count value ΔN _AS =N′ _AS (T ₀ +ΔT)-N′ _AS (T ₀ ).

Furthermore, when When t _i is the time when the reflected light of the i-th grating at L ₂ reaches the single-photon detector, that is, the position L ₂ of the grating coincides with the position L ₃ of the measured optical fiber point, ΔT is used to determine the grating wavelength drift Δλ _T ＝(α+β)λ _B ΔT caused by temperature, and according to formula (9) and formula (5), the total grating wavelength drift Δλ and the grating wavelength drift Δλ _T caused by temperature are determined respectively, and the grating wavelength drift Δλ _ε ＝Δλ-Δλ _T caused by strain is calculated, and then the strain caused by the change of external physical information is obtained/> This enables simultaneous measurement of temperature and strain information.

In summary, due to the adoption of the above scheme, the beneficial effects of the present invention are:

1. The present invention combines quasi-distributed fiber Bragg grating sensing and distributed Raman sensing, and utilizes the characteristic that the fiber Raman temperature sensor is only sensitive to temperature to realize temperature compensation for the fiber Bragg grating stress sensing, thereby effectively solving the temperature/strain cross-sensitivity problem of the fiber Bragg grating sensor.

2. The present invention adopts differential detection to demodulate the central wavelength of the fiber Bragg grating, that is, the dual-wavelength pulse demodulation method is used to replace the traditional single-wavelength pulse demodulation method, which eliminates the error caused by the power fluctuation of the light source and can effectively improve the wavelength resolution of the system, thereby improving the measurement accuracy of the system.

3. The present invention introduces a structure of a combination of a high-reflectivity uniform fiber Bragg grating and a circulator to filter the noise signals of the fiber Bragg grating reflected light and Rayleigh scattered light that crosstalk into the Raman anti-Stokes channel, which can suppress the crosstalk noise to the greatest extent under low-cost conditions and improve the signal-to-noise ratio of the sensing system.

4. The present invention adopts a single photon counter as a detector. Compared with traditional photoelectric detectors, this method can achieve high spatial resolution and high signal-to-noise ratio detection of single photons; high spatial resolution means that the fiber grating sensor array with smaller spatial intervals can be detected, and high signal-to-noise ratio means that the system detection accuracy is higher.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative work, among which:

Fig. 1 is a schematic diagram of a framework of the present invention;

Marked in the figure are: 1-dual-wavelength pulse light source module, 2-first fiber coupler, 3-second fiber coupler, 4-first circulator, 5-sensing unit module, 6-wavelength division multiplexer, 7-filter module, 8-second circulator, 9-uniform fiber grating, 10-adjustable attenuator, 11-signal detection and demodulation module, 12-first single photon detector, 13-second single photon detector, 14-time digital converter, 15-host computer.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

Example

As shown in Figure 1, a temperature-strain dual-parameter sensing system and method based on dual-wavelength pulses, the sensing system includes a dual-wavelength pulse light source module, a first optical fiber coupler, a second optical fiber coupler, a first circulator, a sensing unit module, a wavelength division multiplexer, a filtering module, an adjustable attenuator, and a signal detection and demodulation module; the dual-wavelength pulse light source module is connected to the first optical fiber coupler, the first optical fiber coupler is respectively connected to a port of the first circulator and a second optical fiber coupler, the second port and the third port of the first circulator are respectively connected to the sensing unit module and the com port of the wavelength division multiplexer, the signal of the 1450nm output port of the wavelength division multiplexer enters the signal detection and demodulation module via the filtering module, and the signal of the 1550nm output port of the wavelength division multiplexer enters the signal detection and demodulation module via the second optical fiber coupler and the adjustable attenuator in sequence.

The dual-wavelength pulse light source module is composed of a tunable laser, an electro-optic modulator and a pulse signal generator, and can output picosecond pulse light with adjustable wavelength, and the central wavelength of the output light is within the reflection spectrum of the fiber grating sensor;

The first optical fiber coupler and the second optical fiber coupler are used to divide the pulse signal into reference light and detection light with a power ratio of 1:99;

The first circulator and the second circulator are used to guide incident, reflected or scattered pulsed light;

The sensing unit module is a single Gaussian fiber grating, or a series or/and parallel structure consisting of multiple Gaussian fiber gratings with the same central wavelength;

The filtering module is composed of a second circulator and a high reflectivity uniform fiber Bragg grating, and is used to filter the noise signal of the fiber Bragg grating reflected light and Rayleigh scattered light that crosstalks to the 1450nm output end of the wavelength division multiplexer;

The signal detection and demodulation unit comprises a first single photon detector, a second single photon detector, a time digital converter and a host computer. The single photon detector is composed of an avalanche diode or a superconducting waveguide device, the time digital converter is composed of a single chip microcomputer and/or a programmable logic device, and/or a digital signal processing chip, and/or an embedded chip, and/or a delayed acquisition device, and the host computer contains a signal demodulation and processing program.

The temperature-strain dual-parameter sensing system and method based on dual-wavelength pulses, the specific steps of the sensing method are as follows:

S1, the dual-wavelength pulse light source module outputs picosecond pulse light with central wavelengths of λ ₁ and λ ₂ respectively for the first and second times, λ ₁ and λ ₂ are both around 1550nm with a small wavelength difference, and their peak power and pulse width are the same.

S2. The pulse is divided into two beams through the first optical fiber coupler. One beam is used as detection light and enters the sensor unit module through the circulator to detect the external temperature and strain information; the other beam enters the second optical fiber coupler as reference light.

S3, the fiber Bragg grating reflected light and backward Raman anti-Stokes scattered light generated by the sensing unit module enter the wavelength division multiplexer through the second port and the third port of the circulator, and the wavelength division multiplexer divides the backward Raman Stokes scattered light and the grating reflected light into two paths. The 1450nm output end signal enters the first single-photon detector after passing through the filter module, and the 1550nm output end signal enters the second single-photon detector after passing through the second fiber coupler and the adjustable optical attenuator. The light reflected back from the fiber Bragg grating at different positions of the sensing fiber and at various locations has different energy and propagation time. After being detected by the first and second single-photon detectors, the photon coincidence count value that changes with time will be obtained on the time digital converter;

S4. The host computer can obtain the temperature and strain information of each point of the optical fiber by analyzing and processing the size of the photon coincidence count value; by analyzing the time coordinates corresponding to the photon coincidence count value and using the OTDR positioning principle, high-precision spatial positioning of the fiber grating position point can be achieved.

Furthermore, the intensity of the backward Raman anti-Stokes scattered light generated by the pulse light in step S3 varies with the external temperature, and the center wavelength drift of the grating reflected light varies with the external temperature and strain, thereby realizing sensing;

When the central wavelengths of the pulses sent by the dual-wavelength pulse light source module are λ ₁ and λ ₂ respectively, the photon coincidence count values of the reference pulse light are N ₁ (λ ₁ ) and N ₁ (λ ₂ ), which can be expressed as:

Where k ₁ is a constant with a size of Where m is the power proportion of the reference light, _P0 is the pulse peak power, η is the detection efficiency of the single-photon detector, t is the measurement time, τ is the pulse width, f is the laser repetition frequency, _α0 is the fiber attenuation constant of the incident light, and _L1 is the distance from the first coupler to the single-photon detector.

When the central wavelengths of the pulses sent by the dual-wavelength pulse light source module are λ ₁ and λ ₂ respectively, the photon coincidence count values of the pulse light reflected by the fiber grating are N ₂ (λ ₁ ) and N ₂ (λ ₂ ) respectively, which can be expressed as:

Where k ₂ is a constant with a size of (1-m) is the split power ratio of the detection light, R _max is the peak reflectivity of the fiber Bragg grating, λ _B is the central wavelength of the fiber Bragg grating, ω _B is the 3dB bandwidth of the Gaussian spectrum, L ₂ is the distance from the fiber Bragg grating to the circulator, and the drift Δλ of the central wavelength λ _B of the Gaussian spectrum changes with the temperature and strain, which can be expressed as:

Δλ＝(α+β)λ _B ΔT+(1-P _e )λ _B Δε＝Δλ _T +Δλ _ε (5)

Among them, α is the thermal expansion coefficient, β is the thermo-optic coefficient, _Pe is the effective elastic-optic coefficient, ΔT and Δε are the temperature change and axial stress change, respectively.

When the central wavelengths of the pulses sent by the dual-wavelength pulse light source module are λ ₁ and λ ₂ respectively, the photon coincidence count values of the backward Raman anti-Stokes scattering are N _AS (λ ₁ ,T) and N _AS (λ ₂ ,T) respectively, which can be expressed as:

Among them, k ₂ is a constant with a size of Where η is the detection efficiency of the single-photon detector, Δf _AS is the filter bandwidth of the 1450nm output channel of the wavelength division multiplexer, P ₀ is the pulse peak power, D is the duty cycle of the pulse, L ₃ is the distance between the position of the measured fiber point and the circulator, T is the temperature at the position of L ₃ , g _R,AS is the Raman gain coefficient, α _AS is the fiber attenuation constant of Raman anti-Stokes light, λ _AS is the Raman anti-Stokes wavelength, B _AS is the number of dark counts and background photons caused by Rayleigh backscattering and fiber Bragg grating reflected light crosstalk, and N(T) is the Raman anti-Stokes temperature modulation function, which is / >

Furthermore, in step S4, the host computer performs differential processing on the fiber Bragg grating signal in a logarithmic manner to obtain a grating measurement signal M, which can be expressed as:

Among them, S is the sensitivity coefficient, which is λ _c is the central wavelength of two pulses of different wavelengths, and its size is/> According to formula (9), it can be concluded that the demodulated center wavelength drift Δλ changes linearly with the change ΔM of the grating measurement signal, which can be expressed as:

Furthermore, in step S4, the host computer calculates the average value of the backward Raman anti-Stokes scattered photons generated by the two wavelengths at the same temperature T ₀ , N _AS (λ ₁ , T ₀ ) and N _AS (λ ₂ , T ₀ ) As the backward Raman anti-Stokes scattered photon coincidence count value of the current temperature, when the temperature changes by ΔT, the temperature change ΔT of the optical fiber under test can be calculated according to the change in the backward Raman anti-Stokes scattered photon coincidence count value ΔN _AS =N′ _AS (T ₀ +ΔT)-N _AS (T ₀ ).

Furthermore, when When t _i is the time when the reflected light of the i-th grating at L ₂ reaches the single-photon detector, that is, the position of the grating L ₂ coincides with the position of the measured optical fiber point L ₃ , ΔT is used to determine the grating wavelength drift Δλ _T ＝(α+β)λ _B ΔT caused by temperature, and according to formula (9) and formula (5), the total grating wavelength drift Δλ and the grating wavelength drift Δλ _T caused by temperature are respectively calculated, and the grating wavelength drift Δλ _ε ＝Δλ-Δλ _T caused by strain is calculated, and then the strain caused by the change of external physical information is obtained/> This enables simultaneous measurement of temperature and strain information.

The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions and improvements made by any technician familiar with the field within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims (3)

1. The temperature strain double-parameter sensing system based on the dual-wavelength pulse is characterized by comprising a dual-wavelength pulse light source module (1), a first optical fiber coupler (2), a second optical fiber coupler (3), a first circulator (4), a sensing unit module (5), a wavelength division multiplexer (6), a filtering module (7), a second circulator (8), a high-reflectivity uniform fiber grating (9) adjustable attenuator (10) and a signal detection and demodulation unit (11); the dual-wavelength pulse light source module is connected with the first optical fiber coupler (2), the first optical fiber coupler (2) is respectively connected with one port of the first circulator (4) and the second optical fiber coupler (3), two ports and three ports of the first circulator (4) are respectively connected with the sensing unit module (5) and the com port of the wavelength division multiplexer (6), signals of 1450nm output ports of the wavelength division multiplexer enter the signal detection and demodulation unit (11) through the filtering module (7), and signals of 1550nm output ports of the wavelength division multiplexer enter the signal detection and demodulation unit (11) through the second optical fiber coupler (3) and the adjustable attenuator (10) in sequence;

the dual-wavelength pulse light source module (1) consists of a tunable laser, an electro-optical modulator and a pulse signal generator, and can output picosecond pulse light with adjustable wavelength, and the central wavelength of the output light is positioned in the reflection spectrum of the fiber bragg grating sensor;

the first optical fiber coupler (2) and the second optical fiber coupler (3) are used for dividing pulse signals into reference light and detection light with the power ratio of 1:99;

the first circulator (4) and the second circulator (8) are used for guiding incident, reflected or scattered pulse light;

the sensing unit module is a single Gaussian fiber bragg grating or a serial or/and parallel structure formed by a plurality of Gaussian fiber bragg gratings with the same central wavelength;

the filtering module (7) consists of a second circulator (8) and a high-reflectivity uniform fiber bragg grating (9) and is used for filtering noise signals of fiber bragg grating reflected light and Rayleigh scattered light which are crosstalked to the 1450nm output end of the wavelength division multiplexer;

the signal detection and demodulation unit (11) comprises a first single photon detector (12), a second single photon detector (13), a time-digital converter (14) and an upper computer (15), wherein the first single photon detector (12) and the second single photon detector (13) are composed of avalanche diodes or superconducting waveguide devices, the time-digital converter (14) is composed of a digital signal processing chip, and the upper computer (15) contains a signal demodulation and processing program.

2. A sensing method of a dual wavelength pulse based temperature strain dual parametric sensing system according to claim 1, wherein the sensing method comprises the steps of:

s1, respectively outputting a central wavelength lambda by the dual-wavelength pulse light source module for the first time and the second time ₁ 、λ ₂ Picosecond pulsed light, lambda ₁ 、λ ₂ The peak power and the pulse width are the same, and the peak power and the pulse width are all around 1550nm and have small wavelength difference;

s2, dividing the pulse into two beams through a first optical fiber coupler, wherein one beam is used as detection light, and the detection light enters a sensing unit module through a circulator to detect the external temperature and strain information; one beam enters the second optical fiber coupler as reference light;

s3, enabling the reflected light of the fiber bragg grating and the reflected light of the backward Raman anti-Stokes generated by the sensing unit module to enter a wavelength division multiplexer through two ports and three ports of the circulator, dividing the reflected light of the backward Raman Stokes and the reflected light of the grating into two paths by the wavelength division multiplexer, enabling a 1450nm output end signal to enter a first single photon detector after passing through the filtering module, enabling a 1550nm output end signal to enter a second single photon detector after passing through a second fiber coupler and the adjustable optical attenuator, enabling the light reflected by the fiber bragg gratings at different positions and all positions of the sensing fiber to have different energy and propagation time, and enabling the light reflected by the fiber bragg gratings to obtain photon coincidence count values changing along with time on the time-to-digital converter after being detected by the first single photon detector and the second single photon detector;

s4, the upper computer analyzes and processes the photon to accord with the count value, so that the temperature and strain information of each point of the optical fiber can be obtained; the high-precision space positioning of the fiber bragg grating position point can be realized by analyzing the time coordinate corresponding to the photon coincidence count value and utilizing the OTDR positioning principle.

3. The sensing method according to claim 2, wherein the intensity of the backward raman anti-stokes scattered light generated by the pulsed light in the step S3 varies with the external temperature, and the center wavelength shift of the reflected light of the grating varies with the external temperature and the strain, so as to implement sensing;

the central wavelength of the pulse sent by the dual-wavelength pulse light source module is lambda respectively ₁ And lambda (lambda) ₂ When the photon coincidence count value of the reference pulse light is N ₁ (λ ₁ )、N ₁ (λ ₂ ) It can be expressed as:

wherein k is ₁ Is constant and has a size ofWherein m is the power duty cycle of the reference light, P ₀ For pulse peak power, η is the detection efficiency of the single photon detector, t is the measurement time, τ is the pulse width, f is the laser repetition frequency, α ₀ Optical fiber attenuation constant for incident light, L ₁ Distance from the first coupler to the single photon detector;

the central wavelength of the pulse sent by the dual-wavelength pulse light source module is lambda respectively ₁ And lambda (lambda) ₂ When the photon coincidence count value of the pulse light reflected by the fiber bragg grating is N respectively ₂ (λ ₁ )、N ₂ (λ ₂ ) It can be expressed as:

wherein k is ₂ Is constant and has a size of(1-m) is the spectral power ratio of the probe light, R _max Is the peak reflectivity of the fiber bragg grating lambda _B Is the center wavelength omega of the fiber grating _B Is 3dB bandwidth of Gaussian spectrum, L ₂ For fibre-optic gratings to circulatorsDistance, where Gaussian spectrum center wavelength lambda _B The amount of drift Δλ of (a) varies with the magnitude of the temperature and strain, which can be expressed as:

Δλ＝(α+β)λ _B ΔT+(1-P _e )λ _B Δε＝Δλ _T +Δλ _ε (5)

wherein alpha is the thermal expansion coefficient, beta is the thermo-optic coefficient, P _e For effective elastance, delta T and delta epsilon are respectively the magnitudes of temperature change and axial stress change, delta lambda _T As the temperature-induced grating wavelength drift, Δλ _ε The grating wavelength drift amount caused by strain;

the central wavelength of the pulse sent by the dual-wavelength pulse light source module is lambda respectively ₁ And lambda (lambda) ₂ When the photon coincidence count value of backward Raman anti-Stokes scattering is N _AS (λ ₁ ,T)、N _AS (λ ₂ T), which can be expressed as:

wherein k is ₃ Is constant and has a size ofWhere η is the detection efficiency of the single photon detector, Δf _AS Filter bandwidth, P, for 1450nm output channel of wavelength division multiplexer ₀ For peak pulse power, D is the duty cycle of the pulse, L ₃ Is the distance between the position of the optical fiber point to be measured and the circulator, T is L ₃ Temperature at location g _R,AS Lambda is the Raman gain coefficient _AS Is Raman anti-Stokes wavelength, alpha _AS Fiber attenuation constant, B, for Raman anti-Stokes light _AS For dark counts, the number of background photons due to rayleigh backscattering and fiber grating reflected light crosstalk, N (T) is the raman anti-stokes temperature modulation function,the size is as follows

In the step S4, the upper computer performs differential processing on the fiber grating signal in a logarithmic manner to obtain a grating measurement signal M, which may be expressed as:

wherein S is a sensitivity coefficient, and the size isλ _c The central wavelength of the pulse light with two different wavelengths is +.>The demodulated center wavelength shift Δλ can be obtained according to equation (9) and the change Δm of the grating measurement signal changes linearly, which can be expressed as:

the same temperature T is set in the step S4 ₀ The backward raman anti-stokes scattered photons generated at the next two wavelengths match the count N _AS (λ ₁ ,T ₀ )、N _AS (λ ₂ ,T ₀ ) Average value of (2)As the backward raman anti-stokes scattered photons of the current temperature conform to the count value, when the temperature changes to deltat, photons scattered according to the backward raman anti-stokes conform to the change deltan of the count value _AS ＝N' _AS (T ₀ +ΔT)-N' _AS (T ₀ ) The temperature change delta T of the measured optical fiber can be calculated; when->In which t is _i Is L ₂ The time of arrival of the reflected light of the ith grating at the single photon detector, i.e. the position L where the grating is located ₂ And the position L of the optical fiber point to be measured ₃ Coincidence, the delta T determines the grating wavelength drift delta lambda caused by temperature _T ＝(α+β)λ _B DeltaT, the formula (9) and the formula (5) respectively determine the total grating wavelength drift Deltalambda and the temperature-induced grating wavelength drift Deltalambda _T Calculating the wavelength shift delta lambda of the grating caused by strain _ε ＝Δλ-Δλ _T Thereby obtaining the strain caused by the change of the external physical information>Thereby realizing simultaneous measurement of temperature and strain information.