CN107894245A - A kind of polarization maintaining optical fibre interferometer strained with temperature simultaneously measuring - Google Patents

Abstract

The invention provides a polarization-maintaining optical fiber interferometer for simultaneous measurement of strain and temperature. It includes a narrow-band light source, a fully polarization-maintaining Mach-Zehnder interferometer, an interference signal detection unit, a differential circuit, and a demodulation system. The invention adopts the polarization maintaining optical fiber device to build the full polarization maintaining interferometer, and the optical signal is transmitted in the fast axis and the slow axis of the polarization maintaining optical fiber at the same time, forming two sets of sensing systems; the two sets of sensing systems have different temperature and strain Response, so both can be measured at the same time; Mach-Zehnder interference structure has no back-trans transmission, which effectively suppresses the Rayleigh scattering noise in the process of light transmission; separates the light in the polarization-maintaining fiber from the fast and slow axes , using a differential circuit to differentially process the coaxial signal to reduce noise and improve measurement accuracy. The invention has the advantages of simple manufacture, convenient measurement and high precision, and can effectively overcome the problem of cross-sensitivity. The invention can be used in the fields of petroleum exploration, seismic observation and the like.

Description

A Polarization-Maintaining Optical Fiber Interferometer for Simultaneous Measurement of Strain and Temperature

technical field

The invention relates to an optical fiber sensing technology, in particular to a polarization-maintaining optical fiber interferometer for simultaneous measurement of high-precision strain and temperature.

Background technique

As one of the important research contents in today's sensing field, fiber optic sensor has the advantages of small size, light weight, high sensitivity, large dynamic range, anti-electromagnetic interference, and ability to work in harsh environments. The application of fiber optic sensors in environmental measurement is also becoming more and more extensive.

Since optical fibers are affected by strain and temperature at the same time, and the two interfere with each other, how to separate the two factors of strain and temperature and realize the simultaneous measurement of the two has become a hot spot in research and development. At present, the optical fiber sensors that can be applied to the simultaneous measurement of strain and temperature mainly include distributed optical fiber sensors, fiber Bragg grating sensors, and photonic crystal optical fiber sensors.

The most commonly used method in the method of separately measuring strain and temperature parameters is to construct a binary linear equation system. The basic idea is to use two or more sensors with different responses to strain and temperature to simultaneously sense the two parameters. Or there are two structures in a sensor that respond differently to strain and temperature, so that the following binary linear equations can be obtained:

In the formula and are the overall response of sensor 1 and sensor 2 to strain and temperature; ε——strain, ΔT——temperature change, both are unknown; α ₁ and α ₂ are the sensitivity of the two sensors to strain alone; β ₁ and α β ₂ is the sensitivity of the two sensors to temperature alone. Using such a system of equations, the required strain and temperature values can be solved separately, and the simultaneous measurement of the two can be realized.

In 2009, Li Aiqun of Southeast University and others proposed to package two fiber gratings with different responses to strain and temperature into a stainless steel tube, and then measure strain and temperature (CN201382778Y). The general problem of this method is the structural Complex, bulky, and there is a certain distance between the two sensing structures, the large error leads to low measurement accuracy; therefore, the gradual replacement of the above method is to actively produce two different response structures in a set of sensing devices. sensing unit. In 2012, Song Zhangqi of the University of National Defense Science and Technology of the Chinese People's Liberation Army disclosed a method for simultaneously measuring strain and temperature by obtaining fiber gratings with different diameters by etching (CN102829893A), which is to make two different features on the same optical fiber. The grating makes it respond differently to strain and temperature, but such a method will introduce additional loss and reduce the performance of the sensor, and active fabrication will also have the problem of uncontrollable accuracy. In response to these problems, researchers at home and abroad have begun to pay attention to polarization-maintaining optical fibers. The polarization-maintaining optical fiber has two transmission paths, the fast axis and the slow axis. According to this feature, it can be used as two sets of sensing devices, successfully avoiding the above-mentioned problems.

In 2011, Koji Omichi, Sakura (JP) et al. disclosed a physical quantity measurement device using optical frequency domain reflectometry and a method for simultaneously measuring strain and temperature using the device (US7889332B2). This method utilizes In order to realize the characteristic that the fast and slow axes of polarization-maintaining fiber work at the same time, a double-Michelson interferometer was built with the help of the sensing performance of the grating, and the strain and temperature of the detection position were determined by the OFDR analysis method and the wavelength change of the Bragg reflected light. High spatial resolution, multi-point measurement and other advantages, but the demodulation algorithm is relatively complicated, the grating needs to be fabricated, and the technical cost is relatively high.

In 2016, Jin Jiajun and others from China Jiliang University proposed an optical fiber sensor (CN205719020U) consisting of partial polarization-maintaining optical fibers to simultaneously measure strain and temperature. This sensing structure is composed of two peanut-shaped optical fibers actively fused to form a Mach-Zehnder Interferometer; the sensing unit is a polarization-maintaining optical fiber. By detecting the wavelength value of the transmitted light interference attenuation peak on the spectrometer, the simultaneous measurement of external strain and temperature is realized by using the wavelength changes corresponding to two different valleys in the transmission spectrum. The sensor has a simple structure and is convenient for measurement, but it is measured according to the wavelength change of the valley in the transmission spectrum, the dynamic range is small, and the welding is relatively complicated.

Contents of the invention

The purpose of the present invention is to provide a polarization-maintaining optical fiber interferometer that can eliminate the mutual crosstalk of temperature and strain, suppress noise, and realize simultaneous measurement of strain and temperature for both accurate measurements.

The purpose of the present invention is achieved like this:

It consists of a narrow-band light source 301, a 0° polarizer 311, a fully polarization-maintaining Mach-Zehnder interferometer 320, an interference signal detection unit 330, a differential circuit 340 and a demodulation system 350 connected in sequence,

The full polarization-maintaining Mach-Zehnder interferometer 320 is composed of a first polarization-maintaining fiber coupler 321, a first polarization-maintaining fiber 322, a second polarization-maintaining fiber 323, a second polarization-maintaining fiber coupler 324 and a phase modulator 325; The first output end 320a of the first polarization-maintaining optical fiber coupler 321 is welded at 45° to the first polarization-maintaining optical fiber 322, and the second output end 320b of the first polarization-maintaining optical fiber coupler 321 is welded at 45° to the second polarization-maintaining optical fiber 323. Welding; the first polarization-maintaining fiber 322 is connected to the first input end 320c of the second polarization-maintaining fiber coupler 324 at 0°, and the second polarization-maintaining fiber 323 is connected to the second input end of the second polarization-maintaining fiber coupler 324 at 0° 320d;

The interference signal detection unit 330 is composed of a first polarization beam splitter 331 and a second polarization beam splitter 332, a first photodetector 333, a second photodetector 334, a third photodetector 335 and a fourth photodetector 336; the first output port 320e and the second output port 320f of the second polarization-maintaining fiber coupler 324 are respectively connected to the first polarization beam splitter 331 and the second polarization beam splitter 332; the first polarization beam splitter 331 and the second polarization beam splitter 2 The output ports of the polarization beam splitter 332 are respectively connected to a photodetector for photoelectric conversion;

The differential circuit 340 connects the photodetector 333 corresponding to the fast-axis output end of the first polarization beam splitter 331 and the photodetector 335 corresponding to the fast-axis output end of the second polarization beam splitter 332 to the same differential circuit 341 Among them, the photodetector 334 corresponding to the slow axis output end of the first polarization beam splitter 331 and the photodetector 336 corresponding to the slow axis output end of the second polarization beam splitter 332 are connected to the same differential circuit 342; the differential circuit 340 Connect the data acquisition device 351 .

The present invention may also include:

1. Replace the first polarization maintaining fiber coupler 321, phase modulator 325 and 0° polarizer 311 with a Y waveguide 326, the first output end 320g and the second output end 320h of the Y waveguide 326 are respectively Perform 45° welding with the first polarization-maintaining optical fiber 322 and the second polarization-maintaining optical fiber 323 .

2. The working axis of the first polarization-maintaining fiber coupler 321 is consistent with the transmission axis of the output light of the narrowband light source 301 or connected at 90°; it has at least two optical output signal terminals, and the splitting ratio of the working axis is 50:50.

3. The working axis of the Y waveguide 326 is consistent with the transmission axis of the output light of the narrow-band light source 301 or docked at 90°; it has at least two optical output signal terminals, and the light splitting ratio of the working axis is 50:50.

4. The fast and slow axes of the second polarization-maintaining fiber coupler 324 work simultaneously, and have at least two optical input signal terminals and two optical output signal terminals, and the light splitting ratio is 50:50.

5. Use the third polarization-maintaining fiber coupler 337, the fourth polarization-maintaining fiber coupler 338 and four polarizers to replace the first polarization beam splitter 331 and the second polarization beam splitter for polarization splitting in the interference signal detection unit 330 Polarizing beam splitter 332 .

6. The working wavelength of all optical devices is consistent with the central wavelength of the narrowband light source 301 .

The invention provides a device for simultaneous measurement of strain and temperature, which effectively solves the problem of cross sensitivity between the two, and realizes simultaneous measurement of strain and temperature. The device has the advantages of simple structure, small error and accurate and effective measurement result.

Main technical means of the present invention comprises:

The device of the present invention includes a narrow-band light source 301, a 0° polarizer 311, a fully polarization-maintaining Mach-Zehnder interferometer 320, an interference signal detection unit 330, a differential circuit 340 and a demodulation system 350 connected in sequence. The 0° polarizer 311 is used to ensure that the transmitted light before entering the interferometer is a single linearly polarized light. The full polarization-maintaining Mach-Zehnder interferometer 320 is composed of a first polarization-maintaining fiber coupler 321, a first polarization-maintaining fiber 322, a second polarization-maintaining fiber 323, a second polarization-maintaining fiber coupler 324 and a phase modulator 325; the first The first output end 320a of the polarization-maintaining optical fiber coupler 321 is welded at 45° to the first polarization-maintaining optical fiber 322, and the second output end 320b of the first polarization-maintaining optical fiber coupler 321 is welded to the second polarization-maintaining optical fiber 323 at 45°; At this time, the light transmitted in the polarization-maintaining fiber is welded at 45°, distributed to the fast axis and slow axis of the fiber at a ratio of 1:1 and transmitted simultaneously, and two sets of interferometers are constructed. The working axis of the first polarization-maintaining fiber coupler 321 should be consistent with the light transmission axis of the narrow-band light source 301, or if they are inconsistent, they should be docked at 90°; there are at least two optical output signal terminals, and the optimal splitting ratio of the working axis It is 50:50. In the full polarization-maintaining Mach-Zehnder interferometer 320, the three components of the first polarization-maintaining fiber coupler 321, the phase modulator 325 and the 0° polarizer 311 can be replaced by a Y waveguide 326, and the first output end of the Y waveguide 326 320g and the second output end 320h are welded at 45° to the first polarization-maintaining fiber 322 and the second polarization-maintaining fiber 323 respectively; The first polarization-maintaining fiber 322 is connected to the first input end 320c of the second polarization-maintaining fiber coupler 324 at 0° to form an arm of the Mach-Zehnder interferometer; the second polarization-maintaining fiber 323 is connected to the second polarization-maintaining fiber at 0° The second input end 320d of the polarized fiber coupler 324 constitutes the other arm of the Mach-Zehnder interferometer; the 0° welding here still maintains the simultaneous transmission of the fast axis and the slow axis in the optical fiber. The second polarization-maintaining fiber coupler 324 requires the fast and slow axes to work at the same time, and has at least two optical input signal terminals and two optical output signal terminals, and the optimal splitting ratio is 50:50. The operating wavelengths of all the above optical devices should be consistent with the central wavelength of the narrowband light source 301 .

The interference signal detection unit 330 is composed of a first polarizing beam splitter 331 and a second polarizing beam splitter 332, a first photodetector 333, a second photodetector 334, a third photodetector 335 and a fourth photodetector 336 ; The first output port 320e and the second output port 320f of the second polarization-maintaining fiber coupler 324 are respectively connected to the first polarization beam splitter 331 and the second polarization beam splitter 332 to separate the light transmitted by the fast axis and the slow axis ; The output ports of the first polarizing beam splitter 331 and the second polarizing beam splitter 332 are respectively connected to a photodetector for photoelectric conversion, and each signal is processed separately. The photodetector 333 corresponding to the fast axis output end of the first polarization beam splitter 331 and the photodetector 335 corresponding to the fast axis output end of the second polarization beam splitter 332 are connected to the same differential circuit 341, and the first polarization beam splitter The photodetector 334 corresponding to the slow axis output end of the polarizer 331 and the photodetector 336 corresponding to the slow axis output end of the second polarization beam splitter 332 are connected to the same differential circuit 342; Noise effect, so that the noise is lower and the measurement accuracy is higher. The first polarization beam splitter 331 and the second polarization beam splitter 332 used for polarization beam splitting here can be replaced by using a third polarization maintaining fiber coupler 337 , a fourth polarization maintaining coupler 338 and four polarizers.

Demodulation system 350 is made up of data acquisition equipment 351 and signal processing computer 352; Differential circuit 340 is connected with data acquisition equipment 351, and the data collected carries out phase demodulation process by signal processing computer 352; Simultaneously signal processing computer 352 sets a carrier signal to modulate the phase modulator 325 in the fully polarization-maintaining Mach-Zehnder interferometer 320 accordingly.

The feasibility of the present invention lies in the internal characteristics of the polarization maintaining fiber. Fig. 1 is a schematic diagram of the end-face structure of a polarization-maintaining fiber, which is an example of a Panda polarization-maintaining fiber. Due to the existence of stress rods 102a and 102b in the fiber cladding 101, the internal refractive index of the fiber core 103 changes, and the propagation of light in the fiber core 103 The speed is different due to the difference in the refractive index. The density of the core 103 in the direction of the stress rods 102a and 102b increases, and the refractive index increases, which is the slow axis; otherwise, the vertical direction is the fast axis, so the fast axis and the slow axis are formed. .

In the process of aligning the polarization-maintaining optical fiber, as shown in Figure 2, it is a schematic diagram of the butt joint angle of two sections of Panda polarization-maintaining optical fiber. The welding angle refers to the angle between the coaxial axes, that is, the slow axis of Panda polarization-maintaining optical fiber 201 in the figure. The included angle θ between the direction line 201a and the slow axis direction line 202a of the Panda PM fiber 202 .

The present invention is based on the Mach-Zehnder interferometer, and first obtains the respective response sensitivities of the polarization-maintaining optical fiber fast-axis interferometer and slow-axis interferometer to strain and temperature:

In formula (1), α ₁ and α ₂ are the sensitivities of the two sensors to strain alone; β ₁ and β ₂ are the sensitivities of the two sensors to temperature alone. When the temperature or strain outside the interferometer changes, it will act on the sensing arm of the interferometer. Taking the fast axis as an example, changes in the external environment are transformed into changes in the length of the sensing arm, thereby affecting the phase change after interference. Therefore, the sensitivity of the fast axis to temperature or strain can be obtained; the sensitivity of the slow axis is the same.

The device senses the strain and temperature effects of the external environment, and obtains the phase changes of the fast axis and the slow axis through a phase demodulation algorithm and Solve the unknowns ε and ΔT according to the following formulas.

The present invention is a fully polarized optical path, and builds a Mach-Zehnder interferometer, which has the following characteristics and advantages:

(1) The present invention utilizes the characteristics of the fast axis and the slow axis of the polarization-maintaining optical fiber, and by welding the first polarization-maintaining optical fiber coupler and the polarization-maintaining optical fiber at 45°, the light is distributed to the fast axis and the slow axis of the optical fiber; When the two-axis light is transmitted in the interferometer at the same time, two sets of interference systems are formed; since the two sets of interference systems have different responses to temperature and strain, simultaneous measurement of temperature and strain can be realized, which can effectively solve the actual environment. The problem of cross-sensitivity between the two in the measurement.

(2) Using the full polarization-maintaining optical path, the narrow-band light source is simultaneously transmitted through the fast axis and the slow axis of the polarization-maintaining fiber, and the two interference systems constructed are stored in the same fiber, which eliminates the measurement error caused by the uneven spatial distribution to be measured, The measurement accuracy is improved; and the loss introduced in the manufacturing process is greatly reduced.

(3) The obtained interference signal suppresses the noise by making a difference between the fast axis and the fast axis signal, and between the slow axis and the slow axis signal, so that the measurement accuracy is higher.

(4) Build a Mach-Zehnder interferometer to avoid the reverse transmission of light, eliminate the Rayleigh scattering noise caused by the reverse transmission, and increase the signal-to-noise ratio.

The simple interference structure makes the device small in size and easy to manufacture; the measurement method of the invention opens up a new field for the simultaneous measurement of temperature and strain. The invention can be used in the fields of petroleum exploration, seismic observation and the like.

The invention solves the problems existing in the prior art, constructs a Mach-Zehnder interferometer, avoids the backward transmission of light, eliminates the Rayleigh scattering noise caused by the backward transmission, and increases the signal-to-noise ratio; through 45° welding, the The light is distributed to the fast axis and the slow axis to form a two-way interference system to achieve simultaneous measurement of strain and temperature; and the two-way interference system is at the same position, greatly reducing the measurement error; the simple interference structure makes the device small in size and easy to manufacture ; The obtained interference signal reduces the noise by making the difference between the fast axis and the fast axis signal, and between the slow axis and the slow axis signal, so that the measurement accuracy is higher. The invention opens up a new field for simultaneous measurement of strain and temperature, and can effectively solve the problem of cross sensitivity between the two in actual environment measurement.

Description of drawings

Figure 1 is a schematic diagram of the end face structure of Panda polarization maintaining fiber.

Figure 2 is a schematic diagram of the butt joint angle of two sections of Panda polarization maintaining fiber.

Fig. 3 is a schematic diagram of the optical path and device of Embodiment 1 of the polarization-maintaining fiber optic interferometer for simultaneous measurement of strain and temperature.

Fig. 4 is a schematic diagram of the optical path and device of Embodiment 2 of the polarization-maintaining fiber optic interferometer for simultaneous measurement of strain and temperature.

Figure 5a is the temperature characteristic curve of the fast axis of the interferometer; Figure 5b is the temperature characteristic curve of the slow axis of the interferometer.

Detailed ways

The following examples describe the present invention in more detail.

Embodiment 1: A polarization-maintaining fiber interferometer for simultaneous measurement of strain and temperature A Mach-Zehnder interferometer is used for measurement to realize simultaneous measurement of strain and temperature. The device is shown in FIG. 3 . The light source used in FIG. 3 is a narrow-band light source 301 , which outputs light transmitted in the slow axis, with a center wavelength of 1550 nm and an output power of 5 mW after splitting. The 0° polarizer 311 is used to ensure that the transmitted light before entering the interferometer is a single linearly polarized light. The full polarization-maintaining Mach-Zehnder interferometer 320 is made up of the first polarization-maintaining fiber coupler 321, the first polarization-maintaining fiber 322, the second polarization-maintaining fiber 323, the second polarization-maintaining fiber coupler 324 and the phase modulator 325; here The first polarization-maintaining fiber coupler 321 has at least one input port and two output ports, and the light splitting ratio of the fast and slow axes is 50:50. The first output end 320a of the first polarization-maintaining optical fiber coupler 321 is welded at 45° to the first polarization-maintaining optical fiber 322, and the second output end 320b of the first polarization-maintaining optical fiber coupler 321 is welded at 45° to the second polarization-maintaining optical fiber 323. Welding; at this time, the light transmitted in the polarization-maintaining fiber is welded at 45°, distributed to the fast axis and slow axis of the fiber at a ratio of 1:1 and transmitted simultaneously, and two interferometers are constructed. The working axis of the first polarization-maintaining fiber coupler 321 is consistent with the light transmission axis of the narrow-band light source 301 , and is docked at 0°. The first polarization-maintaining fiber 322 is connected to the first input end 320c of the polarization-maintaining fiber coupler 324 at 0° to form an arm of the Mach-Zehnder interferometer; the second polarization-maintaining fiber 323 is connected to the polarization-maintaining fiber coupler at 0° The second input end 320d of 324 constitutes another arm of the Mach-Zehnder interferometer; the 0° welding here still maintains the simultaneous transmission of the fast axis and the slow axis in the optical fiber. The used second polarization-maintaining fiber coupler 324 requires that the fast and slow axes work at the same time, and has at least two optical input signal terminals and two optical output signal terminals, and the optimal splitting ratio is 50:50. The operating wavelengths of all the above optical devices should be consistent with the central wavelength of the narrowband light source 301 . The light transmitted in the fast axis of the two sensing arms interferes in the second polarization-maintaining fiber coupler 314 , and similarly, the light transmitted in the slow axis also interferes.

The sensing unit senses the external strain and temperature change, which causes the length of the optical fiber of the sensing arm to change. In a Mach-Zehnder interferometer, changes in the length of the sensing fiber cause changes in the phase of the interference signal. Therefore, it is necessary to realize the measurement of strain and temperature by phase demodulation of the interference signal.

The interference signal detection unit 330 is composed of a first polarizing beam splitter 331 and a second polarizing beam splitter 332, a first photodetector 333, a second photodetector 334, a third photodetector 335 and a fourth photodetector 336 ; The first output port 320e and the second output port 320f of the second polarization-maintaining fiber coupler 324 are respectively connected to the first polarization beam splitter 331 and the second polarization beam splitter 332 to separate the light transmitted by the fast axis and the slow axis ; The output ports of the first polarizing beam splitter 331 and the second polarizing beam splitter 332 are respectively connected to a photodetector for photoelectric conversion, and each signal is processed separately. The photodetector 333 corresponding to the fast axis output end of the first polarization beam splitter 331 and the photodetector 335 corresponding to the fast axis output end of the second polarization beam splitter 332 are connected to the same differential circuit 341, and the first polarization beam splitter The photodetector 334 corresponding to the slow axis output end of the polarizer 331 and the photodetector 336 corresponding to the slow axis output end of the second polarization beam splitter 332 are connected to the same differential circuit 342; Noise effect, so that the noise is lower and the measurement accuracy is higher. Demodulation system 350 is made up of data acquisition equipment 351 and signal processing computer 352; Differential circuit 340 is connected with data acquisition equipment 351, and the data collected carries out phase demodulation process through signal processing computer 352; Simultaneously signal processing computer 352 sets a 20kHz The carrier signal modulates the phase modulator 325 in the fully polarization-maintaining Mach-Zehnder interferometer 320 through the data acquisition device 351 .

A polarization-maintaining fiber interferometer proposed for simultaneous measurement of strain and temperature uses a fully polarization-maintaining optical path structure. The polarization-maintaining fiber has two transmission paths, the fast axis and the slow axis. According to this feature, it can be used As two sets of sensing devices, it is simple and convenient to use the full polarization maintaining structure to construct a measuring device with different responses to strain and temperature.

The device in the embodiment senses the temperature and strain of the external environment, and obtains the phase changes of the fast axis and the slow axis through a phase demodulation algorithm and Solve the unknowns ε and ΔT according to formula (2).

Embodiment 2: measuring device is also as shown in Figure 4, and the selection of measuring device and parameter are with embodiment 1, difference is:

1. Since the Y waveguide has three functions of polarization, light splitting and modulation, the 0 ° polarizer 311 in embodiment 1, the first polarization-maintaining fiber coupler 321 and the phase modulator 325 can be formed by the Y waveguide 326 among Fig. 4 replace.

2. The interference signal detection unit 330 uses a third polarization-maintaining fiber coupler 337 , a fourth polarization-maintaining fiber coupler 338 and four polarizers to achieve the purpose of separating two-axis optical signals.

The connection and testing process in this embodiment are roughly the same as in Embodiment 1, and the differences are described in detail as follows: the working axis of the Y waveguide 326 used is the fast axis, so it needs to be docked at 90° with the narrowband light source 301; the Y waveguide 326 The first output end 320g and the second output end 320h are respectively welded at 45° to the first polarization-maintaining optical fiber 322 and the second polarization-maintaining optical fiber 323, with the purpose of distributing the light to the fast axis of the optical fiber at a ratio of 1:1 as in Example 1 Simultaneous transmission in the slow axis, two interferometers are built; the phase modulation part of the demodulation system 350 is to set a 20kHz carrier signal at the signal processing computer 352 and directly to the full polarization-maintaining Mach-Zehnder interferometer 320 through the data acquisition device 351 The Y waveguide 326 in the center is modulated accordingly; the interference signal detection unit 330 uses the third polarization-maintaining fiber coupler 337, the fourth polarization-maintaining fiber coupler 338 and four polarizers to achieve the purpose of separating two-axis optical signals, The 1st output port 320e and the 2nd output port 320f of the 2nd polarization maintaining fiber coupler 324 are respectively connected to the 3rd polarization maintaining fiber coupler 337 and the 4th polarization maintaining fiber coupler 338, then the 3rd polarization maintaining fiber coupler 337 The two output ends are respectively connected to the first photodetector 333 by 90° welding to obtain the fast-axis signal and connected to the second photodetector 334 by 0° welding; the two output ends of the fourth polarization-maintaining fiber coupler 338 are respectively The fast axis signal obtained by 90° welding is connected to the third photodetector 335 and the slow axis signal obtained by 0° welding is connected to the fourth photodetector 336 . Other devices remain unchanged.

Preliminary experimental verification was carried out for the device in Figure 4. The parameters of each device in the polarization-maintaining interferometer are: narrow-band light source 301 - output slow axis light, center wavelength is 1550nm, output power after splitting is 5mW; Y waveguide 326 - fast axis works, the splitting ratio is 50:50; one arm of the interferometer is 2m long, and the other arm is 1m long; polarization maintaining coupler 324—the fast and slow axes work at the same time, and the splitting ratio is 50:50. In this experiment, when the sensing arm is in a relaxed state, the temperature of the experiment is changed to measure the response data of the two working axes to the temperature. The experimental results are shown in Figures 5a and 5b. Figure 5a is the temperature characteristic curve of the fast axis of the interferometer, and the temperature sensitivity is 64.565rad/°C; Figure 5b is the temperature characteristic curve of the slow axis of the interferometer, and the temperature sensitivity is 62.343 rad/°C. In the same way, the sensitivity of the fast-axis and slow-axis interferometers to strain can be obtained, and the unknown quantities ε and ΔT can be solved according to the formula (2), so that the simultaneous measurement of strain and temperature can be realized, and the ubiquitous strain and temperature crossover can be overcome. problem of impact.

Claims (10)

1. A polarization-maintaining optical fiber interferometer for simultaneous measurement of strain and temperature, comprising a narrow-band light source (301), a 0° polarizer (311), a full polarization-maintaining Mach-Zehnder interferometer (320), and an interference signal detection unit (330 ), the differential circuit (340) and the demodulation system (350) are connected in sequence, and it is characterized in that: The full polarization-maintaining Mach-Zehnder interferometer (320) consists of the first polarization-maintaining fiber coupler (321), the first polarization-maintaining fiber (322), the second polarization-maintaining fiber (323), the second polarization-maintaining fiber coupler (324) and a phase modulator (325); the first output end (320a) of the first polarization-maintaining fiber coupler (321) is welded at 45° with the first polarization-maintaining fiber (322), and the first polarization-maintaining fiber is coupled The second output end (320b) of the device (321) is welded at 45° to the second polarization-maintaining fiber (323); the first polarization-maintaining fiber (322) is connected to the second polarization-maintaining fiber coupler (324) at 0° 1 input end (320c), the second polarization maintaining fiber (323) is connected to the second input end (320d) of the second polarization maintaining fiber coupler (324) at 0°; The interference signal detection unit (330) is composed of a first polarizing beam splitter (331) and a second polarizing beam splitter (332), a first photodetector (333), a second photodetector (334), a third Composed of a photodetector (335) and a fourth photodetector (336); the first output port (320e) and the second output port (320f) of the second polarization-maintaining fiber coupler (324) are respectively connected to the first polarization beam splitter Device (331) and the 2nd polarization beam splitter (332); The output ports of the 1st polarization beam splitter (331) and the 2nd polarization beam splitter (332) are respectively connected with a photodetector to carry out photoelectric conversion; The differential circuit (340) is to connect the photodetector (333) corresponding to the fast-axis output end of the first polarization beam splitter (331) and the photodetector corresponding to the fast-axis output end of the second polarization beam splitter (332) The device (335) is connected to the same differential circuit (341), the slow axis output of the photodetector (334) corresponding to the slow axis output end of the first polarization beam splitter (331) and the second polarization beam splitter (332) The photodetector (336) corresponding to the end is connected to the same differential circuit (342); the differential circuit (340) is connected to the data acquisition device (351). 2. The polarization-maintaining fiber interferometer for simultaneous measurement of strain and temperature according to claim 1 is characterized in that: the first polarization-maintaining fiber coupler (321) and phase modulator (325) are replaced by a Y waveguide (326) And 0° polarizer (311) three devices, the first output end (320g) and the second output end (320h) of described Y waveguide (326) are respectively connected with the first polarization maintaining optical fiber (322) and the second polarization maintaining optical fiber (322) The polarized optical fiber (323) is welded at 45°. 3. The polarization-maintaining fiber interferometer for simultaneous measurement of strain and temperature according to claim 1, characterized in that: the working axis of the first polarization-maintaining fiber coupler (321) is consistent with the transmission axis of the output light of the narrow-band light source (301) Or 90° docking; there are at least two optical output signal terminals, and the splitting ratio of the working axis is 50:50. 4. The polarization-maintaining optical fiber interferometer for simultaneous measurement of strain and temperature according to claim 2 is characterized in that: the working axis of the Y waveguide (326) is consistent with the transmission axis of the output light of the narrow-band light source (301) or carries out 90° Docking; there are at least two optical output signal terminals, and the light splitting ratio of the working axis is 50:50. 5. according to the polarization-maintaining optical fiber interferometer that strain and temperature are measured simultaneously according to any one of claim 1 to 4, it is characterized in that: the fast and slow axes of the 2nd polarization-maintaining fiber coupler (324) work simultaneously, and have at least two One optical input signal and two optical output signal terminals, the splitting ratio is 50:50. 6. according to the polarization-maintaining fiber interferometer of the described strain of claim 1 to 4 any one and temperature measurement simultaneously, it is characterized in that: use the 3rd polarization-maintaining fiber coupler (337), the 4th polarization-maintaining fiber coupler ( 338) and four polarizers to replace the first polarization beam splitter (331) and the second polarization beam splitter (332) used for polarization beam splitting in the interference signal detection unit (330). 7. The polarization-maintaining fiber interferometer for simultaneous measurement of strain and temperature according to any one of claim 5, characterized in that: use the 3rd polarization-maintaining fiber coupler (337), the 4th polarization-maintaining fiber coupler (338) and four polarizers to replace the first polarization beam splitter (331) and the second polarization beam splitter (332) used for polarization beam splitting in the interference signal detection unit (330). 8. The polarization-maintaining fiber interferometer for simultaneous measurement of strain and temperature according to any one of claims 1 to 4, characterized in that: the operating wavelengths of all optical devices are consistent with the central wavelength of the narrow-band light source (301). 9. The polarization-maintaining optical fiber interferometer for simultaneous measurement of strain and temperature according to claim 5, characterized in that: the operating wavelengths of all optical devices are consistent with the central wavelength of the narrow-band light source (301). 10. The polarization-maintaining fiber interferometer for simultaneously measuring strain and temperature according to claim 6, characterized in that: the operating wavelengths of all optical devices are consistent with the central wavelength of the narrow-band light source (301).