CN107894245B - Polarization-maintaining optical fiber interferometer capable of simultaneously measuring strain and temperature - Google Patents

Polarization-maintaining optical fiber interferometer capable of simultaneously measuring strain and temperature Download PDF

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CN107894245B
CN107894245B CN201711309566.2A CN201711309566A CN107894245B CN 107894245 B CN107894245 B CN 107894245B CN 201711309566 A CN201711309566 A CN 201711309566A CN 107894245 B CN107894245 B CN 107894245B
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polarization
maintaining fiber
beam splitter
interferometer
strain
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CN107894245A (en
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张晓峻
陈文静
杨军
田帅飞
吕岩
张毅博
李寒阳
苑永贵
苑立波
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Harbin Engineering University
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    • G01D5/35383—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques
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    • G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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    • G—PHYSICS
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    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
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Abstract

The invention provides a polarization-maintaining fiber interferometer for simultaneously measuring strain and temperature. The device comprises a narrow-band light source, a full polarization-maintaining Mach-Zehnder interferometer, an interference signal detection unit, a differential circuit and a demodulation system. The invention adopts a polarization maintaining optical fiber device to build a full polarization maintaining interferometer, and optical signals are transmitted in a fast axis and a slow axis of a polarization maintaining optical fiber simultaneously to form two sets of sensing systems; the two sets of sensing systems respectively have different responses to temperature and strain, so that the two sets of sensing systems can be simultaneously measured; the Mach-Zehnder interference structure has no back-reflection transmission, so that Rayleigh scattering noise in the optical transmission process is effectively inhibited; light in the polarization maintaining optical fiber is separated from the fast axis and the slow axis, and a differential circuit is used for carrying out differential processing on coaxial signals, so that noise is reduced, and the measurement precision is improved. 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 oil exploration, earthquake observation and the like.

Description

Polarization-maintaining optical fiber interferometer capable of simultaneously measuring strain and temperature
Technical Field
The invention relates to an optical fiber sensing technology, in particular to a polarization maintaining optical fiber interferometer for simultaneously measuring high-precision strain and temperature.
Background
The optical fiber sensor is one of important research contents in the sensing field at present, and has the advantages of small volume, light weight, high sensitivity, large dynamic range, electromagnetic interference resistance, capability of working in severe environment and the like. The application of the optical fiber sensor in environmental measurement is also becoming more and more extensive.
Because the optical fiber is affected by the strain and the temperature at the same time, and the two interfere with each other, how to separate the strain and the temperature, and realize the simultaneous measurement of the strain and the temperature becomes a hot spot in research and development at present. The current optical fiber sensors applicable to strain and temperature simultaneous measurement mainly include distributed optical fiber sensors, fiber grating sensors, photonic crystal fiber sensors and the like.
The most common method for respectively measuring the strain and temperature parameters is to construct a two-dimensional linear equation set, and the basic idea is to simultaneously sense the two parameters by using two or more sensors with different responses to strain and temperature, or to obtain a structure with two different responses to strain and temperature in one sensor, so that the following two-dimensional linear equation set can be obtained:
Figure BDA0001502698410000011
in the formula
Figure BDA0001502698410000012
And
Figure BDA0001502698410000013
the overall response of sensor 1 and sensor 2 to strain and temperature, respectively; epsilon-strain, delta T-temperature change, are unknown quantities; alpha is alpha1And alpha2The sensitivity of the two sensors to strain independently; beta is a1And beta2Respectively, the sensitivity of the two sensors to temperature alone. By utilizing the equation system, the solved strain and temperature values can be respectively solved, and the simultaneous measurement of the strain and the temperature values is realized.
The general problem of the method is that the structure is complex and the volume is large, a certain distance exists between two sensing structures, and the measurement precision is low due to large error; therefore, the method replaces the above method step by actively manufacturing two sensing units with different response structures in one set of sensing device. The method (CN102829893A) for simultaneously measuring strain and temperature by obtaining fiber gratings with different diameters through corrosion, disclosed by Song chapter et al of national defense science and technology university of the liberation army of Chinese people in 2012, is to manufacture two gratings with different characteristics on the same optical fiber so that the gratings have different responses to strain and temperature, however, the method can introduce extra loss and reduce the performance of a sensor, and the problem that the precision cannot be controlled in the active manufacturing process can also exist. In response to these problems, researchers at home and abroad are beginning to pay attention to polarization maintaining optical fibers. The polarization maintaining optical fiber has two transmission paths of a fast axis and a slow axis, and according to the characteristic, the polarization maintaining optical fiber can be used as two sets of sensing devices, so that the problems are successfully solved.
2011 Koji Omichi, sakura (jp), and the like disclose a physical quantity measuring device using optical frequency domain reflection measurement and a method (US7889332B2) using the device to simultaneously measure strain and temperature, the method utilizes the characteristic that the fast and slow axes of polarization-maintaining fiber work simultaneously, builds an interferometer with a double Michelson structure by virtue of the sensing performance of a grating, determines the strain and temperature of a detection position by the analysis method of OFDR and the wavelength change of bragg reflected light, and has the advantages of high spatial resolution, multi-point measurement and the like, but the demodulation algorithm is relatively complex, the grating needs to be manufactured, and the technical cost is relatively high.
Jinjiajun et al, the university of China metrology in 2016, proposed an optical fiber sensor (CN205719020U) composed of partial polarization maintaining fibers and used for simultaneously measuring strain and temperature, wherein the sensing structure is a Mach-Zehnder interferometer composed of two peanut-shaped fibers which are actively welded; the sensing unit is a polarization maintaining optical fiber, and the simultaneous measurement of the external strain and the temperature is realized by detecting the wavelength value of the interference attenuation peak of the transmission light on the spectrometer and utilizing the wavelength change corresponding to two different valleys in the transmission spectrum. The sensor is simple in structure and convenient to measure, but the dynamic range is small and the welding is relatively complex according to the wavelength change of the valley in the transmission spectrum.
Disclosure of Invention
The invention aims to provide a polarization-maintaining fiber interferometer capable of eliminating mutual crosstalk of temperature and strain, inhibiting noise and realizing simultaneous measurement of strain and temperature for accurate measurement of the temperature and the strain.
The purpose of the invention is realized as follows:
is formed by sequentially connecting a narrow-band light source 301, a 0-degree polarizer 311, a full polarization maintaining Mach-Zehnder interferometer 320, an interference signal detection unit 330, a differential circuit 340 and a demodulation system 350,
the full polarization maintaining Mach-Zehnder interferometer 320 consists of a 1 st polarization maintaining fiber coupler 321, a 1 st polarization maintaining fiber 322, a 2 nd polarization maintaining fiber 323, a 2 nd polarization maintaining fiber coupler 324 and a phase modulator 325; the 1 st output end 320a of the 1 st polarization-maintaining fiber coupler 321 is welded with the 1 st polarization-maintaining fiber 322 at an angle of 45 degrees, and the 2 nd output end 320b of the 1 st polarization-maintaining fiber coupler 321 is welded with the 2 nd polarization-maintaining fiber 323 at an angle of 45 degrees; a 1 st polarization maintaining fiber 322 is connected with a 1 st input end 320c of a 2 nd polarization maintaining fiber coupler 324 at 0 DEG, and a 2 nd polarization maintaining fiber 323 is connected with a 2 nd input end 320d of the 2 nd polarization maintaining fiber coupler 324 at 0 DEG;
the interference signal detection unit 330 is composed of a 1 st polarization beam splitter 331 and a 2 nd polarization beam splitter 332, a 1 st photodetector 333, a 2 nd photodetector 334, a 3 rd photodetector 335 and a 4 th photodetector 336; the 1 st output port 320e and the 2 nd output port 320f of the 2 nd polarization-maintaining fiber coupler 324 are respectively connected with the 1 st polarization beam splitter 331 and the 2 nd polarization beam splitter 332; the output ports of the 1 st polarization beam splitter 331 and the 2 nd polarization beam splitter 332 are respectively connected with a photoelectric detector for photoelectric conversion;
the difference circuit 340 is to connect the photodetector 333 corresponding to the fast axis output end of the 1 st polarization beam splitter 331 and the photodetector 335 corresponding to the fast axis output end of the 2 nd polarization beam splitter 332 to the same difference circuit 341, and connect the photodetector 334 corresponding to the slow axis output end of the 1 st polarization beam splitter 331 and the photodetector 336 corresponding to the slow axis output end of the 2 nd polarization beam splitter 332 to the same difference circuit 342; the differential circuit 340 is connected to the data acquisition device 351.
The present invention may further comprise:
1. the 1 st polarization maintaining fiber coupler 321, the phase modulator 325 and the 0 ° polarizer 311 are replaced by a Y waveguide 326, and the 1 st output end 320g and the 2 nd output end 320h of the Y waveguide 326 are respectively welded with the first polarization maintaining fiber 322 and the second polarization maintaining fiber 323 by 45 °.
2. The working axis of the 1 st polarization-maintaining fiber coupler 321 is consistent with the transmission axis of the output light of the narrow-band light source 301 or is in 90-degree butt joint; at least two optical output signal ends are provided, 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 is in 90-degree butt joint; at least two optical output signal ends are provided, and the splitting ratio of the working axis is 50: 50.
4. The fast and slow axes of the 2 nd polarization maintaining fiber coupler 324 operate simultaneously and have at least two optical input signals and two optical output signal ends with a splitting ratio of 50: 50.
5. The 1 st polarization beam splitter 331 and the 2 nd polarization beam splitter 332 for polarization beam splitting in the interference signal detection unit 330 are replaced with a 3 rd polarization maintaining fiber coupler 337, a 4 th polarization maintaining fiber coupler 338, and four polarizers.
6. The operating wavelength of all the optics coincides with the center wavelength of the narrow band light source 301.
The invention provides a device for simultaneously measuring strain and temperature, which effectively solves the problem of cross sensitivity of the strain and the temperature and realizes the simultaneous measurement of the strain and the temperature. The device has simple structure, small error and accurate and effective measurement result.
The main technical means of the invention comprise:
the device comprises a narrow-band light source 301, a 0-degree polarizer 311, a full polarization maintaining Mach-Zehnder interferometer 320, an interference signal detection unit 330, a differential circuit 340 and a demodulation system 350 which are sequentially connected. The 0 polarizer 311 is used to ensure that the transmitted light is a single linearly polarized light before entering the interferometer. The full polarization maintaining Mach-Zehnder interferometer 320 consists of a 1 st polarization maintaining fiber coupler 321, a 1 st polarization maintaining fiber 322, a 2 nd polarization maintaining fiber 323, a 2 nd polarization maintaining fiber coupler 324 and a phase modulator 325; the 1 st output end 320a of the 1 st polarization-maintaining fiber coupler 321 is welded with the 1 st polarization-maintaining fiber 322 at an angle of 45 degrees, and the 2 nd output end 320b of the 1 st polarization-maintaining fiber coupler 321 is welded with the 2 nd polarization-maintaining fiber 323 at an angle of 45 degrees; at the moment, light transmitted in the polarization maintaining optical fiber is distributed into a fast axis and a slow axis of the optical fiber according to the proportion of 1:1 by 45-degree welding and transmitted simultaneously, and two sets of interferometers are constructed. The working axis of the 1 st polarization maintaining fiber coupler 321 should be consistent with the transmission axis of the light of the narrow-band light source 301, or 90-degree butt joint is performed when the working axis is inconsistent with the transmission axis; at least two optical output signal ends are provided, and the optimal splitting ratio of the working axis is 50: 50. In the full polarization maintaining Mach-Zehnder interferometer 320, the 1 st polarization maintaining fiber coupler 321, the phase modulator 325 and the 0-degree polarizer 311 can be replaced by a Y waveguide 326, and the 1 st output end 320g and the 2 nd output end 320h of the Y waveguide 326 are respectively welded with the first polarization maintaining fiber 322 and the second polarization maintaining fiber 323 by 45 degrees; and the operating axis of the Y-waveguide 326 should also coincide with the transmission axis of the light of the narrow-band light source 301. The 1 st polarization maintaining fiber 322 is connected with the 1 st input end 320c of the 2 nd polarization maintaining fiber coupler 324 in a 0-degree back mode to form one arm of the Mach-Zehnder interferometer; the 2 nd polarization maintaining fiber 323 is connected with the 2 nd input end 320d of the 2 nd polarization maintaining fiber coupler 324 in a 0-degree back mode to form the other arm of the Mach-Zehnder interferometer; the 0 deg. weld here still keeps the fast and slow axes in the fiber transmitting simultaneously. The 2 nd polarization maintaining fiber coupler 324 requires the fast and slow axes to work simultaneously, and has at least two optical input signals and two optical output signal ends, and the optimal splitting ratio is 50: 50. All of the above-described optical devices should operate at a wavelength that coincides with the center wavelength of the narrow-band light source 301.
The interference signal detection unit 330 is composed of a 1 st polarization beam splitter 331 and a 2 nd polarization beam splitter 332, a 1 st photodetector 333, a 2 nd photodetector 334, a 3 rd photodetector 335, and a 4 th photodetector 336; the 1 st output port 320e and the 2 nd output port 320f of the 2 nd polarization-maintaining fiber coupler 324 are respectively connected with the 1 st polarization beam splitter 331 and the 2 nd polarization beam splitter 332 to separate the light transmitted by the fast axis and the slow axis; the output ports of the 1 st polarization beam splitter 331 and the 2 nd polarization beam splitter 332 are respectively connected to a photodetector for photoelectric conversion, and each path of signal is processed respectively. A photoelectric detector 333 corresponding to the fast-axis output end of the 1 st polarization beam splitter 331 and a photoelectric detector 335 corresponding to the fast-axis output end of the 2 nd polarization beam splitter 332 are connected to the same differential circuit 341, and a photoelectric detector 334 corresponding to the slow-axis output end of the 1 st polarization beam splitter 331 and a photoelectric detector 336 corresponding to the slow-axis output end of the 2 nd polarization beam splitter 332 are connected to the same differential circuit 342; the influence of direct current noise is restrained through the difference between the coaxiality, so that the noise is lower, and the measurement precision is higher. The 1 st and 2 nd polarization beam splitters 331 and 332 used for polarization beam splitting here can be replaced by using the 3 rd polarization maintaining fiber coupler 337, the 4 th polarization maintaining coupler 338 and four polarizers.
The demodulation system 350 is composed of a data acquisition device 351 and a signal processing computer 352; the differential circuit 340 is connected to the data acquisition device 351, and the acquired data is subjected to phase demodulation processing by the signal processing computer 352; while the 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 invention lies in the internal characteristics of the polarization-maintaining fiber. Fig. 1 is a schematic diagram of an end face structure of a polarization maintaining fiber, which is an example of a panda polarization maintaining fiber, in which the refractive index inside a fiber core 103 is changed due to the existence of stress rods 102a and 102b in a fiber cladding 101, the propagation speed of light in the fiber core 103 is different due to the difference in refractive index, the density of the fiber core 103 in the direction of the stress rods 102a and 102b is increased, and the refractive index is increased, which is a slow axis; conversely, the vertical direction is the fast axis, thus forming the fast and slow axes.
In the process of aligning the polarization maintaining optical fibers, as shown in fig. 2, the two segments of panda polarization maintaining optical fibers are schematically shown in a butt joint angle, and the welding angle refers to an included angle between the same axes, that is, an included angle θ between a slow axis direction line 201a of the panda polarization maintaining optical fiber 201 and a slow axis direction line 202a of the panda polarization maintaining optical fiber 202 in the drawing.
Based on a Mach-Zehnder interferometer, the invention firstly obtains the response sensitivities of the polarization maintaining fiber fast axis interferometer and the slow axis interferometer to strain and temperature respectively:
alpha in formula (1)1And alpha2The sensitivity of the two sensors to strain independently; beta is a1And beta2Respectively, the sensitivity of the two sensors to temperature alone. When the temperature or strain outside the interferometer changes, the temperature or strain will act on the sensing arm of the interferometer. Taking the fast axis as an example, the external environment change is converted into the change of the length of the sensing arm, so that the phase change after interference is influenced, and 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 action of the external environment, and obtains the phase change of the fast axis and the slow axis through a phase demodulation algorithm
Figure BDA0001502698410000051
Andthe unknowns ε and Δ T are solved according to the following equations.
Figure BDA0001502698410000053
The invention constructs a Mach-Zehnder interferometer for a full polarization-maintaining optical path, and has the following characteristics and advantages:
(1) the invention utilizes the characteristics of the polarization maintaining optical fiber that the fast axis and the slow axis are provided, and light is distributed into the fast axis and the slow axis of the optical fiber by welding the 1 st polarization maintaining optical fiber coupler and the polarization maintaining optical fiber at 45 degrees; when the light of the two shafts is transmitted in the interferometer at the same time, two sets of interference systems are formed; because the two interference systems respectively have different responses to the temperature and the strain, the simultaneous measurement of the temperature and the strain can be realized, and the problem of cross sensitivity of the two interference systems in the actual environment measurement can be effectively solved.
(2) By using a full polarization-maintaining light path, a narrow-band light source is transmitted simultaneously through a fast axis and a slow axis of a polarization-maintaining optical fiber, and two constructed interference systems exist in the same optical fiber, so that the measurement error caused by uneven distribution of a space to be measured is eliminated, and the measurement precision is improved; and the loss introduced in the manufacturing process is greatly reduced.
(3) The obtained interference signal suppresses noise by differentiating the fast axis and fast axis signals and differentiating the slow axis and slow axis signals, so that the measurement precision is higher.
(4) The Mach-Zehnder interferometer is constructed, reverse transmission of light is avoided, Rayleigh scattering noise caused by reverse transmission is eliminated, and the signal-to-noise ratio is increased.
The simple interference structure enables the device to be small in size and simple and convenient to manufacture; the measuring method of the invention opens up a new field for simultaneous measurement of temperature and strain. The invention can be used in the fields of oil exploration, earthquake observation and the like.
The invention solves the problems in the prior art, constructs the Mach-Zehnder interferometer, avoids backward transmission of light, eliminates Rayleigh scattering noise caused by backward transmission, and increases the signal-to-noise ratio; light is distributed into a fast axis and a slow axis through 45-degree welding to form a two-path interference system, so that strain and temperature can be measured simultaneously; the two interference systems are at the same position, so that the measurement error is greatly reduced; the simple interference structure enables the device to be small in size and simple and convenient to manufacture; the obtained interference signal reduces noise by differentiating the fast axis and fast axis signals and differentiating the slow axis and slow axis signals, so that the measurement precision 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 of the strain and the temperature in actual environment measurement.
Drawings
Fig. 1 is a schematic end face structure diagram of a panda polarization maintaining fiber.
Fig. 2 is a schematic view of the butt joint angle of two panda polarization maintaining fibers.
FIG. 3 is a schematic diagram of the optical path and apparatus of polarization-maintaining fiber interferometer in embodiment 1 for simultaneous measurement of strain and temperature.
FIG. 4 is a schematic diagram of the optical path and apparatus of polarization-maintaining fiber interferometer of embodiment 2 with strain and temperature measured simultaneously.
FIG. 5a is a temperature profile of the fast axis of the interferometer; fig. 5b is a temperature profile of the slow axis of the interferometer.
Detailed Description
The invention is described in more detail below by way of example.
Example 1: a polarization maintaining fiber interferometer for simultaneously measuring strain and temperature is used for measuring by utilizing a Mach-Zehnder interferometer, so that the strain and the temperature can be simultaneously measured, and the device is shown in figure 3. The light source used in fig. 3 is a narrow-band light source 301, which outputs light transmitted in the slow axis, and has a center wavelength of 1550nm and a split output of 5 mW. The 0 polarizer 311 is used to ensure that the transmitted light is a single linearly polarized light before entering the interferometer. The full polarization maintaining Mach-Zehnder interferometer 320 consists of a 1 st polarization maintaining fiber coupler 321, a 1 st polarization maintaining fiber 322, a 2 nd polarization maintaining fiber 323, a 2 nd polarization maintaining fiber coupler 324 and a phase modulator 325; here, the 1 st polarization maintaining fiber coupler 321 has at least one input end and two output ends, and the splitting ratio of the fast axis and the slow axis is 50: 50. The 1 st output end 320a of the 1 st polarization-maintaining fiber coupler 321 is welded with the 1 st polarization-maintaining fiber 322 at an angle of 45 degrees, and the 2 nd output end 320b of the 1 st polarization-maintaining fiber coupler 321 is welded with the 2 nd polarization-maintaining fiber 323 at an angle of 45 degrees; at the moment, light transmitted in the polarization-maintaining optical fiber is distributed into the fast axis and the slow axis of the optical fiber according to the proportion of 1:1 by 45-degree welding and transmitted simultaneously, and two interferometers are constructed. The working axis of the 1 st polarization maintaining fiber coupler 321 is consistent with the transmission axis of the light of the narrow-band light source 301, and the butt joint is carried out at 0 degree. The 1 st polarization maintaining fiber 322 is connected with the 1 st input end 320c of the polarization maintaining fiber coupler 324 in a 0-degree back mode to form one arm of the Mach-Zehnder interferometer; the 2 nd polarization maintaining fiber 323 is connected with the 2 nd input end 320d of the polarization maintaining fiber coupler 324 in a 0-degree back mode to form the other arm of the Mach-Zehnder interferometer; the 0 deg. weld here still keeps the fast and slow axes in the fiber transmitting simultaneously. The 2 nd polarization-maintaining fiber coupler 324 is required to work simultaneously with fast and slow axes, and has at least two optical input signals and two optical output signal ends, and the optimal splitting ratio is 50: 50. All of the above-described optical devices should operate at a wavelength that coincides with the center wavelength of the narrow-band light source 301. Light transmitted in the fast axis in the two sensing arms interferes at the 2 nd polarization maintaining fiber coupler 314, and similarly, light transmitted in the slow axis also interferes.
The sensing unit senses external strain and temperature change to cause the length of the optical fiber of the sensing arm to change. In a Mach-Zehnder interferometer, a change in the length of the sensing fiber results in a change in the phase of the interference signal. It is therefore necessary to achieve strain and temperature measurements by phase demodulating the interference signal.
The interference signal detection unit 330 is composed of a 1 st polarization beam splitter 331 and a 2 nd polarization beam splitter 332, a 1 st photodetector 333, a 2 nd photodetector 334, a 3 rd photodetector 335, and a 4 th photodetector 336; the 1 st output port 320e and the 2 nd output port 320f of the 2 nd polarization-maintaining fiber coupler 324 are respectively connected with the 1 st polarization beam splitter 331 and the 2 nd polarization beam splitter 332 to separate the light transmitted by the fast axis and the slow axis; the output ports of the 1 st polarization beam splitter 331 and the 2 nd polarization beam splitter 332 are respectively connected to a photodetector for photoelectric conversion, and each path of signal is processed respectively. A photoelectric detector 333 corresponding to the fast-axis output end of the 1 st polarization beam splitter 331 and a photoelectric detector 335 corresponding to the fast-axis output end of the 2 nd polarization beam splitter 332 are connected to the same differential circuit 341, and a photoelectric detector 334 corresponding to the slow-axis output end of the 1 st polarization beam splitter 331 and a photoelectric detector 336 corresponding to the slow-axis output end of the 2 nd polarization beam splitter 332 are connected to the same differential circuit 342; the influence of direct current noise is restrained through the difference between the coaxiality, so that the noise is lower, and the measurement precision is higher. The demodulation system 350 is composed of a data acquisition device 351 and a signal processing computer 352; the differential circuit 340 is connected to the data acquisition device 351, and the acquired data is subjected to phase demodulation processing by the signal processing computer 352; while the signal processing computer 352 sets a 20kHz carrier signal through the data acquisition device 351 to modulate the phase modulator 325 in the fully polarization maintaining Mach-Zehnder interferometer 320 accordingly.
According to the characteristic, the polarization maintaining optical fiber can be used as two sets of sensing devices, so that the polarization maintaining structure is simple and convenient to construct a measuring device with different responses to strain and temperature.
The device in the embodiment senses the temperature and the strain action of the external environment, and obtains the phase change of the fast axis and the slow axis through a phase demodulation algorithm
Figure BDA0001502698410000071
And
Figure BDA0001502698410000072
the unknowns ε and Δ T are solved according to equation (2).
Example 2: measurement apparatus as shown in fig. 4, the measurement apparatus was selected and the parameters were the same as in example 1, except that:
1. since the Y waveguide has three roles of polarization, light splitting, and modulation, the 0 ° polarizer 311, the 1 st polarization-maintaining fiber coupler 321, and the phase modulator 325 in embodiment 1 can be replaced with the Y waveguide 326 in fig. 4.
2. The interference signal detection unit 330 uses the 3 rd polarization-maintaining fiber coupler 337, the 4 th polarization-maintaining fiber coupler 338 and four polarizers to achieve the purpose of separating two-axis optical signals.
The connection and testing procedure in this example is substantially the same as in example 1, with the following differences: the working axis of the used Y-waveguide 326 is the fast axis, so it needs to be 90 ° docked with the narrow-band light source 301; the 1 st output end 320g and the 2 nd output end 320h of the Y waveguide 326 are respectively welded with the first polarization maintaining fiber 322 and the second polarization maintaining fiber 323 by 45 degrees, so that light is distributed into the fast axis and the slow axis of the optical fibers according to the proportion of 1:1 and is transmitted simultaneously to construct two interferometers; the phase modulation part of the demodulation system 350 is that a 20kHz carrier signal is set in a signal processing computer 352, and the Y waveguide 326 in the full polarization maintaining Mach-Zehnder interferometer 320 is directly modulated correspondingly through a data acquisition device 351; the interference signal detection unit 330 uses a 3 rd polarization maintaining fiber coupler 337, a 4 th polarization maintaining fiber coupler 338 and four polarizers to achieve the purpose of separating two-axis optical signals, the 1 st output port 320e and the 2 nd output port 320f of the 2 nd polarization maintaining fiber coupler 324 are respectively connected with the 3 rd polarization maintaining fiber coupler 337 and the 4 th polarization maintaining fiber coupler 338, and then two output ends of the 3 rd polarization maintaining fiber coupler 337 are respectively welded by 90 ° to obtain a fast axis signal, and are connected with the 1 st photodetector 333 and are welded by 0 ° to obtain a slow axis signal, and are connected with the 2 nd photodetector 334; two output ends of the 4 th polarization maintaining fiber coupler 338 are respectively welded at 90 degrees to obtain a fast axis signal connected with the 3 rd photoelectric detector 335 and welded at 0 degrees to obtain a slow axis signal connected with the 4 th photoelectric detector 336. The other devices are unchanged.
Preliminary experimental verification is carried out on the device in fig. 4, and the parameters of each device in the polarization maintaining interferometer are as follows: a narrow-band light source 301 which outputs slow axis light, has a central wavelength of 1550nm and outputs 5mW after light splitting; y waveguide 326-fast axis operation with split ratio of 50: 50; one arm of the interferometer is 2m long, and the other arm of the interferometer is 1m long; polarization maintaining coupler 324, the fast and slow axes work simultaneously, and the splitting ratio is 50: 50. In the experiment, the response data of the two working shafts to the temperature are measured by changing the experiment temperature under the condition that the sensing arm is in a loose state. The experimental results are shown in fig. 5a and 5b, fig. 5a is a temperature characteristic curve of the fast axis of the interferometer, and the obtained sensitivity of the temperature is 64.565 rad/DEG C; FIG. 5b is a temperature characteristic curve of the slow axis of the interferometer, resulting in a temperature sensitivity of 62.343 rad/deg.C. In the same way, the sensitivities of the interferometers of the fast axis and the slow axis to the strain can be obtained, and the unknown quantities epsilon and delta T are solved according to the formula (2), so that the simultaneous measurement of the strain and the temperature can be realized, and the problem of cross influence of the strain and the temperature in general is solved.

Claims (10)

1. The utility model provides a strain and temperature simultaneous measurement's polarization-maintaining fiber interferometer, is formed by connecting in proper order narrow band light source (301), 0 polarizer (311), full polarization-maintaining Mach-Zehnder interferometer (320), interference signal detecting element (330), difference circuit (340) and demodulation system (350), characterized by:
the full polarization-maintaining Mach-Zehnder interferometer (320) consists of a 1 st polarization-maintaining fiber coupler (321), a 1 st polarization-maintaining fiber (322), a 2 nd polarization-maintaining fiber (323), a 2 nd polarization-maintaining fiber coupler (324) and a phase modulator (325); a 1 st output end (320a) of the 1 st polarization-maintaining fiber coupler (321) is welded with the 1 st polarization-maintaining fiber (322) at an angle of 45 degrees, a 2 nd output end (320b) of the 1 st polarization-maintaining fiber coupler (321) is welded with one end of a phase modulator (325) at an angle of 45 degrees, and the other end of the phase modulator (325) is connected with the 2 nd polarization-maintaining fiber (323); the 1 st polarization maintaining fiber (322) is connected with the 1 st input end (320c) of the 2 nd polarization maintaining fiber coupler (324) at an angle of 0 DEG, and the 2 nd polarization maintaining fiber (323) is connected with the 2 nd input end (320d) of the 2 nd polarization maintaining fiber coupler (324) at an angle of 0 DEG;
the interference signal detection unit (330) is composed of a 1 st polarization beam splitter (331), a 2 nd polarization beam splitter (332), a 1 st photoelectric detector (333), a 2 nd photoelectric detector (334), a 3 rd photoelectric detector (335) and a 4 th photoelectric detector (336); a 1 st output port (320e) and a 2 nd output port (320f) of the 2 nd polarization-maintaining fiber coupler (324) are respectively connected with a 1 st polarization beam splitter (331) and a 2 nd polarization beam splitter (332); the output ports of the 1 st polarization beam splitter (331) and the 2 nd polarization beam splitter (332) are respectively connected with a photoelectric detector for photoelectric conversion;
the difference circuit (340) connects a 1 st photoelectric detector (333) corresponding to the fast-axis output end of the 1 st polarization beam splitter (331) and a 3 rd photoelectric detector (335) corresponding to the fast-axis output end of the 2 nd polarization beam splitter (332) to the first difference circuit (341), and connects a 2 nd photoelectric detector (334) corresponding to the slow-axis output end of the 1 st polarization beam splitter (331) and a 4 th photoelectric detector (336) corresponding to the slow-axis output end of the 2 nd polarization beam splitter (332) to the second difference circuit (342); the differential circuit (340) is connected with the data acquisition equipment (351).
2. The polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to claim 1, wherein: a Y waveguide (326) replaces three devices of a 1 st polarization maintaining optical fiber coupler (321), a phase modulator (325) and a 0-degree polarizer (311), and a 1 st output end (320g) and a 2 nd output end (320h) of the Y waveguide (326) are respectively welded with the 1 st polarization maintaining optical fiber (322) and the 2 nd polarization maintaining optical fiber (323) at an angle of 45 degrees.
3. The polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to claim 1, wherein: the working axis of the 1 st polarization-maintaining fiber coupler (321) is consistent with the transmission axis of the output light of the narrow-band light source (301) or is in 90-degree butt joint; at least two optical output signal ends are provided, and the splitting ratio of the working axis is 50: 50.
4. The polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to claim 2, wherein: 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 is in 90-degree butt joint; at least two optical output signal ends are provided, and the splitting ratio of the working axis is 50: 50.
5. A polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to any of claims 1 to 4, wherein: the fast and slow axes of the 2 nd polarization-maintaining fiber coupler (324) work simultaneously, and the fiber coupler at least has two optical input signals and two optical output signal ends, and the splitting ratio is 50: 50.
6. A polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to any of claims 1 to 4, wherein: a1 st polarization beam splitter (331) and a 2 nd polarization beam splitter (332) for polarization beam splitting in the interference signal detection unit (330) are replaced with a 3 rd polarization-maintaining fiber coupler (337), a 4 th polarization-maintaining fiber coupler (338), and four polarizers.
7. The polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to claim 5, wherein: a1 st polarization beam splitter (331) and a 2 nd polarization beam splitter (332) for polarization beam splitting in the interference signal detection unit (330) are replaced with a 3 rd polarization-maintaining fiber coupler (337), a 4 th polarization-maintaining fiber coupler (338), and four polarizers.
8. A polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to any of claims 1 to 4, wherein: the operating wavelength of all the optical devices coincides with the central wavelength of the narrow-band light source (301).
9. The polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to claim 5, wherein: the operating wavelength of all the optical devices coincides with the central wavelength of the narrow-band light source (301).
10. The polarization maintaining fiber interferometer for simultaneous strain and temperature measurement according to claim 6, wherein: the operating wavelength of all the optical devices coincides with the central wavelength of the narrow-band light source (301).
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