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

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

technical field [0001] 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 [0002] 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. [0003] 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 me...

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Problems solved by technology

[0007] 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 this method will introduce additional losses and reduce the performance of the sensor, and active fabrication will also have the problem of uncontrollable accuracy

[0008] 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

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

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