A strain measuring device based on ultra-large measuring range pdh sensing

Abstract

The invention provides a strain measuring device based on PDH sensing with a super large measuring range, which comprises four parts: a cyclic frequency shifting module, a phase modulation module, a fiber grating sensing module and a demodulation module. The invention adopts a cyclic frequency shifting module, so that after the light undergoes multiple cycles of single-sideband modulation, new sub-carriers are continuously generated, and an optical frequency comb with stable frequency interval is generated. The comb teeth with similar frequencies are used as the benchmark for comparison. When the offset frequency is greater than the maximum frequency range of the light source modulation, the resonant frequency can be aligned with the next comb tooth by adjusting the frequency of the output signal of the RF signal generator to achieve continuous locking. Therefore, the strain measurement range of the system is improved, and the nonlinear influence in wavelength scanning is avoided, the measurement accuracy is maintained, and it can be flexibly applied to the observation equipment of physical quantities such as fiber grating strain based on PDH technology.

Description

technical field [0001] The invention relates to a strain measuring device based on super large measuring range PDH sensing, belonging to the technical field of photoelectric detection. Background technique [0002] Natural disasters such as earthquakes pose a great threat to the safety of people's lives and properties around the world. Long-term monitoring of crustal deformation has become crucial. In order to accurately grasp the movement and strain information of the crust, various strain gauges have emerged. Among the existing various fiber Bragg grating strain sensing systems, the multiplexed strain sensing system based on ordinary fiber Bragg grating (FBG) has the characteristics of low cost and easy multi-point multiplexing. However, due to the reflection peak width of ordinary fiber Bragg grating wider, and its strain resolution is generally in the order of microstrain (10 -6 ε), which cannot meet the requirements of sensor accuracy in geophysical research; and the a...

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Problems solved by technology

[0004] In 2008, D.Gatti used phase-shifted fiber grating for measurement and obtained higher sensitivity (Gatti D, Galzerano G, Janner D, et al. Fiber strain sensor based on aπ-phase-shifted Bragg grating and the Pound-Drever-Hall technique[J].Optics Express,2008,16(3):1945-50.), in 2010, Shaddock D A used atomic spectrum as a reference to realize high-precision static strain sensing (Lam T Y, Chow J H, Shaddock D A, et al.High-resolution absolute frequency referenced fiber optic sensor for quasi-static strain sensing[J].Appl Opt,2010,49(21):4029-4033.), but the sensor is limited by the bandwidth of the atomic spectrum, the strain measurement range For several microstrains; in 2011, He Zuyuan’s team at Shanghai Jiaotong University proposed to use a tunable laser to scan a pair of fiber Fabry-Perot resonators, which improved the strain measurement range (Liu Q, Tokunaga T, He Z.Ultra-high- resolution large-dynamic-range optical fiber static strain sensor using Pound–Drever–Hall technique[J].Optics Letters,2011,36(20):4044-4046.), but the nonlinearity in the laser wavelength scanning process has a negative effect on the measurement accuracy In 2013, the optical fiber ring cavity was used as a reference element to achieve a strain measurement range of more than 1000 microns (CN203100689U), but the modulation device is complex and the hardware overhead is large. In 2016, a dual feedback loop was used to realize an ultra-high-precision optical fiber strain sensor , but the strain measurement range is still limited by the frequency range of the sideband modulating signal

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