Fiber bragg grating temperature/strain sensing system and demodulation method thereof

Abstract

The invention relates to a fiber bragg grating temperature / strain sensing system and a demodulation method thereof. The method comprises the following steps: after seed layer generated by a narrow linewidth laser light source module generates a sideband through a phase modulation module, injecting into active fiber grating stimulated by pump light through a circulator and a wavelength division multiplexer in an active fiber grating module; and performing photovoltaic conversion on return light and a photoelectric detector connected with the circulator to acquire a beat frequency signal, extracting a component, namely an error signal reflecting the center frequency deviation between the narrow linewidth laser and the active fiber grating, at the phase modulation frequency position by a phase-locked amplifier, and generating a feedback voltage signal by a feedback control module by virtue of the error signal to control the center frequency of the narrow linewidth laser so as to realize injection locking between the narrow linewidth laser and the active fiber grating. The quasi-static accuracy of p-epsilon can be achieved; the characteristic of adjustable strain sensitivity is achieved; and the problems of mode jump, relaxation shock and low-frequency phase noise in a fiber laser sensor can be effectively solved.

Description

technical field [0001] The invention relates to a technology in the field of optical fiber sensing, in particular to a high-resolution optical fiber grating temperature / strain sensing system and a demodulation method thereof. Background technique [0002] Strain sensing technology is widely used in engineering fields, such as underwater sound field monitoring, structural health monitoring, oil pipeline safety monitoring, seismic wave monitoring, etc. Traditional strain sensors are generally mechanical or electromagnetic, and there are many problems. For example, in a strong electric field environment, traditional strain sensors are susceptible to electromagnetic interference and cannot work normally; in flammable and explosive environments, electric sparks will be generated. Cause accidents; in underwater or underground environments, electrical components will corrode; in applications that require arraying, traditional strain sensors are difficult to connect into large-scale...

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Problems solved by technology

Although this scheme has the characteristics of low cost and easy multiplexing, it is difficult to improve the sensitivity performance due to the wide reflection bandwidth of FBG

The second is the PDH demodulation technology that has emerged in recent years, using a single-frequency laser to lock on the edge of the reflection peak of FBG, the resonance peak of PSFBG (π-phase-shifted FBG) or FFPI (fiber FP cavity), and the strain resolution can even reach However, there are some shortcomings in the PDH demodulation scheme: a. The strain accuracy of this scheme is directly affected by the frequency stability of the single-frequency laser, which puts forward high requirements for the frequency stability performance of the laser; b , In long-distance, large-scale multiplexing sensing applications, the power attenuation of signal light reduces the strain accuracy of the system

However, if the resonant cavity becomes longer, it will generate multi-mode excitation; b. The fiber laser sensor depends on the interferometer for demodulation, and the interferometer will be affected by external low-frequency noise (such as temperature, vibration), thus reducing the strain accuracy of the low-frequency band; c 1. The noise problem of fiber lasers. Any free-running laser inevitably has a certain intensity and phase noise, which affects the accuracy of fiber laser sensors.

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