Phi-OTDR quadrature phase demodulation system and phase demodulation method

Abstract

The invention provides a phi-OTDR quadrature phase demodulation system and phase demodulation method. Laser of a narrow linewidth laser device is split by an optical fiber coupler, a large beam is connected into an acoustic optical modulator as sensing light, a modulated frequency shift is delivered into sensing optical fiber, a small beam is used as reference light, sensing light returned by a circulator is subjected to heterodyne coherence in a 2*2 optical fiber coupler, is then split into two beams of identical signal light to be converted into an electric signal through a balanced probe and is divided into two circuits through a power divider after being filtered, and after one circuit is delayed by an electric adjustable delay chip, the two circuits of electric signals are mixed with a sinusoidal signal with the frequency of fc sent by a signal generating module in a mixer separately and are then sent into a control center through a low-pass filter and an analog-digital conversion module to obtain phase information of a sensor light signal. According to the Phi-OTDR quadrature phase demodulation system and phase demodulation method, an interferometer does not need to be introduced, and additional environment noise cannot be introduced; complex high-speed data acquisition and processing are not needed, the system is simple, the price is low, and the system and method are more suitable for engineering application.

Description

technical field [0001] The invention relates to an optical fiber sensing system, in particular to a φ-OTDR (phase-sensitive optical time-domain reflectometer) quadrature phase demodulation system and a phase demodulation method based on a balanced detector and an electrical time delay. Background technique [0002] Phase sensitive optical time domain reflectometer φ-OTDR is a distributed optical fiber sensing technology. Compared with the conventional optical time domain reflectometer OTDR, the same is that when the light pulse is injected from one end of the fiber, it is detected by the detector and then scattered to Rayleigh. The difference is that the light injected into one end of the fiber in Φ-OTDR is strongly coherent. Therefore, the output of the φ-OTDR system is the result of the phase interference of backscattered Rayleigh light within the pulse width range. When the optical fiber line is disturbed by the outside world, the refractive index of the optical fiber a...

AI Technical Summary

Problems solved by technology

The first two require the introduction of an interferometer structure, which is easily affected by the environment and thus introduces additional noise

Digital coherent demodulation requires complex high-speed data acquisition and processing mechanisms, so it is expensive, difficult to implement, and difficult to achieve real-time measurement

Images