Weak reflection fiber bragg grating demodulated by adopting double square waves and B-spline wavelets

Abstract

The invention discloses a weak reflection fiber bragg grating demodulated by adopting double square waves and B-spline wavelets. The method comprises the following steps that 1, a digital signal generator generates a double-square-wave signal to drive an acousto-optic modulator, so that a continuous single-frequency laser converts same into double-square-wave laser; 2, the weak reflection fiber bragg grating reflects the double-square-wave laser; 3, the photoelectric detector receives a light intensity signal; the method further includes: 4, extracting an interference characteristic value of an interference interval under the double-square wave signals in a plurality of continuous periods to form an interference intensity signal; 5, performing B-spline wavelet denoising processing on the interference intensity signal; 6, performing Hilbert transform on the interference intensity signal after noise reduction processing; and 7, performing arc tangent operation on the ratio of the interference intensity signal to the phase-shifted signal, and finally obtaining an interference phase signal to reflect an external vibration signal. The invention has the advantages of being capable of obtaining stable vibration signals, simple in structure and small in calculation amount.

Description

technical field [0001] The invention relates to the technical field of signal processing of an optical fiber sensing system, and more specifically relates to a method for demodulating a weak reflection fiber Bragg grating by using bidirectional waves and B-spline wavelets. Background technique [0002] Weakly reflective fiber Bragg gratings (WFBG) are prepared online by drawing towers, and have the same weak reflectivity, central wavelength and spacing length. Through the time division multiplexing of WFBG, it can be used for underwater submarine detection, earthquake early warning and structural health monitoring. WFBG signal demodulation is the key to realize the application, and it has been paid more and more attention by scholars. [0003] The microwave photonic method can realize high-speed signal demodulation, but due to the existence of frequency shift, difference frequency and frequency discrimination devices, the demodulation structure is huge and complex. The tun...

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Problems solved by technology

[0005] In the single pulse method, the single pulse width is set to 4 / 3 times the time of laser round-trip transmission in the fiber between adjacent WFBGs, then the pulses reflected by adjacent WFBGs have 1 / 3 pulse width overlapping interference, and the interference area and the left and right non-interference areas are tested. Simple mathematical operations to obtain interference information; the same pulse combined with 3×3 coupler symmetrical demodulation can also be used to detect interference information. The core problem of these two methods is that the interference length is short and the spacing accuracy of WFBG is high.

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