Demodulation of Weak Reflection Fiber Bragg Gratings Using Double Square Wavelet and b-Spline Wavelet

Abstract

The invention discloses a weak reflection fiber Bragg grating for demodulation by using square wave and B-spline wavelet. It includes the following steps, step 1: generating a double-wave signal from a digital signal generator to drive the acousto-optic modulator, so that the continuous single-frequency laser is converted into a double-wave laser; step 2: weakly reflecting fiber Bragg grating reflects the double-wave laser, step 3: The photodetector receives the light intensity signal; step 4: extracting the interference eigenvalues ​​in the interference interval under the double-wave signal of multiple consecutive cycles, to form an interference intensity signal; step 5: performing B-spline wavelet noise reduction processing on the interference intensity signal; step Step 6: Perform Hilbert transform on the interference intensity signal after noise reduction; Step 7: Perform arctangent operation on the ratio of the interference intensity signal and the phase-shifted signal, and finally obtain the interference phase signal to reflect the external vibration signal. The invention has the advantages of being able to obtain 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, in particular to a weak reflection optical fiber Bragg grating demodulated by square wave and B-spline wavelet. Background technique [0002] Weakly reflective fiber Bragg gratings (WFBGs) are fabricated in-line from draw towers and have the same weak reflectivity, center wavelength, and spacing length. Through 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 the demodulation structure is huge and complicated due to the existence of frequency shift, frequency difference and frequency discrimination devices. Tunable laser method and tunable Fabry-Pero...

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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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