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Direct detection szD-OTDR based on UWFBG array using linear-phase-modulated double-pulse
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DOI：10.1364/OE.519419.png)
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Abstract
En 中文
We propose what we believe to be a novel direct detection phase -sensitive optical time -domain reflectometry ( szD -OTDR) based on ultra -weak fiber Bragg grating (UWFBG) array to achieve distributed vibration measurements with exceptional sensitivity and remarkable stability. Our system employs a pulse modulator to generate a double pulse and achieves linear phase modulation of one pulse by one cycle through a phase modulator. The phase change can be quantitatively demodulated using our proposed N -step phase -shifted demodulation algorithm. This method effectively mitigates the influence of phase noise of the laser and the pulse modulator, while also eliminating fluctuations in the half -voltage of the phase modulator. Compared with the existing phase modulation methods, our method avoids stringent requirements for the stability and precision of phase modulation. Moreover, we propose a phase -shifted approximation method, breaking the limitation of sensing length on the traditional differential approximation method and improving the accuracy significantly. The technique's effectiveness is experimentally demonstrated on a 1 km UWFBG array with a reflectivity of - 40 dB to - 45 dB and a spatial resolution of 10 m. Vibrations with different amplitudes are measured quantitatively with good linearity. The low -frequency self -noise is greatly suppressed and the overall self -noise is - 54.3 dB rad 2 /Hz. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
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3.3
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