Bipolar differential phase encoding ultrahigh spatial resolution Brillouin optical time domain reflectometer

Abstract

The invention provides a bipolar differential phase encoding ultrahigh spatial resolution Brillouin optical time domain reflectometer. The reflectometer comprises a narrow linewidth laser, a polarization-maintaining coupler, a differential encoder, a Mach-Zehnder modulator, an optical pulse amplifier, an optical circulator, a sensing optical fiber, an optical amplifier, a coherent photoelectric receiver, a sideband separator and a result measurement module. By implementing the method, the spatial resolution of Brillouin scattering spectrum measurement can be effectively improved, meanwhile, the measurement precision can be effectively improved by increasing the superposition average frequency, and in addition, the measurement performance is effectively improved by directly adopting a bipolar coding sequence mode.

Description

technical field [0001] The invention relates to the technical field of distributed optical fiber sensing, in particular to a Brillouin optical time domain reflectometer with bipolar differential phase encoding and ultra-high spatial resolution. Background technique [0002] Brillouin Optical Time Domain Reflectometer (BOTDR) is a distributed optical fiber sensing technology. The basic principle is to launch a laser pulse with a very narrow width (generally 10-500ns) at one end of the fiber. When the laser pulse propagates along the optical fiber, it will be scattered by Brillouin scattering (Brillouin scattering) caused by phonons in the optical fiber everywhere in the optical fiber, so that part of the laser light will be scattered back in the direction of propagation, and the frequency of the scattered laser light There is a frequency shift relative to the frequency of the emitted light pulses. In standard single-mode fiber, this frequency shift is about 10.8 GHz and is ...

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Problems solved by technology

After the noise is squared, a constant positive noise power level is formed, which cannot be eliminated by multiple average superposition, which limits the final measurement distance of these technologies

[0006] 2. For the measurement of the Brillouin scattering spectrum, no matter whether it is a frequency sweeping scheme or an FFT scheme, the spectrum cannot be continuously analyzed in frequency, and there must be a frequency interval in frequency analysis, so that the resolution of the spectrum is limited, and ultimately limits the accuracy of the measurement

[0007] 3. Encoding to improve measurement performance is severely limited due to the need to rely on intensity detection

Moreover, unipolar encoding is susceptible to intensity noise and nonlinear effects, and its performance is greatly restricted.

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