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Phase sensitivity light time domain reflection system and method for improving SNR (signal to noise ratio) thereof

A technology of phase-sensitive light and time-domain reflection, applied in the direction of using wave/particle radiation, measuring devices, instruments, etc., can solve the problems of narrowing frequency measurement range, reducing spatial resolution, and increasing measurement time, so as to improve signal-to-noise Ratio, improve signal-to-noise ratio, extend the effect of sensing distance

Inactive Publication Date: 2012-08-15
UNIV OF ELECTRONICS SCI & TECH OF CHINA
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0004] At present, domestic and foreign methods for improving the signal-to-noise ratio of the Φ-OTDR system mainly include changing the amplification mechanism on the hardware, or using polarization-maintaining devices and plastic sensitizing optical cables; using coherent detection instead of direct detection; or denoising by wavelet in signal processing methods and short-time Fourier analysis (STFT) to suppress noise, these methods have certain limitations
Other general methods, such as increasing the laser power, increasing the emission pulse width, and the cumulative average method, are based on the premise of sacrificing other performance indicators of the system: increasing the laser power is likely to cause near-end signal saturation; increasing the emission pulse width will reduce the spatial resolution. ;Although the cumulative average method has always been used as a general and effective method to improve the signal-to-noise ratio of the Φ-OTDR system, with the increase of the number of accumulations, the measurement time increases correspondingly, and the frequency measurement range of the system decreases accordingly

Method used

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  • Phase sensitivity light time domain reflection system and method for improving SNR (signal to noise ratio) thereof
  • Phase sensitivity light time domain reflection system and method for improving SNR (signal to noise ratio) thereof
  • Phase sensitivity light time domain reflection system and method for improving SNR (signal to noise ratio) thereof

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Embodiment 2

[0032] The Simplex code is a unipolar matrix composed of 1 and 0, which can be transformed from the Hadamard matrix. Compared with Simplex coding, Hadamard coding itself is a more efficient coding method for reducing the influence of noise, but because it is a bipolar matrix, and the actual optical system is non-negative, so most of them still use Simplex coding. Simplex code is a coding method with the highest decoding efficiency; in addition, Simplex code is a coding method with short code length and high gain; it has linear properties and does not have strict requirements on the pulse code amplitude, which can suppress the instability of pump power in the optical system , Modulator extinction ratio change and other factors affect the coding effect; another advantage of using Simplex coding is that it can use the fast Hadamard code transformation (FHT) algorithm to decode, further improving the decoding efficiency. In addition, among the modulation methods for encoding pulse...

Embodiment 3

[0044] As a third embodiment of the present invention, the following describes the specific implementation process based on 3-order Simplex code return-to-zero modulation coding and coherence reduction processing:

[0045] The upper computer (1) controls the waveform generation card according to the stored Simplex matrix sequence code, such as 101, 011, 110 (3) according to the following figure 2 In the return-to-zero modulation mode shown in (a), the serial code signal is periodically transmitted outward. The emitted sequence code signal drives the intensity modulator (acousto-optic modulator or electro-optic modulator) (4) to perform sequence coding on the coherent light output by the ultra-narrow linewidth laser (1), and the first group corresponding to the first group of sequence codes P 1 (t)+P 3 (t), the second sequence of pulsed light corresponding to the second group of sequence codes is P 2 (t)+P 3 (t), the third sequence of pulsed light corresponding to the thir...

Embodiment 5

[0047] As a fifth embodiment of the present invention, the sliding fast decoding method involved in the present invention is introduced below:

[0048] Still taking a 3-order Simplex encoding matrix as an example, the encoding matrix is,

[0049] S = 1 0 1 0 1 1 1 1 0

[0050] The conventional fast decoding method of Hardamard code is to decode every three transmission cycles to obtain a complete decoding signal group ω 1 (t), ω 2 (t), ω 3 (t), the decoded inverse matrix is,

[0051] S - 1 = ...

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Abstract

The invention discloses a phase sensitivity light time domain reflection system and a method for improving SNR (signal to noise ratio) thereof. The method comprises the following steps of: changing an initial phase of each code word of a sequence coded pulse randomly through an external modulation method when a pulse is coded based on a Simplex sequence and a zero adjustment modulation mode; carrying out coherence reduction treatment on the coherence among sequence codes, and keeping the coherence in a unit code; and decoding through a rapid sliding decoding method. According to the system and the method, as well as the system SNR is improved and the sensing distance is prolonged, not only can the system space resolution not be reduced, but also the space resolution can be improved effectively; by utilizing the rapid sliding decoding method, the measuring time of the coded pulse is equal to the measuring time per time, the efficiency is higher compared with that by using a progressive average measuring method, and the frequency measuring range of the system is expanded, and thus the light pulse coding method is a high-efficiency method for improving the SNR of the phase sensitivity light time domain reflection system, and the integral performance of the system can be improved effectively.

Description

technical field [0001] The invention belongs to the field of fully distributed optical fiber vibration measurement systems, and in particular relates to a phase-sensitive optical time-domain reflection system based on optical pulse coding and a method for improving the signal-to-noise ratio. Background technique [0002] The phase-sensitive optical time-domain reflectometry (Φ-OTDR) system based on the Rayleigh scattering mechanism is currently the most important fully distributed vibration measurement technology. By injecting a coherent narrow pulse at one end of the fiber, detecting the change of the interference fringe of the Rayleigh scattered light, and judging the phase change introduced by the external disturbance and its spatial distribution along the fiber. The Φ-OTDR system is based on the phase-sensitive detection mechanism with extremely high sensitivity. At the same time, it is superior to other optical fiber distributed vibration measurement systems in terms of...

Claims

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Application Information

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IPC IPC(8): G01H9/00
Inventor 吴慧娟彭正谱李小玉王杰贾新鸿饶云江
Owner UNIV OF ELECTRONICS SCI & TECH OF CHINA
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