Three-pulse dislocation interference grating enhanced distributed vibration demodulation system and method

Abstract

The invention discloses a grating enhanced distributed vibration demodulation system based on three-pulse dislocation interference. The system comprises a laser device, a pulsed light modulator, a three-pulse generation polarization-maintaining structure, a first erbium-doped optical fiber amplifier, a first optical circulator, a fiber grating array, a second erbium-doped optical fiber amplifier, a second optical circulator, a three-in-three optical coupler, a first Faraday rotator mirror, a second Faraday rotator mirror and a four-channel data acquisition card. Based on the distributed fiber grating vibration sensing system, the three-pulse dislocation interference and three-in-three optical coupler digital phase demodulation technology is adopted, XX and XY pulses are utilized to complement interference visibility, and demodulation is performed by selecting a better one, so that polarization fading resistance and interference signal high visibility in the distributed fiber grating vibration sensing system are realized.

Description

technical field [0001] The invention relates to the technical field of optical fiber sensing, in particular to a grating-enhanced distributed vibration demodulation system and method for three-pulse misalignment interference. Background technique [0002] Since the advent of optical fiber sensing technology, it has been widely concerned and studied deeply due to its many advantages. Optical fiber as a sensor has been widely researched and applied because of its passive, small size and easy multiplexing. Using Phase Sensitive Optical Time Domain Reflectometry The optical fiber sensing system has the characteristics of high sensitivity and has very important application value in many fields. Compared with the traditional electrical sensing system, it has better sensing performance and wider application in various harsh environments. prospect. In order to improve the positioning accuracy and detection sensitivity to realize the sensing of tiny signals, researchers have intr...

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Problems solved by technology

The optical path full polarization maintaining technology is to replace the ordinary optical device in the optical path with a polarization maintaining optical device. There is basically no birefringence effect in the optical path, but the cost is high and it is not easy to reuse; the polarization diversity receiving technology performs polarization detection according to the polarization direction at the receiving end , usually three receiving ends, the polarization states are 60 degrees to each other in space, which can ensure that at least one of the three receiving ends will not produce polarization fading, but this method makes the receiving end complicated and the minimum visibility is only 0.38; The polarization scrambling method uses a polarizer to modulate the linearly polarized light in the optical path into depolarized light at high speed. This method ensures that the interfering light will not be affected by the polarization state, but it will introduce large polarization noise and reduce the light intensity; Faraday rotation The mirror method uses a Faraday rotation mirror to cancel the birefringence effect when going back and forth in the optical path, but each sensing point requires two Faraday rotation mirrors, which is too expensive and has a narrow application area; the polarization switching technology uses a polarization controller to make the output pulse The polarization state of the sensor changes in two orthogonal directions (set as X and Y directions). By constructing the Jones matrix of the sensing fiber to eliminate the influence of polarization fading, the visibility can be kept constant at 1, but polarization switching is required in the polarization switching technology system It cannot be passive and the polarization switcher needs negative feedback control. In addition, because it is necessary to obtain 4 interference pulses in the same sensing area to demodulate a signal, the utilization rate of the sampling rate is only 1 / 4 of the actual

[0005] The existing anti-polarization fading methods have their own shortcomings, and most of the methods are not low in cost. Therefore, it is necessary to find an anti-polarization fading method with high minimum visibility, wide application range and high cost performance

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