Anti-polarization-induced-fading interference type optical fiber hydrophone system

Abstract

The invention relates to the fields of optical fiber sensing and underwater acoustic signal measurement, in particular to an anti-polarization-induced-fading interference type optical fiber hydrophone system comprising a light source modulation unit (1), a multi-wavelength single-frequency laser emitting unit (2), a wavelength multiplexing unit (3), a pulse modulation unit (4), a first amplifier (5), a fiber circulator (6), a sensing array (7), a matched interference unit (8), a second amplifier (9), a wavelength demultiplexing unit (10), A photoelectric conversion and demodulation unit (11), and a display and control unit (12). Therefore, under the circumstance that the hydrophone array is processed into a fine array less than or equal to 30mm, a polarization induced-fading phenomenon is avoided.

Description

Technical field: [0001] The invention relates to the fields of optical fiber sensing and underwater acoustic signal measurement, in particular to an anti-polarization fading interference type optical fiber hydrophone system. Background technique: [0002] Optical fiber hydrophone is an underwater acoustic signal sensor based on optical fiber and optoelectronic technology. It is a new type of optical fiber sensor, also known as optical fiber sonar. It converts underwater acoustic vibrations into optical signals through high-sensitivity optical coherent detection, and transmits them to the signal processing system through optical fibers to extract acoustic signal information. It has the characteristics of high sensitivity and good frequency response characteristics. Due to the use of optical fiber as the information carrier, it is suitable for long-distance and large-scale monitoring. Optical fiber hydrophones are mainly used for the detection of sound propagation, noise, re...

AI Technical Summary

Problems solved by technology

When the polarization states of the two interfering beams of light are orthogonal, that is, the vibration directions of the two beams of light are vertical, the visibility of the interferometer will be zero, causing the phenomenon of "polarization-induced signal fading", which limits the application of the interferometric fiber optic hydrophone. Application range

In recent years, people have reduced or even eliminated the occurrence of polarization fading by using polarization-maintaining fiber, using Faraday Rotator Mirror (FRM, Faraday Rotator Mirror) in Michelson interferometer, using polarization controller, polarization diversity, etc., using polarization-maintaining Although the optical fiber and polarization diversity scheme can avoid the occurrence of polarization fading in principle, the cost of polarization-maintaining optical fiber and related devices is relatively high, especially with the increase of sensing distance and scale, the system cost will increase significantly, which is not conducive to the development of the scheme. Practical

The polarization control scheme is suitable for laboratory debugging or occasions that do not require high real-time performance. The best polarization state can always be found through continuous debugging. However, for the field of underwater acoustic sensing that requires more and more automation and integration, this The large-scale application of the method is obviously restricted

At present, the scheme of using FRM in Michelson interferometer is widely used. Because the cost of FRM is significantly higher than that of ordinary mirrors, and its shortcomings of being difficult to accommodate, under the background of increasing requirements for array size, its further development is limited. application

[0004] Since the various applications of underwater acoustic detection have high enough requirements for the phase shift sensitivity of the fiber optic hydrophone, the array elements of the fiber optic hydrophone must be sensitized to meet the requirements. The signal arm is wound on the elastic medium, but due to the large mode field diameter (MFD, Mode Field Diameter) of ordinary single-mode optical fiber (8-10μm), when the outer diameter of the elastic medium is further reduced (less than 10mm), the optical fiber hydrophone The loss of the array will increase significantly until it returns to the "dry end", that is, the signal of the photoelectric detection and demodulation system will not be detected, resulting in system failure

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