Research On Interference Fiber-optic Hydrophone Of Acoustic Modulation And PGC Technique

As a detection device for underwater acoustic signals,fiber-optic hydrophones are widely use in numerous areas,such as environmental monitoring,resource exploration and military science.The interference fiber-optic hydrophone is one of the fiber-optic hydrophones with high precision and sensitivity.The interference fiber-optic hydrophone detects the signals by the phase change of interference signal.Phase generated carrier(PGC)technique is a homodyne detecting technique used in interference fiber-optic hydrophones.The technique has high sensitivity and brand dynamic range,and could deal with phase fading.Based on traditional interference fiber-optic hydrophone and PGC technique,this paper researches that acoustic modulation applies to PGC technique.To solve the problem in PGC demodulation,the parameter estimation algorithms are proposed.Also,this paper researches the design of optical path to enhance the sensitivity.The main contents of this paper are as following:First,this paper researches the modulation scheme of acoustic modulation.The acoustic modulation scheme is introduced and compared with other two modulation schemes.After analyzing the key parameters and simulation,the fiber-optic hydrophone using acoustic modulation scheme is realized,whose SNR reaches 40 d B.Second,two parameter estimation algorithms are proposed.The former one is based on the analysis of interference signals,and the latter one is based on calculations of mixing signals in three channels.The algorithms could estimate the modulation depth of PGC technique.The estimation algorithms solve the difficulty of adjusting and setting modulation depth in acoustic modulation scheme.Also,the algorithms could be used in other conditions to advance the performance of signal detection.The relative error of the algorithms less than1% and 5% respectively in simulations and experiments.Third,an optical design based on fiber loop is proposed,which could enhance the sensitivity of hydrophone system.The design is a cascade connection of a two-beam interference and a fiber loop,and the sensor is placed in the fiber loop.When traveling in the fiber loop,the optical signals are modulated for several times,which could amplify the optical path and enhance the sensitivity.When the ratio of the path-length difference in the interference to the length of the fiber loop is k,the magnifications of phase change could reach to k and 0.95 k respectively in simulations and experiments.