Analyses Of Crosstalks And Noises In Multiplexing Arrays Of Fiber Optic Hydrophones

With the development of the large-sale arrays of fiber-optic hydrophones, time-division multiplexing(TDM) and wave-division multiplexing (WDM) have been adopted widely. Crosstalks and noises in the system become the key necks that baffled greatly the progress of large-scale arrays. In this dissertation, the problems of crosstalks and noises in the large-scale arrays were analyzed on the base of reseaching on multiplexing technologies, and the techniques suppressing or decreasing the crosstalks and noises were sought for. A reasonable design for a large-scale array of fiber-optic hydrophones is grounded on this dissertation. The forming mechanism of crosstalks in the TDM system was analyzed theoretically, and the relationship between crosstalks and the extinction ratio of optical pulse modulator used in the TDM system was investigated. The interchannel and intrachannel crosstalks in the WDM system were discussed separately, and the contributions to crosstalks were appraised from architecture's alteration, the finite isolation between channels in multiplexers or demultiplexers, and nonlinear effects in the system. Noises in the large-scale multiplexing system were studied theoretically, and all kinds of factors were considered that have relation to noises, phase resolution, and dynamic range of the system, such as multiplexing channel number, the length of the transmission fiber, using in-line Erbium-dropped fiber amplifiers or not, and so on.The main results and creative points in the dissertation were as follows:a) By means of studying on the fiber-optic hydrophones'TDM array based on phase generated carrier(PGC) demodulation with laser frequency modulation, the mathematic models were set up, used for theoretical analyses of noncoherent crosstalks in the system using low coherent laser and coherent crosstalks in the system using high coherent laser. The formulas calculating crosstalks were given, and the method measuring crosstalks was shown definitely.b) Crosstalks in WDM system of fiber-optic hydrophones were analyzed roundly, and the relation of isolation ratio between channels in multiplexers to crosstalks was pointed out.c) The noise mode was established for a large-scale array of fiber-optic hydrophones using TDM and WDM, and the methods were presented that suppress noises and enlarge dynamic range.d) A scheme was given of constituting the very large-scale array composed of 512...