Pressure phase sensitivity is one of the most important performance indexes of the fiber-optic hydrophone. Maximizing
the pressure phase sensitivity is a basic principle in the fiber-optic hydrophone design. In this work, the orthogonal
experimental method has been used to optimize the design of the pressure phase sensitivity of the fiber-optic air-backed
mandrel hydrophone. A general three-dimensional theoretical model is carried out, and nine fiber-optic hydrophones are
fabricated for orthogonal experiment. Several factors which affect the sensitivity are analyzed in the experiments, and the
results validate the theory. The optimized designs are also gained by the analysis of the results to maximize the pressure
phase sensitivity.
In this work, the acceleration responsivity of the optical-fiber air-backed mandrel hydrophone is proposed and
investigated both analytically and experimentally. The acceleration responsivity is a significant index of the hydrophone,
and it would be a serious noise source of pressure phase sensitivity of the fiber-optic hydrophone in high vibration
environments. The three-dimensional quazistatically theoretical model of the hydrophone is created and the acceleration
responsivity of the hydrophone is analyzed. On the basis of the analyses of the parameters of the theoretical model, main
restrictively factors and the improved methods are obtained. According to general format which is proposed, certain
structures of the mandrel fiber-optic hydrophone is produced with determined parameters, and the acceleration responses
validate our theory model. The theoretical and experimental treatment give a set of guidelines, which should be followed
in order to minimize the acceleration responsivity of the fiber-optic mandrel hydrophone, and the symmetrical structure
could be applied to reduce the acceleration noises greatly. The hydrophone could be designed to achieve the required
performances according to the model created above.
KEYWORDS: Interferometry, Fiber optics sensors, Digital signal processing, Algorithm development, Signal processing, Sensors, Field programmable gate arrays, Homodyne detection, Linear filtering, Lead
One important advantage of interferometric optical fiber sensor is high sensitivity. The development of the
interferometric optical fiber sensor is partly restricted with the demodulating technique. Because of advantages such as
high sensitivity, high dynamic range, and good linearity, PGC (Phase Generated Carrier) demodulating scheme is widely
applied for interferometric optical fiber sensor now. In this paper, an arctangent approach of the PGC demodulating
scheme is introduced. CORDIC (Coordinate Rotation Digital Computer) algorithm is used to realize the arctangent
function. CORDIC algorithm is a method for computing elementary functions using minimal hardware such as shifts,
adds/subs and compares. CORDIC algorithm works by rotating the coordinate system through constant angles until the
angle is reduces to zero. The angle offsets are selected such that the operations on X and Y are only shifts and adds. This
method will lead in less complexity and higher accuracy. Since digital signal processing technology has achieved great
development, especially the appearances of high speed processors such as FPGA and DSP, PGC demodulating scheme
based on CORDIC algorithm is implemented conveniently. The experiments are carried out to verify the PGC demodulating scheme based on CORDIC algorithm.
In this work, a study of a new type of optical fiber interferometer with three-beam system has been carried out. Some
analyses of the performances of the interferometer have been considered and reported upon. A theoretical model of the
optical fiber interferometer and demonstration that such system could be constructed by optical fiber structures are
presented. To achieve the goal which ensures higher performance and stability of the interferometer the simulations for
intensity noises, phase noise in the interference path and phase shift noise of the certain three-beam optical fiber
interferometer have been carried out. The results indicate that the 3 ×3 coupler is key factor. The optical fiber
interferometer could be used to constitute an optical fiber sensor such as optical fiber hydrophones array. Other
applications of optical fiber sensor with the three-beam interferometer also have been discussed.
An improved passive demodulation method for optical fiber interferometer with 3×3 coupler is described in this work, and
some analyses have been considered and reported upon. Theoretical models of former passive demodulation method and the
improved demodulation method are presented, both of which could be used to obtain phase signals of optical fiber
interferometer with 3×3 coupler. To investigate the high performance and stability of the interferometer, simulations and
experiments for different demodulation methods are carried out, and characters of different methods are indicated. Analyses
and simulations for some factors such as intensity noises, phase noises and phase shift noises of the interferometer are proposed,
and effects of different demodulation methods are compared. The results indicate that the improved demodulation method has
better performances and is suitable to be constructed and operated by digital processing system. The further application
fields to which this optical fiber sensor with the three-beam interferometer is applied also have been discussed in this work.
In this work, a study of a new type of optical fiber interferometer with three-beam system has been carried out. Some analyses of the performances of the interferometer have been considered and reported upon. A theoretical model of the optical fiber interferometer and demonstration that such system could be constructed by optical fiber structures are presented. To achieve the goal which ensures higher performance and stability of the interferometer the simulations for intensity noises, phase noise in the interference path and phase shift noise of the certain three-beam optical fiber interferometer have been carried out. The results indicate that the 3×3 coupler is key factor. The optical fiber interferometer could be used to constitute an optical fiber sensor such as optical fiber hydrophones array. Other applications of optical fiber sensor with the three-beam interferometer also have been discussed.
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