Reflective Fiber-optic Acoustic Sensors, Key Technology Research

Fiber optic acoustic sensor (FOAS) is a novel type of acoustic sensor. It has many excellences such as high sensitivity,anti-EMI,anti-RFI,high security and credibility.It can be used in harsh environments such as intense electromagnetic interference,radio frequency, military,security,explosive and inflammable field.Therefore,it is very important to develop a stable,credible and high fiber optic acoustic sensor.Different types of reflective intensity modulation FOAS is analysed.It is pointed out that FOAS will be miniatured,intelligent,linked and multi-information fusion.The key technique of FOAS will be more investigated.A Y-type reflective intensity modulation scheme, which uses sigle mode fiber as the transive and receive fiber, simplifies the configuration.A laser diode of a wavelength of 1310nm is used as its light source.It has excellences of low power loss,high sensitivity and good anti-interference ability.Basic theories of diaphragm stretched at the edge and diaphragm clamped at the edge is summarized.Finite element analysis,which simplifies the diaphragm configuration,is used to analyse flat circular diaphragms and corrugation diaphragms.The result indicates that when the flat diaphragms is more thicker and its diameter is more bigger,it is more sensitive,its narural frequency is more higher.The corrugated diaphragms is more sensitive than flat diaphragms,but its narural frequency is lower.The sensitivity of the corrugated diaphragms increases with the corrugation number and corrugation length,decreases with the corrugation height.Its narural frequency changes the other way.The research of the output optical field intensity distribution model is summarized.The Gauss distribution assumption and the principle of conservation of energy are used to simplify the model. The normalized intensity modulation model of the FOAS is derived from the intensity distribution model and the principle of flat mirror imaging.A stable laser diode driver is designed and the experimental system of the FOAS is set up.Experimental results indicate that the APC driver does steady the light power. The intensity modulation model of the FOAS fits quite well with the theoretical value.The experimental results of the FOAS approximately agree with the finit element analysis results.