The Design Of Passive Optical Fiber Acoustic Pickup System Based On FPGA

Optical fiber sensing technology is a hot research filed of sensor in recent years.Fiber optic sensor has good potentials that include high sensitivity, anti-electromagnetic interference, excellent environmental adaptability, distributing sensing and so on, which makes it has good prospects for development.Extensive national fiber resources have provided favorable conditions for the application of optical fiber sensing technology. Based on fiber-optic sensing technology, specifically Sagnac fiber interferometer principle, this paper designed a passive optical fiber acoustic pickup system on FPGA platform. The innovation of this system is that it can achieve the full light collection and immediate reduction of the sound signal in the specific area, and its sampling point and background processing system can reach80km distances.The optical fiber sensor is passive and free from electromagnetic,these features will make it develop rapidly in some fields such as national security,military reconnaissance,security monitoring etc.Passive optical fiber acoustic pickup system is composed of six basic module, including power supply module, optical unit module, audio collection module, signal processing module,audio output module and display module.Power supply module provides standard voltage input and voltage conversion for other modules. optical unit module is divided into laser light transmitting circuit and photoelectric receiving circuit, respectively responsible for the emission of specific wavelength laser on the sending end and the signal conversion and amplification at the receiving end. The audio acquisition module is mainly composed of optical fiber sensing head. Through the optical fiber sensing heads into the fiber connection of Sagnac loop, the optical interferometric sensing can be realized. FPGA is the core of signal processing module. It controls the entire system and completes software demodulation of the sensing signal.Audio output module and display module complete sound sensing signal audio output and display.In this paper, the system hardware circuit is designed by using protel. The whole software system is programmed using verilog HDL under the platform of Quartus Ⅱ.A simulation about the optical receiving circuit is provided through Multisim software in the paper. And in chapter five, two samples respectively taken by passive optical fiber acoustic pickup and mobile phone recording software about some same sound signals were compared using cool pro edit software. The results shows that the passive optical fiber acoustic pickup system is able to precisely and reliably accomplish sound data sensing, acquisition, processing processing and restore etc. And it fully meets the design requirements.