Research On The Photoelectric Signal Processing Technologies Of Optical Fiber Microphone

Among the most of sensing technologies,optical fiber sensing technology has great significance in research and practical application because of its unique excellent characteristics.As a typical application of optical fiber sensing technology,signal and information processing and other interdisciplinary disciplines,optical fiber microphone has the advantages of high sensitivity,strong anti-interference ability,high signal-to-noise ratio,long-distance low distortion,small size,etc.Compared with traditional electric microphone,it has a wide application prospect in the fields of nuclear magnetic medicine,security interception,flow monitoring and so on.In this paper,an instrumented demodulation system for Fabry-Perot(FP)interferometric fiber-optic microphone is designed based on the principle of intensity demodulation,and the photoelectric control technology and demodulation performance of the system are also studied.The main content is shown as follows:In the first chapter,the characteristics of optical fiber sensing technology and various microphones are summarized.Compared with traditional microphones,the unique advantages of optical fiber microphone and the significance of this research are pointed out.The research status of optical fiber microphone technology is also introduced.In the second chapter,the main theory of the optical fiber microphone sensing and demodulation system involved in this paper is introduced.Firstly,the structure of intensitymodulated and phase-modulated optical fiber microphone is summarized,and the principle of intensity demodulation of closed-loop control system of optical fiber microphone is introduced emphatically,and the method of controlling the working point used in this paper is analyzed emphatically.Secondly,the basic principle of semiconductor lasers and the module structure of Sampled Grating Distributed Bragg Reflector(SG-DBR)semiconductor lasers and the principle of controlling the constant temperature are introduced.Finally,the working principle and selection basis of PIN photoelectric detector are introduced,and the definitions of several important parameters of the photoelectric detector are described.In the third chapter,the hardware circuit of the closed-loop control system of optical fiber microphone is designed and manufactured,and the detection and processing of interferometric optical signals are introduced in detail.Firstly,aiming at the intra-frequency modulation scheme of the laser,a 12-bit digital current source chip ADN8810 is used as the core to fabricate the current source driving circuit of the laser.In order to achieve the effect of adjusting the internal working temperature of the laser,the temperature control circuit of the laser is designed with MAX1968 chip as the core.Secondly,a linear preamplifier circuit is designed and manufactured with a current feedback chip AD810 as the core,and the amplification factor of weak signal can be also adjusted.In the process of designing the circuit,its functions are calibrated and simulated in detail.After photoelectric conversion,the signal is transmitted to the PC program written in LabVIEW language through A/D analog-to-digital conversion and acquisition,and the demodulation of sound signal and the output of audio signal are also finished.In order to verify and optimize the functions of the photoelectric detection system designed,the comparison between commercial Thorlabs detection module and USB-NI-6211 data acquisition module is added.In the fourth chapter,the acoustic signal index of the demodulation system of optical microphone is tested.The whole closed-loop control system of optical fiber microphone is instrumented,higher sensitivity and wider frequency response range are also achieved.In the process of testing,the working point is stable at ±?/4,which basically meets the requirements of acoustic signal measurement.Finally,the research results of optoelectronic control system for optical microphone are summarized.In view of the existing problems of the system,the improvement scheme is put forward.The optoelectronic control system of the optical fiber microphone designed in this paper will be applied in practice in the field of nuclear magnetic medicine.