Research On Optical Signal Detection Technology Based On Acousto-optic Modulation

The light signal detection technology based on acoustooptical modulation has the advantages of good confidentiality in detecting and high detection efficiency,and thus has been rapidly developed and applied.Based on the principle of acousto-optic grating and the characteristics of Bragg diffraction,an acousto-optic modulation grating system is designed.The acoustic wave is induced into the fiber with a titled angle to produce the oblique fiber grating Structure.The light in the optical fiber is diffracted when it travels through the grating structure,and in the case of certain conditions the light escape from the fiber,and then captured by the spatial photodetector,thus the detection of the optical signal in the fiber is achieved.The main contents of this dissertation are as follows:Through the analysis of the characteristics and diffraction rules of the Bragg grating in the optical fiber,an ultrasonic generator suitable for the acousto-optic modulation grating system is designed in the grating modulation system.According to the theory of the Bragg diffraction,the conditions for radiation mode detection are analyzed.The ZnO thin film ultrasonic transducer was deposited on one side of the wedge-shaped YAG crystal by magnetron sputtering.The experimental results show that the ultrasonic transducer has good electrical and acoustic harmonic characteristics,The optical fiber is embedded in the other side of the YAG crystal,and the acoustic wave generated by the ultrasonic transducer is introduced in fiber in a titled angle for acousto-optic modulation.According to the transmission law of ultrasonic wave at ordinary acoustic layer and solid interface,the characteristics and loss of acoustic wave propagation in the device are analyzed,and an improved acoustic transmission coupling structure is designed.Based on the study of acousto-optic interaction,the characteristics of acousto-optic oblique fiber grating are analyzed.By using the fiber-mode complex vector solution algorithm,the grating characteristics of different tilted angles,acousto-optic interaction length and external refractive index are analyzed.And the radiation spectrum is studied to simulate the radiation energy under different conditions,and the basis of the experiment is given for the radiation detection.Based on the diffraction and mode coupling theory of the tilted fiber grating,the transmission loss of the acoustic wave tilting fiber grating is experimentally tested.The experimental results show that the Bragg diffraction occurs on the specific wavelength band of the acousto-optic grating and satisfies the condition of the light escape.The increase of the power of the light source,the optical loss of the transmitted light and the reception value of the escape light are correspondingly meet.And the effectiveness of the acousto-optic modulation grating system is proved by the detection of the transmitted light loss and the escape light.The results of this paper show that the grating structure based on acousto-optic modulation is efficient when applied to selective filtering and real-time monitoring of optical fiber communication system.