Research For 1.55μm Acousto-Optic Frequency Shifter Characteristic

Coherent wind lidar is one of the major means which measures the atmospheric wind fields, with a high signal-to-noise ratio and receive short bandwidth by the advantages, many scientists from various countries attention it. Lidar has important significance and a good prospect in many fields, such as numerical weather prediction, atmospheric dynamics, aviation safety warning and defense applications. Based on the need of coherent wind lidar system weak signal detection, coherent wind lidar systems acoustic frequency shifter technical problems were studied, including:(1)From the coupling equation about light waves and sound waves in the medium, using momentum matching and momentum mismatch analysis the law about acousto-optic interaction, come to the acousto-optic frequency shifter in normal Bragg diffraction conditions. acousto-optic deflection characteristics and acousto-optic modulation characteristics. Meanwhile, on the basis of acousto-optic frequency shifter the main indicators, analysis the design method on acousto-optic frequency shifter, including selecting the acousto-optic materials, designing size. At last, analysis the acoustic frequency shifter bandwidth and select work bandwidth.(2)Voice frequency shifter characteristics of the simulation, experimental study provides a theoretical basis;(3)For normal Bragg acousto-optic frequency shifter, we can make use of ultrasonic tracking technique to resolve the inconsistency between device BW and the length of acoustic transducer, compare with non-ultrasonic tracking, the length is improved by 4.96 times, relative BW is improved by 5.5 times.(4)According to some experiment about acousto-optic frequency shifter, we acquire characteristic curves about acousto-optic deflection and acousto-optic modulation, Meanwhile we know the mean frequency of acousto-optic frequency shifter to be 102.8MHz, Bragg BW to be 23.4MHz, Bragg angle to be 17.4mrad by measurement, and we calculate the maximum diffraction efficiency of the acousto-optic frequency shifter to be 22%. The result from experiment is almost consistent with theory.