Development And Characteristic Analysis Of Tilted Fiber Bragg Grating Based On Acousto-optic Modulation

Because of its small size, low loss and low energy consumption, acousto-optical devices are widely used in optical communications and various other occupations. In this paper, with the method of the magnetron sputtering, an ultrasonic wave transducer based on ZnO thin film of piezoelectric characteristics on tilted YAG crystal, by mechanically coupling the ultrasonic wave into the fiber, tilted fiber Bragg gratings(TFBG) based of bulk acoustic wave(BAW) were built. The characteristics of the BAW TFBG were analyzed based on the study of the sound and light interaction.Transmission among general acoustic layer and incident among different media interface of ultrasonic wave were discussed and got prepared for the analysis of the transmission and coupling of ultrasonic wave between different medium. Analysis based on the diffraction efficiency of Bragg diffraction and sound and light coupling theory ware made which provided a reference for the design of the piezoelectric ultrasonic transducer.The process of making piezoelectric ultrasonic transducer based on magnetron sputtering was introduced and the quality of the Zn O film was confirmed. The harmonic frequency characteristics of the piezoelectric ultrasonic transducer were measured and its piezoelectric properties was verified. The energy conversion loss was calculated by analyzing the Mason equivalent model. By mechanically coupling the ultrasonic wave into the fiber, the BAW TFBG was built.Analysis of the effect of the tilted angle and high order mode to the mode coupling efficiency in TFBG was made and the effect of tilted angle and the power of the ultrasonic wave to the transmission spectrum of TFBG was confirmed by experiment. Facts proved that the modulation depth of refractive efficiency in fiber by BAW coupling meets the practical requirements. By theoretical calculations we found that when the tilted angle meet certain conditions, some optical signals in the fiber would escape from the fiber. The escaped optical signals were received in a special designed experiment which also proved that TFBGs made by BAW coupling of practicality.