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All-fiber acousto-optic intensity modulator using surface acoustic wave

In this paper, a fiber coupled-mode equation between front-wave and back-wave of optical guided modes with micro disturbance is given from parameter interaction equation. Considering surface acoustic wave (SAW) as the micro disturbance, a coupled-wave equation group of SAW all-fiber acousto-optic (AO) effect is deduced. The equation group includes front-wave equation and back-wave equation. A back-wave efficiency formula is demonstrated through solving the equation group. It is proved, that the back-wave efficiency is directly proportional to power of the SAW under condition of weak AO interaction. Quartz crystal is considered as the best base crystal. It is because acoustic impedances of the quartz crystal and the fiber are equal approximately. According to form of SAW basic equations or Christofell equations the best SAW mode of the quartz is determined. All-fiber AO intensity modulator using SAW is designed and manufactured. Modulation curve of optic power of the back-wave vs power of electric signals driving the device is measured. The experimental results indicate, optic power of the back-wave is directly proportional to power of electric signals driving the device. The experimental results are consistent with the theory. Advantages of the device are smaller volumes, less energy consumes, less inset-losses and so on. Besides, it is easy to integration and can be used in optic fiber communication.