The waveguide-type acoustooptic frequency shifter (AOFS) driven by a surface acoustic wave (SAW) in a tapered crossed-channel waveguide on a 128°-rotated Y-cut LiNbO{sub}3 substrate have been proposed for an optical wavelength of 1.55μm. In this paper, to clarify the condition for the AOFS with a high diffraction efficiency, the SAW power required for 100% diffraction (P{sub}100) dependences on the length of the AO interaction region and the driving frequency are investigated. First, the AOFS with the length of the AO interaction region of 3 mm was fabricated and the diffraction efficiency of 65% was obtained. Next, the measured values of P{sub}100 for the driving frequencies of 125 MHz and 200 MHz were found to be in agreement with the calculated P{sub}100, which shows that there is an optimum driving frequency. Furthermore, an optical frequency domain ranging using the frequency shifted-feedback fiber laser with the AOFS was demonstrated.
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