The characteristics and applications of the acoustooptic frequency shifter is introduced in this paper.Aiming at the limitations of conventional acoustooptic frequency shifter with shifting frequency of larger than 20 MHz,a novel acoustooptic frequency shifter based on the difference frequency principle is proposed.Its operating principle,optical path design and circuit design are introduced.The test results show that the diffraction efficiency of larger than 60%,shifting frequency of ±1 MHz,and frequency stability of better than 10-6/2 h have been obtained at the wavelength of 1 550 nm.