3-channel acousto-optic modulator for laser projection display system

A small laser projection display system is designed with a hybrid dichroic mirror for color separation, a hybrid dichroic mirror for color recombination, a 3-channel acousto-optic modulator(AOM) and a scanning part. The 3-channel AOM modulates red, green and blue laser breams. The wavelengths of red, green and blue beams are 647, 515 and 488 nm respectively. The carrier frequencies of each channel of AOM were adjusted to minimize the diffraction angle differences among red, green and blue laser beams. The carrier frequencies are 130, 168, 178 MHz for red, green and blue laser beams respectively. The measured diffraction angle after the carrier frequency control equals to the calculated diffraction angle. The transducer structure of AOM was optimized to get a high diffraction efficiency and to maximize isolation between adjacent channels by a slicing saw, which enhanced the electrical and acoustic isolation. The impedance matching-circuit of each electrode is housed in a separate compartment to suppress electrical crosstalk. The diffraction efficiency and risetime of the 3-channel AOM are over 85% and 50 nsec per each cell. The crosstalk between the channels is less than -30 dB.