Nonlinear Effects in Microwave Acoustic LiNbO3 Surface-Wave Delay Lines

Nonlinear effects have been observed in LiNbO3 acoustic surface-wave delay lines operating at a fundamental frequency of 905 MHz. Second-, third-, and fourth-harmonic generation, and their buildup and subsequent decay with distance, have been measured using laser-light deflection. The acoustic power entering these harmonics can be made comparable to that in the fundamental, since surface-wave attenuation has been seen to be dependent on input power. In fact, under certain conditions harmonic power is returned to the fundamental causing a region of negative attenuation or “gain.” Similar effects have been observed for the sum and difference frequencies (mixing) when two input frequencies are used. For linear operation at 905 MHz, surface-wave devices using Y-cut Z-propagating LiNbO3 should be limited to power densities of 10 mW/mm.