Surface acoustic wave properties of z-cut LiNbO3 waveguides fabricated by proton exchange using octanoic acid

Surface acoustic wave (SAW) properties of z-cut LiNbO3 waveguides fabricated by proton exchange using octanoic acid are investigated. The phase velocity V-p and electromechanical coupling coefficient K-2 of SAWS are significantly decreased by the increase of kd, where k is the wavenumber (2 pi/lambda) and d is the waveguide depth. The insertion loss IL of a SAW is increased by the increase of kd and becomes nearly constant at kd greater than or equal to 0.13. The temperature coefficient of delay TCD of a SAW calculated from the frequency change shows an apparent increase with kd, reaching a maximum at kd = 0.213, then slightly decreasing at higher kd. On the other hand, the effects of annealing on V-p and IL are also investigated. The results show that post-annealing can result in a restoration of the decreased V-p and an improvement of IL.