Performance of LiTaO(3) and LiNbO(3) light modulators at 4 GHz.

Two light intensity modulators have been constructed using LiTaO3 and LiNbO3, respectively, in a reentrant microwave cav­ ity tuned to 4.2 GHz. The loop-coupled cavity is shown sche­ matically in Fig. 1. The crystal is attached to the chisel-shaped center post with silver paste and is oriented so that the (peak) voltage V is along the c axis. The cavity diameter D is 1.91 cm, the post diameter d is 0.38 cm and the resonant frequency is deter­ mined by the cavity height h. Not all the electric field is concentrated in the gap containing the crystal. A rough estimate of the added capacity Ca in paral­ lel with the crystal is ε0πD/4h. The ratio of total capacity CT to crystal capacity C is then