Donald L. Hammond

Optimum crystal orientation for acoustically tuned optical filters

Theoretical and experimental studies of the acoustically tuned optical filter show that suitable crystal orientations can be divided into two broad classes based on the acoustic properties of the propagation path used. In acoustically isotropic cases, the acoustic phase and group velocities are collinear. All 32 crystalline point groups are examined for acoustically isotropic orientations that may be useful in tunable optical filters. In acoustically anisotropic cases, the phase and group velocities are not collinear. Methods are presented with which the effects caused by acoustic divergence in these cases may be compensated by similar effects due to changes of birefringence. In particular, anisotropic propagation collinear with acoustic group velocity on a path 101.2° from the optic axis in the Y, Z plane of quartz allows operation at a lower acoustic frequency and power level than that required by isotropic orientations for equivalent performance.

The crystal resonator- a digital transducer

Precision piezoelectric quartz resonators have evolved during a half century of research, development, and engineering. It is an evolution that started with rudimentary concepts and a precision of one part in a thousand, and emerged today with a precision of a few parts in 1012. Although there have been significant steps forward through single contributions, the evolution has been a continuous improvement with an order of magnitude achieved every five to seven years. Not that anyone was particularly aware of these milestones, but, viewed in total, this improvement of a billion to one must stand as one of the truly amazing developments of this electronic age.