Experimental Exploration of the Limits of Achievable Q of Grooved Surface-Wave Resonators.
Abstract
An important basic question that remains to be answered for the surface-wave resonator is that of maximum achievable Q. Intrinsic material loss imposes a limit of Q approximately equal to 100,000 at 150 MHz on LiNbO3 and quartz. However, devices produced to date have been limited by grating reflection loss to Q approximately equal to 20,000. This paper compares two alternative approaches to the problem of minimizing the grating reflection loss and hence maximizing the Q of the grooved Fabry-Perot resonator. In one approach, the number of elements (grooves) in the reflecting arrays is modest, and increasing array reflectivity (and hence Q) is obtained by increasing the element reflectivity (deepening the grooves). Experimental measurements show that Q can be increased in this way until a groove depth of roughly 0.025 Lambda (or a step reflectivity of about 1%) is attained on a 300-groove YZ LiNbO3 resonator, at which point excessive losses due to bulk-wave scattering preclude the existence of a resonance. In the second approach, the element reflectivity (groove depth) is kept at a minimum and increasing reflectivity and Q are obtained by increasing the number of elements in the array. In either approach, element reflectivity is increased by a closer control of groove width-to-period ratio to values of 0.5 or less. Measurements of Q for various devices on LiNbO3 and ST quartz are compared with theory. In addition, the maximum Q values measured will be compared with the theoretical maximum Q's set by intrinsic material losses. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 22, 1975
- Accession Number
- ADA031696
Entities
People
- John A. Alusow
- Richard C. Williamson
- Robert C. Li
Organizations
- Massachusetts Institute of Technology