Bulk Wave Reflection-Grating Devices

摘要

Devices using reflections of bulk acoustic waves from optically generated holograms stored in iron doped lithium niobate have been demonstrated. High frequency signal-processing devices such as filters and resonators may be built utilizing this effect. Fabrication is simple and they can potentially operate with center frequencies and bandwidths of several gigahertz and interaction times of tens of microseconds. This is an order of magnitude improvement in bandwidth and operating frequency over surface acoustic wave devices. Measurements of reflection coefficients as a function of iron doping have been carried out. The maximum was found in LiNbO3 doped with 0.055 iron by weight, and is approximately .0004 per grating element. This is large enough for practical devices because at high frequencies, a grating of 10,000 elements occupies only a small (1 cm) extent of the crystal yet has a large total reflection coefficient. High Q resonators operating at fundamental frequencies in the gigahertz range are a potential and important application. Prototype single-port resonators with Qs of up to 10,000 and center frequencies of 1.5 GHz have been demonstrated. Other holographic materials are of interest, especially LiTaO3 because it has several temperature compensated propagation directions. (Reprints)