Photorefractive volume holographic grating recording with applied electric fields.

摘要

Photorefractive bismuth silicon oxide (Bi12SiO20) single crystals are often utilized in the transverse electrooptic configuration with applied electric fields for both photorefractive parameter measurements and a number of device applications. In this thesis, unexpected internal electric field nonuniformities are shown to occur and could potentially affect measurements of various materials parameters and characterizations of device performance.;For the important case of holographic grating recording (lambda = 514 nm), a collapse of the field in the bulk of the crystal occurs on the order of tens of milliseconds, and is followed by a slow recovery of the bulk electric field that occurs on the order of tens of seconds. Typically, minimum values of the bulk field ranged from 10% to 30% of the initially applied field, while steady-state bulk field values ranged from 50% to 80% of the initially applied field.;We postulate that a blocking contact forms at the metal electrode/BSO interface and is responsible for the internal field nonuniformities. Two distinct approaches were taken to model the field collapse phenomena, a numerical simulation that successfully predicted the collapse of the bulk electric field, and a heuristic tunnelling current injection model that successfully predicted the time dependence of both the collapse and rise of the bulk electric field. We estimate that a peak electric field at the negative electrode of 2.1 x 106 V/cm is reached with only 3000 V applied across a crystal of 1cm in width. However, a unique reverse polarity technique was found to strongly reduce the magnitude of the field collapse.;The effects of the field collapse phenomena on holographic grating recording have been explored. The lower post-collapse bulk fields limited the grating recording process by increasing the apparent response time, in some cases by over an order of magnitude, and by reducing the achievable diffracted intensity in steady state by up to a factor of two. The potential effects of the field collapse phenomena on holographic interconnect device performance in the application of optically-implemented neural networks have also been addressed.