University of Edinburgh; College of Science and Engineering; School of Physics
Abstract
Many optical processing systems rely critically on the availability of high
performance, electrically-addressed spatial light modulators. Ferroelectric liquid
crystal over silicon is an attractive spatial light modulator technology because it
combines two well matched technologies. Ferroelectric liquid crystal modulating
materials exhibit fast switching times with low operating voltages, while very
large scale silicon integrated circuits offer high-frequency, low power operation,
and versatile functionality.
This thesis describes the design and characterisation of the SBS256 - a general
purpose 256 x 256 pixel ferroelectric liquid crystal over silicon spatial light modulator
that incorporates a static-RAM latch and an exclusive-OR gate at each
pixel. The static-RAM latch provides robust data storage under high read-beam
intensities, while the exclusive-OR gate permits the liquid crystal layer to be fully
and efficiently charge balanced.
The SBS256 spatial light modulator operates in a binary mode. However,
many applications, including helmet-mounted displays and optoelectronic implementations
of artificial neural networks, require devices with some level of
grey-scale capability. The 2 kHz frame rate of the device, permits temporal multiplexing
to be used as a means of generating discrete grey-scale in real-time.
A second integrated circuit design is also presented. This prototype neuraldetector
backplane consists of a 4 x 4 array of optical-in, electronic-out processing
units. These can sample the temporally multiplexed grey-scale generated by the
SBS256. The neurons implement the post-synaptic summing and thresholding
function, and can respond to both positive and negative activations - a requirement
of many artificial neural network models
