William Alden Crossland

Active backplane spatial light modulators using chiral smectic liquid crystals (Invited Paper)

We consider the addressing requirements associated with some analogue and binary electro- optic effects in chiral smectic liquid crystals driven from silicon VLSI backplanes. This class of liquid crystals offers major improvements in switching speed over electro-optic effects in nematic liquid crystals, but their non-RMS response to impressed voltages leads to addressing difficulties. Their spontaneous polarization also leads to limitations in using pixel drive circuits resembling dynamic random access memory cells (DRAMs), which are commonplace in display technology. Some illustrative examples of the performance of electro-optic effects with currently available materials are given, followed by a discussion of the problems associated with the charging phenomena occurring when ferroelectric liquid crystals are driven from active backplane drive circuits. Addressing schemes are then considered, particularly those that are aimed at providing electro-optic modulators with continuous optical access and with no temporal noise in their transfer characteristic, such as might be needed in optical switching devices. Some examples of experimental pixel circuits are given.

Transmissive analogue SLM using a chiral smectic liquid crystal switched by CdSe TFTs

A transmissive, analogue, active backplane electrically addressed SLM using chiral smectic liquid crystals is described with CdSe TFTs to switch the pixels. The device consisted of a matrix of 200 im x 200 im pixels forming 128 rows by 190 columns. The liquid crystal used was 854E (BDH Ltd. England) which allowed observation of the device behaviour in both the smectic C* (ferroelectric switching) and smectic A (electrocinic effect switching) liquid crystal phases. Some observations are made concerning each of these.