Dynamic and Static Diffractive Optics - some Examples

Doktorsavhandling, 1999

Diffractive optics is a modern branch of optics, that exploits microstructures to manipulate the propagation of light. Fast computers and the progress in manufacturing technique of microelectronics have made possible a rapid development of diffractive optics during the past 10 years. Static diffractive optical elements (DOEs), are typically realized as microreliefs generated in polymer films on quartz plates. Today, high quality static DOEs can be manufactured, but applications of diffractive optics are yet in their infancy. In this thesis, an optical scheme for ultra-fast analog-to-digital conversion where static DOEs are the key components, is proposed. To reduce the Fresnel reflection losses from DOEs, subwavelength gratings can be superimposed on them. Promising experiments to achieve such DOEs are reported in this thesis. The use of diffractive optics would be much wider if they could be dynamically computer controlled, which requires high quality spatial light modulators (SLMs). However, such SLMs are not yet available, although substantial progress has been made the last few years, thanks to the driving force of the consumer display market. Today, a promising type of SLMs is that based on liquid crystal (LC) materials. The use of binary type ferroelectric liquid crystal (FLC) SLMs was investigated in the following studies presented in the thesis: The degree of control of the area between pixel elements in an FLC SLM was investigated by analysis of the diffracted light from the SLM. The diffraction efficiency of an FLC SLM was iteratively optimized using a feedback signal from the diffracted light. A new scheme to achieve beam steering, utilizing two FLC SLMs, modulating phase and amplitude respectively, was proposed and tested experimentally. An optical switch scheme, based on two phase modulating FLC SLMs, was analyzed theoretically with the optical signals assumed to be carried in single mode fibers. Part of this scheme was tested experimentally.