Optical Information Storage and Processing

Abstract

Optical information storage and optical information processing are the two themes of this thesis. Chapter two and three discuss the issue of storage while the final two chapters investigate the topic of optical computing. In the second chapter, we demonstrate a holographic system which is able to record phenomena in nanosecond speed. Laser induced shock wave propagation is recorded by angularly multiplexing pulsed holograms. Five frames can be recorded with frame interval of 12ns and time resolution of 5.9ns. We also demonstrate a system which can record fast events holographically on a CCD camera. Carrier multiplexing is used to store 3 frames in a single CCD frame with frame interval of 12ns. This technique can be extended to record femtosecond events. Information storage in subwavelength structures is discussed in the third chapter. A 2D simulation tool using the FDTD algorithm is developed and applied to calculate the far field scattering from subwavelength trenches. The simulation agrees with the experimental data very well. Width, depth and angle multiplexing is investigated to encode information in subwavelength features. An eigenfunction approach is adopted to analyze how much information can be stored given the length of the feature. Finally we study the effect of nonlinear buffer layer. We switch gear to holographic correlators in the fourth chapter. We study various properties of the defocused correlator which can control the shift invariance conveniently. An approximate expression of the shift selectivity is derived. We demonstrate a real time correlator with 480 templates. The cross talk of the correlators is also analyzed. Finally, in the fifth chapter we apply the optical correlator to fingerprint identification and study the performance of the correlation based algorithms. The windowed correlation can improve the rotation and distortion tolerance.