Subwavelength structures, optical diffraction, and optical disc memories

Citation

Marx, David Solomon (1996) Subwavelength structures, optical diffraction, and optical disc memories. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/9a76-bg20. https://resolver.caltech.edu/CaltechETD:etd-09142006-154808

Abstract

Conventional optical memory discs store information in the form of pits embossed on the disc. The minimum size of the pit marks is limited by the resolution of the optical system used to read the disc. Our investigations, presented in this thesis, are primarily concerned with the question, "Can an optical disc memory be designed so that an optical system can recover information from symbols (pit marks or otherwise) which are normally unresolved?" When an optical system can determine unresolved features of an object, then superresolution has been accomplished.

We describe an experiment to recover information about lines with a width one fifth the minimum resolvable feature size. The result uncovers an important difference between an optical memory and a classical optical imaging system: in an optical memory, we can use a priori information about the finite number of possible stored states. The next investigation is for superresolution in depth, rather than for a lateral direction. We select the method of conoscopic holography and demonstrate the ability to measure the depth of a reflecting surface with an accuracy better than one-tenth the depth of focus of the optical system.

To allow the design and analysis of a memory format, we formulate an integral method to calculate diffraction for large numerical aperture focused beams on nonperiodic two-dimensional structures. The numerical method is tested for numerical convergence and accuracy, and some comparisons of numerical results and experimental measurements are also shown. We then use the numerical method extensively to analyze a variety of formats and structures.

Thesis Files