Multi-Layer Optical Memory Systems

by Park, Sang-Ki.

A master and slave servo technique that maintains tracking and focus registration inside a volumetric two-photon disc is presented, and a dynamic test stand with full capability of closed-loop focusing and tracking servo is designed and experimentally demonstrated. The stability of the servo control is experimentally verified. Also, the misregistration of the slave beam with respect to the master beam due to disc tilt and beam skew is calculated. Conventional multiple-layered reflective thin-film systems, which detect reflected light from data layer using focused illumination, are also of interest, because they have higher readout data transfer rate than fluorescent media and more conventional fabrication technology and materials are available. The capacity and performance of a conventional multiple-layered bit-wise optical memory system are affected by several factors, like spherical aberration, layer transmission and inter-layer crosstalk. Characteristics and limitations due to each factor are investigated, and ways to improve capacity are presented. A new technique to analyze inter-layer crosstalk based on Babinet’s principle is also presented. The inter-layer crosstalk is calculated for both coherent and incoherent illumination, and results for several combinations of track geometries are compared. Primary results include that the total crosstalk is minimized at certain layer spacings for both coherent and incoherent illumination through optimization of media parameters. The incoherent case shows lower values of total crosstalk and more 16 generous tolerances than the coherent case. A simplified model is also presented to explain the existence of local crosstalk minima. Media satisfying the optimum condition to minimize inter-layer crosstalk are designed by using numerical optimization with merit function and admittance diagram. 17