MOTIONLESS-HEAD PARALLEL READOUT OPTICAL-DISK SYSTEM

The design, analysis, and feasibility of a novel motionless-head parallel readout optical-disk system are presented. The system is designed to read data blocks distributed radially on the disk's active surface, and it has the unique advantage that no mechanical motion of the head is required for fast access, focusing, or tracking. Data access is achieved solely through the disk rotation, and the entire memory can be read in one rotation. In principle, this permits a data rate of up to 1 Gbyte/s. The data blocks are one-dimensional Fourier-transform computer-generated holograms, each reconstructing one column of a two-dimensional output image. Owing to the information redundancy and shift invariance properties of Fourier-transform holograms, tracking and focusing servo requirements are eliminated. A holographic encoding method is developed to produce high signal-to-noise ratio reconstructions and to reduce significantly the radial alignment requirements of the recorded data bits. The optical readout system consists of only three cylindrical lenses. Two of these may be replaced by a single hybrid diffractive-refractive optical element for easier system alignment and better optical performance, i.e., reduced aberrations and improved resolution. The throughputs and retrieval times of this parallel readout optical-disk system make it well suited to a variety of parallel computing architectures, including a high-performance optoelectronic associative memory [Proc. Soc. Photo-Opt. Instrum. Eng. 1347, 86 (1990)].