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16 September 1992 Diffractive optical system for tracking on Floptical disks
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The Floptical 3.5 inch floppy disk drive uses optical track sensing for 'Very High Density' (VHD) mode, and is also downward compatible with the DD and HD formats. A new optical head for Floptical Technology developed by Iomega uses a laser diode and a Computer Generated Hologram (CGH) to accomplish high signal levels and signal-to-noise ratio, long depth of focus, and low manufacturing cost. The new optical head uses a detection scheme of projecting--with very long depth of focus--a patch of sinusoidal grating pattern with the same spacing as the VHD tracks onto the disk surface, and detects the amount of reflected light. The track detection function is the convolution of the light pattern and the reflectivity function of the disk tracks. Depth of focus of the head is hundreds of microns. Integration across several tracks improves signal-to-noise ratio of the tracking signals. Utilization of a laser diode provides high signal levels. A computer generated binary hologram replaces several conventional optical elements. The HOE is replicated at much lower cost than conventional optics, and mechanically it simplifies head assembly, saving head cost on both counts.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Stephen W. Farnsworth, Scott D. Wilson, and Brian D. Cohn "Diffractive optical system for tracking on Floptical disks", Proc. SPIE 1690, Design of Optical Instruments, (16 September 1992);

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