International Business Machines Corporation

William C Williams

Glen Alan Jaquette

Blair I Finkelstein

James J Dente

This invention provides an optical disk device with a switchable filter for reducing the light intensity from a write level to a read level or an erase level. The filter can further be used to modulate the light intensity between a write level and a gap level for the process of recording data. For semiconductor laser sources, this filter reduces laser feedback noise by allowing the laser to operate at a higher, more stable power level during data sensing, and by reducing the amount of light reflected from the storage disk back to the laser cavity. Because the filter transmission can be high during the write process, the power requirements of the semiconductor laser are not increased in the device of this invention. In one embodiment, the switchable filter of this invention includes a variable retarder with means to select light on the basis of its phase or polarization, for example, with polarizers. This retarder can comprise a liquid crystal cell wherein either the optical orientation or retardance is electro-optically tunable.

Switchable filter for modulating laser intensity and reducing laser

Apparatus and method are provided to increase the capacity of spiral track data storage disks while improving the reliability of access to sectors on the disk. In one embodiment, employed when logical tracks on an optical disk are grouped into concentric bands, previously unusable sectors immediately following a band boundary can be reliably accessed. In accordance with this embodiment, when the target sector is, for example, the first sector of band N and a laser beam from a read head lands on a sector in the previous band N-1, the clock governing the data transfer rate is set to the frequency of the band N-1 and a sector in that band is detected and identified. Based upon the period of sectors in the band N-1, a delay interval is computed which ends when the last sector in the band N-1 rotates past the laser beam. Sector mark detection is disabled during the delay interval and the clock frequency changed to that of band N. Sector mark detection is re-enabled at the end of the delay, the band boundary passes, and the target sector can be detected and accessed. The present invention is also applicable when the target sector is not the first sector in a band as well as when the sector on which the laser beam lands is in the same band as the target sector.

Apparatus and method for accessing sectors of a rotating disk

To sense the presence of written data on an optical disk, the readback signal from the disk is detected, and the intervals between detected signal events are measured. That signal event occurring at an expected time delta after the preceding signal event indicates a valid data signal time delta. Those signal events occurring at an unexpected time delta after the preceding signal event indicates the readback signal to be noise. If the count of valid signal time deltas minus the unexpected time deltas attributed to noise accumulates rapidly along a given track within a given sector of the optical disk that sector is determined to be written. Provision is made for counting signal events in accordance with the specific run-length limited in use.

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Tucson, AZ, United States of America

William C Williams