Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Reexamination Certificate
2000-08-16
2001-09-11
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
C359S001000, C359S019000, C359S022000, C359S024000, C369S275100, C430S001000
Reexamination Certificate
active
06288804
ABSTRACT:
BACKGROUND
The present invention relates to bit-wise holographic data storage systems and methods, and in particular to reflective optics for bit-wise holographic storage systems.
In holographic storage, data are stored in holograms resulting from the interference of a signal and reference beam. During storage, both the reference and signal beams are incident on the storage medium. During retrieval, only the reference beam is incident on the medium. The reference beam interacts with a stored hologram, generating a reconstructed signal beam proportional to the original signal beam used to store the hologram. Relative to conventional magnetic and optical data storage methods, holographic data storage promises high storage densities, short access times, and fast data transfer rates. Conventional page-based volume storage, however, typically requires specialized components such as spatial light modulators and charge-coupled detectors.
The storage of localized holograms (bit-wise storage) may allow the use of simpler optical components than page-base holographic storage. Localized-hologram storage systems may be sensitive to tilts and misalignments of the optical components used to direct the signal and reference beams to the storage medium.
SUMMARY
Briefly, and in general terms, the present invention provides a localized-hologram digital data storage system and method having a relatively high tolerance for tilts and lateral misalignments between a primary head and a corresponding reflective head. Such tolerance becomes increasingly important with increased numerical apertures (N.A.), as the size of the holograms is decreased.
The present invention provides a holographic digital data storage system comprising a holographic storage medium, a light source comprising a laser for generating a primary storage light beam incident on the medium, a primary head in optical communication with the laser and facing the medium, for focusing the primary beam at storage locations within the medium, and a reflective head comprising positive unit magnification reflective optics positioned facing the medium opposite the storage head. The reflective optics reflect the primary beam to generate a reflected storage beam substantially counterpropagating with respect to the primary beam at the accessed storage locations. The primary and reflected beams are coincidentally focused at the accessed storage locations. The interference of the primary and reflected beams causes storage of localized reflection holograms at the accessed storage locations.
In one embodiment, the reflective optics comprise a flat mirror and imaging optics appropriately positioned between the mirror and the medium. The imaging optics image an accessed storage location onto a spot on the mirror. In another embodiment, the reflective optics comprise a corner cube reflector. The use of positive unit magnification reflective optics provides for a relative tolerance of the system to tilts and lateral misalignments of the reflective optics relative to the primary optics.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrates by way of example the invention.
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Daiber Andrew J.
McDonald Mark E.
Curtis Craig
Lumen Intellectual Property Services
Siros Technologies, Inc.
Spyrou Cassandra
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