Optical: systems and elements – Holographic system or element – Hardware for producing a hologram
Reexamination Certificate
2003-01-15
2004-11-30
Boutsikaris, Leo (Department: 2872)
Optical: systems and elements
Holographic system or element
Hardware for producing a hologram
C359S003000, C359S024000, C369S103000, C369S273000
Reexamination Certificate
active
06825960
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to the general field of holographic storage systems and methods. More specifically the invention relates to a system and method for a bitwise readout of a holographic ROM that may be backward compatible to existing or future storage formats such as DVD or CD-ROM.
2. Description of Related Art
General holographic storage systems are discussed in “Holographic Memories,” by Demetri Psaltis et al.,
Scientific American
, November 1995, which is hereby incorporated by reference. Holography is also discussed in the text Holographic Data Storage, by H. J. Coufal, D. Psaltis, and G. T. Sincerbox, Eds., copyright 2000, Springer-Verlag which is hereby incorporated by reference. The basic principles of holography involve the recording of an interference pattern formed between two beams of light, referred to as an object beam and a reference beam. The object beam is encoded with data in a two dimensional pattern. The reference beam is used to form the interference pattern with the encoded object beam and is subsequently used to reconstruct the data by illuminating the recorded pattern.
In volume holographic storage, a large number of holograms are stored in the same volume region of a holographic storage medium. There are several method of holographic storage, such as shift multiplexing, angle multiplexing, wavelength multiplexing, correlation multiplexing and phase multiplexing. Volume holography uses a thick recording medium, where the thickness dimension is associated with Bragg selectivity in the movement of the holographic storage medium in shift multiplexing or the angle change in angle multiplexing.
A prior art holographic system is described in “Holographic 3-D Disc using In-line Face-to-Face Recording,” by Kimihiro Saito and Hideyoshi Horimai. The system described utilizes a photosensitive layer with a reflecting unit underneath. A reference beam passes through a first region of the media downward and a second region upwards. The direction of the information beam is opposite to that of the reference beam. Intersection between the reference beam and information beam results in a reflection type hologram. Shift multiplexing can be utilized for multiple recording.
Angle multiplexing is a volume holography method for storing a plurality of images within a single storage medium. Such angle multiplexing is discussed, for example, in “Holographic Memories,” by Demetri Psaltis et al.,
Scientific American
, November 1995, and by P. J. van Heerden in, “Theory of Optical Information Storage In Solids,”
Applied Optics
, Vol. 2, No. 4, page 393 (1963). A typical system employing angle multiplexing described in “Holographic Data Storage,” pages 343-397, by H. J. Coufal, D. Psaltis, and G. T. Sincerbox, Eds., copyright 2000, Springer-Verlag. Angle multiplexing generally involves storage of multiple pages of data in the same photorecording medium by altering the angle of the reference beam entering the media during storage of each page while maintaining the position of the object beam. Each hologram is stored in the same volume and is differentiated by Bragg selectivity. Bragg selectivity during angle multiplexing is described in Holographic Data Storage, pages 30-38, by H. J. Coufal, D. Psaltis, and G. T. Sincerbox, Eds., copyright 2000, Springer-Verlag. Any of the recorded holograms can be viewed by illuminating the photorecording medium with a reference beam set at the appropriate angle.
Wavelength multiplexing is a further method for storing a plurality of images within a single medium, whereby the addressing mechanism is the wavelength of incidence of the reference beam. Wavelength multiplexing is simpler to implement than angle multiplexing, but it is highly dependent on the range over which lasers can be tuned. Wavelength multiplexing is described in “Holographic Data Storage,” pages 7-8 and 25-26, by H. J. Coufal, D. Psaltis, and G. T. Sincerbox, Eds., copyright 2000, Springer-Verlag.
A prior art system geometry in which the encoded object beam and the recording reference beam are counterpropagating is described in “Volume Holographic Multiplexing Methods”, by G. Barbastathis and D. Psaltis, published in Holographic Data Storage, pages 22-59, by H. J. Coufal, D. Psaltis, and G. T. Sincerbox, Eds., copyright 2000, Springer-Verlag, which is expressly incorporated herein by reference. This geometry is often preferred in wavelength multiplexed systems because it maximizes the optical wavelength Bragg selectivity.
Compact discs (CDs) and digital video disks (DVDs) are currently popular optical recording formats. Both CD and DVD players are readily available at low cost.
FIG. 5
illustrates the basic setup of a typical read system utilized to recall data stored on an optical media such as a CD or DVD. The read system
500
includes a laser light source
502
, which provides a plane wave readout beam
503
. The readout beam from the laser light source
502
travels through a diffraction grating
504
, a collimator
508
, a beam splitter
506
, quarter waveplate
510
, and objective lens
512
. Objective lens
512
focuses the readout beam onto a reflective layer
514
that is the bottom layer of the CD or DVD containing data. Readout beam
503
is a spherical beam passing through objective lens
512
. Readout beam
503
is reflected or not reflected depending on the data, with the reflected readout beam
503
a spherical wave off the reflective layer
514
.
The readout beam is then reflected back through objective lens
512
, quarter wave plate
510
, and to the beam splitter
506
. A plane wave is produced after the reflected spherical beam retro-reflects through objective lens
512
. The readout beam is reflected towards lens
516
and is imaged onto the plane of an optical detector
520
, which is typically a quad detector. Laser light source
510
is generally a low power (5-10 mW), relatively inexpensive laser with multiple longitudinal mode emission. Collimator lens
508
is placed a distance away from the laser, on the opposite side of the beam splitter
506
from the laser. Readout beam
503
diverges rapidly, resulting in the collimator lens
508
illuminated by the central core of readout beam
503
. In addition to beam splitter
506
, a beam-turning element may be placed between laser
502
and collimator lens
508
in order to flatten the system profile for use in a compact drive. After the readout beam
503
passes through collimator lens
508
, it is well collimated and can be focussed by objective lens
512
. The reflected readout beam is recollimated by objective lens
512
and proceeds back through the collimator lens
508
, which acts as a field lens. The reflected readout beam is deflected by the beam splitter and focussed on the detector, which senses the high-frequency data signal as well as tracking and focus error signals. It should be recognized that
FIG. 5
is illustrative only. Current read systems or optical pick-up systems typically combine various elements to reduce the number of elements and cost of the system.
Additionally, the current use of holography in commercial ROM systems and storage media is on the backside (i.e., the side opposite the reflective layer) of the CD or DVD. Here single holograms of pictures and words (e.g., names or titles) are sometimes recorded for security or authenticity reasons.
Although prior art DVD and CD players are readily available, low cost players that can also read holographic ROM discs are not available. Furthermore, ROM disc replication is done by stamping the information onto the surface of the disk. Thus, there has been a need for improvements in the recording (replication of the information efficiently and quickly) and readout of holograms. More specifically, there has been a need for improved systems capable of reading holograms and other optical media.
SUMMARY OF THE INVENTION
According to one example of one aspect of the present invention a method is provided for manufacturing a holographic storage medium. The method includes providing one or more da
Curtis Kevin R.
King Brian M.
Wilson William L.
Boutsikaris Leo
InPhase Technologies Inc.
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