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Fine-Adjust of Holographic-Image Magnification via Variable-Wavelength Laser

IP.com Disclosure Number: IPCOM000176251D
Original Publication Date: 2008-Nov-11
Included in the Prior Art Database: 2008-Nov-11
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Abstract

This invention describes an apparatus and method for providing a fine-adjust focus system for a holographic read/write data storage drive. The novel system disclosed uses a wavelength-shift of the laser source in the holographic drive to change the focus of the image on the read-detector.

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Fine-Adjust of Holographic-Image Magnification via Variable-Wavelength Laser

This invention describes an apparatus and method for providing a fine-adjust focus system for a holographic read/write data storage drive. The novel system disclosed uses a wavelength-shift of the laser source in the holographic drive to change the focus of the image on the read-detector.

Referring to FIG. 1, patents which teach variable wavelength lasers 101 are: (a) US 4,792,956 which is entitled Laser Diode Intensity and Wavelength Control; (b) US 5,706,301 which entitled Laser wavelength control system; and (c) IBM patent 6,816,517 which is entitled Micro-Electromechanical Devices for Wavelength Tunable Lasers. In addition to these patents, mode hopping can be used to change the wavelength of the laser, as in US 4,807,992 which is entitled Method of Detecting Semiconductor Laser Mode Hopping and Semiconductor Laser Beam Source Apparatus.

The image distance shift for recording of a hologram at wavelength, R

λ and reconstruction at

wavelength, C

1

λ , may be derived from Eqn. 1:

=

±

1λ⎛ −

1

1

C

R

I R

R

λ

R

C

R

O

R

, Eqn. 1,

where I

R is the distance from the hologram to the image, C

R is the distance from the hologram

R is the

distance from the hologram to the reference wave. For reference and reconstruction plane waves
(i.e. collimated laser beams),

to the reconstruction source, O

R is the distance from the hologram to the object, R

R and

C

R , Eq. 1 reduces to Eq: 2:

R

RI R

λ

=

±

R

λ( )

R with wavelength.

FIG. 1 shows holographic system 100. Variable wavelength laser 101 emits laser light 102. Laser light 102 may be centered about a specific wavelength, such as violet (405 nm), green (514 or 532 nm), or red (680 nm) in wavelength. (Please see Table 1 for color versus wavelength). However, there is a range associated with each nominal...