Browse Prior Art Database

High Density Optical Disk Recording System

IP.com Disclosure Number: IPCOM000034735D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 66K

Publishing Venue

IBM

Related People

Gambino, RJ: AUTHOR

Abstract

A technique is described whereby optical disk high-density recording is obtained by utilizing a low-power laser of short wavelength in conjunction with higher-powered longer wavelength laser concentration. The low-power laser is used for supplying joule heating. This technique makes it possible to write very small spots during the writing of information, enabling higher density recording to be accomplished. In prior art, the ability to provide high-density recording onto optical disks required high laser power, which is only available for long wavelengths, approximately 800 nm. So as to increase the recording speed further, laser power has been increased through the use of high-power (40 mw) injection lasers. However, these lasers have a limited life cycle when compared to low-powered lasers (5 mw).

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High Density Optical Disk Recording System

A technique is described whereby optical disk high-density recording is obtained by utilizing a low-power laser of short wavelength in conjunction with higher-powered longer wavelength laser concentration. The low-power laser is used for supplying joule heating. This technique makes it possible to write very small spots during the writing of information, enabling higher density recording to be accomplished. In prior art, the ability to provide high-density recording onto optical disks required high laser power, which is only available for long wavelengths, approximately 800 nm. So as to increase the recording speed further, laser power has been increased through the use of high-power (40 mw) injection lasers. However, these lasers have a limited life cycle when compared to low-powered lasers (5 mw). High-density recording typically uses diffraction limited optical storage (bit size Z laser wavelength), such that the band gap energy of suitable semiconductors for the injection laser sets a limit of approximately 800 nm. Semiconductor devices have been developed to produce

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shorter wavelengths, with a low efficiency, such that at 400 nm the incident power will be less than 1 mw. The shorter wavelength, however, means that the bit diameter can be cut in half, thereby increasing the density by four times. Utilizing the innovations, the concept described herein provides a means of using joule heating, to supplement the laser heating on a disk, for optical storage. It is considered an improvement over previous concepts, such as [*] which described random-access (fixed medium) low-density storage. The concept involves an optical recording head containing two light sources of different wavelengths; a five mw injection laser providing 800 nm light, and a one mw laser source of 400 nm coherent light, as shown in Fig. 1. The light from both sources passes through common lens system 10 and is designed so that the lens can also be used to collect light reflected from the medium for data read-out purposes.

The 400 nm light source is focused to a diffraction limited spot on the medium. The 800 nm injection laser source is focused to a concentric spot with a much larger radius, as much as ten times in size. The medium consists of seven distinct layers, as shown in Fig. 2: transparent substrate layer 10, transparent conductor 11, small band gap photoconductive layer 12, a second transparent conductive layer 1...