Light drive

Details Light drive Light drive

2000-11-01

2004-10-19

Tran, Thang V. (Department: 2653)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S095000

Reexamination Certificate

active

06807138

ABSTRACT:

FIELD
This invention relates to optical storage devices typically to replace magnetic disks in digital data processing equipment. Herein usually called the light drive, it typically is characterized by high-speed parallel access to stored data and is a medium size/power/weight device. The light drive uses an optical storage medium to retain data. A photoreceptive material (PRM) retains both wavelength and relative brightness levels of light to encode digital data.
DISCLOSURE
FIG. 1
shows schematically a conceptual diagram of the light drive. A spinning disk coated with PRM provides the data storage. Fixed read and write head arrays provide the electro-optical conversion to the PRM. The light drive includes a data formatter and host interface, both being digital circuits. A power supply is included also.
The Light Drive typically comprises four major subsystems, namely an input/output subsystem, a write subsystem, a read subsystem, and a storage subsystem. The input/output subsystem provides the data interface between the host computer and the light drive, and provides the interface to the read and write subsystems. The input/output subsystem includes the high-speed host data interface and the data formatter/multiplexer, made up of digital circuitry.
The write subsystem provides the electronic data-to-optical conversion for writing data onto the PRM, and includes a number of LED arrays or other high-density light emitting arrays. The write heads use both multiple color arrays and multiple output levels to encode optical data onto the PRM.
The read subsystem provides the optical-to-electronic data conversion for reading data from the PRM, and includes a number of high density CCD arrays or other high density detector arrays. The detector arrays are color filtered for each band of wavelength detection, and provide multiple level output.
The storage subsystem provides the optical data storage, including the spinning disk coated with PRM, and any required uninterruptable power supply (UPS). The storage subsystem includes the disk, motor, and physical mounting assembly for the light drive.
Input/Output Subsystem
The input/output subsystem requires both a host data interface and a data formatter. The host data interface provides a high-speed mass storage interface. This interface typically is an industry standard interface in the one to five gigabytes per second range. There is no pressing requirement to exceed the useful data rate of the host.
Current enabling technologies for the host data interface include Fibre Channel, both in single and multiple links. The host data interfaces typically are identical to those for high-speed magnetic disk arrays, with no unique problems for the light drive.
The data formatter buffers data for disassembly and reassembly to/from the read/write system. The data formatter multiplexes data into parallel channels, corresponding to the parallel (concentric) tracks on the disk. The formatter partitions data bits between wavelength and level prior to optical encoding, and provides the massive interconnect to the read and write subsystems. Additionally, the data formatter may need to provide a refresh capability for destructive-read PRM (see PRM section).
Current high speed digital design methodology and materials are sufficient to realize the data formatter. The multiplexing functions can be provided by current field programmable gate array (FPGA) and application specific integrated circuit (ASIC) technology. Buffering functions can be provided by current static read only memory (SROM) technology.
TABLE I
Input/Output Subsystem Technology Status
Function
Technology
Status
Host data interface
Fibre Channel, etc.
Currently available
Data buffeting
SRAM
Currently available
Data multiplexing
FPGA, ASIC
Currently available
Data refresh
FIFO, FPGA, ASIC
Currently available
Write Subsystem
The write subsystem typically comprises a large number of parallel tracks (T) at high-density spacing (S). A number of multiple monochromatic light sources (C) are provided at controlled brightness levels (L bits, or 2
L
levels). The combination of all of these preferably provide a terabyte or more of storage (T×S×C×L>1 terabyte). The multiple light sources preferably have sufficiently narrow light spectra for separation at L levels. The light sources also preferably have sufficient uniformity to accurately modulate 2
L
levels, and a high switching speed to allow a write throughput of at least about 100 megabytes per second. The write head should have sufficient light conversion efficiency to meet reasonable power requirements and should have reasonable component costs.
Write head-enabling technologies include light emitting diode (LED) linear arrays. These were originally developed by OKI Electric Industry for laser quality printers. OKI Data is currently (November 1999) in production with LED array printers at both 300 and 600 dots per inch (dpi). In July 1998, OKI developed a new fabrication process to make 1200 dpi LED arrays. The fabrication process currently limits a single array to 1200 dpi resolution. It may be possible to achieve 2400 dpi using dual offset write heads. The multi-color support of the process is not known. The 1200 dpi array is about 6% efficient, which is sufficient for this application. The approximately 3% corrected uniformity of this array allows up to four bit modulation (16 levels). OKI suggests usage at 44 kHz or more. The switching speed may not be limited by the LED technology but more by power considerations.
Typical multicolor LED technology limits the Light Drive to five colors maximum. These are yellow (570 nm), Red (660 nm), and three infrared (850, 880, and 940 nm). It is currently not known whether other colors besides red can be fabricated into high-density arrays using the OKI process.
Another potential write head technology is organic LED (OLED). Emerging OLED technology may allow higher density or more colors than current LED technology. Other flat panel display technologies currently under development may be applicable to a write head array, including field emission display (FED), gas plasma, and liquid crystal display (LCD).
TABLE II
Write Subsystem Technology Status
Function
Technology
Status
Light emitter
LED array
Currently available in Red only
Light emitter
OLED array
>3 years to develop
High resolution
LED array
1200 dpi currently available
High resolution
LED array
2400 dpi within 2 years
Multi-color
LED array
Possibly 3 colors within 3 years
>5 colors
LED array
Never
Multiple levels
On-chip correction
Currently allows 4-bit modulation
Multiple levels
On-chip correction
6 to 8 bits within 3 years
Speed
LED array
Currently at least 44 kHz
High speed
LED array
Much faster possible (power?)
Read Subsystem
The read subsystem typically comprises a large number of parallel tracks (T) at high density spacing (S), and some multiple filtered light detectors (C) with sufficient detection levels (typically L bits, or 2
L
levels). The combination of all of these should provide a terabyte or more of storage (T×S×C×L>1 terabyte). The multiple filtered detectors should have sufficiently narrow light spectra for separation at L levels, with sufficient uniformity and low noise to accurately detect 2
L
levels. The detectors should have a high enough sensing speed to allow a read throughput of at least about 100 megabytes per second. The read head should have sufficient sensitivity to match PRM output, and should have reasonable component costs.
The read head enabling technologies typically include charge coupled device (CCD) linear arrays, contact image sensors (CIS), and a unique LED read/write head. The CCD-based read head typically uses multiple color filtered monochrome arrays. The CCDs have a wide dynamic range (typically about 10,000:1) and high sensitivity (typically about 0.6 &mgr;J/cm
2
for 100% output). Current CCDs are high density with pixels typically sized down to about 6.5 &mgr;m square. Current CCDs, however, are not high-speed devices. The fastest available CCD arr

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