Write-once optical disks

As described above, write-once optical disks (CD-R and DVD-R) using organic molecular materials are now commercially available. The next target is to develop erasable memory media. At present inorganic materials, such as magneto-optic or... 

Okino, Y. 1987. Reliability test of write-once optical disk. Japanese J. Appl. Phys. 26. 

Write once, read many, or WORM systems, are a bit more complicated than ROM systems. Though they have essentially the same optical system for data retrieval, for writing operations they require a more powerful laser and a modified storage disk. 

Optical information storage, which has been a dream since the discovery of the laser, is now becoming a commercial reality. Read-only consumer products (video and digital audio disks) have provided a solid technological base for the development and introduction of the more sophisticated write-once and erasable recording systems. This chapter will review the current status of polymeric materials as substrates, protective layers, and active recording media in laser recording. 

This chapter will review the present position and opportunities for polymeric materials in write-once and reversible optical recording. At present, no consensus has been reached on the optimal recording or disk substrate materials. Several alternatives are still being actively investigated. 

The major applications of lasers are CD players, optical storage devices including CD-ROM (optical read-only memory), WORM (write once, read many times) and true optical disks (unlimited read and write). The amount of information that can be packed on a disk presently is limited to the size of the spot generated by the laser. The shorter the wavelength, the smaller the spot. Other applications include laser printers, spectroscopy, and communications. Lasers operating at 1.3 micrometers and 1.55 micrometers are used for low loss quartz fiber optic communications. AlGaAs is used for... 

Because of the potential of repetitive usage, an obvious application of the amorphous azo polymers is in erasable optical memory disks or cards. The rate of recording" is in the milliseconds range. For read only memory, or write once read many times, liquid crystalline or semicrystalline polymers may be preferred, because the time to "write" the information is not critical, while the "contrast" (birefringence) is greater than in amorphous polymers. 

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