Blue-ray disks

Finally, Part IV reviews miscellaneous technical developments that do not fit neatly into the scheme of the preceding parts. These concern, in particular, the application of polymers in the field of optical memories, treated in Chapter 12, which refers also to currently important data storage systems (compact disks, digital versatile disks, and blue-ray disks). Moreover, the application potential of polymers in the fields of photosensors and photocatalysts is outlined in Chapters 13 and 14, respectively. 

Phase Change Materials (PCMs) are nowadays widely used for data recording and increasingly present non-volatile memories [1, 2]. Since Ovshinsky s precursor work [3], PCMs have been studied extensively, both experimentally [4-6] or with ab initio calculations [7-11], The operating principle of PCMs is based on the easy and reversible switching between the crystalline (C) and amorphous (A) states, each phase possessing very different electrical and optical properties. These materials are nowadays found in commercial applications for optical information storage and dissemination, such as CD-RW, DVD-RW or Blue-Ray disk, and could be used for the achievement of PC-RAM. 

Blu-ray An optical disk format. Developed by a consortium of over 180 companies led by Sony, Blu-ray disks are intended to supersede the DVD both for the distribution of video and for data storage - they can hold up to 25 Gb on each ot up to two layers. Blu-ray achieves this greater capacity by using a blue (actually, a violet) laser rather than the red laser used for DVDs the shorter wavelength allows the beam to be focused more precisely and so more data to be packed into a given space. Currently (2009) some high-deflnition DVDs have been released in Blu-ray format, and computer Blu-ray drives are becoming available. 

A special case of nanocrystal that is comprised of a semiconductor is known as a quantum dot Typically, the dimensions of these nanostructures lie in the range 1-30 nm, based on its composition (see below). Quantum dots currently find applications as sensors, lasers, and LEDs. In fact, new high-density disks (e.g., HD-DVD and Blu-ray high-definition DVD formats) may only be read via blue lasers, which... 

As blue diode lasers became available on a large scale [10], a new generation of storage disks with further increased storage capacity was developed by the Blu-ray Disc Association and by Toshiba and NEC within the DVD Forum [4j. As can be seen in Table 12.1, a HD-DVD holds 15 GB and BDs hold 25 GB (singlelayer DB) or 50 GB (dual-layer BD). Figure 12.3 shows, as a typical example, the cross-section of a novel disk type having a triple-layer structure one BD layer and a dual DVD layer to be read by a blue and a red laser, respectively. 

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