Blu-ray disk

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. 

Laser diodes are used in a variety of applications. Most bar-code scanners are now based on laser diodes (previously, they used He-Ne lasers). Optical media, such as compact disks (CDs), digital video disks (DVDs), and Blu-ray disks, use laser diodes given the proliferation of personal media devices in many societies, it is understandable that laser diodes are the most common form of laser. Laser diodes are also used in fiber-optic communications. Because they can be made very small (Figure 15.38), laser diodes can be used in applications where other types of lasers are precluded because of space, size, or power limitations. 

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. 

Fig. 12.3 Schematic depiction of the cross-section of a Blu-ray DVD ROM disk having a triple-layer structure. BD single layer 25 GB, DVD dual layer 8.5 GB.

Fig. 5 Microsphere nanoscope in reflection mode images a commercial Blu-ray DVD disk. The 100 pm-thick transparent protection layer of the disk was peeled off before using the microsphere (size 4.7 pm). The sub-diffraction-limited 100 nm lines (a SEM image) are resolved by the microsphere superlens (b ON image). In a second example, reflectionmode imaging of a star structure made on a DVD disk thin film (c SEM image) is clearly discerned (d ON image)—including the complex shape of the star and its 90 nm-diameter corners.

Optical media is more durable than electromagnetic tape and is less vulnerable to environmental conditions. With the exception of Blu-ray Discs, the speed of data retrieval is considerably slower than that of a computer hard drive. The storage capacity of optical disks is significantly less than that of hard drives. Another, less common form of optical storage is optical tape, which consists of a long, narrow strip of plastic upon which patterns can be written and fi-om which the patterns can be read back. 

Entertainment AppUcations. Optical disk players are a common form of home entertainment. Most play DVDs as well as CDs. As with computer apphca-tions, the presence of Blu-ray devices is rapidly increasing. Some load a single optical disk at a time others load a magazine, which holds five or six optical disks others have a capacity for several hundred disks. The higher-capacity players often have a TV interface in which the user can make a selection from a list of the disks contained within. Often, the list contains a thumbnail image of the CDs or DVDs. These devices contain audio and video outputs to... 

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