Near-Field Optical Storage

One disadvantage of CD-like systems is that the lens used to focus laser light onto the recording layer must be located some distance from the disc due to the presence of the protective substrate. Systems that do not have a protective substrate can use lens systems that are essentially in contact with the recording layer. This type of system is called a near-field system, because the electric field of the focused spot is partially in the lens and partially in the recording layer. A much smaller spot size can be produced by near-field systems; thus disc capacity can be dramatically improved.

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