Demetri Psaltis, Douglas G. Stinson,and G.S. Kino, Tom D. Milster
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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