Page 485 - Introduction to Information Optics

470 8. Information Storage with Optics

LD

Disk

Detector

8.20 (a) Why does the size of the readout beam have to be larger than the
width of the pit on a CD?
(b) On the other hand, why does the beam size have to be smaller than
the size of the pit on a WORM and an MO disk?
8.21 The following figure shows the surface structure of the CD. Determine the
pit depth d, in terms of the wavelength of light /, and the refractive index
of the clear coating n. If A = 0.78 /mi, and n = 1.5, what is dl

Clear Coating

Land
Pit

8.22 If bit 1 at a MO disk rotates polarization of light by 1°, and bit 0 does
not rotate polarization of light, what are the output intensities of bit 1
and bit 0 by placing a polarization at 0° and 90° relative to the original
polarization of readout beam? (Hint: Use Malus's law.)
8.23 A laser beam is focused onto a layer of a multilayer optical storage
forming a spot with l-/mi diameter as shown in the following figure. If
the layer separation is 50 /mi and the NA of the focusing lens is 0.45, what