Page 487 - Introduction to Information Optics

472 8. Information Storage with Optics

8.26 For stacked-layer 3-D optical storage using ET materials, show that the
NA of the addressing cylindrical lens is

where n l is the refractive index of the ET thin film, and n 2 is the refractive index
of the cladding layer.
8.27 Why is a photoplastic device good for a hologram but not appropriate
for photographic uses?
8.28 A thin-phase grating can be made using a photoplastic device. The
thin-phase grating can be expressed as

t(x, y) — exp[za co$(2nby)~] = £ i"J n(&) cxp(in2nby),

where J n is the Bessel function of the first kind and the nth order, and a is a
constant. Show that the maximum efficiency is 33.9%. (Hint: Use a Bessel
function table.)
8.29 The amplitude transmittance of a grating recorded on a photographic
plate can be expressed graphically in the following figure. What is the
diffraction efficiency when the photographic plate is illuminated by a
plane wave?

1 Amplitude

Sinusoidal
Function

8.30 What is the optical gain of ET thin film? Assume the quantum efficiencies
of ET thin film to blue and infrared exposures are 10% and 5%,
respectively.
8.31 Can we employ an ET thin film to record and reconstruct a hologram?
Explain why or why not.
8.32 We want to write a hologram into a photorefractive crystal that has a
2
sensitivity of 200 nJ//mi using an Ar laser with 10 mW output at 488 nm.
Assume all the laser light can be utilized and focused onto an area of
2
0.5 x 0.5 mm . How long is the required exposure time?
8.33 Assume that a photorefractive crystal is employed as holographic storage
that stores a 1000 x 1000 bit pattern for a computer. The stored pattern