azu_td_1349475_sip1_... - Arizona Campus Repository

CHAPTER 3
28
DIFFRACTIVE LENS THEORY
The advantages of using diffractive lenses and the intended application
for them have been discussed in the preceding chapters. In this chapter, the
discussion will focus on the basic operating principles and fabrication methods
of diffractive lenses. It is necessary to point out there is a hierarchy of
components that can be thought of as diffractive lenses. The operating effect of
these components can be based on diffraction by a Fresnel zone plate (FZP).
The operating principal of the FZP is thus considered first. This theory is then
extended to discuss binary diffractive lenses, kinoforms, and multilevel
approximations to the kinoform. The diffraction efficiency and method of
fabrication of diffractive lenses are also discussed.
3.1 Basic Principles
For a general case, a diffractive lens illuminated by a plane
monochromatic wave (Figure 3-1) splits the incoming wave into many spherical
waves or diffraction orders. The foci of the lens occur where these diffracted
orders cross the optical axis. The diffraction angle of each order is controlled by
the period of the lens and may be calculated using the grating equation. The
amount of light directed into each of these orders is in turn determined by the
shape of the lens which modulates the phase of the incoming wave.
The principle of operation of a diffractive lens may be better understood
by first examining the zone construction of Fresnel. 31,32 A monochromatic