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OPTICS LETTERS / Vol. 21, No. 18 / September 15, 1996
Continuous-level phase-only computer-generated hologram
realized by dislocated binary gratings
Ming Li, Anders Larsson, Niklas Eriksson, and Mats Hagberg
Department of Optoelectronics and Electrical Measurements, Chalmers University of Technology, S-412 96 Göteborg, Sweden
Jörgen Bengtsson
Department of Microwave Technology, Chalmers University of Technology, S-412 96 Göteborg, Sweden
Received March 19, 1996
It is proposed and experimentally demonstrated that a multilevel or even continuous-level phase-only computer-
generated hologram can be realized by use of a binary (two-level) structure. The desired phase shift is
invoked by introduction of a lateral dislocation of a high-frequency binary grating within each of the elements
that constitute the hologram. An asymmetrically distributed spot array has been generated experimentally,
and a uniformity error of 6% and an efficiency of 42% have been measured. 1996 Optical Society of America
Phase-only computer-generated holograms (CGH’s) are
usually preferable to amplitude CGH’s because the for-
mer provide higher diffraction efficiency.1 To increase
the diffraction efficiency, multilevel or continuous-level
phase-only holograms are desirable.2,3 So far, most ef-
forts have concentrated on achieving different phase
levels by utilization of steplike surface-relief struc-
tures. There are a number of fabrication diff iculties
associated with this type of multilevel surface relief
structure. Here we propose a different approach to
realizing continuous-level phase-only holograms that
uses two-level (or binary) surface-relief structures.
In most CGH’s, different phase levels are achieved
by use of a structure such as that shown in Fig. 1(a).
A planar wave front, passing through a transparent
substrate with a surface-relief steplike structure, is
split into two planar wave fronts with a phase shift fd
between them described as
fd sn 2 1dk0d ,
(1)
where n is the refractive index of the substrate mate-
rial,