Yoshihisa TAKAYAMA and Werner KLAUS

Optical Space Communications Group, Wireless Communications Division Communications Research Laboratory, 4-2-1 Nukui-Kita, Koganei, Tokyo 184-8795, Japan

(Received January 29, 2003; Accepted June 2, 2003)

We present a passive method for reducing the size of a focal spot blurred by wavefront distortions in an optical system. The key to this reduction lies in the rather unique behavior of photonic crystals to exhibit negative refraction. First, we review the design of such a photonic crystal structure and analyze its dispersion property to find the proper condition where negative refraction occurs. The predictions derived from theoretical infinite structures are confirmed by rigorous electromagnetic analysis using both the finite-difference time-domain (FDTD) and rigorous coupled wave analysis (RCWA) methods in combination with more realistic finite structures. Second, we discuss an unconventional approach to exploit the negative refractive behavior in reducing the focal spot area spread caused by a blurred wavefront. A proof-of-principle calculation of this approach is performed with the ray trace method to visualize the reduction of the illumination area while preserving the propagation angle of the incoming beam. Finally, we investigate the crystal's performance when its two-dimensional structure is exposed to conical illumination.

Key words: photonic crystal, negative refractive behavior, field-of-view, optical receiver