ARTIFICIAL UNIAXIAL AND BIAXIAL DIELECTRICS WITH THE USE OF PHOTOINDUCED GRATINGS

We investigate the form birefringence due to photoinduced one- and two -dimensional Volume index gratings in DuPont photopolymers. The effect ive medium theory has been applied to the continuous volume subwavelen gth gratings. With the presence of a one-dimensional volume subwavelen gth grating, the originally isotropic photopolymer exhibits a negative form birefringence and behaves like a uniaxial dielectric. A form bir efringence of -1.2x10(-3) at lambda=632.8 nm is measured at a grating period of Lambda=447 nm. Experimental results on the dispersion of the form birefringence versus the illumination wavelength and the grating period are presented. With the presence of a two-dimensional grating, in general, the originally isotropic photopolymer exhibits a biaxial form birefringence and behaves like a biaxial dielectric. Positive for m birefringence can also be obtained by recording two volume gratings with different grating wave vectors. By recording two photoinduced vol ume gratings we can synthesize biaxial dielectrics with the principal axes along any desired directions. We also report the measured princip al refractive indices of the medium due to the presence of two-dimensi onal volume gratings in DuPont photopolymer. (C) 1997 American Institu te of Physics.