Some effects of anisotropy on planar antiresonant reflecting optical waveguides

In this paper, propagation characteristics of some planar antiresonant reflecting optical waveguides (ARROW´s) comprised of anisotropic media are studied using an integral equation approach. The integral equation method is rigorous and general, with the added advantage that multiple layers of crystalline material with arbitrary anisotropy can be accommodated in a straightforward manner. The integral equation method is applied to study basic propagation characteristics of the ARROW structure where one or more dielectric layers are allowed to be anisotropic. Practically, the presence of anisotropy may be unintentional, due to material fabrication or processing techniques, or it may be intentionally utilized to allow integration of anisotropy-based devices and waveguiding structures on a single semiconducting substrate. Propagation characteristics and field distributions are shown for a uniaxially anisotropic ARROW where the material´s optic axis is rotated in each of the three principal geometrical planes of the structure. It Is found that even moderately large levels of anisotropy do not significantly affect the propagation characteristics of the ARROW if either the optic axis of the material is aligned with one of the geometrical axes of the waveguide, or if the optic axis is rotated in the equatorial plane. In these cases, pure TE ₀ modes can propagate, resulting in a low-loss structure. In the event of misalignment between the geometrical axes and the material´s optic axis in the transverse or polar planes, the influeuce of even small levels of anisotropy is quite pronounced. In this case, pure TE₀ modes do not exist, and attenuation loss increases significantly due to the hybrid nature of the fundamental mode