Diffraction, Dielectric Waveguides, Optical Fibers, and the Kerr Effect

Abstract

Physical conductors (metals) that model adequately the behavior of a perfect conductor at microwave frequencies are too lossy at optical frequencies to provide low-loss enclosures. The same holds for reflectors. Whereas a metallic reflector is perfectly adequate at microwave frequencies, at optical frequencies reflectors have to be constructed using layered dielectrics of the proper thickness and dielectric constant. Total internal reflection is utilized in the construction of dielectric waveguides at microwave frequencies as well as at optical frequencies. At optical frequencies these dielectric waveguides are realized as fibers. Optical beams can also be contained in free space, if periodically refocused by lenses or mirrors. Optical resonators can be built with two or more curved mirrors that balance the diffraction of the beam bouncing back and forth and maintain a resonance mode in the space between the mirrors. The modes in dielectric waveguides and the modes of optical resonators share many of the properties of microwave waveguides and resonators discussed in the preceding chapter.