Metal-clad optical waveguides with cardioid-shaped cross sections and their modal characteristics

Abstract

Using Goell's point-matching method, we obtain the modal characteristic equation for metal-clad waveguides with cardioid-shaped cross sections having different aspect ratios. For small aspect ratios, the cardioid is a good representation of a nonsymmetrical distortion of the circular cross section. Such a distortion may arise from fabrication defects, and can also be introduced deliberately. Comparing the sustained modes in the waveguides with those of a metal-clad waveguide of circular cross section of comparable size, it is shown that the general effect of a lopsided distortion is to increase the number of modes. It is found that the aspect ratio 0.2 is critical, and only distortions with aspect ratios greater than this value are likely to induce considerable modification in modal behavior. © 1997 John Wiley & Sons, Inc.