Abstract

An accurate measurement of the difference in the propagation constant between two modes is essential in the design of several devices. For example, tapered velocity couplers¹ or cross couplers^2-4 require adiabatic transitions, and an accurate knowledge of the propagation constant of each of the two individual waveguides is, therefore, necessary. Prism couplers are often used for measurement of the mode indices to moderate accuracies. However, buried guides cannot be characterized by using the prism coupler. In this paper we demonstrate the use of a Mach-Zehnder interferometer to measure differences in mode indices between modes in different waveguides with an accuracy of 1 x 10^-4 or better. The technique can also be used to determine absolute value of the mode index in cases where waveguides near cutoff are available on the same substrate.

© 1990 Optical Society of America