Novel technique for the measurement of coupling length in directional couplers

Abstract

ABSTRACT A novel technique to determine the coupling length as a function of wavelength in directional couplers,especially in the case of weakly coupled, symmetrical directional couplers is described. The technique is illus- trated by using Ag — Na ion-exchanged directional couplers in BK7 glass. Application of this technique toasymmetrical directional couplers is also addressed. 1.INTRODUCTION Guided wave devices using directional couplers e.g., optic1 modulators and switches 13, wavelength demultiplexers 46, power dividers ', eic. have very wide applications in the optical communication systems.In almost all of the applications the knowledge of coupling lengths of the directional couplers is essential inthe design of these devices. Estimation of the coupling length in the case of Ti:LiNbO3 waveguide directionalcouplers over a broad wavelength range 8 has been accomplished by approximating the diffusion and the modeprofile using the formalism of Korotky et al. In the case of dual wavelength demultiplexers 6