Theory of an Efficient Electronic Phase Shifter Employing Multilayer Dielectric Waveguide Structure

The possibility of enhancing the modulation In an electrooptic single-slab dielectric waveguide by exciting high-order modes in thick slabs was first pointed out by Lotspeich [1]. Later, Buckman [2] showed that, for a three-layer dielectric slab structure, the modulation in the effective refractive index of a guided mode could be made to exceed that of the “bulk” refractive index of the active layer by up to a factor of n
g
²
, where n
h
²
is the highest refractive index in tne system. This enhancement in modulation of the effective refractive index n, and hence of the propagation constant β, is critically dependent on the value of n in the absence of modulation, which is, in turn, dependent on the layer thickness.