The extinction ratio in optical two-guide-coupler Delta beta switches with asymmetric detuning

Two-guide asymmetrically detuned Delta beta optical coupler switches with two equal-length sections that operate as on-off switches are examined by means of the exact eigenmodes of a slab waveguide model of the coupler. Two input/output configurations are analyzed, namely (1) where a single output guide is connected to the same guide of the coupler as the input guide, and (2) where a single output guide is connected to the coupled guide. For both cases, ideal switching, i.e. complete extinction in the off state, can be obtained in the two-section Delta beta coupler over a wide range of coupler lengths. The results differ from those of conventional coupled-mode theory in that when the two sections of the coupler are antisymmetrically detuned, i.e. delta = delta /sub 1/=- delta /sub 2/, complete extinction can be obtained only in a few special cases.<>