Abstract

Tapered multicore couplers have been developed utilizing controlled coupling between adjacent fiber cores,¹ and tapered single-core waveguides are being considered for use as beam expanders. In beam expanders, nonadiabatic mode coupling has generally been avoided as a possible source of loss.² Previous work in this area has focused on attempts to decrease the mode coupling via changes in the taper shape³; little significant improvement can be obtained over the behavior of a simple smooth curve. More recently, it has been shown that nonadiabatic effects are useful in the fabrication of blocking filters.⁴ In the work reported here, we studied the behavior of nonadiabatic mode coupling in multi-index tapered waveguide structures.

© 1989 Optical Society of America