Kazuya HAYATA

Department of Social Information, Sapporo Gakuin University, Bunkyodai 11, Ebetsu, 069 Japan

(Received November 5, 1996; Accepted December 20, 1996)

It is shown that, at a critical point where the effective refractive index of a mode coincides with the bulk index of a cladding region, optical waveguide modes exhibiting a lognormal feature are supportable for a hyperlong-range refractive-index profile. As a typical example of waveguides that support lognormal modes a parabolic-index core surrounded by a depressed-index cladding is presented.

Key words : lognormality, optical waveguide, extended power-law decay, long-range graded-index medium