title: Adiabatic invariance in GRIN channel waveguides and its use in 3-dB cross couplers.
abstract: We have extended the local normal mode approach of Burns and Milton to derive the condition for adiabatic invariance in graded-index channel waveguides. The results show that in spite of the index-grading and 2-D confinement, the inequality describing the adiabatic condition is basically the same as that for step-index slab waveguides. To verify the predictions of the theory, we have fabricated, using ion exchange in glass, a cross coupler with two asymmetric input channel waveguides and two symmetric output guides. The experimental results show equal output power (3.0 +/- 0.1 dB) from the two symmetric guides when either of the two unequal guides is excited, demonstrating excellent agreement with the theory.
authors.forename: C P
authors.initials: CP
authors.lastname: Hussell
authors.forename: R V
authors.initials: RV
authors.lastname: Ramaswamy
authors.forename: R
authors.initials: R
authors.lastname: Srivastava
authors.forename: J L
authors.initials: JL
authors.lastname: Jackel