title: Refractive index profiling of an optical waveguide from the determination of the effective index with measured differential fields.
abstract: The evanescent tails of a guiding mode as well as its first and second derivatives were measured by a modified end-fire coupling method. The effective index of the waveguide can be obtained by simultaneously fitting these three fields using single parameter. Combined with an inverse calculation algorithm, the fields with fitted evanescent tails showed great improvement in the refractive index profiling of the optical waveguide, especially at the substrate region. Single-mode optical fibers and planar waveguides of proton-exchanged (PE) and titanium-indiffusion (Ti:LiNbO3) on lithium niobate substrates with different refractive index profiles were measured for the demonstration.
authors.affiliation: Department of Applied Materials and Optoelectronics Engineering, National Chi-Nan University, Puli, Nantou County 54561, Taiwan.
authors.forename: Wan-Shao
authors.initials: WS
authors.lastname: Tsai
authors.forename: San-Yu
authors.initials: SY
authors.lastname: Ting
authors.forename: Pei-Kuen
authors.initials: PK
authors.lastname: Wei
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D006801:Humans; D055096:Optical Devices; D012031:Refractometry / Q000379:methods*