Low-loss two-channel fiber-optic waveguide

The losses and cross talk in a two-channel fiber-optic waveguide were investigated experimentally. The minimum losses were 1.5 dBAm in the central channel and 3.5 dB/km (at λ = 1.55 μ) in the annular channel, the channels being optically decoupled by better than 35 dB. A modified near-field method is described for measuring the absolute refractive index profile