Abstract

Recently many kinds of large-scale planar lightwave circuit (PLC) have been developed for use in optical communication systems. Since the characteristics of large scale PLCs depend on the losses in waveguides, PLC performance can be improved by reducing such losses. The propagation losses in silica-based waveguides have been evaluated by using long waveguides such as that shown in Fig. 1. The lowest loss value ever reported with silica-based long waveguides is 3.5 dB/m [1]. This was obtained in a 1.6-m long waveguide with a relative index difference Δ of 0.75%. It was deduced that the main reason for the loss is the scattering ascribed to the fluctuation of the refractive index and the core-cladding interface. This means that lower loss waveguides can be fabricated using lower Δ waveguides, though these require larger bending radii, and therefore a lager circuit size. This indicates that the minimum Δ value should be determined by taking account of the size of the substrate on which the long waveguides are laid out. Here we report the fabrication and loss characteristics of a 10-m long waveguide with a Δ of 0.45 % which has a very low loss of 1.7 dB/m.

© 1995 Optical Society of America