Planar lightwave circuits (PLCs) incorporating arrayed-waveguide gratings (AWGs) are excellent in terms of circuit density, design flexibility, multi-channeling and mass-production, and are widely deployed in optical networks.1 NTT and NEL developed such PLCs using GeO2-doped silica waveguides with a core-to-cladding index contrast ∆ of less than 0.8% and a minimum bending radius of 5 mm or more, taking account of the waveguide propagation loss and the coupling loss with conventional single-mode fiber (SMF). Table 1 summarizes the characteristics of silica waveguides with different ∆ values. The continuing demand for more broadband and cost-effective networks leads to larger scale and/or smaller size PLCs with a higher density. An increase in the index contrast ∆ can make it possible to upgrade PLC density due to the corresponding reduction in the minimum bending radius of a waveguide. From a practical viewpoint, NTT has been improving the methods it normally uses for fabricating GeO2-doped silica waveguides, and has recently achieved a low propagation loss of 0.05 dB/cm at a ∆ of 1.5%.2 By comparison with previously developed silica waveguides, these higher ∆ waveguides are referred to as super-high (SH) ∆ waveguides. In addition, we have realized a large scale AWG with 256 channels2 and a small size AWG module with low-loss SMF connection accomplished by fusion splicing a high-NA (numerical aperture) fiber and SMF.3 At present, we are developing even larger scale AWGs and low-loss SMF connection methods suitable for high-channel-count AWGs. This paper reviews our recent progress on SH ∆ PLC technologies focusing on ultra-high density AWGs and SMF connection methods using spot size converters (SSCs) in PLCs.
© 2002 Optical Society of AmericaPDF Article
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