Loss reduction in a coplanar waveguide on a planar lightwave circuit (PLC) platform by quenching

The hybrid integration of semiconductor optoelectronic devices on a silica-based optical circuit is one of the key technologies by which to realize opto-electronic components for high-speed wavelength division multiplexing (WDM). However, a coplanar waveguide (CPW) on a silicon-terraced silica (STS)-type planar lightwave circuit (PLC)-platform has a large propagation loss compared with one on a conventional ceramic substrate. We discuss the reduction of the propagation loss of a CPW on a PLC-platform. First we prove that this CPW loss originates from an increase of the loss tangent (tan /spl delta/) induced by the thermal donors (TD's) which connect with oxygen in the silicon substrate during the silica deposition process. Second we introduce quenching to eliminate the TD's, and drastically reduce the loss of a CPW on a 30 /spl mu/m-thick silica from 2.7 to 0.6 dB/cm at 10 GHz. This loss value is almost the same as that of a CPW on a ceramic substrate. Moreover we fabricated a LD module using a 50 mm-long improved CPW on a PLC-platform. The small signal frequency response characteristics of this module reveal that the improved CPW can be applied as a cm-order electrical circuit in a 10 Gb/s module. This exhibits that an established electronic circuit technology including a multi-chip module (MCM) for a microwave application can be developed on a PLC-platform.

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