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 δ) 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 μm-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