The extension of optical add/drop multiplexing (OADM) systems to metro-core and metro-access networks has led to the need for economical and compact OADM devices. In this paper, we demonstrate a 1-in.<sup>2</sup> 100 GHz spacing 40-channel (ch) single-chip variable attenuator multiplexer/demultiplexer based on a monolithic 2.5%-Δ silica planar lightwave circuit (PLC) and stacked photodiode arrays. We also investigate the particular issues raised by monolithic integration with such high Δ waveguides. One is the loss increase caused by high index contrast of the waveguides. Performance fluctuation and thermal interference between the integrated circuits are also inherent issues. By utilizing effective solutions, we have successfully overcome such problems and confirmed that a 2.5%-Δ silica PLC is effective for use in monolithic integration.
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