Pushing the technology boundary from compact CWDM to compact DWDM.(Focus on)(coarse wave division multiplexing, dense wavelength division multiplexing)

Thin-film filters (TFFs) and arrayed wave-guide gratings (AWGs) are the two major optical platforms for DWDM multiplexer/ demultiplexers. AWGs have the advantage of semiconductor batch processing and thus of fer cost advantages at the chip level. However, the technology's fundamental temperature sensitivity means a higher packaging complexity than TFFs for temperature stability. Although athermal packaging technologies recently have become available, they have a higher cost unless the multiplexer/ demultiplexer channel count is higher than 16 channels. For these reasons, as well as the fact that AWG insertion loss typically is independent of channel count, most long-haul transport applications featuring 32, 40, or more channels use AWG technology.

TFF technology, on the other hand, offers modular flexibility, lower insertion loss, and lower cost if the multiplexer/demultiplexer channel counts are small. Today's metro DWDM applications that are typically eight channels grouped and expandable in future to 32 or 40 channels prefer the TFF technology. Since many current metro WDM applications started with CWDM and are amplifier-flee, as bandwidth expansion continues, the need to upgrade to DWDM by vacating one or two CWDM channels becomes increasingly visible. Thus, technologies need to be developed to continue to improve optical performance and lower cost.

For metro CWDM multiplexer/demultiplexer applications, it has been previously shown that pushing the integration of TFF solutions down to the substrate level provides more compact module dimensions about 1-dB lower insertion loss, lower overall per-channel device cost, and better device stability measured by temperature-dependent loss (TDL), versus the traditional approach of three-port filter device-level integration. …

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