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This paper reports on the development of planar-lightwave-circuit wavelength-division-multiplexing (PLC-WDM) filters based on double polynomial curve directional couplers, which will be integrated into compact and low-cost bidirectional optical transceivers for FTTx systems. Silica-based PLC-WDM filters smaller than 5 mm×100 μm for Ethernet passive optical network (E-PON) applications were designed and fabricated to have low bidirectional crosstalk (lower than -40 dB) as well as low insertion losses (lower than 1 dB) within the operating temperatures of -40 to 80°C. Several features and design guides that can reduce the size of directional couplers and improve the level of bidirectional crosstalk are discussed.
Date of Publication: May 2005