Wavelength-division multi demultiplexers for two-channel single-mode transmission systems

Low-loss lensless 2-channel wavelength-division multiplexing (WDM) couplers may be produced on the beam-splitter principle with interference filters and three butt-coupled fiber ends not only for multi-mode Operation but also for single-mode transmission links. These devices are constructed with single-mode fibers-for bidirectional transmission only in the transmission channel, but for unidirectional operation in all channels. The interference filter, used in the experiment to separate the emissions of two LD´s with wavelengths of 834 and 868 nm, may be implemented both as a longwave-pass (LWP) and a shortwave-pass (SWP) edge filter with high edge steepness and low polarization effects. WDM single-mode couplers exhibit very low insertion losses lying in the O.5-dB region. Their fat-end crosstalk attenuations attain values of between 15 and 30 dB and their near-end crosstalk attenuations are better than 65 dB.