Interference filter all-fibre directional coupler for w.d.m.

Abstract
Directional couplers for wavelength division multiplexing using l.e.d.s as transmitters have been realised without imaging elements. Their total insertion loss (MUX + DEMUX) is of the order of 4 dB; their crosstalk attenuation and near-end crosstalk attenuation are 30 dB and >60 dB, respectively.