Single-mode fused biconical couplers for wavelength division multiplexing with channel spacing between 100 nd 300 nm

The authors report on single-mode fused biconical couplers tailored to the requirements of wavelength-division-multiplexing systems. The wavelengths of the two channels can be chosen arbitrarily for wavelength separations between 100 and 30 nm. For separations between 150 and 300 nm, the couplers can be manufactured with an accuracy of ±5 nm at the two operating wavelengths. For decreasing wavelength separation of the channels, the influence of the state of polarization results in an increased inaccuracy of the two wavelengths, increased far-end crosstalk, and power fluctuations after the coupler. This sets a lower limit for channel separation. Good agreement between theory and experiment is achieved