POLARIZATION INDEPENDENT NARROW CHANNEL WAVELENGTH DIVISION MULTIPLEXING FIBER COUPLERS FOR 1.55 MU-M

A polarization independent narrow channel (PINC) wavelength division multiplexing (WDM) coupler for 1.55-mu-m has been designed based on the birefringent properties of fused single-mode couplers. The couplers are made so that they are highly overcoupled so that the coupling coefficient-length products for the two orthogonal coupler polarizations are pi out of phase for input wavelengths near 1.55-mu-m. The resulting wavelength separation between adjacent maxima and minima of the coupled power is on the order of 22 nm. The devices have been packaged in an environmentally insensitive casing, and show minimal variations in coupling characteristics with changing pressure and temperature.