Highly broadband buried channel couplers

It is shown that, by taking advantage of the maximum in the spectral dependence of the coupling coefficient, very wideband symmetric and asymmetric singlemode couplers can be designed. The symmetric coupler design will allow at least 98% coupling between the two cores over the wavelength range 1.3-1.59 μm, while the asymmetric coupler can act as a 3 dB splitter with only ±0.8% variation in splitting ratio over the wavelength range 1.31-1.75 μm