Integrated optical demultiplexer for WDM systems

The authors propose a wavelength division multiplexing (WDM) duplexer based on a nonuniform frequency-dependent coupler whose spectral selectivity depends on appropriate taper-functions for the coupling coefficient in the case of codirectional interaction. The frequency response of the codirectional tapered coupler is governed by the Riccati equation, the coupling characteristics being calculated in terms of the supermodes of the overall structure and of the modes of the individual waveguides. The design parameters spring from the technological constraints imposed by Ti:LiNbO₃ technology and the mask design rules obtainable by the current photolithographic apparatus. The optimized insertion losses are 0.9 and 2.3 dB for the filters centered at the wavelengths 1330 and 1550 nm, respectively. The crosstalk level is about 25 dB