Guided-wave multi/demultiplexers with compensation for centre wavelength shift by fabrication process fluctuations

A new multi/demultiplexer is proposed together with its fabrication method, which can compensate for the centre wavelength shift ¿¿0 caused by fabrication process fluctuations. This device consists of a directional coupler with three different-refractive-index (nb, nw and nc) layers; i.e. an underlayer with index nb, a middle core waveguide layer with index nw and an upper layer with index nc (nw > nc, nw > nb and nc ¿ nb). In the method, ¿¿0 can be compensated for selecting the optimum nc, which is calculated by measuring deviations in core widths, core heights and waveguide separation before coating the waveguides with cladding material. Then, cladding material with the optimum nc is coated on to the core waveguides. This method offers high reproducibility and stability.