Passband-flattened periodic multi/demultiplexer using a Mach-Zehnder interferometer with ring resonator fabricated in SiON waveguide technology

In this paper, we demonstrate a thermo-optically tunable periodic wavelength filter (interleaver) with a 50 GHz free spectral range (FSR). It has an almost rectangular wavelength response and consists of an asymmetric Mach-Zehnder Interferometer (MZI) consisting of two tunable 3dB couplers interconnected by two waveguide channels of unequal length, with a ring resonator coupled to one of the branches of the MZI. The filter is fabricated in silicon oxynitride (SiON) waveguide technology. The bar and cross transmission spectra and chromatic dispersion of the filter have been measured and passband flattening and stopband broadening was observed in good agreement with the simulation. The isolation was 15 dB and 12 dB for TM and TE polarized light respectively, which was lower than the designed 29 dB. The main cause of lower isolation is an inaccuracy of the realization of the power coupling coefficient to the ring (59% instead of the designed 82%). The measured dispersion of the filter varies from 0 ps/nm at the center to 1660 ps/nm at the edge of the passband.