Tunable WDM add/drop components in silicon-oxynitride waveguide technology

We report the realization of tunable wavelength division multiplexing (WDM) add/drop components in high-index-contrast silicon-oxynitride (SiON) technology. The add/drop components are of the resonant coupler type, which is a structure with a large amount of bends. Our SiON technology allows bending radii of 1.5 mm, which is a factor 10 smaller than for standard fiber-matched technology. Hence our high-index-contrast technology permits the realization of these devices with a large number of stages and accordingly the implementation of complex functions. Two tunable add/drop devices are demonstrated. First we discuss a 1-from-4 add-after-drop device in which the add and drop functions were optimized individually. The add-after-drop concept eliminates the homo-wavelength crosstalk issue. As a second example, a 1-from-8 add/drop component is presented. Both devices are thermo-optically tunable, polarization-insensitive, and show good isolation values. The on-chip loss of the devices is about 3 dB. The 1-from-4 component was packaged using lensed fibers, which resulted in insertion losses of between 5 and 7 dB.