Wavelength tunable 1-from-16 and flat passband 1-from-8 add-drop filters

Tunable add-drop filters for wavelength-division multiplexing networks are presented. The compact devices are realized in high-index-contrast silicon-oxynitride planar waveguide technology and are based on the resonant coupler principle. The first device selects one wavelength channel from a comb of up to eight wavelengths and exhibits a flat passband. Scalability of the filter concept to a larger number of wavelength channels is illustrated with a 1-from-16 add-drop filter. Tunability is obtained using the thermo-optic effect and chromium heater stripes. The devices show negligibly small polarization sensitivity. The isolation of the transit channels to the drop port is between 15 and 20 db and the rejection of the drop channel ranges from 18 to 23 dB. The design and scalability trade-offs are discussed.