Adaptive gain equalizer in high-index-contrast SiON technology

An adaptive gain equalization filter is presented. The filter is based on the resonant coupler principle, a cascade of power couplers and delay lines. Reconfigurability and tuning is achieved by varying coupling strength and delay line length via the thermo optic effect. A device consisting of seven delay line stages was realized in high-index-contrast silicon-oxynitride technology. This device flattens the ASE spectrum of an EDFA to a ripple of less than 0.5 dB over 35 nm. The on-chip losses are 2 dB.