Dynamic gain equalizer using hybrid integrated silica-based planar lightwave circuits with LiNbO3 phase shifter array

This paper proposes a dynamic gain equalizer (DGE) using hybrid integrated silica-based planar lightwave circuits (PLCs) with a LiNbO₃ (LN) phase shifter array to achieve a DGE that offers both excellent optical performance and control of the phase shifters. The structure consists of two PLCs having arrayed-waveguide gratings (AWGs) and couplers directly attached to the LN phase shifter array at its end faces. To reduce polarization-dependent characteristics, a polarization diversity technique using a polarization beam splitter (PBS) and a circulator was employed. To reduce polarization-dependent loss (PDL) due to the reflected light at the PLC-LN interfaces, tilted waveguides from the normal direction to the interfaces were introduced, and the relation between PDL and power reflectivity was theoretically investigated. A hybrid integrated DGE using super-high-Δ PLCs and a 25-channel electrooptic (EO) phase shifter array was demonstrated. The PDL was effectively suppressed with the introduced polarization diversity technique, and the measured spectra were in good agreement with designed profiles. These results indicate that the proposed hybrid integrated DGE offers good performance and controllability for practical applications.