Multiwavelength heterogeneously integrated lithium niobate on silicon nitride tunable filters and switches

Heterogeneous integration of lithium niobate (LN) onto silicon nitride (SiN) enables compact electro-optic tuning by combining LN its strong Pockels effect with CMOS-compatible low-loss SiN photonics. Building on earlier demonstrations of LN-on-SiN all-pass modulators, we demonstrate micro-transfer printed racetrack-shaped LN slabs of 250 nm and 200 nm thickness onto add–drop SiN racetrack resonators to achieve tunable filtering and switching at 1550 nm and 1310 nm. By varying the bus–resonator gap from 510 nm to 710 nm, critical coupling is obtained, with passive measurements showing 26 dB extinction, a 940 pm FSR, and a 24 pm FWHM at C-band.