Hybrid Si3N4/electro-optic polymer waveguide Mach-Zehnder interferometer for high-speed electro-optic switching

Abstract

Silicon nitride (Si3N4) waveguides have significant applications in silicon photonics because of their low transmission loss, large transparent band range, and compatibility with CMOS processes. However, there is no electro-optic (EO) effect in Si3N4 waveguide and consequently it lacks active EO-tuning capacity. To activate Si3N4 waveguide, we propose the hybrid integration of EO polymer as cladding on Si3N4 waveguide. The waveguide is rationally designed to optimize the overlap factor of optical and electric fields on EO cladding for efficient EO modulation. Mach-Zehnder interferometer (MZI) EO switches are fabricated by photolithography and ICP etching. To enable the EO effect of cladding, electric field poling is carried out by applying high-voltage electric field and high-temperature thermal field to generate the strong in-device EO effect. By the optimization of waveguide engineering and electric-field poling, the lowest switching voltage of 11.4 V is achieved, showing a half-wave voltage length (VπL) product of 5.7 Vcm. The extracted in-device Pockels coefficient (EO coefficient, γ33) is as high as 72 pm/V, much higher than that of lithium niobate. The measured rise time and fall time of high-speed EO switching are 48.75 ns and 57.78 ns. The extinction ratio for on and off state was higher than 10 dB. This Si3N4/EO polymer hybrid EO switch may find application in optical cross connect, optical add-drop multiplexing, high-speed filter for DWDM and optical phase array for high-speed beam steering.