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.