Mid-infrared integrated waveguide modulators based on silicon-on-lithium-niobate photonics

Heterogeneous integration techniques, such as direct bonding, have enabled solutions to many problems facing integrated photonics. In particular, the relatively new field of mid-infrared (mid-IR) integrated photonics has been hindered by the availability of functional, transparent substrates in this wavelength range. The key to achieving compact, high-performance optical modulation and frequency conversion is the monolithic integration of silicon photonics with a material with high second-order nonlinear susceptibility. By transferring large areas of thin, monocrystalline silicon to bulk lithium niobate (LiNbO3) substrates, the first silicon-based platform to exploit the Pockels or linear electro-optic effect in the mid-IR range is achieved. Integrated Mach–Zehnder interferometer modulators with an extinction ratio of ∼8 dB, a half-wave voltage-length product of 26 V · cm, and an on-chip insertion loss of 3.3 dB are demonstrated at a wavelength of 3.39 μm. Ultrathin optical waveguides fabricated and characterized on this platform exhibit a low transverse electric mode linear propagation loss of 2.5 dB∕cm. Future capabilities such as wideband difference frequency generation for integrated mid-IR sources are envisioned for the demonstrated silicon-on-lithium-niobate platform. © 2014 Optical Society of America