Abstract
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.
Highlights
The mid-infrared region of the optical spectrum (3– 8 μm) is an important range for applications in remote sensing, free-space communications, and defense technology [1]
Integrated photonics offers the best outlook for achieving these functions at low cost, while maintaining good yield and consistent performance
The silicon-on-insulator (SOI) platform has proven highly effective for near-infrared photonics [2], the presence of the buried silicon dioxide (SiO2) layer limits its usefulness in the mid-IR range due to the onset of optical absorption [3]
Summary
The mid-infrared (mid-IR) region of the optical spectrum (3– 8 μm) is an important range for applications in remote sensing, free-space communications, and defense technology [1]. It is desirable to use a platform that exhibits transparency at least through the first atmospheric transmission window of 3–5 μm. The silicon-on-insulator (SOI) platform has proven highly effective for near-infrared (near-IR) photonics [2], the presence of the buried silicon dioxide (SiO2) layer limits its usefulness in the mid-IR range due to the onset of optical absorption [3]. Third-order optical nonlinearities [9,10,11,12] are made possible by the low multiphoton absorption in the mid-IR region, but the pump power to achieve these effects is still relatively high
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