Abstract

Near-infrared nanophotonics has been massively studied due to its promising ability in addressing the interconnect bottleneck problem [1] and achieving resonator-based sensors with high quality factor [2][3]. Among the various material platforms that have been applied in near infrared nanophotonics, silicon-on-insulator (SOI) platform offers advantages such as high optical mode confinement, low loss, CMOS compatibility, and mature fabrication [4]. Some research attentions have migrated to mid-infrared region since it could on the one hand potentially offer better solution for environment sensing due to the fact that the vibration resonance peaks of many environmental chemicals are in the mid-infrared region, and on the other hand provide thermal imaging ability which near-infrared nanophotonics is not able to [5]. On top of that, free carrier plasma dispersion effect is stronger in mid-infrared while two photon absorption is weaker; and better fabrication tolerance is granted [6]. However, a major concern about SOI mid-infrared nanophotonics is high loss due to absorption caused by silicon dioxide [7]. Research have been performed to confine optical power mostly in silicon to reduce silicon dioxide absorption. After optimization, at 3.74 µm, 3.76 µm, 3.80 µm and 3.84 µm, previous channel waveguides still showed propagation loss more than 4 dB/cm typically, which might hinder the use of mid-infrared nanophotonics in some long wire applications [5][8][9]. We demonstrate SOI channel waveguide with propagation loss < 3 dB/cm at various wavelengths in the range of 3.70 - 3.85 µm. Bending loss of the same waveguide is also measured to be ~ 0.02 dB/90° with the smallest reported bending radius. Our result improves the performance of the state-of-the-art SOI waveguide devices in mid-infrared and shows that ultra-compact bends are possible for SOI mid-infrared application. Since our waveguide achieves low propagation loss and bending loss at various mid-infrared wavelength, it is also a promising candidate for broadband operation.

© 2017 Optical Society of America