Octave-spanning low-loss mid-IR waveguides based on semiconductor-loaded plasmonics

Plasmonic waveguides are crucial building blocks for integrated on-chip mid-infrared (mid-IR) sensors, which have recently attracted great interest as a sensing platform to target enhanced molecular sensing. However, while hosting a wide range of applications from spectroscopy to telecommunication, the mid-IR lacks suitable broadband solutions that provide monolithic integration with III-V materials. This work reports a novel concept based on hybrid semiconductor-metal surface plasmon polariton waveguides, which result in experimentally demonstrated low loss and broadband devices. Composed of a thin germanium slab on top of a gold layer, the waveguiding properties can be directly controlled by changing the geometrical parameters. The measured losses of our devices are as low as 6.73 dB/mm at 9.12 mu m and remain <15 dB/mm in the mid-IR range of 5.6-11.2 mu m. The octave-spanning capability of the waveguides makes them ideal candidates for combination with broadband mid-IR quantum cascade laser frequency combs and integrated spectroscopic sensors. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Automated summary

This study introduces a novel concept based on hybrid semiconductor-metal surface plasmon polariton waveguides, which exhibit experimentally demonstrated low loss and broadband characteristics. By changing the geometrical parameters, the waveguide properties can be directly controlled, making them suitable for combination with broadband mid-IR quantum cascade laser frequency combs and integrated spectroscopic sensors.