Silicon Waveguides for Mid-infrared Integrated Photonics

In recent years, there has been a rise in interest in mid-infrared (mid-IR) silicon photonics. This paper investigates the single-mode condition, mode confinement, and scattering loss for silicon-on-insulator (SOI), silicon-on-nitride (SON), and silicon-on-sapphire (SOS) waveguides at mid-IR wavelengths (2–5 $\mu\mathrm{m})$. The mode confinement factor is calculated from the effective index method. The Payne-Lacey model is used in the calculation of scattering loss. Scattering loss is low $(< 0.01\mathrm{dB}/\mathrm{cm})$ for SOI waveguides in the 2-2.5 $\mu \mathrm{m}$, whereas for SOS it is in the 3–5 $\mu \mathrm{m}$. SON waveguide has moderate scattering loss through out $2-5\mu\mathrm{m}$. In 2-2.5 wavelengths, SOS has better($>$ 70 %) mode confinement. In 3–5 $\mu\mathrm{m}$ wavelengths, SOI has better confinement.