Low-loss Ge-rich Si_02Ge_08 waveguides for mid-infrared photonics

TLDR

We demonstrate low‑loss Ge‑rich Si0.2Ge0.8 waveguides on graded Si1‑xGex substrates operating at 4.6 µm in the mid‑infrared. We fabricated these waveguides and characterized their mode profiles and effective areas via near‑field optical measurements, confirming agreement with simulations. Measured propagation losses of 1.5 ± 0.5 dB/cm (quasi‑TE) and 2 ± 0.5 dB/cm (quasi‑TM) with only 10 dB total coupling loss for widths >7 µm, and near‑field mode profiling confirmed effective area measurements, demonstrating the viability of high‑Ge Si1‑xGex waveguides as building blocks for mid‑infrared photonic integrated circuits.

Abstract

We demonstrate low-loss Ge-rich Si0.2Ge0.8 waveguides on Si1-xGex (x from 0 to 0.79) graded substrates operating in the mid-infrared wavelength range at λ=4.6 μm. Propagation losses as low as (1.5±0.5)dB/cm and (2±0.5)dB/cm were measured for the quasi-TE and quasi-TM polarizations, respectively. A total coupling loss (input/output) of only 10 dB was found for waveguide widths larger than 7 μm due to a good fiber-waveguide mode matching. Near-field optical mode profiles measured at the output waveguide facet allowed us to inspect the optical mode and precisely measure the modal effective area of each waveguide providing a good correlation between experiments and simulations. These results put forward the potential of low-index-contrast Si1-xGex waveguides with high Ge concentration as fundamental blocks for mid-infrared photonic integrated circuits.