Abstract

We demonstrate low-loss Ge-rich ${\mathrm{Si}}_{0.2}{\mathrm{Ge}}_{0.8}$ waveguides on ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ ($x$ from 0 to 0.79) graded substrates operating in the mid-infrared wavelength range at $\lambda =4.6\mathrm{\mu m}$. Propagation losses as low as $(1.5\pm 0.5)\mathrm{dB}/\mathrm{cm}$ and $(2\pm 0.5)\mathrm{dB}/\mathrm{cm}$ 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 ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ waveguides with high Ge concentration as fundamental blocks for mid-infrared photonic integrated circuits.

© 2016 Optical Society of America

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