title: Low-loss Ge-rich Si0.2Ge0.8waveguides for mid-infrared photonics.
abstract: We demonstrate low-loss Ge-rich Si0.2Ge0.8waveguides 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-xGexwaveguides with high Ge concentration as fundamental blocks for mid-infrared photonic integrated circuits.
authors.forename: Joan Manel
authors.initials: JM
authors.lastname: Ramirez
authors.forename: Vladyslav
authors.initials: V
authors.lastname: Vakarin
authors.forename: Clement
authors.initials: C
authors.lastname: Gilles
authors.forename: Jacopo
authors.initials: J
authors.lastname: Frigerio
authors.forename: Andrea
authors.initials: A
authors.lastname: Ballabio
authors.forename: Papichaya
authors.initials: P
authors.lastname: Chaisakul
authors.forename: Xavier Le
authors.initials: XL
authors.lastname: Roux
authors.forename: Carlos
authors.initials: C
authors.lastname: Alonso-Ramos
authors.forename: Gregory
authors.initials: G
authors.lastname: Maisons
authors.forename: Laurent
authors.initials: L
authors.lastname: Vivien
authors.forename: Mathieu
authors.initials: M
authors.lastname: Carras
authors.forename: Giovanni
authors.initials: G
authors.lastname: Isella
authors.forename: Delphine
authors.initials: D
authors.lastname: Marris-Morini