title: Ge-rich graded-index Si1-xGex waveguides with broadband tight mode confinement and flat anomalous dispersion for nonlinear mid-infrared photonics.
abstract: This work explores the use of Ge-rich graded-index Si1-xGex rib waveguides as building blocks to develop integrated nonlinear optical devices for broadband operation in the mid-IR. The vertical Ge gradient concentration in the waveguide core renders unique properties to the guided optical mode, providing tight mode confinement over a broadband mid-IR wavelength range from λ = 3 µm to 8 µm. Additionally, the gradual vertical confinement pulls the optical mode upwards in the waveguide core, overlapping with the Ge-rich area where the nonlinear refractive index is larger. Moreover, the Ge-rich graded-index Si1-xGex waveguides allow efficient tailoring of the chromatic dispersion curves, achieving flat anomalous dispersion for the quasi-TM optical mode with D ≤ 14 ps/nm/km over a ~1.4 octave span while retaining an optimum third-order nonlinear parameter, γeff. These results confirm the potential of Ge-rich graded-index Si1-xGex waveguides as an attractive platform to develop mid-IR nonlinear approaches requiring broadband dispersion engineering.
authors.forename: J M
authors.initials: JM
authors.lastname: Ramirez
authors.forename: V
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authors.lastname: Vakarin
authors.forename: J
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authors.lastname: Frigerio
authors.forename: P
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authors.lastname: Chaisakul
authors.forename: D
authors.initials: D
authors.lastname: Chrastina
authors.forename: X
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authors.lastname: Le Roux
authors.forename: A
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authors.lastname: Ballabio
authors.forename: L
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authors.lastname: Vivien
authors.forename: G
authors.initials: G
authors.lastname: Isella
authors.forename: D
authors.initials: D
authors.lastname: Marris-Morini