Joan Manel Ramirez

Vladyslav Vakarin

Papichaya Chaisakul

Samuel Serna

Qiankun Liu

Jacopo Frigerio

Andrea Ballabio

Xavier Le Roux

Laurent Vivien

Giovanni Isella

Eric Cassan

Nicolas Dubreuil

Delphine Marris-Morini

(Invited) Silicon Photonics Based on Ge/Sige Quantum Well (QW) Structures and Ge-Rich Materials for Near-IR and Mid-IR

. Interestingly, tuning the QW design allows fine tuning of the absorption band edge of devices over a wideband range. Moreover, light emission from the direct bandgap transition HH1-CΓ1 has also been reported in SiGe/Ge quantum wells,

opening the route towards the development of light emitting devices fully integrated in a silicon chip [START_REF] Chaisakul | Room temperature direct gap electroluminescence from Ge/Si0. 15Ge0. 85 multiple quantum well waveguide[END_REF].

Noticeably, all the above described activities are meant to develop Si-based photonic platforms in the nearinfrared wavelength range, where most applications are foreseen. Lately, however, there is an increasing interest in the exploitation of Ge-based photonic platforms at longer wavelengths up to the mid-infrared [START_REF] Soref | Mid-infrared photonics in silicon and germanium[END_REF]. Having Ge a transparency window up to 15 µm, there are good prospects for the development of advanced photonic sensing platforms leveraging from the strong mid-IR molecular absorption bands of several chemical and biological substances. Besides, Ge-based platforms have also been proposed as ideal candidates to exploit the nonlinear properties at mid-IR wavelengths, owing to a higher χ(3) nonlinearity and the absence of twophoton absorption beyond λ ≈ 3.15 µm [START_REF] Zhang | Nonlinear Group IV photonics based on silicon and germanium: from near-infrared to midinfrared[END_REF]. Important benefits are also expected in data communications, taking advantage from the two atmospheric transparency windows at λ ≈ 3-5 µm and λ ≈ 8-13 µm and the relaxed wavelength regulations put in place.

Thus, in this presentation we will show our recent work on the development of Ge-based photonic devices for telecom and mid-IR applications. For that, a review of the advanced optoelectronic devices demonstrated so far in our group will be presented, including high-speed SiGe/Ge QWs electro-absorption modulators and detectors exploiting the QCSE. Then, further insight on the room temperature luminescence of QWs will be provided, followed by its integration in light emitting diodes in waveguide configuration for planar emission. In addition, a novel mid-IR photonic platform based on Ge-rich graded-index SiGe alloys will be presented. This platform offers an interesting set of advantages over other existing mid-IR approaches such as low-loss propagation and optimal modal area over an unprecedentedly broadband wavelength range [START_REF] Ramirez | Low-loss Ge-rich Si0.2Ge0.8 waveguides for mid-infrared photonics[END_REF]. As a consequence, the first demonstration of ultra-wideband mid-IR Mach-Zehnder interferometers operating from λ = 5.5 µm to 8.5 µm was performed using the graded-index SiGe platform [START_REF] Vakarin | Ultra-wideband Ge-rich silicon germanium integrated Mach-Zehnder interferometer for mid-infrared spectroscopy[END_REF]. Finally, the third-order nonlinear properties of this platform will be discussed, supported by experimental data on Ge-rich SiGe waveguides using a bidirectional top hat D-scan method [START_REF] Ramirez | Ge-rich graded-index SiGe waveguides with broadband tight mode confinement and flat anomalous dispersion for nonlinear mid-infrared photonics[END_REF]. Promising results were obtained, thus providing a promising scenario to develop broadband optical sources based on the supercontinuum generation.