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Article Dans Une Revue Scientific Reports Année : 2017

Nonlinear Properties of Ge-rich Si 1−x Ge x Materials with Different Ge Concentrations

Résumé

Silicon photonics is a large volume and large scale integration platform for applications from long-haul optical telecommunications to intra-chip interconnects. Extension to the mid-IR wavelength range is now largely investigated, mainly driven by absorption spectroscopy applications. Germanium (Ge) is particularly compelling as it has a broad transparency window up to 15 µm and a much higher third-order nonlinear coefficient than silicon which is very promising for the demonstration of efficient non-linear optics based active devices. Si 1−x Ge x alloys have been recently studied due to their ability to fine-tune the bandgap and refractive index. The material nonlinearities are very sensitive to any modification of the energy bands, so Si 1−x Ge x alloys are particularly interesting for nonlinear device engineering. We report on the first third order nonlinear experimental characterization of Ge-rich Si 1−x Ge x waveguides, with Ge concentrations x ranging from 0.7 to 0.9. The characterization performed at 1580 nm is compared with theoretical models and a discussion about the prediction of the nonlinear properties in the mid-IR is introduced. These results will provide helpful insights to assist the design of nonlinear integrated optical based devices in both the near-and mid-IR wavelength ranges. Chemical and biological sensing devices exploiting the strong rotational-vibrational absorption lines of molecules in the mid-infrared (mid-IR) region of the spectrum, i.e. targeting wavelengths between 3 and 20 µm, are showing a tremendous progress and have been already tested in daily-life applications 1. In parallel, nonlinear optical phenomena in integrated platforms used for frequency combs, supercontinuum or photon pair generation are subject of intense research with potential applications in molecular spectroscopy 2 , quantum optics 3,4 and metrology 5. The extension of the operation wavelength of silicon photonics from the near-IR towards the mid-IR allows taking advantage of the reliable and high-volume fabrication developed in microelectronic foundries to offer higher performance, new functionalities, lower costs, smaller size, reduced weight and low power consumption photonics circuits 6. The well-known Silicon-on-Insulator (SOI) waveguides have been successfully used to demonstrate nonlinear based optical sources such as frequency combs between 1.5 and 3.3 μm 2. However, while silicon itself is transparent up to a wavelength of about 8 μm, the SiO 2-buried layer limits the transmission of SOI waveguides at around 4 μm wavelength. Alternative solutions including silicon-on-sapphire 7 , silicon nitride 8 or suspended waveguides 9 have been developed. Among the materials compatible with large volume and large scale integration, germanium (Ge) is particularly compelling as it exhibits a large transparency window from 1.9 to 15 μm 10. Furthermore, Ge is expected to have a much higher third-order nonlinear coefficient than silicon in mid-IR wavelength range, at which low loss Ge strip waveguides 11,12 , and wavelength (de)multiplexers 13,14 up to 5.8 μm have been successfully demonstrated. Low loss graded Si 1−x Ge x /Si waveguides were also demonstrated 15,16 at 4.6 and 7.4 μm wavelengths. Modeling of the nonlinear optical (NLO) coefficients of the Si
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Dates et versions

hal-02883627 , version 1 (29-06-2020)

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Samuel Serna, Vladyslav Vakarin, Joan-Manel Ramírez, Jacopo Frigerio, Andrea Ballabio, et al.. Nonlinear Properties of Ge-rich Si 1−x Ge x Materials with Different Ge Concentrations. Scientific Reports, 2017, 7 (1), ⟨10.1038/s41598-017-15266-z⟩. ⟨hal-02883627⟩
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