Design, fabrication and characterization of an AWG at 4.5 µm.

In this paper, we present the design, the fabrication and the characterization of an Arrayed Waveguide Grating (AWG) based on a SiGe graded index waveguide platform, operating at 4.5 µm. These devices were specifically designed to work together with an array of Distributed Feedback Bragg Quantum Cascade Lasers (DFB-QCL) emitting at different wavelengths. The AWG enables to combine the different light sources into a single output and the design adopted allows to maximize transmission over the entire spectral range defined by the array of DFB-QCLs.

Low loss SiGe graded index waveguides for mid-IR applications.

In the last few years Mid InfraRed (MIR) photonics has received renewed interest for a variety of commercial, scientific and military applications. This paper reports the design, the fabrication and the characterization of SiGe/Si based graded index waveguides and photonics integrated devices. The thickness and the Ge concentration of the core layer were optimized to cover the full [3 - 8 µm] band. The developed SiGe/Si stack has been used to fabricate straight waveguides and basic optical functions such as Y-junction, crossings and couplers. Straight waveguides showed losses as low as 1 dB/cm at λ = 4.5 µm and 2 dB/cm at 7.4 µm. Likewise straight waveguides, basic functions exhibit nearly theoretical behavior with losses compatible with the implementation of more complex functions in integrated photonics circuits. To the best of our knowledge, the performances of those Mid-IR waveguides significantly exceed the state of the art, confirming the feasibility of using graded SiGe/Si devices in a wide range of wavelengths. These results represent a capital breakthrough to develop a photonic platform working in the Mid-IR range.