The linear and nonlinear optical response of SiGe waveguides in the mid-infrared are experimentally measured. By cutback measurements we find the linear losses to be less than 1.5dB/cm between 3μm and 5μm, with a record low loss of 0.5dB/cm at a wavelength of 4.75μm. By launching picosecond pulses between 3.25μm and 4.75μm into the waveguides and measuring both their self-phase modulation and nonlinear transmission we find that nonlinear losses can be significant in this wavelength range due to free-carrier absorption induced by multi-photon absorption. This should be considered when engineering SiGe photonic devices for nonlinear applications in the mid-IR.
We present a scheme for the realization of high performances, large tuning range, fully integrated and possibly low cost mid infrared laser source based on quantum cascade lasers and silicon based integrated optics. It is composed of a laser array and a laser combiner. We show that our metal grating approach gives many advantages for the fabrication yield of those laser arrays. We show the results of such a fabrication at 1350 cm<sup>-1</sup> with 60 cm<sup>-1</sup> tuning range. The silicon is a low cost option for the size consuming combiner. In the development of the SiGe platform, we present the loss measurement set up and we show losses below 1dB/cm at 4.5μm.
We report on the advanced optical characterizations of microfabricated solid immersion lenses with 2-μm diameter,
operating at λ= 642 nm. The main feature, the spot size reduction, has been investigated by applying a focused Gaussian
beam of NA = 0.9. Particular illuminating beams, e.g., Bessel-Gauss beams of the zeroth and the first order, a doughnutshape
beam and its decompositions, i.e. two-half-lobes beams, have also been used to influence the shape of the
immersed focal spot. Detailed optical characterizations have been conducted by measuring the amplitude and phase
distributions with a high-resolution interference microscope (HRIM) in volume around the focal spot. The immersion
effect of the SiO<sub>2</sub> solid immersion lens leads to a spot-size reduction of approximately 1.5 which agrees well with theory.
Particularly shaped incident beams exhibit a comparable size reduction of the immersed spots. Such structured focal
spots are of significant interest in optical trapping, lithography, and optical data storage systems.