At least four groups have demonstrated GeSn direct bandgap material and shown cryogenic temperature lasers under optical pumping. With up to 16% of Sn, our lasers operate up to 180K and lase up to wavelengths of 3.1 um.
We will describe our efforts to reduce the threshold, increase the operating temperature, and evolve towards electrical pumping in these lasers.Thes efforts involve improvements of epi growth, electrical passivation, doping, heterostructures, strain control...
Photonic crystal and plasmonic structures are the two main approaches used in nanophotonic for efficiently confining and enhancing the electromagnetic field at subwavelength scale. For these reasons, these two approaches have been both used for the optical trapping of nanometric particle. We present, here, experimental results showing that structures combining both photonic crystal and nanoantennas could lead to improved trapping performances.
In previous theoretical papers [1, 2] we have shown that when the critical coupling between a photonic crystal and a nanoantenna is reached, a large Gaussian beam could be efficiently coupled to a single nanoantenna. In this way, it is possible to generate a nanometric hotspot in the nanoantenna leading to a very efficient optical trap.
The experimental demonstration of this effect has been obtained on an SOI sample consisting in a gold nanoantenna located at the centre of a photonic crystal cavity. Stable trapping of 100 nm diameter nanoparticle has been observed using a 5mW laser at 1.31µm with a 5µm waist. The nanoparticle are trapped above the nanoantenna gap and a normalized trap stiffness of 0.3 fN.nm-1.mW-1 is measured. This result demonstrates the interest of this approach. We will discuss and compare it to the state of the art of nanotweezers.
 A. El Eter et al. Opt. Express 22, 14464 (2014).
 A. Belarouci et al. Opt. Express 18, A381 (2010).
The demonstration of a CMOS compatible laser working at room temperature has been eagerly sought since the beginning of silicon photonics. Although bulk Germanium (Ge) is an indirect bandgap material, Tin (Sn) can be incorporated into it to turn the resulting alloy into a direct band-gap semiconductor. Recently, lasing was demonstrated at cryogenic temperatures using thick GeSn layers with Sn contents of 8.5% and above. Optical micro-cavities were later added to reduce the laser threshold. Here, an under-etching of thick GeSn layers selectively with regard to Ge confines optical modes and relaxes the compressive strain built inside the layers, resulting in more direct band-gaps behavior. Such photonic components rely on technological processes dedicated to GeSn. In this paper, we present our recent developments on (i) anisotropic etching of GeSn and (ii) isotropic etching of Ge selective with regard to GeSn. Even for GeSn with a Sn content as low as 6%, the etching selectivity is of 57. For 8% Sn content, the selectivity reaches 433. We used these processes to fabricate micro-disk optical cavities in thick GeSn layers. Under continuous wave pumping, optical modes were detected from photoluminescence spectra.