This paper reports on SiGeSn/GeSn multi-quantum-well microdisk lasers. The fabrication of the devices includes a selective under-etching step, which enhances the guiding of the whispering gallery modes inside the cavity. Lasing occurs under different electrical pumping conditions with a very low threshold current and for long, quasi-continuous wave pulses compared to previously reported GeSn-based microdisk lasers. Furthermore, the lasing threshold current is reduced by a factor of ten compared to similar double-heterostructure devices.
A crucial element for the next generation of portable gas sensors for high-volume applications, especially involving chemical sensing of important greenhouse and pollutant gases, is the development of a low-cost, low-power consuming, single-frequency laser operating in the mid-infrared spectral range.
In this regard, we propose the implementation of a Quantum Cascade Surface Emitting Laser (QCSEL). Our design involves a linear microcavity with high reflectivity coated end-mirrors and a buried semiconductor diffraction grating to extract the light from the surface.
We present a suspended SiGeSn microring laser design that enables strain relaxation of the material layer stack, electrical pumping and adequate heat sinking. Using both strain and composition as two degrees of freedom to engineer the band structure, a direct bandgap is obtained in the gain material of a double heterostructure layer stack, and the L- to Γ-valley energy difference increased to 78 meV, by 66% compared to a non-underetched structure. The temperature dependent current threshold is modeled for the designed device and determined to be 18 kA/cm2 at 50 K. The fabrication process is outlined and first experimental electroluminescence results indicating the effectiveness of our approach are reported. At the time this proceedings paper is being submitted, electrically pumped lasing has also been achieved with a similar structure, with results that will be reported in a future publication.
Interfacing semiconductor with photonic qubits plays an important role in quantum networks. We model a photon to spin qubit interface based on an optically active gate-defined quantum dot embedded in a two-dimensional photonic crystal cavity constraining its emission profile with a low enough quality factor for emission wavelength tuning. By matching the cavity-mode k-vector and reciprocal lattice of the crystal, vertical emission is obtained. A reflector below the cavity increases not only the light extraction efficiency, but also tailors the extracted beam profile to match that of a single mode fiber, into which photons emitted by the quantum dot are coupled with a probability above 50%. The efficiency is primarily limited by metal electrode absorption. In addition to trapping the exciton, the electrode system embedded inside the cavity allows trapping, manipulation and readout of a pair of electrons encoding a spin qubit in a singlet-triplet configuration, whose quantum state can be transferred to and from the exciton by utilizing an existing protocol. Experimental realization of these devices is currently in progress with first results in regard to fabrication also reported.
Hybrid integration of prefabricated III-V laser diodes with sub-micrometric silicon photonic waveguides suffers from a tradeoff between alignment tolerance and coupling efficiency. In this work, we demonstrate integrated coupling devices that substantially alleviate this problem by means of a balanced distribution of the laser power between two on-chip single mode SOI waveguides. With the reported coupling devices, a horizontal misalignment of the laser is converted in a variation of the relative phase of the light coupled into the two waveguides, allowing to satisfy the reciprocity principle while maintaining a high total coupling efficiency and a balanced power splitting. The relaxed alignment tolerances facilitate passive assembly of the lasers with pick-and-place tools. The balanced splitting of the power between waveguides is particularly well suited for optical interconnects with parallel transmitters. Here, the device design is discussed for both edge couplers and grating couplers relying on similar design principles. Furthermore, experimental characterization of edge-coupling structures with a lensed fiber and a Fabry-Pérot laser is presented. These devices have been fabricated with 193nm DUV optical lithography and are compatible with mainstream CMOS technology. The edge couplers with the best horizontal misalignment exhibits an excellent 1 dB loss horizontal misalignment range of 3.8 μm with excess insertion losses below 3.1 dB (in addition to the 3dB splitting). The back-reflection induced by the device has been assessed to be below -20 dB and measured relative intensity noise is better than measured from the same laser coupled to a lensed fiber.
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