Enhanced light output power of quantum cascade lasers from a tilted front facet

Unidirectional mode selection in bistable quantum cascade ring lasers

Ideal ring resonators are characterized by travelling-wave counter-propagating modes, but in practice travelling waves can only be realized under unidirectional operation, which has proved elusive. Here, we have designed and fabricated a monolithic quantum cascade ring laser coupled to an active waveguide that allows for robust, deterministic and controllable unidirectional operation. Spontaneous emission injection through the active waveguide enables dynamical switching between the clockwise and counterclockwise states of the ring laser with as little as 1.6% modulation of the electrical input. We show that this behavior stems from a perturbation in the bistable dynamics of the ring laser. In addition to switching and bistability, our novel coupler design for quantum cascade ring lasers offers an efficient mechanism for outcoupling and light detection.

Ring quantum cascade lasers with twisted wavefronts

We demonstrate the on-chip generation of twisted light beams from ring quantum cascade lasers. A monolithic gradient index metamaterial is fabricated directly into the substrate side of the semiconductor chip and induces a twist of the light's wavefront. This significantly influences the obtained beam pattern, which changes from a central intensity minimum to a maximum depending on the discontinuity count of the metamaterial. Our design principle provides an interesting alternative to recent implementations of microlasers operating at an exceptional point.

High power spiral cavity quantum cascade superluminescent emitter

Quantum Cascade devices with an emission wavelength centered around 5 μm have been shaped into compact, yet long (8 mm and 12 mm) spiral cavities to increase mid-infrared superluminescence (SL) power. Up to ~57 mW of SL power at 250 K is obtained with a Gaussian emission spectrum with a full width at half maximum of 56 cm(-1) and a coherence length of ~107 μm.

Quantum cascade lasers with a tilted facet utilizing the inherent polarization purity

We report on quantum cascade lasers (QCLs) with a tilted facet utilizing their polarization property. Contrary to diode lasers, QCLs generate purely TM polarized light due to the intersubband selection rules. This property enables the utilization of reflectivity in terms of only TM polarized light (TM reflectivity). The TM reflectivity is reduced by tilting the front facet, resulting in enhanced light output power from the tilted facet. The peak output power of a QCL with a facet angle of 12° are increased by 31 %. The slope efficiency of a QCL with a facet angle of 17° are increased by 43 %. Additionally, a peculiar property of TM reflectivity, the Brewster angle, is investigated by using COMSOL simulations to find its availability in QCLs.

Monolithically integrated mid-infrared lab-on-a-chip using plasmonics and quantum cascade structures

The increasing demand of rapid sensing and diagnosis in remote areas requires the development of compact and cost-effective mid-infrared sensing devices. So far, all miniaturization concepts have been demonstrated with discrete optical components. Here we present a monolithically integrated sensor based on mid-infrared absorption spectroscopy. A bi-functional quantum cascade laser/detector is used, where, by changing the applied bias, the device switches between laser and detector operation. The interaction with chemicals in a liquid is resolved via a dielectric-loaded surface plasmon polariton waveguide. The thin dielectric layer enhances the confinement and enables efficient end-fire coupling from and to the laser and detector. The unamplified detector signal shows a slope of 1.8–7 μV per p.p.m., which demonstrates the capability to reach p.p.m. accuracy over a wide range of concentrations (0–60%). Without any hybrid integration or subwavelength patterning, our approach allows a straightforward and cost-saving fabrication.

Quantum cascade lasers and detectors enable photonic integration of semiconductor devices across a broad spectral range. Here, Schwarz et al. present a bi-functional laser and detector structure, monolithically integrated with plasmonic waveguides for mid-infrared chemical sensors on a chip.