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We demonstrate the monolithic integration of a mid-infrared laser and detector utilizing a bi-functional quantum cascade active region. When biased, this active region provides optical gain, while it can be used as a detector at zero bias. With our novel approach we can measure the light intensity of the laser on the same chip without the need of external lenses or detectors. Based on a bound-to-continuum design, the bi-functional active region has an inherent broad electro-luminescence spectrum of 200 cm-1, which indicates its use for single mode laser arrays. We have measured a peak signal of 191.5 mV at the on-chip detector, without any amplification. The room-temperature pulsed emission with an averaged power consumption of 4 mW and the high-speed detection makes these devices ideal for low-power sensors. The combination of the on-chip detection functionality, the broad emission spectrum and the low average power consumption indicates the potential of our bi-functional quantum cascade structures to build a mid-infrared lab-on-a-chip based on quantum cascade laser technology.

This work provides a detailed study on the growth of AlxIn1-xAsySb1-y lattice-matched to InAs by Molecular Beam Epitaxy. In order to find the conditions which lead to high crystal quality deep within the miscibility gap, AlxIn1-xAsySb1-y with x = 0.462 was grown at different growth temperatures as well as As2 and Sb2 beam equivalent pressures. The crystal quality of the grown layers was examined by high-resolution X-ray diffraction and atomic force microscopy. It was found that the incorporation of Sb into Al0.462In0.538AsySb1-y is strongly temperature-dependent and reduced growth temperatures are necessary in order to achieve significant Sb mole fractions in the grown layers. At 480 ∘ C lattice matching to InAs could not be achieved. At 410 ∘ C lattice matching was possible and high quality films of Al0.462In0.538AsySb1-y were obtained.

We directly measure optical bound states in the continuum (BICs) by embedding a photodetector into a photonic crystal slab. The BICs observed in our experiment are the result of accidental phase matching between incident, reflected and in-plane waves at seemingly random wave vectors in the photonic band structure. Our measurements were confirmed through a rigorously coupled-wave analysis simulation in conjunction with temporal coupled mode theory. Polarization mixing between photonic crystal slab modes was observed and described using a plane wave expansion simulation. The ability to probe the field intensity inside the photonic crystal and thereby to directly measure BICs represents a milestone in the development of integrated opto-electronic devices based on BICs. Photonic crystal slabs: built-in detector monitors light levels Embedding a photodetector in a photonic crystal slab enabled the slab’s internal light intensity and photonic band structure to be probed. Roman Gansch and co-workers from Harvard University in the USA and Vienna University of Technology in Austria fabricated a two-dimensional photonic crystal slab featuring an integrated a GaAs/AlGaAs quantum-well infrared photodetector. Photocurrents measured from the photodetector were used to characterize the structure’s bound states in the continuum, which occur due to phase matching between in-plane and out-of-plane waves. The experimental results agreed well with theoretical models. They demonstrated that the band structures of photonic crystal slabs are more complex than those estimated by commonly used approximations based on two-dimensional photonic crystals. The findings are expected to be useful for designing optoelectronic devices based on photonic crystals, especially resonant sensors.

We present a bi-functional surface emitting and surface detecting mid-infrared device applicable for gas-sensing. A distributed feedback ring quantum cascade laser is monolithically integrated with a detector structured from a bi-functional material for same frequency lasing and detection. The emitted single mode radiation is collimated, back reflected by a flat mirror and detected by the detector element of the sensor. The surface operation mode combined with the low divergence emission of the ring quantum cascade laser enables for long analyte interaction regions spatially separated from the sample surface. The device enables for sensing of gaseous analytes which requires a relatively long interaction region. Our design is suitable for 2D array integration with multiple emission and detection frequencies. Proof of principle measurements with isobutane (2-methylpropane) and propane as gaseous analytes were conducted. Detectable concentration values of 0–70% for propane and 0–90% for isobutane were reached at a laser operation wavelength of 6.5 μm utilizing a 10 cm gas cell in double pass configuration.

We introduce ring lasers with continuous π-phase shifts in the second order distributed feedback grating. This configuration facilitates insights into the nature of the modal outcoupling in an optical cavity. The grating exploits the asymmetry of whispering gallery modes and induces a rotation of the far field pattern. We find that this rotation can be connected to the location of the mode relative to the grating. Furthermore, the direction of rotation depends on the radial order of the whispering gallery mode. This enables a distinct identification and characterization of the mode by simple analysis of the emission beam.

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.

The development of In 0.53 Ga 0.47 As/GaAs 0.51 Sb 0.49 terahertz quantum cascade lasers is reviewed, starting with the first demonstration, through growth direction dependent performance issues, to high performance devices. This InP-based material system is an attractive alternative to the almost exclusively used GaAs/Al x Ga 1-x As. Devices achieve maximum operating temperatures of 142 K and exhibit broadband lasing over a range of 660 GHz. A special focus has to be put on the growth direction related interface asymmetry for this material system. Symmetric active region designs are an elegant technique to investigate such asymmetries. A significant impact on the device performance is observed and attributed to interface roughness scattering.

We demonstrate the monolithic integration of a mid-infrared laser and detector utilizing a bi-functional quantum cascade active region. When biased, this active region provides optical gain, while it can be used as a detector at zero bias. With our novel approach we can measure the light intensity of the laser on the same chip without the need of external lenses or detectors. Based on a bound-to-continuum design, the bi-functional active region has an inherent broad electro-luminescence spectrum of 200 cm−1, which indicate sits use for single mode laser arrays. We have measured a peak signal of 191.5 mV at theon-chip detector, without any amplification. The room-temperature pulsed emission with an averaged power consumption of 4 mW and the high-speed detection makes these devices ideal for low-power sensors. The combination of the on-chip detection functionality, the broad emission spectrum and the low average power consumption indicates the potential of our bi-functional quantum cascade structures to build a mid-infrared lab-on-a-chip based on quantum cascade laser technology.

The addition of boron to GaAs nanowires grown by self-catalyzed molecular beam epitaxy was found to have a strong effect on the nanowire morphology, with axial growth greatly reduced as the nominal boron concentration was increased. Transmission electron microscopy measurements show that the Ga catalyst droplet was unintentionally consumed during growth. Concurrent radial growth, a rough surface morphology and tapering of nanowires grown under boron flux suggest that this droplet consumption is due to reduced Ga adatom diffusion on the nanowire sidewalls in the presence of boron. Modelling of the nanowire growth puts the diffusion length of Ga adatoms under boron flux at around 700-1000nm. Analyses of the nanowire surfaces show regions of high boron concentration, indicating the surfactant nature of boron in GaAs.

A cavity ringdown system for probing the spatial variation of optical loss across high-reflectivity mirrors is described. This system is employed to examine substrate-transferred crystalline supermirrors and quantify the effect of manufacturing process imperfections. Excellent agreement is observed between the ringdown-generated spatial measurements and differential interference contrast microscopy images. A 2 mm diameter ringdown scan in the center of a crystalline supermirror reveals highly uniform coating properties with excess loss variations below 1 ppm.