A low index layer between the boundary of a first-order grating combined with a high index cover layer provides significantly higher reflected power per unit length and reduces losses at the waveguide-grating interface compared to conventional gratings in III-V waveguides. The dependence of the peak and spectral width of the reflected power for Enhanced Coupling Strength (ECS) gratings is analyzed for two different ECS grating geometries. These properties of ECS gratings allow integration of optical components such as high-speed modulators with short horizontal cavity lasers that can operate without temperature control over wide temperature and wavelength ranges.

InP-based quantum dot (QD) laser devices emitting at 1.3 µm were realized by incorporating a GaAs nucleation layer underneath the InAs QD layers. A good carrier confinement while retaining the waveguiding properties is achieved by embedding the QDs in In0.528Al0.371Ga0.101As. Length dependent P-I characteristics yielded static parameters, which were comparable to static parameters obtained for InP-based lasers emitting at 1.55 µm. Additionally, temperature dependent measurements were conducted and evaluated. The lasers show ground mode lasing up to high operation temperatures with good temperature stability of the threshold current density and external quantum efficiency.

The parasitic electron-hole recombination outside of a quantum-confined active region still presents a challenge in conventional injection lasers. The use of asymmetric barrier layers (ABLs) (one on each side of the active region) should efficiently suppress this recombination. However, even in lasers with ABLs, excited states may be present in the active region in addition to the ground state. Excited states may strongly affect delivery of charge carriers to the lasing ground state. In this work, dynamic properties of quantum dot (QD) lasers with ABLs are studied in the presence of excited states in QDs. The situation is considered when the carrier capture into the lasing ground state in QDs is excited-state-mediated. It is shown that the modulation bandwidth of the ABL QD laser can be considerably impacted by excited-to-ground state relaxation delay in QDs. Hence a strict control of the intradot relaxation time will be required to enhance the modulation bandwidth in ABL QD lasers.

The performance of O-band InAs/GaAs quantum-dot (QD) lasers grown by molecular beam epitaxy with three different doping strategies are investigated in a temperature range 17 °C – 97 °C. We demonstrate lasers with a reduced threshold current using direct n-doping (during the dot formation) in the active region compared lasers with a nominally undoped active region. We explain results using calculations of the dot and wetting layer potentials and the electron and hole energy levels.

Optically pumped waveguide coherent laser arrays are demonstrated in an 1-micron-thick-semiconductor-membrane-InGaAs-quantum-well laser transferred on a silicon carbide heat spreader emitting at 1010 nm. We employ a real and Fourier space imaging setup to study the emission of single and arrays of laser cavities. We are able to create waveguide laser arrays with modal widths of approximately 5-10 μm separated by 5-10 μm which maintain their mutual coherence while operating on either single or multiple longitudinal modes. This laser geometry can be accurately controlled by the laser pump and they offer a new high gain laser platform that permits integration with photonic structures.

Quantum cascade laser combs enable the generation of high average power coherent optical frequency combs. Combination of RF injection in specially designed devices enable the recompression of the emission into high peak power pulses for non-linear optics applications. A combination of techniques are used to analyse the temporal profile of the emission.

The recent generalised theory of frequency comb generation in externally pumped cavities with and without population inversion suggested an intimate link between quantum cascade lasers (QCLs) and Kerr resonators. In this talk we overview recent experimental developments in chip-scale ring cavity QCLs with and without output coupling ports, that allow operation in self-pumped and externally pumped configurations, and their ability to support cavity solitons.

We propose and design a high-brightness, ultra-compact electrically pumped GaSb-based laser source of polarization-entangled photons generated by intracavity parametric down-conversion of lasing modes. We develop a nonperturbative quantum theory of parametric down-conversion of waveguide modes which takes into account the effects of modal dispersion, group and phase mismatch, propagation, dissipation, and coupling to noisy reservoirs. We provide convenient analytic expressions for interpreting experimental results and predicting the performance of monolithic quantum photonic devices based on nonlinear wave mixing of laser modes.

We report a type-II interband cascade laser grown on an on-axis silicon substrate. We demonstrate continuous-wave lasing operation at temperatures up to 50°C at 3.5µm with a threshold current of 45 mA at room temperature and 20 mW/facet output power. We extrapolate a mean time to failure of at least 300,000 h, which we attribute to the design of the active region eliminating the non-radiative recombination process.

In this work present high performance QCL-based THz combs operating on fundamental and harmonic comb states operating up to 110 K in the spectral region from 2 to 4 THz . We employ double-metal, Copper- based laser resonators planarized with a polymer allowing high performance with CW operation up to 118 K . Such waveguide layout allows as well optimized RF coupling facilitating injection of high RF power. We analyze the laser emission by means of SWIFTS technique employing an Hot-Electron-Bolometer based on NbN. Different regimes are observed as the RF injection power is increased, going from FM emission to a pure AM. Spectral bandwidths as large as 700 GHz are observed corresponding to a fully coherent laser operation. For specific waveguide geometries and injection conditions pulses as short as 4 ps are observed. We present as well SWIFTS measurements for THz QCL combs operating on harmonic states under RF injection at the harmonic frequency of 17.6 GHz.

The study of high Al containing barriers in Terahertz Quantum Cascade lasers has led to the improvement of operation temperature and of the quantum efficiency. This is mainly caused by the reduction of transport channels through higher states. In consequence, the electron transport in these new devices is dominated by photon assisted tunneling. The originating non-linearity provides a huge potential for different operation modes. We try to further study this by coupling distributed QCL devices on a chip which has led to the observation of bi-stable operation and THz switching. We use the non-linear behavior for the control of the emission spectra of surface emitting random laser structures. Furthermore, ring structures can be realized which can be tuned from single mode to frequency comb operation.

Different phase-locking schemes are developed for surface-emitting terahertz quantum-cascade lasers (QCLs) with watt-level output power and radiating in symmetric single-lobed beams. In the first-scheme, multiple metallic microcavities are coupled through surface-plasmon-polaritons traveling in surrounding medium of cavities, that leads to peak-power output of 2.03W for a single-mode 3.3THz QCL with a slope-efficiency of 1.57W/A. In the second-scheme, a phase-locking scheme with hybrid second- and fourth-order Bragg gratings is demonstrated to realize a multi-mode surface-emitting THz QCL with 2.13W output power. Both QCLs operate at ~60K. Preliminary data for a scheme to achieve electrical tunability of such lasers is also reported.

A terahertz quantum-cascade VECSEL is demonstrated to exhibit multi-mode operation, despite the fact that spatial-hole burning is nominally suppressed within the amplifying metasurface. A specially designed output coupler mirror is used such that large numbers of modes have nearly identical lasing thresholds. Up to nine lasing modes with a FSR of approximately 21 GHz are demonstrated – a significant increase from previous QC-VECSELs in which only 2 or 3 modes have been observed to lase at once. This work is an intermediate step towards eventually demonstrating THz QC-VECSELs as broadband incoherent emitters or frequency combs.

Accurate simulation of V-I characteristics for mid-IR quantum cascade lasers (QCLs) with photon-induced carrier transport (PICT) is achieved by using the non-equilibrium Green’s function method coupled with the interface-roughness scattering formalism taking into account graded interfaces and axial correlation lengths. Analysis of 4.9 µm- and 8.3 µm-emitting, buried-heterostructure (BH) QCLs reveals that PICT action reduces the differential resistance by a factor of 2.5 and increases the maximum-current density by ~ 30 % compared to conventional BH QCLs, which explains their record-high, single-facet wall-plug efficiency values (i.e., 27 % and 17 %). Interface grading allows obtaining emission wavelengths close to experiment.

The integration on silicon of light sources emitting in the 2-5 µm wavelength range for sensing applications is currently under the focus of attention. In this work we have studied the influence of the quantum well number (from 1 to 4 QWs) on the performances of GaSb-based laser diodes grown on silicon and emitting at 2.3 µm. We have observed that – somewhat counterintuitively – the best performances in terms of threshold current and internal losses are achieved with 1 QW. The results will be discussed in comparison with similar laser diodes grown on native GaSb substrates.

Quantum-cascade lasers (QCL) enable emission in a broad range of infrared radiation unavailable for convectional quantum well bipolar lasers. However in-plane geometry of QCLs hinders achieving properties required in numerous applications which are inherently possessed by vertical-cavity surface-emitting lasers (VCSELs). In proposed design of QC-VCSEL the role of top mirror and element inducing component of electric field necessary to stimulated emission in quantum cascades is served by subwavelength monolithic high-refractive-index contrast grating (MHCG) in which quantum cascade active region is embedded. This paper based on numerical analysis presents influence of QC-VCSELs configuration details on threshold currents and mode distributions.

We present a novel InGaAs/InAlAs/InP quantum cascade detector (QCD) operating in the long wave infrared (LWIR) range, crucial for the exploitation of new free-space optical telecommunication channels at wavelengths between 8-12 µm. The comparison of differently sized detector ridges, processed on substrates with a 15-period as well as a single-period design, allows a characterization of the spectral photocurrent and a comparison of their performance in terms of sensitivity, spectral responsivity, detector noise etc. The goal is to distinguish design guidelines for the best candidate to establish a monolithic-integrated heterodyne detection system, able to secure high-speed and low-noise free-space data transmission.

In this work we monolithically integrate a quantum cascade laser (QCL) and detector (QCD) addressing the same wavelengths lambda=1550-1650 cm-1 for liquid spectroscopy. QCL and QCD are combined using a 50-100 µm-long dielectric-loaded surface-plasmon-polariton (DLSPP) waveguide, which typically guides >>90% of the mode outside of the cavity. We show the analysis of the protein bovine serum albumin (BSA) and its denaturation process between 25°C-90°C in real time in a microfluidic cell (60 µl) for 20-60 mg/ml BSA-concentrations. To further test the sensor-robustness, we directly submerge it into a beaker and detect H2O up to 35%-40%, solved in isopropyl alcohol.

Semiconductor-loaded plasmonic (SLSPP)-waveguides are a very efficient link for optoelectronic devices, facilitating miniaturized photonic integrated circuits. However, for long-wave infrared applications (8-12 µm), the material selection is challenging as most commonly used mid-IR materials absorb in this region. Therefore, we selected and investigated the properties of germanium in a hybrid semiconductor-metal-configuration to overcome these limitations. The experimental characterization of Si(substrate)-Au-Ge fabricated SLSPP-waveguides show very good agreement with FEM-simulations. Moreover, the realized devices offer low losses between 8.8 and 22 dB/mm (single device) and even within 8.8-15 dB/mm (multiple devices), respectively, for the entire investigated octave-spanning 5.6 – 11.2 µm range.

Enhanced Coupling Strength (ECS) outcoupler gratings theoretically provide an order of magnitude reduction of grating length compared with conventional outcoupler gratings in III-V photonic waveguides. The dependence of the magnitude and spectral width of the outcoupled power of ECS outcoupling gratings is analyzed using a Floquet-Bloch space-harmonic approach for two different ECS grating geometries. ECS outcoupler gratings allow near-surface normal emission of integrated optical devices such as laser transmitters consisting of short horizontal cavity lasers combined with high-speed modulators that can operate without temperature control over a wide temperature and wavelength ranges.