Type-II GaInAs/GaAsSb “W”-active regions offer the potential for greater control over the temperature sensitivity of semiconductor lasers operating in the near-IR. In this paper we explore the theoretical design space available using “W”-QWs and discuss the interplay between active region design choices and waveguide optimisation, highlighting the importance of simultaneous optimisation in these systems. We demonstrate the molecular beam epitaxy growth of GaAs-based “W”-lasers emitting around 1250 nm, achieving a room temperature threshold current density of 480±10 A/cm². These initial results demonstrate the promising potential of "W"-lasers for energy-efficient O-band applications in data communications networks.

We present a postgrowth selective-area-intermixing approach for on-chip III-V based monolithically integrated laser-waveguide structures for photonic integrated circuits. Implanting selective areas with an energy of 300 KeV and dose of 5 ×1012 cm-2 induced crystal defects in the InAs quantum dot gain material, results in a shifted absorption edge and complete quenching of optical emission. We successfully recovered the optical quality of the gain material through optimized rapid thermal annealing at 635 OC and achieved enhanced intermixing in the implanted region thus causing a relative blueshift of 20 nm in the passive waveguides, mitigating absorption at the laser emission wavelength.

We successfully designed and fabricated semiconductor lasers emitting at 626 nm at room-temperature to improve research and scaling of 9Be+ ion qubits. The design is based on the calculation of the energy band structure by k·p theory for strained semiconductors, the vertically guided mode, and the modal gain in dependence of carrier density as well as threshold sheet densities and wavelengths. Promising designs are grown on three-inch wafers by metal-organic vapor-phase epitaxy for experimental investigations. Broad area lasers are used for evaluation of the laser performance.

We present broad area distributed Bragg reflector lasers with up to five active regions epitaxially stacked in a common waveguide emitting nanosecond pulses around 905nm for LIDAR. Optimized for pulsed operation and implementation of a surface Bragg grating, the diode laser emits in a higher order vertical mode. 2mm long diode lasers with five active regions and a 200µm wide current aperture integrated in an inhouse high pulse current electronic driver provide pulse powers >200W at slightly >100A in 10ns long pulses. The emission spectrum features a spectral bandwidth of <0.3nm and a temperature-related shift of <70pm/K.

It has been shown that ring quantum cascade lasers can emit solitons when the driving current is large enough such that spontaneous symmetry breaking occurs between the clockwise and counter-clockwise modes . We show that ring devices with very low backscattering will emit an optical frequency comb when injected with RF close to the round trip frequency. This result is interpreted as a new form of active mode-locking with a fast saturable gain. The transient behavior of the device is studied by time resolved spectroscopy.

Ultrashort signals are integral for conducting high-resolution measurements. In the mid-infrared, the generation of ultrashort pulses is notoriously difficult to achieve and usually requires large optical setups. In our work we use direct sampling to demonstrate the spontaneous generation of stable ultrashort features in the time-domain signal of a mid-infrared quantum cascade laser frequency comb. The full-width at half-maximum of these features is measured to be ~500 fs, right below the Fourier-limit derived from the corresponding optical spectrum and RF-injection can be used for stabilization and manipulation. Using Maxwell-Bloch equation-based simulations, we can reproduce the generation of such features, including the position in relation to the instantaneous frequency and show their width can be lowered even further below the Fourier limit, thus opening new possibilities for high-resolution measurements based on quantum cascade laser frequency combs.

Standard Fourier Transform Infrared Spectrometers (FTIR) rely on a Michelson Interferometer scheme which uses a linear delay line to retrieve an interference pattern. Here, we demonstrate a fast FTIR based on a rotational delay line which allows us to achieve kHz acquisition rates. We perform spectrometry measurements using it in combination either with a Mid-IR Quantum Cascade Laser (QCL) frequency comb or a strongly, low-frequency, RF-modulated QCL. Regarding the latter, the modulation enables to broaden the laser emission up to 250cm^-1 (from 6.5µm to 7.5µm) and to reduce its amplitude noise compared to the free-running case. The combination of a strongly modulated QCL with a rotational FTIR opens the possibility to fast and broadband spectroscopy in the Mid-IR region, with possible applications spanning from gas detection to process control

Active resonators based on semiconductor gain media encompass a large optical nonlinearity that arises from gain saturation and enables bright soliton generation. The ability to operate these resonators below the lasing threshold as tunable passive devices –– filters, modulators, phase shifters –– opens up an untapped potential of seamlessly integrated reconfigurable devices for both generation of multimode mid-infrared (4 – 12 μm) light and its manipulation.

Bright pulses of light are unstable states in free-running semiconductor lasers. Stable bright solitons require an optical bistability---as predicted by mean-field theories such as the Complex Ginzburg Landau Equation (CGLE) or the Lugiato-Lefever Equation (LLE). However, this restriction is relaxed when two lasers are coupled to one another. Here, we identify a new state of light in a pair of semiconductor ring lasers with fast gain dynamics. Two racetrack (RT) quantum cascade lasers (QCLs) when coupled along their straight sections spontaneously produce a frequency comb over the hybridized modes of the coupled cavity. Waveform reconstruction measurements reveal the hybridized comb manifests itself as a pair of bright and dark pulses circulating the coupled cavity simultaneously. In addition, split-step integration of a pair of mutually forced CGLEs faithfully reproduces our experimental measurements, providing some insight on the formation of such states.

Integrated Si photonics offers a promising solution to address the rising demand for data processing capability and energy efficiency spurred by AI and high-performance computing. However, the integration of on-chip lasers has been hindered by the inherent indirect bandgap of Si, limiting integration density, production efficiency, and cost-effectiveness. In this work, we overcome this challenge through the heterogeneous integration of quantum dots (QDs) with Si-on-insulator based photonic integrated circuits. Our objective is to advance the post-Moore performance scaling of electronic systems and explore the potential applications of this integration in quantum communication and optical computation.

In this talk, we will discuss our recent progress in developing various types of chip-scale integrated Pockels lasers, based upon hybrid integration between III-V gain media and thin-lm lithium niobate photonic integrated circuits.

High peak-power, room-temperature operation is reported for ridge waveguide quantum cascade lasers (QCLs) monolithically integrated onto a silicon substrate. The 55-stage laser structure with an AlInAs/InGaAs core and InP cladding was grown by molecular beam epitaxy directly onto an 8-inch diameter germanium-coated silicon substrate template via a III–V alloy metamorphic buffer. Atomic force microscope imaging demonstrated a good quality surface for the full QCL structure grown on silicon. Fabricated 3mm by 26µm lasers operate at room temperature, deliver more than 3W of peak optical power, and show approximately 3% wall plug efficiency and 4.3 kA/cm2 threshold current density with emission wavelength centered at 11.5µm. The lasers had a high yield with only around 15% max power deviation and no signs of performance degradation were observed over a 10h burn in period at maximum power. Singled-lobed high quality output beam was measured for 3mm by 22 µm devices. Correlation between laser performance and defect density in the laser core for several QCL structures grown on lattice-mismatched substrates will also be discussed in this talk.

We demonstrate phase-locked, high power, tree-array quantum cascade lasers based on ridge waveguides with near diffraction-limited beam quality from the single-emitter side at a wavelength of 8.6μm. Tree-arrays based on ridge waveguides are promising for power scaling of QCLs, and are simpler to fabricate than buried heterostructure waveguides. Understanding the fabrication sensitivity of ridge waveguide tree-array QCLs is important for assessing their viability for mass fabrication. An analysis of fabrication tolerance and guidelines for the design of efficient MMI couplers is presented.

Low dissipation integrated frequency combs are ideal candidates to realize miniaturized spectrometers without moving parts and hence are of great interest for integrated photonics. After reviewing frequency comb generation in interband cascade lasers (ICLs), the nonlinear dynamics and performance limiting mechanisms of ICLs will be discussed. A newly developed k-space resolved non-equilibrium carrier transport model combined with experimental studies enables us to explore different loss mechanisms, as well as to explore the reasons, why passive mode-locking of ICLs for short pulse generation remains challenging.

Semiconductor quantum dots (QDs) offer various unique properties that make them interesting candidates for the use as gain media in semiconductor laser diodes. MOVPE is used as the method of growth for the QD structures with high area density and vertically stacked QD layers. This leads to a broad gain spectrum, which enables laser devices with wide tuning ranges around 1300nm. We incorporate this active region into edge-emitting laser structures, for the characterization of optical gain and absorption properties, as well as the inner losses.

1-port and 2-port multi-mode interference reflectors (MMIR) are excellent components for Photonic Integrated Circuits, being highly reflective and easy to fabricate. We demonstrate InAs-Quantum-Dot MMIR lasers, where the high reflectivity is particularly advantageous, with lower threshold current than Fabry-Perot ridge lasers with the same cavity length e.g. 6mA compared to 46-mA. The threshold current density of the 1-mm MMIR laser is equivalent to the Fabry-Perot laser with a 3-mm cavity length. MMIRs have a higher optical slope efficiency, indicating mirror reflectivity above 85%.

We will present new developments in THz coherent photonics enabled by a recently demonstrated broadband planarized platform based on quantum cascade gain medium. The possibility to integrate onto the same chip active (lasers, detectors, amplifiers) and passive (waveguides, splitters, antennas, chirped mirrors,) photonic elements results extremely attractive, naturally bridging microwaves to THz waves. Such approach allows the adoption of advanced photonics design techniques (inverse design) to tailor facet reflectivities in double metal, subwavelength waveguides. We will present frequency combs exceeding 1 THz bandwidth, operating above liquid nitrogen temperature, with regular far fields and vertical emission. We will as well discuss laser dynamics engineering exploiting extreme field confinement in narrow waveguides, clearly demonstrating FM comb operation in THz QCLs. By exploiting dispersion compensation in planarized double ring cavities we will finally present the achievement of dissipative Kerr solitons with pulses of 10 ps. The application of such waveguides to high-temperature active regions allows the operation of 4 THz QCLs on Peltier cooler with currents below 2.5 A

Terahertz Quantum Cascade lasers are very versatile sources of terahertz radiation. Frequency comb operation, surface emitting arrays, external cavity tuning have been demonstrated. For all these implementations broadband gain is strongly demanded. The intersubband gain mechanism allows to the design of different wavelength active region and their integration in the same waveguide. We have developed active regions consisting of up to four different intersubband designs. To enable a common operation not only the gain curve needs to be aligned over all sections but also the alignment electric field and subsequently the operating current. Fabry-Perot devices fabricated from the four-section active region show lasing over more than one octave. Ring resonators show also broadband laser operation and comb formation. Broadband operation is a large advantage of random lasers which we turn into useful devices by an optical machine learning approach. This allows the control of the emission wavelength beyond discrete cavity modes.

There have been only few reports of THz QC-lasers operating over 5 THz, and none operating in CW mode. As the laser frequency increases, it approaches the Reststrahlen band (8-9 THz in GaAs) which increases the optical losses and degrades the gain. Here, we discuss design strategies to improve operating temperature for THz QCLs targeting 5.3-5.6 THz. These strategies are investigated numerically using a Non-equilibrium Green’s Function solver. We demonstrate a metal-metal waveguide emitting in 4.76 – 6.03 THz with pulsed and CW operating temperature of 117 K and 68 K, respectively, and modes up to 5.71 THz in CW mode.

RF modulation of the injected current at the cavity round trip frequency is a viable path towards multi-mode operation in a THz metasurface quantum-cascade VECSEL. Under weak RF modulation, pulling and locking of the round-trip frequency to the injected RF signal is observed; under strong RF modulation, broadening of the lasing spectrum with a maximum observable bandwidth as large as 300 GHz is demonstrated. It is shown that the injection locking behavior is sensitive to the cavity length (varied between 35-50 mm), as well as the presence of optical feedback. Long-travel FTIR measurements enable resolution of the lasing modes.

The effects of optical feedback on a terahertz (THz) quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) are investigated via self-mixing. A nominally single-mode 2.8 THz QC-VECSEL operating in continuous-wave is subjected to various optical feedback conditions while monitoring variations in its terminal voltage associated with self-mixing. Due to its large emitting aperture, and flat highly-reflective output coupler, the VECSEL architecture is found to be strongly susceptible to optical feedback. Regions of instability are observed, as is evidence of multiple roundtrip re-injection within the feedback cavity.

Transition metal dichalcogenides (TMD) are promising 2D materials with possible usage in wide range of applications, owing to a bandstucture flexibility that can be uniquely engineered depending on the number of atomic layers. This can be probed by the generation of ultrafast photocurrents with femtosecond excitation, leading to emission of terahertz picosecond-scale pulses that depends on nonlinearities of the studied material. Here we will show layer controlled nonlinearities in semi-conducting and sem-imetal 2D PtSe2, opening up a new class of circular dichroism materials beyond the monolayer limit, and impacting a range of domains from THz valleytronics to THz spintronics.

We study optical response and the electromagnetic wave propagation in an emerging class of topological materials named nodal ring semimetals, in which the low-energy quasiparticle dispersion is parabolic in two directions in momentum space and is linear in the third direction. This leads to a highly anisotropic dielectric permittivity tensor in which the optical response is plasmonic in one spatial direction and dielectric in the other two directions. The resulting normal modes (polaritons) in the bulk material become hyperbolic over a broad frequency range, which is furthermore tunable by the doping level. These tunable hyperbolic materials show a range of fascinating optical properties from anomalous refraction and waveguiding to perfect absorption in ultrathin subwavelength films. They promise a broad range of the optoelectronic applications in the infrared an terahertz spectral regions.

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.

GaSb-based interband cascaded lasers (ICLs) have now become a leading laser source to cover the mid-infrared (mid-IR) spectral range (3-6 µm). In the last decade, the success of the silicon photonics industry thanks to its optical properties, low cost and easy commercialization of its large wafers size. However, this requires all Sb-based optoelectronics functions on a Si platform. We will discuss about our recent results on single mode distributed feedback interband cascade lasers (ICL) directly grown on Si emitting between 3 and 4 µm.

In this work optimization of technology of QCLs operating at λ~13 µm wavelength is presented. The devices were grown by Molecular Beam Epitaxy and combined MBE and MOVPE overgrowth. Room temperature operation of QCLs was achieved. The influence of the waveguide design in terms of thickness, growth conditions as well as doping has been studied. We have performed electro-optical and spectral characterization of LWIR QCL extracting crucial device parameters. The analysis of laser parameters is presented. Additional results of single mode operation are presented for devices in coupled cavity configuration. Acknowledgements: This work was supported by Polish National Science Centre (NCN) grant: SONATA BIS: UMO-2021/42/E/ST7/00263