We introduce direct n-doping of quantum dots together with modulation p-doping as a technique to reduce both the threshold current density and the temperature dependence of threshold current density in 1.3um emitting quantum dot lasers. Threshold current density in 1mm long QD lasers with cleaved and uncoated facets is effectively halved at both 27°C and at 97°C when using co-doping as compared to the undoped case. Results indicate that modulation p-doping can improve the threshold current temperature dependence and direct n-doping reduces the magnitude of threshold current density and that the benefits of each is maintained when used together.

InAs QD lasers emitting in the 1.3-μm-region have suitable device properties important for integrated applications and growth on silicon. Sensing applications have encouraged further development of these wavelengths for high-volume-manufacturing. Assessment of epitaxial wafers is demonstrated here by fabrication of oxide isolated broad-area edge-emitting-lasers and on-wafer characterization of 150-mm p-doped InAs QD wafers grown via MBE. We report on spatial variations through Power-Current-Voltage-Wavelength measurements with Jth of EELs calculated using current spreading structures. A 9 nm decrease in center-to-edge emission wavelengths is observed for 2mm devices, with a threshold current density variation of approximately 0.63 kA/cm² for a particular epitaxial design.

We demonstrate high-gain InAs QDs targeting C-band and L-band using a five QD-layer structure grown via MOCVD, with a photoluminescence broadening of ~55 meV. Lasers were fabricated with cavity lengths from 2000-µm down to 333-µm, with cleaved un-coated facets. Threshold current density increases monotonically with temperature over a range of 300 K to 380 K for all cavity lengths with a factor of 3.0 and 3.4 increase for the longest and shortest cavities, respectively. Measurements of lasing spectrum reveal that even the shortest cavity maintains a stable increase in wavelength up to 390 K with no observable transition to the excited state.

GaAs/AlGaAs Distributed Feedback Semiconductor (DFB) lasers with laterally-coupled gratings are demonstrated at 778.1 nm wavelength with output powers up to 48 mW, over 35 dB side-mode suppression ratios, tuning ranges of 0.8 nm, and vertical beam divergences of 20.5. An asymmetrical mode expander and aluminum-free active layers have been used in the material epilayer to reduce the linewidth to 3.67 kHz and relative intensity noise (RIN) of –140 dBc/Hz while maintaining high output powers. The fabricated lasers demonstrate high-resolution spectroscopy of the hyperfine levels of the 87Rb two-photon transitions and are suitable for integration into miniaturized cold atom systems.

UV lasers have a wide range of applications in engineering, environment, medicine, biotechnology, and other fields. According to the “Report on Patent Application Technology Trend”, the market size is extremely large at approximately two billion US dollars a year. AlGaN is the most suitable material for the realization of UV Laser Diodes (LDs) because of its direct-transition band structure and high-performance UV LEDs. On the other hand, it has been considered extremely difficult to realize high-quality crystals that can achieve high optical gain with low carrier injection, and to simultaneously form the current injection and optical cavity required for laser oscillation. In this presentation, I would like to introduce our UV-B and UV-A LDs. These LDs have achieved breakthroughs in the above issues by realizing high quality AlGaN with lattice relaxation by 3D growth and by using polarized doping structures in the p-type cladding layer. I would like to explain its technical details and future prospects.

Large area 2D Selective Area Growth (SAG) of Multi-Quantum Well (MQW) structures is a key methodology required for realization of monolithic multicolor arrays of Photonic Crystal Surface Emitting Lasers (PCSELs) We present a study of InGaAs/GaAs MQWs selectively grown in square SAG windows with dimensions up to 300 x 300 μm², by MOCVD. The range of QW emission wavelengths and thickness enhancements are elucidated by room-temperature μ-Photoluminescence (PL) and Optical Profilometry (OP) mapping, respectively. It is shown that large areas, ⪅ 100 x 100 μm2, with uniform PL emission can be achieved within a PL tuning range of 86 nm.

This conference presentation was prepared for the Novel In-Plane Semiconductor Lasers XXII conference at SPIE OPTO, 2023.

Long wavelength quantum dot in plane lasers have been scaled to both high volume and the larger 200mm GaAs substrates. Scaling to 300mm on a silicon platform has also been achieved. All wafers are grown on production-ready MBE platforms. Other material systems such as InGaAs and dilute nitride have been similarly scaled often by going back to first principle of process design in conjunction with substrate engineering. The main drivers for this transition to high volume are the need to integrate compound semiconductors with silicon foundries for not only data communications but other applications like automotive sensing and health care.

We present the first realization of substrate-emitting double-ring Interband Cascade Lasers (ICLs) in Continuous-Wave (CW) mode. The devices are realized in the GaSb material system and emit at around 2.77 µm wavelength. Through the implementation of second-order distributed feedback gratings, single-mode and simultaneous vertical emission through the GaSb substrate are realized. By implementing a concentric double-ring arrangement (diameters of approximately 700µm and 900 µm), two-wavelengths emission on the same optical axis can be achieved, which is desirable for spectroscopic applications. For improved thermal management, the devices are mounted epitaxial side down on custom-made AuSn/AlN heatsinks, enabling individual laser operation.

We present GaSb based interband cascade lasers with a center emission wavelength of 6170 nm that emit in cw operation up to a temperature of 40°C. While the pulsed threshold current density for a broad area laser is as low as 500 A/cm² at a temperature of 20°C a ridge waveguide laser with 23µm ridge width reaches more than 25mW of output power, the results were achieved by careful optimizations of the active region design, the waveguide design and epi down mounting of the laser chips.

Compact, multi-spectral laser sources emitting in the mid-infrared (mid-IR) are in high demand for applications. Integration of several multi-spectral, mid IR quantum cascade lasers on silicon-based waveguide platforms is a necessary step towards realization of functional and complex mid-infrared photonic integrated circuits. This paper focuses on the thermal aspects of integration of multi-spectral QCLs toward the integration of QCL chips on silicon-based platform. The experimental results registered by means of CCD-thermo-reflectance are supported by numerical simulations of heat dissipation. The effects of thermal cross-talk between individual emitters are presented and discussed, leading to design guidelines for placement of laser chips in mid-infrared integrated photonics systems.

In this talk, we review our recent progress on short-pulse, high-peak-power Photonic-Crystal Surface-Emitting Lasers (PCSELs). First, we propose PCSELs that have 2D arranged gain and loss, which enable high-peak-power, short-pulse operation in the fundamental mode while suppressing lasing in higher-order modes. Based on this design, we demonstrate short-pulse generation with a peak power of several tens of watts and a short pulse width of <40 ps. To further increase the peak power, we also propose the concept of self-Q-switched PCSELs, where short-pulse generation with a 100-W-class peak power is induced even without saturable absorbers.

The scaling of lasers and in-particular of surface emitting lasers is a multi-decade long question that has been investigated since the invention of lasers. It is an important question with numerous applications. In the first part of this talk, I will briefly discuss my invention of topological lasers: integrable non-reciprocal coherent light sources as well as compact bound state in continuum sources. In the second part of the talk, I will discuss an infinitely scalable aperture that solves the optics challenge of single apertures scaling. I will discuss the physics of the invention that I named Berkeley Surface Emitting Laser (BerkSEL).

Because their phase can be compensated by a grating-based stretcher compressor and further controlled by RF injection, quantum cascade laser based optical frequency comb generation allowed the generation of pulse as short as 630fs after compression, value confirmed using an upconversion technique with a sub-picosecond time resolution. Another possibility is the direct generation of optical solitons using ring quantum cascade lasers in which, by using a very low lateral loss waveguide, the symmetric counter-propagating modes undergo a spontaneous symmetry breaking and generate solitons.

Optical nonlinearities are known to coherently couple the amplitude and the phase of light, which can lead to the formation of perfectly periodic waveforms – known as frequency combs. Recently, self-starting frequency combs that do not rely on the emission of short pulses are appearing in numerous semiconductor laser types, among which is the quantum cascade laser. Here we discuss the role of a Bloch gain induced giant Kerr nonlinearity in Fabry-Pérot and ring cavity QCLs, paving the way towards electrically pumped Kerr combs.

Quantum cascade lasers and other semiconductor laser types constitute an attractive integrated platform for spectroscopic applications, as they emit self-starting Frequency Combs (FCs), unlike traditionally-used mode-locked lasers. Here, we explain self-starting FCs due to nonlinear effects arising from the laser gain itself, with particular attention on the coupling of the amplitude and phase of light, quantified by the Linewidth Enhancement Factor (LEF). We study both cavity geometries, Fabry-Perot and ring, reporting the conditions for stable comb formation and different methods of optimizing their performance. In analogy with Kerr microresonators, ring lasers show the formation of temporal localized soliton-like structures, indicating towards an untapped potential for discovering new states of light.

We demonstrate a novel waveguide design for dispersion compensation in short wavelength quantum cascade lasers for frequency comb operation. The addition of two highly doped InP plasmon layers, above and below the active region, and the precise control of the distance between them and their dimensions, allows to engineer waveguide structures with low group velocity dispersion around any central wavelength between 4 μm and 6 μm, while keeping the optical losses low. Based on this design, we show high-performance frequency comb operation at 5.3 μm that exhibits up to 350 mW of output power, and operates in coherent comb mode up to 50ºC with a spectral width of ~50 cm^-1.

Monolithic ring Quantum Cascade Lasers (QCLs) have recently emerged as a new platform for frequency comb generation in the mid-infrared with immediate applications in molecular gas spectroscopy and photonic generation of stable coherent sub-THz tones. In this talk I will show that depending on the way they are driven, ring QCLs can act as carrier generators, integrated intensity modulators, tunable filters, and on-chip optical amplifiers. The natural predisposition of these components to photonic integration opens a route to compact mid-infrared WDM transceivers for free space optical links and miniaturized 2D IR spectrometers.

We use a prototypical model based on the Complex Ginzburg Landau Equation to study the dynamics of a multimode ring quantum cascade laser. We predict the existence and stability of different classes of localized structures in the system. In presence of coherent injection, we report the formation dissipative Temporal Solitons (TSs) which manifest multi-stability and coexistence with a stable CW solution. We show how these features allow for external manipulation of the spectral content of the optical frequency combs associated with TSs with a big impact on applications in the field of e.g. high precision spectroscopy and wireless communications.

Quantum-cascade-laser-based mid-infrared (mid-IR, wavelengths in the range of approximately 3 microns to 15 microns) Photonic Integrated Circuits (PICs) on the InP platform allow for monolithic integration of high-power laser sources, passive and active photonic elements, and low-loss optical interconnects with transparency in the entire mid-IR spectral region. We will report on our progress in developing InP-based mid-IR PICs, including characterization of linear and nonlinear optical properties of InP/InGaAs waveguides in the mid-IR spectral range, demonstration of low-loss passive mid-IR photonic components, such as ring resonators and wavelength multiplexers, and monolithic integration of these passive components with the active devices.

High bit rate data transmission using Free Space Optics (FSO) is an interesting application that could open an entire unregulated range of optical frequencies for earth-to-earth or earth-to-sky communications. The advent of this technology requires a new set of semiconductor devices operating in 8 µm to 12 µm wavelength range that can be implemented in already existing communication systems. Using unipolar quantum optoelectronic devices, we have demonstrated data transmission with bitrate in excess of 20 Gbit s−1 in the thermal atmospheric window at ~ 10 μm wavelength. All our devices operate at room temperature and have an intrinsic frequency bandwidth of several GHz.

This work presents the design, fabrication and characterization of a Master Oscillator Power Amplifier (MOPA) quantum cascade laser in the mid infrared region. In this configuration, higher output power is achieved while maintaining a single transverse mode emission spectrum. The MOPA has been designed to display a single mode emission in continuous wave, at 9 µm wavelength, with a 12 dB amplification. These characteristics make it suitable for free space data transmission.

This conference presentation was prepared for the Novel In-Plane Semiconductor Lasers XXII conference at SPIE OPTO, 2023.

We present a new integrated photonic platform based on active and passive elements integrated in a double-metal, high confinement waveguide layout planarized with a low-loss polymer. An extended top metallization results in low waveguide losses and improved dispersion, thermal and RF properties, as it enables to decouple the design of THz and microwave cavities. Free-running on-chip quantum cascade laser combs spanning 800 GHz, harmonic states over 1.1 THz and RF-injected broadband incoherent states spanning over nearly 1.6 THz are observed. With a strong external RF drive, actively mode-locked pulses as short as 3 ps can be produced, as measured by SWIFTS. We demonstrate as well passive waveguides with low insertion loss, enabling the tuning of the laser cavity boundary conditions and the co-integration of active and passive components. The same platform is employed to demonstrate dispersion compensated ring combs operating at 3 THz.

Ring resonators are interesting alternative cavity solutions to the commonly used ridge type waveguide for THz Quantum Cascade lasers. They either support a standing wave pattern showing spatial hole burning if there are defects implemented or a traveling mode in a defect-free cavity. We have fabricated two devices structures. The first one is episide-up with bonding pads. The measurements show a complex behavior of comb-formation most probably influenced by spatial hole burning. The second structure is a pure ring mounted episode down on Si-substrate. This structure shows a totally different comb formation as well as much reduced threshold currents.

RF injection locking of a terahertz Quantum-Cascade Vertical-External-Cavity Surface-Emitting Laser (QC-VECSEL) is demonstrated. The intra-cryostat focusing VECSEL cavity design allows continuous wave lasing in an external cavity length over 30 mm with a round-trip frequency near 5 GHz. Strong RF current modulation is applied to the QC-metasurface near the cavity round-trip frequency; this broadens the THz emission spectrum from a single mode to multi-mode operation around a 200 GHz spectral width. Round-trip frequency pulling and locking to the injected RF signal is observed.

Self-heating in mid-infrared QCLs leads to beam instabilities and facet related failures. Single-element 4.6 μm-emitting BH QCLs were fabricated, where a tapered region scales the output power and, ahead of the emitting aperture, a narrow section provides mode filtering for suppressing high-order spatial modes. Beam-stability measurements indicate a small degree of collimated-beam centroid motion (< 0.25 mrad) can be achieved at >1.5W QCW output powers. Comparisons between short-pulse current and QCW operation reveal the impact of thermal lensing on the beam properties, while full 3D modeling provides insights into influence of device geometry on mode selection.

We present a scheme for homogeneous integration and multiplexing of the outputs of continuous-wave distributed feedback quantum cascade lasers for multi-species gas sensing and similar applications using the concept of monolithic InP-based photonic integrated circuits.

Accurate nonequilibrium Green’s-functions simulations of record-performance 4.9 µm- and 8.3 µm-emitting QCLs, employing Photon-Induced Carrier Transport (PICT), require inclusion of graded interfaces when calculating Interface-Roughness (IFR) scattering. Matching threshold-current densities and V-I characteristics, all IFR parameters were extracted. The root-mean-square height and in-plane correlation length are found to be higher and lower, respectively, than when assuming abrupt interfaces. Abrupt-interfaces’ modeled 4.9 µm-emitting QCLs lack PICT action, which reduces the calculated maximum wall-plug efficiency, η(wp,max), value from 27% to 18.7%. Abrupt-interfaces’ modeled 8.3 µm-emitting QCLs have approximately 70% higher relative leakage-current density, which reduces the calculated η(wp,max) value from 17% to 11.7%.