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A fully-functional photonic integrated circuit (PIC) platform with supporting active and passive components in the green part of the visible spectral regime is of significant research interest for next-generation optical systems. Here we design highly-integrated ∼3.5 mm long PICs at green wavelengths, which consist of on-chip GaAs-based near-infrared pump lasers, SiN-LiNbO3 hybrid waveguides and ring resonators for nonlinear frequency conversion. The waveguides in the PICs are designed to eliminate etching of LiNbO3, reducing fabrication challenges. Efficient wavelength of 1062 nm pump to 531 nm coherent light is achieved by employing modal phase matching. Unlike a quasi-phase matching technique, modal phase matching enables poling-free operation and further eases device fabrication with comparable performance in terms of second harmonic generation efficiency. The effective nonlinear mode-overlap factor between 1062-nm-TE00 and 531-nm-TE01 modes in the hybrid waveguide is calculated to be 26%. For robust on-chip light coupling between pump laser and waveguide, a calculated maximum coupling efficiency of −2.3 dB is achieved. The theoretical work presented is an initial step towards demonstrating complex non-telecom PICs which could offer a comprehensive range of photonic functionalities.

Electrically-pumped AlGaN-based edge-emitting laser diodes with a buried tunnel junction (TJ) for sub-300 nm emission are designed in this paper. Hole injection is one of the major concerns for the design of ultraviolet (UV) lasers based on this material system. The use of a low-resistive TJ as an intracavity contact within the devices will offer an opportunity to replace highly resistive p- type AlGaN-based cladding and contact layers by their n- doped counterparts. This advanced polarization-engineered interband TJs will lead to improved hole injection and a significantly reduced threshold voltage. The thermal properties of the tunnel-injected devices are thoroughly studied theoretically. For the demonstration of continuous-wave operating lasers, possible improvements in terms of better thermal management of the device are also discussed. Our improved design allows CW-operating AlGaN lasers with a threshold current density of 220 mW, yielding a wall-plug efficiency of > 2.8%.

In this paper, we report a low-loss photonic integrated circuits (PICs) platform at blue wavelengths of the visible spectral regime. Silicon nitride (SiN) is a popular passive waveguide material due to its fabrication flexibility, CMOS compatibility and spectral transparency in this wavelength regime. For active devices including lasers, gallium nitride (GaN) and its alloys are considered. Several basic building blocks for the development of a complete integrated platform, including blue diode lasers, in-plane- and out-of-plane light couplers, as well as on-and off-chip coupling between these active and passive components are theoretically investigated. The proposed in-plane and out-of-plane architectures operate through edge- and vertical grating couplers (VGCs), respectively. With edge-coupling, large mode-mismatch between the GaN laser diode and SiN waveguide is alleviated through nanotapers on both the active and passive sections and the calculated peak coupling efficiency is achieved to be 74% at a wavelength of 450 nm. We also separately designed efficient VGCs for coupling light from standard, commercial, off-the-shelf fibers to the SiN chip, and edge couplers for fiber-chip coupling, exhibiting coupling efficiencies of 51% and 83%, respectively. For robust on-chip light-coupling between active and passive circuit elements, with relaxed alignment tolerances, two approaches, i.e., flip-chip based hybrid integration and evanescent coupling based heterogeneous integration are studied. Calculated maximum coupling efficiencies of 40% (−4 dB) are achieved for both the hybrid and heterogeneous schemes. The theoretical work performed is an initial step towards demonstrating complex blue PICs which could offer a comprehensive range of photonic functionalities.

Nonlinear photonic integrated circuits at green wavelengths with on-chip pump lasers and hybrid waveguides are designed. The calculated nonlinear mode overlap factor and maximum laser-to-waveguide coupling efficiency are 26% and -2.3 dB, respectively.

An inter-cavty contact single mode 850 nm VCSEL was fabricated with a graphene assisted self-assembly curved dielectric bubble Bragg mirror for the first time. Taking the advantage of graphene’s uniform low surface energy, the low cost dielectric bubble DBR (Si 3 N 4 /SiO 2 ) was deposited on top of the graphene/half-VCSEL structure via van der Waals Force (vdWF) without using any additional spacing elements and sacrificial layer release-etch process. The continuous-wave operating VCSELs with an aperture diameter of 7 μm exhibit single-mode output power of more than 1 mW with a slope efficiency of 0.2 W/A. The sidemode suppression ratios are >40 dB. This novel modification into the lasers can also be applied to a variety of other optoelectronic devices, such as resonance photodetecter and super narrow linewidth VCSEL.

The development of electrically pumped semiconductor diode lasers emitting at the ultraviolet (UV)-B and -C spectral bands has been an active area of research over the past several years, motivated by a wide range of emerging applications. III-Nitride materials and their alloys, in particular AlGaN, are the material of choice for the development of this ultrashort-wavelength laser technology. Despite significant progress in AlGaN-based light-emitting diodes (LEDs), the technological advancement and innovation in diode lasers at these spectral bands is lagging due to several technical challenges. Here, the authors review the progress of AlGaN electrically-pumped lasers with respect to very recent achievements made by the scientific community. The devices based on both thin films and nanowires demonstrated to date will be discussed in this review. The state-of-the-art growth technologies, such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD); and various foreign substrates/templates used for the laser demonstrations will be highlighted. We will also outline technical challenges associated with the laser development, which must be overcome in order to achieve a critical technological breakthrough and fully realize the potential of these lasers.

The efficiency limiting mechanisms in type-I GaInAsSb-based quantum well (QW) lasers, emitting at 2.3 μm, 2.6 μm and 2.9 μm, are investigated. Temperature characterization techniques and measurements under hydrostatic pressure identify an Auger process as the dominant non-radiative recombination mechanism in these devices. The results are supplemented with hydrostatic pressure measurements from three additional type-I GaInAsSb lasers, extending the wavelength range under investigation from 1.85-2.90 μm. Under hydrostatic pressure, contributions from the CHCC and CHSH Auger mechanisms to the threshold current density can be investigated separately. A simple model is used to fit the non-radiative component of the threshold current density, identifying the dominance of the different Auger losses across the wavelength range of operation. The CHCC mechanism is shown to be the dominant non-radiative process at longer wavelengths (> 2 μm). At shorter wavelengths (< 2 μm) the CHSH mechanism begins to dominate the threshold current, as the bandgap approaches resonance with the spin-orbit split-off band.

Ultra-compact, widely-tunable and low-power InP­based four-section coupled-cavity lasers are designed and analyzed. Two Fabry–Perot cavities of unequal lengths, each containing an amplifier and a phase­tuning section, are coupled together through low-loss Bragg grating. The theoretical analysis of such multisection lasers starts with calculating the poles of a linear transfer function of the entire resonator in order to obtain resonant wavelengths and wavelength-dependent threshold gains. The differential quantum efficiency and the power-current characteristics are then calculated to evaluate the laser performance. The effectiveness of the design procedure is verified by the experimental and proof­of-principle demonstration using simplified three-section lasers. Devices exhibit single-mode operation with a side-mode suppression ratio of over 24 dB and tuning range of 11.2 nm. These telecom-suitable lasers can be used as on-chip local oscillators in low-power integrated optical coherent receivers.

We report the design of electrically-pumped high-power vertical-external-cavity surface-emitting lasers emitting at the mid-wave infrared wavelength regime. The device is designed with a monolithic configuration that can provide multiwatts of continuous-wave output power in a single transverse mode with an excellent beam quality.

This paper reports the recent progress on the development of GaSb-based vertical-cavity surface-emitting lasers (VCSELs) with a record-long emission wavelength of above 4 μm using type-II quantum wells. Mid-wave infrared (MWIR) spectral region, covering the 3-6 μm wavelength range, is technologically very interesting for enabling two major application areas such as sensing and defense/security. Among several types of diode lasers, electricallypumped continuous-wave operating VCSELs seem to be the most attractive choice owing to their low-power consumption, inherent longitudinal single-mode emission, and simple electro-thermal wavelength tunability. The applicability of MWIR VCSELs for these two major areas are also discussed in this paper. Single-mode low-power (a few mWs) VCSEL operating at room-temperature with reasonable tunability is essential for the sensing application. For the advanced military application, high optical power (with at least a few watts), high-efficiency and high-brightness (>1 W/mm2) MWIR lasers are important. Given that the MWIR wavelength regime is eye-safe and has a low-loss atmospheric window, the development of next-generation MWIR laser sources is currently in high demand.

A sidewall activation process was optimized for buried magnesium-doped p-GaN layers yielding a significant reduction in tunnel junction-enabled light emitting diode (LED) forward voltage. This buried activation enabled the realization of cascaded blue LEDs with fully transparent GaN homojunction tunnel junctions. The initial optimization of buried p-GaN activation was performed on PN junctions grown by metal organic chemical vapor deposition (MOCVD) buried under hybrid tunnel junctions grown by MOCVD and molecular beam epitaxy. Next the activation process was implemented in cascaded blue LEDs emitting at 450 nm, which were enabled by fully transparent GaN homojunction tunnel junctions. The tunnel junction-enabled multi-active region blue LEDs were grown monolithically by MOCVD. This work demonstrates a state-of-the-art tunnel junction-enabled cascaded LED utilizing homojunction tunnel junctions which do not contain any heterojunction interface.

This feature issue contains a series of papers that report the most recent advances in the field of mid-infrared light sources used for medical applications, including tissue imaging, reconstruction, excision, and ablation. Many biomolecular compounds have strong resonances in the mid-infrared region and medicine is ideally suited to exploit this. The precision, sterility, and versatility of light in mid-infrared is opening more opportunities and this feature issue captures some of the most exciting.

A novel heteroepitaxial growth technique, quasi-van der Waals epitaxy, promises the ability to deposit three-dimensional GaAs materials on silicon using two-dimensional graphene as a buffer layer by overcoming the lattice and thermal expansion mismatch. In this study, density functional theory (DFT) simulations were performed to understand the interactions at the GaAs/graphene hetero-interface as well as the growth orientations of GaAs on graphene. To develop a better understanding of the molecular beam epitaxy-grown GaAs films on graphene, samples were characterized by x-ray diffraction (θ–2θ scan, ω-scan, grazing incidence XRD and pole figure measurement) and transmission electron microscopy. The realizations of smooth GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using this deposition technique are a milestone towards an eventual demonstration of the epitaxial growth of GaAs on silicon, which is necessary for integrated photonics application.

A power-efficient and highly-integrated photonic system, producing low phase-noise coherent optical signal with a wavelength range of 23 nm in the C-band, is presented. The system includes novel InP-photonic integrated coherent receiver circuits that consume record-low (approximately 184 mW) electrical power.

An InP-based photonic integrated circuit was demonstrated for offset locking an on-chip broadly tunable laser to a heterogeneously integrated optical frequency comb oscillator based on a crystalline whispering gallery mode resonator. Optical tuning within 60nm band is demonstrated. The locked laser has excellent spectral purity, sub-kHz linewidth, and good frequency stability.

Semiconductor lasers operating in the 2–3 μm wavelength range are useful for a variety of applications including environmental monitoring, non-invasive medical diagnosis and industrial processing [1]. While type-I GalnAsSb/GaSb quantum well (QW) lasers have achieved room temperature operation up to 3.73 μm, they are limited by the effects of non-radiative Auger recombination, inter-valence band absorption and carrier leakage due to inadequate hole confinement, all of which induce sensitivity to temperature [2]. Here we report studies of the non-radiative recombination mechanisms in type-I GalnAsSb based lasers, in order to assist device optimisation [3-5].

Compact, tunable, low-power consumption coupled-cavity lasers are designed and experimentally demonstrated. Single-mode operation with an SMSR >24 dB and >11 nm tuning range are achieved, being suitable as on-chip local oscillators in low-power integrated optical coherent receivers.

We demonstrate an integrated heterodyne optical phase-locked loop for potential RF remoting. Offset-locking of the two on-chip lasers is achieved by applying a RF signal to an on-chip optical phase modulator and locking to an optical sideband.

Van der Waals growth of GaAs on silicon using a two-dimensional layered material, graphene, as a lattice mismatch/thermal expansion coefficient mismatch relieving buffer layer is presented. Two-dimensional growth of GaAs thin films on graphene is a potential route towards heteroepitaxial integration of GaAs on silicon in the developing field of silicon photonics. Hetero-layered GaAs is deposited by molecular beam epitaxy on graphene/silicon at growth temperatures ranging from 350 °C to 600 °C under a constant arsenic flux. Samples are characterized by plan-view scanning electron microscopy, atomic force microscopy, Raman microscopy, and X-ray diffraction. The low energy of the graphene surface and the GaAs/graphene interface is overcome through an optimized growth technique to obtain an atomically smooth low­ temperature GaAs nucleation layer. However, the low adsorption and migration energies of gallium and arsenic atoms on graphene result in cluster-growth mode during crystallization of GaAs films at an elevated temperature. In this paper, we present the first example of an ultrasmooth morphology for GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using quasi van der Waals epitaxy, making it a remarkable step towards an eventual demonstration of the epitaxial growth of GaAs by this approach for heterogeneous integration.

This paper discusses the design of electrically-pumped AlGaN-based in-plane lasers emitting at ~290 nm. Our laser design utilizes strained Al0.5Ga0.5N quantum wells, and a novel polarization engineered AlGaN/InGaN/AlGaN-based tunnel junction. The low ­resistive tunnel junction is used as an intracavity contact in the device in place of the resistive p-type contact; which leads to improved hole injection and a reduced threshold voltage. Hence, room-temperature continuous-wave laser operation could be enabled. Strategies to improve the performance of the tunnel junction contact through the incorporation of low concentrations of boron in the highly-doped AlGaN tunnel junction layers as a means to increase the polarization sheet charge are also discussed.

GaInAsSb/GaSb based quantum well vertical cavity surface emitting lasers (VCSELs) operating in mid-infrared spectral range between 2 and 3 micrometres are of great importance for low cost gas monitoring applications. This paper discusses the efficiency and temperature sensitivity of the VCSELs emitting at 2.6 μm and the processes that must be controlled to provide temperature stable operation. We show that non-radiative Auger recombination dominates the threshold current and limits the device performance at room temperature. Critically, we demonstrate that the combined influence of non-radiative recombination and gain peak – cavity mode de-tuning determines the overall temperature sensitivity of the VCSELs. The results show that improved temperature stable operation around room temperature can only be achieved with a larger gain peak – cavity mode de-tuning, offsetting the significant effect of increasing non-radiative recombination with increasing temperature, a physical effect which must be accounted for in mid-infrared VCSEL design.

We report the transverse-mode characteristics of GaSb-based vertical-cavity surface-emitting lasers (VCSELs) with buried-tunnel junctions (BTJs). The optical-index guiding in the devices is achieved by an effective refractive index step due to the presence of a laterally structured BTJ in the cavity. All lasing modes in VCSELs of different active diameters are experimentally measured. Then the experimental results are compared against the theoretical data for two different VCSEL designs emitting at 2.3 and 2.6 μm yielding a good agreement. The transverse-mode spacing between the excited modes is also determined and the results are compared with the theory. The far-field patterns ensure that devices with reasonable aperture diameters operate in single-fundamental LP01 mode, showing that the devices are well-designed.

In this work, we present our approach towards the growth of active regions and cladding layers for GaSb based record low-threshold lasers emitting in the range of 2.5–2.7 μm. First, a study on Sb incorporation in the AlGaAsSb cladding layers and GaInAsSb QWs is presented as a function of growth temperature. A linear decrease in Sb incorporation was observed for both cases. Second, a choice of well-barrier material is presented. Here, the best results have been achieved with a GaSb/GaInAsSb combination, yielding a low-temperature (20 K) photoluminescence (PL) response with a very narrow full-width at half-maximum (FWHM) of 4.5 meV. The latter is followed by an investigation of active region degradation with increased annealing temperatures. The rapid degradation has been confirmed by PL and X-ray diffraction studies. Finally, device results are presented. Lasers show ultra-low CW threshold current densities (44 A/cm 2 at L →∞), in the wavelength range of 2.5–2.7 μm.

In this paper, we present a device concept and results of an electrically pumped vertical-cavity surface-emitting laser in the (AlGaIn)(AsSb) material system grown on GaSb substrate. The structure consists of an n-doped GaSb/AlAsSb distributed Bragg reflector and a type-I GaInAsSb/AlGaAsSb active region, and incorporates a type-III p+-GaSb/n+-InAsSb buried tunnel junction for current as well as optical confinement. Continuous-wave operation up to 75degC has been achieved at a wavelength of 2.3 mum. The mid-IR emission, the large tunability over a wavelength range of more than 10 nm combined with its single-mode operation makes this device ideally suited for gas-sensing applications.

A saturated semiconductor-optical-amplifier exhibited 6.3 dB of phase-sensitive gain using two tunable laser pumps coherently injection-locked from sidebands of a modulated tone, all integrated on a single InP chip.

We design and experimentally demonstrate a highly integrated heterodyne optical phase-locked loop (OPLL) consisting of an InP-based coherent photonic receiver, high-speed feedback electronics, and an RF synthesizer. Such coherent photonic integrated circuits contain two widely tunable lasers, semiconductor optical amplifiers, phase modulators, and a pair of balanced photodetectors. Offset phase-locking of the two lasers is achieved by applying an RF signal to an on-chip optical phase modulator following one of the lasers and locking the other one to a resulting optical sideband. Offset locking frequency range >16 GHz is achieved for such a highly sensitive OPLL system which can employ up to the third-order-harmonic optical sidebands for locking. Furthermore, the rms phase error between the two lasers is measured to be 8°.

An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines. An arbitrary frequency synthesis between the comb lines is demonstrated by tuning the RF offset source, and better than 100Hz tuning resolution with ± 5 Hz accuracy is obtained. Frequency switching of the on-chip laser to a point more than two dozen comb lines away (~5.6 nm) and simultaneous locking to the corresponding nearest comb line is also achieved in a time ~200 ns. A low residual phase noise of the optical phase-locking system is successfully achieved, as experimentally verified by the value of -80 dBc/Hz at an offset of as low as 200 Hz.

We report angle dependent and temperature dependent (9 K–300 K) photo-modulated reflectance (PR) studies on vertical-cavity surface-emitting laser (VCSEL) structures, designed for 2.3 μm mid-infrared gas sensing applications. Changing the temperature allows us to tune the energies of the quantum well (QW) transitions relative to the VCSEL cavity mode (CM) energy. These studies show that this VCSEL structure has a QW-CM offset of 21 meV at room temperature. Consequently the QW ground-state transition comes into resonance with the CM at 220 ± 2 K. The results from these PR studies are closely compared with those obtained in a separate study of actual operating devices and show how the PR technique may be useful for device optimisation without the necessity of having first to process the wafers into working devices.

GaInAsSb-GaSb strained quantum-well (QW) ridge waveguide diode lasers emitting in the wavelength range from 2.51 to 2.72 mum have been grown by molecular beam epitaxy. The devices show ultralow threshold current densities of 44 A/cm2 (L rarr infin) for a single QW device at 2.51 mum, which is the lowest reported value in continuous-wave operation near room temperature (15degC) at this wavelength. The devices have an internal loss of 3 cm-1 and a characteristic temperature of 42 K. By using broader QWs, wavelengths up to 2.72 mum could be achieved.

In this work, temperature and hydrostatic pressure have been used independently to tune the bandgap of GaInAsSb type-I edge emitting lasers. The dependence of Jth, Auger current (JAuger) and radiative current (Jrad) on the band gap of these devices is presented.

This paper discusses several performance-related aspects of electrically-pumped GaSb-based buried tunnel junction VCSELs with an emission wavelength of 2.6 μm based on theoretical and experimental results. These results allow a deeper insight into the internal device physics, such as radial diffusion of carriers, maximum continuous-wave operating temperature, diffraction loss, internal temperature, gain and loss parameters, internal quantum efficiency of the active region etc. These parameters can be taken into account while designing mid-infrared lasers which leads to an improved device performance. A simple thermal model of the devices based on the two-dimensional (2-D) finite element method using the material data from the literature is also presented. In addition, an application-based result utilizing these lasers for the measurement of absolute water vapor concentration by wavelength modulation spectroscopy (WMS) method are also described, hinting that devices are well-suited for the targeted sensing applications.

We present long-wavelength buried tunnel junction (BTJ) VCSELs for emission wavelengths around 2.3 μm. Two different device concepts have been realized utilizing either InP- or GaSb-based materials. The InP-VCSELs are based on a BTJ-design which has been well-proven for wavelengths up to 2 μm in recent years. To extend this range up to emission wavelengths around 2.3 μm, the main focus is set on an optimization of the active region. In this context, we use a graded and heavily strained quantum well design in conjunction with optimized growth conditions. The photoluminescence and x-ray characterization shows a very good material quality. Room-temperature operated VCSELs exhibit around 0.5 mW of output power with singlemode-emission at 2.36 μm representing the longest wavelength that has been achieved with InP-based interband lasers so far. GaSb-based devices comprise an epitaxial back mirror and a dielectric output mirror while the basic BTJ-principle is maintained. Using GaInAsSb quantum wells, the active region reveals excellent gain characteristics at 2.3 μm. Singlemode VCSELs show room temperature threshold currents around 1 mA and output powers of 0.7 mW, respectively. Both laser types have been implemented in a tuneable diode laser spectroscopy (TDLS) setup to evaluate their capability for sensing of carbon monoxide. Using an absorption path length of only 10 cm, concentration measurements down to a few ppm have been successfully demonstrated.

The first electrically-pumped single-mode GaSb-based vertical-cavity surface-emitting lasers emitting at ∼ 2.6 °m are presented. The devices operate in continuous-wave with low threshold currents (I th = 3.8 mA at RT) up to 50°C.

The first 2.5 μm electrically-pumped (I th = 8 mA) single-mode (SMSR > 27 dB) GaSb-based vertical-cavity surface-emitting lasers are presented. The devices that are based on the buried tunnel junction structure operate continuous-wave up to 20°C.

Vertical-cavity surface-emitting lasers (VCSELs) are perfect light sources for spectroscopic applications, where properties such as continuous- wave (cw) operation, single-mode emission, high lifetime and often low power consumption are crucial. For applications such as tunable diode laser absorption spectroscopy (TDLAS), there is a growing interest in laser devices emitting in the near- to mid-infrared wavelength range, where many environmentally and technologically important gases show strong absorption lines. The (AlGaIn)(AsSb) material system based on GaSb is the material of choice for covering the 2.0-3.3µm range. In this paper, we report on electrically pumped single-mode VCSELs with emission wavelengths of 2.4 and 2.6µm, operating cw at room temperature and beyond. By (electro-) thermal tuning, the emission wavelength can be tuned mode-hop free over a range of several nanometers. In addition, low threshold currents of several milliamperes promise mobile application. In the devices, a structured buried tunnel junction with subsequent overgrowth has been used in order to achieve efficient current confinement, reduced optical losses and increased electrical conductivity. Furthermore, strong optical confinement is introduced in the lasers due to laterally differing cavity lengths.

One-dimensional compound semiconductor nanolasers, especially nanowire (NW)-based nanolasers utilizing III-nitride (AlGaInN) materials system, are an emerging and promising area of research. Significant achievements have been made in developing III-nitride NW lasers with emission wavelengths from the deep ultraviolet (UV) to the near-infrared spectral range. The types of lasers under investigation include Fabry-Perot, photonic crystal, plasmonic, ring resonator, microstadium, random, polariton, and two-dimensional distributed feedback lasers. The lasing thresholds vary by several orders of magnitude, which are a direct consequence of differing NW dimensions, quality of the NWs, characteristics of NW cavities, and coupling with the substrate. For electrically injected, such as ultralow-threshold and continuous-wave III-nitride NW lasers that can operate at room temperature, the following obstacles remain: carrier loss mechanisms including defect-related nonradiative surface recombination, electron overflow, and poor hole transport; low radiative recombination efficiency and high surface recombination; poor thermal management; and highly resistive ohmic contacts on the p -layer. These obstacles must be overcome to fully realize the potential of these lasers.

The GaSb and InAs(Sb) material combination results in a type-III (broken gap) band alignment and is of particular interest for use as an ohmic, low-resistive intra-cavity contact in complex optoelectronic devices, such as buried-tunnel-junction vertical-cavity surface-emitting lasers. In this work, we report electrical characteristics of MBE-grown p+-GaSb/n+-InAs tunnel junctions. The investigated structures exhibit ultra-low resistive behavior, yielding specific resistivity values below 2.8 × 10−7Ω cm2. This value is nearly ten times better than previously reported best values.

In this paper, electrically pumped GaSb-based vertical-cavity surface-emitting lasers operating continuous wave at a record long emission wavelength of ∼2.6 μm are presented. Owing to the excellent thermal heat management, the devices exhibit single-mode operation up to a heat-sink temperature of 55 °C. Lateral current confinement and index guiding in the device are accomplished by utilizing the buried tunnel junction concept. Devices with aperture diameters of 6 μm show maximum output powers of 0.3 mW at room temperature with quantum efficiencies around 10%.

We present the design and results of a continuous wave room temperature operating GaSb-based edge emitter at 2.65 µm with threshold current densities as low as 50 A/cm2 (L →∞).

By using a stable comb as an input reference to an integrated heterodyne optical-phase-locked-loop consisting of a coherent receiver photonic IC with a widely-tunable laser, high-speed feedback electronics, and an RF synthesizer, accurate optical frequencies across multiple comb lines can be generated. Initial results will be presented.

We report the design and process development efforts made towards realizing electrically-pumped InP-based topological lasers. Preliminary data on optically-pumped structures reported here serve as the stepping-stone for achieving this new class of lasers.