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The authors present continuous wave (CW) high‐power broad area and ridge waveguide lasers with laser emission at 626 nm at room temperature. For this, the authors employ GaAs‐based diode lasers in the AlGaInP system for laser emission at 626 nm at room temperature. The laser structure is grown on three‐inch wafers by metal organic vapour phase epitaxy. Broad area and ridge waveguide lasers are fabricated. Pulsed broad area laser characterisation on bar level shows laser operation at 20 C heat sink temperature. The authors measured peak lasing wavelengths as short as 625 nm and total maximum output power of both facets up to 1.4 W at an injection current of 2 A. Both, broad area and ridge waveguide lasers show laser operation and CW excitation at room temperature. The ridge waveguide lasers emit output powers of over 90 mW at 626 nm at a maximum injection current of 200 mA with a nearly diffraction‐limited beam profile. [ABSTRACT FROM AUTHOR]

Optical frequency combs with equidistant frequency modes have revolutionized metrology and spectroscopy. The most widespread combs consist of periodic pulse trains generated by mode-locked lasers. However, it has recently been demonstrated that most semiconductor lasers based on Fabry–Pérot cavities, such as quantum well laser diodes, quantum cascade lasers, and quantum dot lasers, can enter an unconventional regime without traditional mode-locking mechanisms. The time-domain profile of these self-locked combs features a frequency-modulated (FM) wave with quasi-continuous-wave intensity and near-linear frequency chirp. The observation of the FM mode of operation in lasers with significantly different dynamics suggested that this mode is a fundamental operating state of semiconductor lasers, stemming from a deeper underlying mechanism. Thanks to recent theoretical and experimental advances, the origin of FM behavior has become clear. In this Perspective, we discuss the current status of FM combs in semiconductor lasers based on Fabry–Pérot cavities, focusing on their physical origin, modeling, characterization, bandwidth enhancement, and potential in future applications. [ABSTRACT FROM AUTHOR]

Falling within the safe bands for human eyes, 1550 nm semiconductor lasers have a wide range of applications in the fields of LIDAR, fast-ranging long-distance optical communication, and gas sensing. The 1550 nm human eye-safe high-power tunnel junction quantum well laser developed in this paper uses three quantum well structures connected by two tunnel junctions as the active region; photolithography and etching were performed to form two trenches perpendicular to the direction of the epitaxial layer growth with a depth exceeding the tunnel junction, and the trenches were finally filled with oxides to reduce the extension current. Finally, a 1550 nm InGaAlAs quantum well laser with a pulsed peak power of 31 W at 30 A (10 KHz, 100 ns) was realized for a single-emitter laser device with an injection strip width of 190 μm, a ridge width of 300 μm, and a cavity length of 2 mm, with a final slope efficiency of 1.03 W/A, and with a horizontal divergence angle of about 13° and a vertical divergence angle of no more than 30°. The device has good slope efficiency, and this 100 ns pulse width can be effectively applied in the fields of fog-transparent imaging sensors and fast headroom ranging radar areas. [ABSTRACT FROM AUTHOR]

A silicon‐based room temperature (RT) continuous wave (CW) operation quantum well (QW) laser emitting at 850 nm is reported in this article. By applying the dislocation filter superlattice, the threading dislocation density of the GaAs pseudosubstrate on Si is reduced to 1.8 × 107 cm−2. The metal‐organic chemical vapor deposition‐grown laser structure with GaAs/GaAsP QW and InAlAs active region dislocation blocking layer are fabricated into broad‐stripe Fabry–Perot laser diodes. A typical threshold current and threshold current density of 286 mA and 715 Acm−2 are obtained with 2 mm cavity length and 20 um stripe width samples. A 94.2 mW single‐facet output power lasing around 854 nm and a 0.314 WA−1 slope efficiency is measured under RT CW operation. After a 10‐min aging process, the tested laser can operate stably under continuous operation conditions at RT and the lifetime can be approximated using an exponential fitting curve, indicating a good life reliability of this QW laser. [ABSTRACT FROM AUTHOR]

Since there are few research reports on semiconductor lasers in the yellow wavelength, this manuscript proposes the design of a semiconductor laser with an excitation wavelength of 589 nm, using a Ge/SiGe substrate, combined with GaInP quantum wells with high Ga composition and AlGaInP series of materials as the main structural layer of the laser. Simulation software is used for feasibility verification, and the effects of different parameters are discussed to optimize the device structure. The effects of interfacial states and electron leakage on the device characteristics are discussed, and a solution to the electron leakage problem is given. The results show that under the influence of the interfacial state, the threshold current of the 589-nm laser reaches 3.3 A, and the output power is about 0.6 W. Through optimization, by adding two layers of AlP electron-blocking layer with a thickness of 5 nm between the P-type cladding and the upper waveguide layer, the concentration of electrons in the P-type cladding layer can be reduced to 1.53 × 1015 cm−3, the threshold current of the device is reduced to 2.13 A, and the output power reaches 0.87 W. [ABSTRACT FROM AUTHOR]

A systematic study of a series of InGaAs/GaAs lasers in the 1–1.3 μm optical range based on quantum wells (2D), quantum dots (0D), and quantum well-dots of transitional (0D/2D) dimensionality is presented. In a wide range of pump currents, the dependences of the lasing wavelength on the layer gain constant, a parameter which allows comparing lasers with different types of active region and various waveguide designs, are measured and analyzed. It is shown that the maximum optical gain of the quantum well-dots is significantly higher, and the range of lasing rawavelengths achievable in edge-emitting lasers without external resonators is wider than in lasers based on quantum wells and quantum dots. [ABSTRACT FROM AUTHOR]

The performance of ultraviolet (UV) laser diodes (LDs) with a low Al mole fraction AlGaN cladding layer was investigated by varying the thicknesses of the waveguide layer. It is found that (1) the loss of carriers in the waveguide layer is much larger than that in blue or green LDs due to the shallower quantum well and consequently a weaker carrier confinement of UV lasers. (2) Carrier loss in the waveguide layer can be suppressed by using a thinner waveguide layer. Therefore, the threshold current of LDs can be reduced. (3) The ultraviolet GaN/AlGaN single quantum well laser diodes lasing at 366 nm are fabricated by using relatively thin AlGaN waveguide layers and low Al mole fraction AlGaN cladding layers. [ABSTRACT FROM AUTHOR]

The enhancement of the reliability of the silicon-based III–V quantum well lasers, especially of those on an on-axis Si (001) substrate, is of great importance now a days for the development of Si-based photonic and even optoelectronic integrated circuits and is really quite challenging. As an experimental advancement, mainly by inserting a pair of InAlAs strained layers separately into the upper and lower AlGaAs cladding layers to effectively prevent the formation of the in-plane gliding misfit-dislocations within the boundary planes of the active region, the longest room-temperature and continuous-wave lifetime of the InGaAs/AlGaAs quantum well lasers on an on-axis Si (001) substrate with a cavity length of 1500 µm and a ridge width of 20 µm has been prolonged from a very initial record of ∼90 s to the present length longer than 31 min. While, the highest continuous-wave operation temperature of another one with a cavity length of 1000 µm and a ridge width of 10 µm has been shown as 103 °C with an extracted characteristic temperature of 152.7 K, further enhancement of the device reliability is still expected and would mainly depend on the level of the threading-dislocation-density reduction in the GaAs/Si virtual substrate. [ABSTRACT FROM AUTHOR]

In this study, the operational durability of laser diodes (LDs) with CdSe quantum dot (QD) active region is examined through a detailed comparison with its BeZnCdSe quantum well (QW) counterpart. To focus on the impact on the difference caused by the nature of the active region, other layers such as the waveguide layer, cladding layer, and contact layer, which influence the mode profile of the optical confinement and electrical properties, are maintained under the same condition. Although the threshold current of the CdSe QD LD is higher than that of the BeZnCdSe QW LD by a factor of 1.6–1.7 under a fresh condition, the degradation of the former proceeds much more slowly than that of the latter. This is confirmed by a reliability test conducted under the current injection condition both below and above the lasing threshold. The result indicates that the stronger carrier localization in the CdSe QDs compared to that in the BeZnCdSe QWs prevents the interaction with remote defects in the active layer. Consequently, the CdSe QD LD is less sensitive to degradation due to recombination-enhanced defect reactions. [ABSTRACT FROM AUTHOR]

Scanning transmission electron microscope and temperature-dependent photoluminescence were used to study the effects of AlGaN interlayer (IL) following InGaN quantum wells (QWs) on the structural and optical properties of InGaN green laser diodes (LDs) grown on c-plane GaN substrate. It is found that AlGaN IL improves InGaN QW interface sharpness, whereas it does not suppress the localization effect, and moreover, it leads to increasing nonradiative recombination centers in the active region of green InGaN LD. We believe AlGaN IL has advantages and disadvantages to green InGaN LD structures. The advantage is to suppress indium (In) surface segregation, but the disadvantage is that it covers In-rich clusters, which evolve into dark spots during the growth of p-type layers of green LD structures. [ABSTRACT FROM AUTHOR]

Nanowire lasers are sought for near‐field and on‐chip photonic applications as they provide integrable, coherent, and monochromatic radiation: the functional performance (threshold and wavelength) is dependent on both the opto‐electronic and crystallographic properties of each nanowire. However, scalable bottom‐up manufacturing techniques often suffer from inter‐nanowire variation, leading to differences in yield and performance between individual nanowires. Establishing the relationship between manufacturing controls, geometric and material properties, and the lasing performance is a crucial step toward optimisation; however, this is challenging to achieve due to the interdependance of such properties. Here, a high‐throughput correlative approach is presented to characterise over 5000 individual GaAsP/GaAs multiple quantum well nanowire lasers. Fitting the spontaneous emission provides the threshold carrier density, while coherence length measurements determine the end‐facet reflectivity. The performance is intrinsically related to the width of a single quantum well due to quantum confinement and bandfilling effects. Unexpectedly, there is no strong relationship between the properties of the lasing cavity and the threshold: instead the threshold is negatively correlated with the non‐radiative recombination lifetime of the carriers. This approach therefore provides an optimisation strategy that is not accessible through small‐scale studies. [ABSTRACT FROM AUTHOR]

We propose a type-II AlInN/ZnGeN2 quantum well (QW) structure serving as the active region for ultraviolet (UV) laser diodes. A remarkably low threshold current density can be achieved using the type-II AlInN/ZnGeN2 QW structure, providing a pathway for the realization of electrically-driven nitride-based semiconductor UV laser diodes. ZnGeN2 has both a very similar lattice constant and bandgap to GaN. Its large band offsets with GaN enable the potential of serving as a hole confinement layer to increase the electron-hole wavefunction overlap in the active region. In this study, we investigate the spontaneous emission and gain properties of type-II AlInN/ZnGeN2 QWs with different ZnGeN2 layer thicknesses. Our findings show that the use of ZnGeN2 layers in the active region provides a significant improvement in hole carrier confinement, which results in ∼5 times enhancement of the electron-hole wave function overlap. Such an enhancement provides the ability to achieve a significant increase (∼6 times) in the spontaneous emission rate and material gain, along with a remarkable reduction in threshold carrier density compared to the conventional AlGaN-based QW design, which is essential for practical UV laser diodes. [ABSTRACT FROM AUTHOR]

We present InAsP multi-functional metamorphic buffers (MFMBs) designed to enable mid-infrared Type-I InAs quantum well (QW) lasers on InP substrates. InAsxP1-x/InP MFMBs with x = 0.5–0.7 provide a versatile platform for Type-I InAs QW laser diodes in the mid-infrared regime by bridging the lattice mismatch between InAs and InP while simultaneously functioning as the bottom cladding layer for laser structures. Cross-sectional transmission electron microscopy shows that InAs multi-QWs can be grown as thick as 15 nm without forming misfit dislocations on an InAs0.7P0.3 buffer, enabling room-temperature photoluminescence at wavelengths >3 μm. We then compare the performance of lasers grown on InAsP MFMBs and show that the temperature dependence strongly depends on the energy band offset between the QW and the metamorphic InAsP waveguides. Future work could improve performance at longer wavelengths by investigating the use of electron blocking layers and adjusting the device design to minimize parasitic heating. [ABSTRACT FROM AUTHOR]

Mid‐wave infrared (MIR, 3–5 µm) optical frequency combs (OFC) are of critical importance for spectroscopy of fundamental molecular transitions in space and terrestrial applications. Although in this band OFCs can be obtained via supercontinuum or difference frequency generation using optical pumping schemes, unprecedented source miniaturization, and monolithic design are unique to electrically‐pumped semiconductor laser structures. To date, high‐brightness OFC generation in this region has been demonstrated in quantum‐ and interband cascade lasers (QCL/ICL), yet with sub‐optimal spectral properties. Here, an MIR quantum well diode laser (QWDL) OFC is shown, whose excellent spectral uniformity, narrow optical linewidths, and milliwatt optical power are obtained at a fraction of a watt of power consumption. The continuously tunable source offers ≈1 THz of optical span centered at 3.04 µm, and a repetition rate of 10 GHz. As a proof‐of‐principle, a directly‐battery‐operated MIR dual‐comb source is shown with almost 0.5 THz of optical coverage accessible in the electrical domain in microseconds. These results indicate the high suitability of QWDL OFCs for future chip‐based real‐time sensing systems in the mid‐infrared. [ABSTRACT FROM AUTHOR]

In edge-emitting high power laser diodes, the longitudinal spatial hole burning (LSHB) effect induced by the inhomogeneous photon and carrier distributions and the non-linear process, two-photon absorption (TPA), are demonstrated to the key causes of power saturation at the high injection level even in the absence of thermal roll-over. Laser diodes based on extreme, double/triple asymmetric (EDAS/ETAS) epitaxial structures show great potentials in high-power and high-efficiency applications owing to the reduced series resistance, low optical loss, and suppressed power saturation. In this paper, a novel semi-analytical calculation method is proposed to systematically analyze the impact of LSHB and TPA effects on the output characteristics of EDAS/ETAS-based broad area lasers (BALs). By leveraging the feature that it is flexible to adjust the confinement factor of ETAS epitaxial structure without compromising the internal loss and resistance level, the laser parameters are first optimized to minimize power saturation of ETAS-based BALs under pulsed and Continuous Wave (CW) operation.

Catastrophic optical mirror damage (COMD) is one of the main failure mechanisms limiting the reliability of GaAs based laser diodes. Here, we compare the facet stability of ZnSe-passivated ridge-waveguide lasers (RWLs) that are cleaved in air and subsequently cleaned using atomic hydrogen with RWLs that are cleaved in ultra-high vacuum. RWLs cleaved in ultra-high vacuum show a superior performance and reach power densities up to 58 MW/cm2 under extended continuous wave operation at 1064 nm. This is attributed to the reduction of defects at the interface between ZnSe and the cleaved facet as evidenced by transmission electron microscopy and X-ray diffraction.

In edge-emitting high power laser diodes, the longitudinal spatial hole burning (LSHB) effect induced by the inhomogeneous photon and carrier distributions and the non-linear process, two-photon absorption (TPA), are demonstrated to the key causes of power saturation at the high injection level even in the absence of thermal roll-over. Laser diodes based on extreme, double/triple asymmetric (EDAS/ETAS) epitaxial structures show great potentials in high-power and high-efficiency applications owing to the reduced series resistance, low optical loss, and suppressed power saturation. In this paper, a novel semi-analytical calculation method is proposed to systematically analyze the impact of LSHB and TPA effects on the output characteristics of EDAS/ETAS-based broad area lasers (BALs). By leveraging the feature that it is flexible to adjust the confinement factor of ETAS epitaxial structure without compromising the internal loss and resistance level, the laser parameters are first optimized to minimize power saturation of ETAS-based BALs under pulsed and Continuous Wave (CW) operation. [ABSTRACT FROM AUTHOR]

Catastrophic optical mirror damage (COMD) is one of the main failure mechanisms limiting the reliability of GaAs based laser diodes. Here, we compare the facet stability of ZnSe-passivated ridge-waveguide lasers (RWLs) that are cleaved in air and subsequently cleaned using atomic hydrogen with RWLs that are cleaved in ultra-high vacuum. RWLs cleaved in ultra-high vacuum show a superior performance and reach power densities up to 58 MW/cm2 under extended continuous wave operation at 1064 nm. This is attributed to the reduction of defects at the interface between ZnSe and the cleaved facet as evidenced by transmission electron microscopy and X-ray diffraction. [ABSTRACT FROM AUTHOR]

A monolithic two-section InGaAs/GaAs double quantum wells (DQWs) mode-locked laser (MLL) emitting at 1.06 μm is demonstrated. Stable mode locking operation is achieved up to 80 °C. The fundamental repetition rate is at ~9.51 GHz with a signal-to-noise ratio (SNR) of more than 55 dB, and up to the fourth harmonic at ~38.04 GHz is observed. The characteristic temperature (T0) of the laser and the influences of absorber bias voltage on T0 have been systematically investigated. From our findings, T0 shows a two-segment feature, and is slightly affected by the absorber bias voltage for photon saturation.

n this letter, the authors present a monolithic edge emitting diode laser intended as a potential key component for the generation of terahertz radiation in a compact time-domain spectroscopy system. The 6 mm long multi-section InGaAsP double quantum well (DQW) laser, featured with a 3.6 mm long tapered (TP) gain section, operates at a wavelength of ∼832 nm and generates pulses at a fundamental repetition rate of ∼6.3 GHz in passive mode-locking operation. Pulses with 2.6 ps width and 40 W peak power are measured. The generated pulses are not bandwidth-limited and should be compressible for further applications. [ABSTRACT FROM AUTHOR]

The improvement of the performance of a distributed Bragg reflector laser bar emitting near 905 nm through the use of multiple epitaxially stacked active regions and tunnel junctions is reported. The bar consisting of 48 emitters (each having an aperture of 50 µm) emits an optical power of 2.2 kW in 8 ns long pulses at an injection current of 1.1 kA. This corresponds to an almost threefold increase of the pulse power compared to a bar with lasers having only a single active region. Due to the integrated surface Bragg grating, the bar exhibits a narrow spectral bandwidth of about 0.3 nm and a thermal tuning of only 68 pm/K. [ABSTRACT FROM AUTHOR]

The performance characteristics of semiconductor lasers based on quantum wells (QWs) are theoretically studied as functions of the thickness of the waveguide region [optical confinement layer (OCL)]. The maximum modal gain, optical-confinement factor (in QWs, OCLs, and emitters), threshold current density, electron and hole densities (in QWs and OCLs), internal optical loss (in QWs, OCLs, and cladding layers), internal differential quantum efficiency, currents of stimulated and spontaneous recombination and the output optical power of the laser are calculated as functions of the OCL thickness. It is shown that up to pump current densities of 50 kA/cm2 the dependence of the output power of the considered lasers on the OCL thickness is weak in the thickness range of 1.5–2.8 μm. This result is important for the development of high-brightness lasers, since such lasers use a wide waveguide to ensure low radiation divergence. It is shown that, at very high pump-current densities, the output power has a maximum as a function of the OCL width. [ABSTRACT FROM AUTHOR]

We demonstrated high efficient circularly polarized emission from the InGaN/GaN quantum well green laser diode (LD) integrated with GaN metasurface quarterwave plates. Optical properties of the nanoscale thin GaN nanograting metasurface were numerically studied and optimized for a quarter-wave plate. The fabricated nanogratings then were integrated on the emission facet of the LD. Both conversion efficiency and the polarization state of the device were measured, and the conversion efficiency is around 80% while the degree of circular polarization is maintained around 0.99. Our results of achieving a high degree of polarization and a high conversion efficiency at the integrated LD device pay the way for multi-functional applications in bio-imaging, submarine optical communication, quantum communication, and holographic display. [ABSTRACT FROM AUTHOR]

We report a GaSb-based type-I quantum well cascade diode laser emitting at nearly 2-μm wavelength. The recycling of carriers is realized by the gradient AlGaAsSb barrier and chirped GaSb/AlSb/InAs electron injector. The growth of quaternary digital alloy with a gradually changed composition by short-period superlattices is introduced in detail in this paper. And the quantum well cascade laser with 100-μm-wide, 2-mm-long ridge generates an about continuous-wave output of 0.8 W at room temperature. The characteristic temperature T0 is estimated at above 60 K. [ABSTRACT FROM AUTHOR]

Generating optical combs in a small form factor is of utmost importance for a wide range of applications such as datacom, LIDAR, and spectroscopy. Electrically powered mode‐locked diode lasers provide combs with a high conversion efficiency, while simultaneously allowing for a dense spectrum of lines. In recent years, a number of integrated chip scale mode‐locked lasers have been demonstrated. However, thus far these devices suffer from significant linear and nonlinear losses in the passive cavity, limiting the attainable cavity size and noise performance, eventually inhibiting their application scope. Here, we leverage the ultra‐low losses of silicon‐nitride waveguides to demonstrate a heterogeneously integrated III‐V‐on‐silicon‐nitride passively mode‐locked laser with a narrow 755 MHz line spacing, a radio frequency linewidth of 1 Hz and an optical linewidth below 200 kHz. Moreover, these comb sources are fabricated with wafer scale technology, hence enabling low‐cost and high volume manufacturable devices. [ABSTRACT FROM AUTHOR]

Operation of semiconductor lasers in the 20–50 µm wavelength range is hindered by strong non-radiative recombination in the interband laser diodes, and strong lattice absorption in GaAs-based quantum cascade structures. Here, we propose an electrically pumped laser diode based on multiple HgTe quantum wells with band structure engineered for Auger recombination suppression. Using a comprehensive model accounting for carrier drift and diffusion, electron and hole capture in quantum wells, Auger recombination, and heating effects, we show the feasibility of lasing at λ = 26, ..., 30 µm at temperatures up to 90 K. The output power in the pulse can reach up to 8 mW for microsecond-duration pulses. [ABSTRACT FROM AUTHOR]

We carried out a study of the strain-compensated InxGa1-xN/GaN and InxGa1-xN/InyGa1-yN multiple quantum wells, In order to carry out this analysis, we choose a set of three different types of samples. The optimization of this laser structure allowed us to determine the optimal values of the functional parameters, in order to adjust their performance and interest. We also studied the electronic and structural properties of compound semiconductor alloys used in wurtzite phase and we have presented a comparative theoretical study of both structures. Our studies show the improvement of the spontaneous emission spectra and better carrier confinement from the use of InxGa1-xN/InyGa1-yN MQW with higher In-content in barrier as active regions for diode lasers and this structure is useful for the design of new high performance Laser diodes emitting in the Blue/Violet range, and it's also shows that the process of the electron-holes transition is strongly affected by the quantum well width and the Indium composition, and the InGaN lattice mismatch that increases with In-content causing the strain accumulation inside the QW structure. However, strain is undesirable as it can cause defects such as cracking at the interface. We can optimize the InGaN/GaN strained quantum well structures to achieve a reliable optoelectronic component. It suffices to incorporate small amounts of indium in the barrier enhances the annihilation of the defect and strain, thereby improving their structural properties. [ABSTRACT FROM AUTHOR]

Temperature of a commercial AlGaInP/GaInP quantum well laser diode (LD) is measured using two methods: peak wavelength shift and the diode voltage drop caused by working current. Time evolutions of temperature obtained by the two methods during the LD self-heating are measured and compared. No significant difference between the thus obtained temperature evolutions is obtained. Correlation between the LD voltage drop and the laser radiation frequency is established using a simple four-level semiconductor laser scheme and the LD gap energy is estimated. The LD gap energy decreases from 1.66 eV to 1.56 eV for temperature increase of 21 K, at close to room temperature. It is found that LD's frequency decrease is caused by the gap energy decrease. [ABSTRACT FROM AUTHOR]

Optical gain spectra for ~250 nm stimulated emission were compared in three different AlGaN-based structures grown on single crystalline AlN substrates: a single AlGaN film, a double heterostructure (DH), and a Multiple Quantum Well (MQW) structure; respective threshold pumping power densities of 700, 250, and 150 kW/cm2 were observed. Above threshold, the emission was transverse-electric polarized and as narrow as 1.8 nm without a cavity. The DH and MQW structures showed gain values of 50–60 cm–1 when pumped at 1MW/cm2. The results demonstrated the excellent optical quality of the AlGaN-based heterostructures grown on AlN substrates and their potential for realizing electrically pumped sub-280 nm laser diodes. [ABSTRACT FROM AUTHOR]

A novel surface emitting distributed feedback quantum cascade laser emitting around λ 4.6 µm is demonstrated by employing an equivalent phase shift (EPS) of quarter-wave (λ/4). The EPS is fabricated through extending one sampling period by 50% in the center of a sampled Bragg grating. Single-lobed far-field radiation pattern with a low divergence angle of about 0.6º x 16.8º is obtained. Selective single-mode lasing with a mean side mode suppression ratio above 20 dB and wavelength coverage range of 72 nm is achieved simultaneously on a single wafer only by changing the sampling period. [ABSTRACT FROM AUTHOR]

Experimental light–current characteristics of high-power semiconductor lasers operating at ultrahigh drive currents have been studied in terms of numerical models taking into account the effect of the carrier drift velocity saturation. It was shown that the simplest diffusion–drift (DD) model underestimates the optical loss at high drive currents, which leads to overestimation of the peak optical power when compared with the experimental results. The inclusion of the carrier drift velocity saturation effect into the DD model results in that a strong-electric-field domain is formed at the interface with the active region on the side of the p-emitter already at low drive currents. The amplitude of this field substantially grows as the current increases further, which restricts application of this model to description of high-power semiconductor lasers at high drive currents. With the nonlocal energy-balance model used to describe the carrier transport in the laser heterostructure, it becomes possible to take into account the effect of carrier heating by the electric field. As a result of the carrier heating, the drift velocity decreases and the concentration of excess carriers in the waveguide layer grows, compared with the simplest DD model. The inclusion of the additional internal optical loss mechanism obtained in the energy-balance model provided a satisfactory coincidence of the calculated light–current characteristics with the experimental dependences. [ABSTRACT FROM AUTHOR]

The temperature-dependent phase noise properties of a monolithic two-section mode-locked semiconductor laser are first investigated. This is performed on a GaSb-based quantum well laser emitting at ∼2 μm. Stable mode locking operation with a fundamental repetition frequency of ∼13.3 GHz is achieved on this laser up to 60 °C. At a fixed temperature, there is no monotonous dependence of integrated jitter on the bias condition. For a given gain current or absorber voltage, there exists a corresponding optimal absorber voltage or gain current, respectively, that minimizes the integrated jitter. More important, the phase noise properties improve obviously at elevated temperatures with the lowest achievable jitter reducing obviously from 3.15 ps at 20 °C to 1.39 ps at 60 °C (100 kHz–1 GHz). We consider that the reason is reduced amplified spontaneous emission noise at high temperatures. This is confirmed by the extracted peak-to-valley ratio of the involved laser modes. We believe that this study provides an important insight into the carrier behaviors and noise performance of mode-locked semiconductor lasers, which is meaningful to their applications especially at high temperatures. [ABSTRACT FROM AUTHOR]

Comparison of performance of semiconductor mode-locked laser diodes fabricated using AlGaInAs/InP material containing 5 and 3 quantum wells (QWs) inside the active region is reported. The simulations and experimental results show that lasers containing five QWs materials produce larger beam divergence and temporally broader optical pulses. For improvement in the mode-locking of lasers and reducing the far-field pattern, the number of QWs inside the active region was decreased from five to three and a far-field decreasing layer along with a thick spacer layer were introduced in the n-cladding region of epitaxial material. Before growing the material, simulations were carried out to optimise the design. The lower optical confinement factor and higher gain saturation energy of three QWs based mode-locked lasers provide higher average and peak output power, reduced and symmetric far-field pattern, better radio frequency (RF) spectra, shorter optical pulses, and stable optimal modelocking for a wide range of gain current and saturable absorber reverse voltage. [ABSTRACT FROM AUTHOR]

Two-section distributed feedback lasers containing an active section and a modulated reflection section have been demonstrated for direct modulation with negative chirp. The reflection section has the same waveguide core and grating pitch as the active section. The active section of the laser has fixed current injection and the modulation voltage is loaded onto the reflection section when the laser normally works. This modulation method can obtain negative chirp because the carrier density variation in the active section during modulation is contrary to traditional current modulation. The threshold current and side-mode suppression ratio of the fabricated laser are about 10-mA and 60-dB at 20 °C, respectively. A 20-GHz modulation bandwidth at 0.9-V reverse bias of the modulated reflection section has been achieved. The negative chirp generated by the modulation is about 45 GHz. 10 Gb/s transmission over 10-km single-mode fiber with error-free-operation over a wide temperature range has been demonstrated as well. The sensitivity of the 10-km transmission was better than BTB configuration at all temperatures due to the negative chirp characteristic. [ABSTRACT FROM AUTHOR]

Chip-scale electrically pumped optical frequency combs (OFCs) are expected to play a fundamental role in applications ranging from telecommunications to optical sensing. To date, however, the availability of such sources around 2 μ m has been scarce. Here, we present a frequency-modulated OFC operating around 2060 nm of wavelength exploiting the inherent gain nonlinearity of single-section GaSb-based quantum well diode lasers. A 2 mm long device operating as a self-starting comb outputs 50 mW of optical power over more than 10 nm of bandwidth while consuming <1 W of electrical power. Using the shifted-wave interference Fourier transform spectroscopy technique, we characterize the generated frequency-modulated waveform and demonstrate a linearly chirped intermodal phase relationship among the entire emission optical bandwidth. Furthermore, by compensating for the linear chirp using a single-mode optical fiber with opposite dispersion, 6 ps long optical pulses are generated. The frequency stability of the devices with ∼19.3 GHz repetition rates allows us to perform mode-resolved free-running dual-comb spectroscopy. All rights reserved. [ABSTRACT FROM AUTHOR]

Photonic integrated circuits (PICs) have enabled numerous high performance, energy efficient, and compact technologies for optical communications, sensing, and metrology. One of the biggest challenges in scaling PICs comes from the parasitic reflections that feed light back into the laser source. These reflections increase noise and may cause laser destabilization. To avoid parasitic reflections, expensive and bulky optical isolators have been placed between the laser and the rest of the PIC leading to large increases in device footprint for on-chip integration schemes and significant increases in packaging complexity and cost for lasers co-packaged with passive PICs. This review article reports new findings on epitaxial quantum dot lasers on silicon and studies both theoretically and experimentally the connection between the material properties and the ultra-low reflection sensitivity that is achieved. Our results show that such quantum dot lasers on silicon exhibit much lower linewidth enhancement factors than any quantum well lasers. Together with the large damping factor, we show that the quantum dot gain medium is fundamentally dependent on dot uniformity, but through careful optimization, even epitaxial lasers on silicon can operate without an optical isolator, which is of paramount importance for the future high-speed silicon photonic systems. [ABSTRACT FROM AUTHOR]

Featured Application: Linebroadening functions are essential in extracting material quality data from the optical spectra. The presented, unified lineshape function applies to the simulation of inhomogeneously and homogeneously broadened LED lineshapes. The broadening functions for quantum wells in LEDs and laser diodes below the lasing threshold are examined. Inhomogeneous and homogeneous broadening mechanisms are included. Hydrogen-atom-like exciton and the electron-hole plasma recombination models are considered. Material disorder and the Urbach tail are reviewed as the main reasons for the inhomogeneous broadening. Charge carrier scattering and relaxation times in the conduction and valence bands are examined as the origin for the homogeneous lifetime broadening. Two homogeneous lineshapes are compared using the momentum relaxation times obtained from the electron and hole mobilities available for GaAs. In addition to crystal disorder, the mutual collision of charge carriers in the quantum wells is examined as the reason for the relaxation time shortening. The analogy to pressure broadening in gases is used to combine the proper homogeneous and inhomogeneous broadening functions to a unified quantum well lineshape. [ABSTRACT FROM AUTHOR]

In this study, Fabry-Perot quantum well lasers with shortened cavity designs (25 and $50~\mu $ m) were fabricated. The devices had dry-etched and cleaved facets and exhibited an output power of up to 2.36 mW for a cavity length of 25 $\mu $ m; good spectral performance was achieved. Single-optical-mode operation with better than 25dB of side mode suppression ratio can be achieved for the fabricated devices with 25- and 50- $\mu $ m cavities. The short-cavity devices also exhibited high-speed modulation at elevated temperatures. Moreover, 25 Gb/s eye diagrams could be obtained at 65°C for the 25 $\mu $ m device and 55°C for the 50 $\mu $ m device. Due to their small area, ultra-short-cavity Fabry-Perot laser can be suitably used in next-generation light sources for optical communication. [ABSTRACT FROM AUTHOR]

A traveling wave model for a semiconductor diode laser based on quantum wells is presented as well as a comprehensive theoretical model of the lasing dynamics produced by the intensity discrimination and controllable loss of mode-coupling in a waveguide array. By leveraging a recently developed model for the detailed semiconductor gain dynamics, the temporal shaping effects of the nonlinear mode-coupling induced by the waveguide arrays can be characterized. Specifically, the enhanced pulse shaping and loss provided by the waveguides is capable of generating stable frequency combs at a wavelength of 800 nm in a GaAs device, a parameter regime for which it is difficult to obtain stable, broad comb generation using a single waveguide. Extensive numerical simulations showed that stable waveform generation could be achieved and optimized by an appropriate choice of the linear waveguide coupling coefficient, quantum well depth, and the input currents to the first and second waveguides. The model provides a demonstration that a compact, efficient and robust on-chip comb source can be produced in GaAs. [ABSTRACT FROM AUTHOR]

Mode-locked fiber and solid state lasers have played an essential role in several scientific and technological developments. The integration of mode-locked lasers on chips could enable their use in a wide range of applications. The advancement of semiconductor mode-locked laser diodes has been going on for several decades, but has recently seen the development of novel devices based on generic InP and III-V-on-silicon photonic integration platforms. These photonic integration platforms enable the use of standardized components and low-loss waveguides within the laser cavity, allowing for the design of advanced extended cavities. In this manuscript we give a review of these novel devices and compare their performance. [ABSTRACT FROM AUTHOR]

Abstract: We experimentally investigate and analyze the electrical and optical characteristics of InGaAs/GaAs conventional quantum well laser diode and the quantum well laser diode with slightly-doped tunnel junction. It was found that the laser with slightly-doped tunnel junction has a nonlinear S-shape current-voltage characteristic. The internal quantum efficiencies of the laser with slightly-doped tunnel junction and the conventional laser are 21 and 87.3%, respectively. This suggests that the slightly-doped tunnel junction increased the barrier width and free carrier absorption, thus could reduce the electron tunneling probability and increase the internal loss. Furthermore, compared with the conventional laser, it was found that we could achieve 15 nm broadband spectrum from the laser with slightly-doped tunnel junction, due to the lasing dynamics reflecting the current dynamics. The results show that the slightly-doped tunnel junction plays a crucial role in the laser diode performances, which may lead to the realization of more applications. [ABSTRACT FROM AUTHOR]

We demonstrate an InGaAsP multiple quantum well tunable laser diode consisting of two gain sections with different bandgap energy levels. This tunable laser is used as a probing source for an optical sensor that makes use of surface plasmon resonance (SPR). Lasers fabricated on a single monolithic substrate can have widely differing output wavelengths. Therefore, by controlling the extent of the intermixing, the bandgap energy of the material can be accurately tuned over a broad spectral range. The regions of different bandgap energies are achieved using selective area intermixing of the multiple quantum wells, through impurity-free vacancy-induced disordering. By varying the current combination that was injected to each section, the laser wavelength can be effortlessly tuned from 1538 to 1578 nm with relatively constant output power. The free spectral range of the tunable laser is found to be 0.25 nm. This tunable laser was launched into an optical SPR sensor head that was fabricated on an inverted rib dielectric waveguide to provide an input light source for the SPR sensor. The average sensitivity of the SPR sensor devices was determined to be S = 334 nm RIU-1. [ABSTRACT FROM AUTHOR]

Abstract A two-chip vertical external cavity surface emitting laser with dual- wavelength output is presented. The active region of gain chip 1, designed for 960 nm wavelength, is composed of 6 repeats of strain uncompensated In 0.185 Ga 0.815 As/ GaAs multiple quantum wells, and the active region of gain chip 2, targeted for 1100 nm emission, is consisted of 16 repeats of strain compensated In 0.26 Ga 0.74 As/ GaAs 0.94 P 0.06 multiple quantum wells. Two 1 mm thick uncoated fused silica birefringent filters are employed as the tuning elements, and the shorter wavelength can be tuned between 949 and 957 nm, while the longer wavelength can be changed from 1071 to 1106 nm by rotating the filters. The total intracavity power under dual-wavelength operation exceeds 36 W when the pump power is 10.5 W. For the use of intracavity different frequency generation, the wavelength tunability of down-converted mid-infrared radiation can cover a wavelength range from 6.7 to 9.0 µm. [ABSTRACT FROM AUTHOR]

Abstract: The results of studying edge-emitting quantum-well lasers with a layered design having coupled planar waveguides, capable of suppressing the generation of excited transverse modes, are presented. In this case, a low internal loss (0.4 cm-1) is provided, combined with a small depth (~0.9 μm) of the active region, which results in a low thermal resistance of 6.0 (K/W) mm without a submount. [ABSTRACT FROM AUTHOR]

We investigate the influences of ridge-waveguide shape and width on performances of InP-based coupled ridge waveguide laser arrays emitting at $2.1~\mu \text{m}$. Four devices with different shapes and widths of ridge elements are fabricated. The trapezoid ridges reduce the optical losses at regions between ridge elements in the trapezoid devices, thus enhances the optical coupling between ridge elements and lead to larger coherent output powers compared with the rectangular ones. Meanwhile, narrower ridges with the same shape give a stronger optical confinement to the lateral modes in every single ridge and improve the overall modal and far-field characteristics of the device. The results show that the trapezoid and narrower ridges can lead to a comprehensive improvement in the performances of the coupled ridge waveguide laser arrays emitting at $2.1~\mu \text{m}$. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, digital modulation performance of two‐section, multiple quantum well gain‐levered laser diode in a fiber optic link is analyzed. This study involves numerical simulation of gain‐levered laser diode along with single‐mode fiber for evaluating gigabit rate digital transmission. The optical link performance is analyzed by evaluating the eye diagram, extinction ratio, and quality factor for different bit rates, modulation current, and fiber lengths. The results are compared with unlevered or normal laser diode–based fiber optic link with similar operating conditions. A 12‐dB improvement in extinction ratio is obtained for gain‐levered laser diode when the longer section and shorter section currents are kept as 30 and 0.5 mA, respectively. The Q parameter is found to increase with increasing modulation current in the gain‐levered case, and a maximum Q factor of 11 is obtained for a modulation current of 5 mA. The Q value is improved by a factor of 8 and 5 at 1‐ Gbps and 10‐Gbps data rates, respectively, under gain‐levered condition, when compared to normal laser diode–based link. [ABSTRACT FROM AUTHOR]

The paper presents the measurements results of optical and electrical parameters of quantum well laser diodes and heteroepitaxial photodiodes under gamma-ray and neutron irradiation. The testing results of transceiver modules gamma irradiation tolerance are introduced. The most vulnerable elements of module are highlighted. [ABSTRACT FROM AUTHOR]