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An investigation has been performed of 1.55-μm vertical-cavity surface-emitting lasers based on heterostructures with a buried tunnel junction (BTJ) with a height difference of 15 nm. The devices are obtained by wafer fusion of heterostructures grown by molecular beam epitaxy and provide single-mode lasing at a BTJ diameter of up to 8 μm. A decrease in the BTJ size leads to a sharp increase in the threshold current, the output optical power, and the resonance frequency at the lasing threshold. Stable single-mode lasing takes place due to the smoothed boundary of the buried surface relief, which induces a gradual change in the profile of the effective refractive index in the lateral direction with the effective current confinement retained. This makes it possible to reduce significantly the transverse optical confinement factor for the higher-order modes even at a large BTJ size. However, at a small BTJ size, it leads to the formation of a saturable absorber in unpumped parts of the active region.

A design of a tunnel junction (TJ) based on n++-InGaAs/p++-InGaAs/p++-InAlGaAs layers for vertical-cavity surface-emission lasers (VCSELs) for the 1.55-μm spectral range fabricated by wafer fusion of an InAlGaAsP/InP optical cavity and wafers with AlGaAs/GaAs distributed Bragg reflectors has been suggested and tested. The presence of the oxidation-resistant InGaAs layers makes it possible to employ the molecular-beam epitaxy in all stages of the fabrication technology of VCSELs, including the overgrowth of the surface profile in the TJ layer. Owing to the Burstein–Moss effect and to the thickness minimization of the p++-InGaAs layer, it was possible to avoid a buildup of the internal optical loss. As a result, the characteristics of the thus fabricated devices are comparable with those of VCSELs having an n++-/p++-InAlGaAs TJ and a similar level of the mirror losses.

We study theoretically and experimentally superradiant dynamics in multiple-section GaAs/AlGaAs laser structures. We develop a model based on the one-dimensional Maxwell curl equations without making use of the slowly-varying envelope approximation and demonstrate that strong transient periodic modulation of both e – h density and refractive index drastically affect the dynamics of emission generation in semiconductor media. We show that the coherent λ/2 transient population and the relative permittivity gratings facilitate e – h self-ordering and the onset of the superradiant phase transition in the e – h system.

The low-temperature terahertz and near-infrared photoluminescence from the near-infrared laser nanostructure with GaAs/AlGaAs quantum wells doped with shallow donors is studied under intense interband optical excitation. The optical electron transitions involving excited and ground donor states in quantum wells are revealed in terahertz and near-infrared photoluminescence spectra. Impurity assisted near-infrared stimulated emission under interband optical pumping and its influence on the terahertz optical electron transitions are observed and investigated. It is demonstrated, that at the various pumping levels the competition between different impurity assisted stimulated optical transitions in the near-infrared range leads to appearance of the different impurity related emission lines in terahertz spectra.

In this paper, we present measurements and simulations of the small-signal modulation response of monolithic continuous-wave 1.3 μ m InAs/GaAs quantum dot (QD) narrow ridge-waveguide lasers on a silicon substrate. The 2.5 mm-long lasers investigated demonstrate 3 dB modulation bandwidths of 1.6 GHz, D -factors of 0.3 GHz/mA1/2, modulation current efficiencies of 0.4 GHz/mA1/2, and K -factors of 2.4 ns and 3.7 ns. Since the devices under test are not designed for high-speed operation due to their long length and hence long photon lifetime, the modulation response curves are used as a fitting template for numerical simulations with spatiotemporal resolution to gain insight into the underlying laser physics. The obtained parameter set is used to unveil the true potential of the laser material in an optimized device geometry by modeling the small-signal response at different cavity lengths, mirror reflectivities, and for different numbers of QD layers. The simulations predict a maximum 3 dB modulation bandwidth of 5 GHz to 7 GHz for a 0.75 mm-long cavity with 99% and 60% high-reflection coatings and ten QD layers. Modeling the impact of dislocations on the dynamic performance qualitatively reveals that enhanced non-radiative recombination in the wetting layer leaves the modulation bandwidth of QD lasers on silicon almost unaffected, while dislocation-induced optical loss does not pose a problem, as long as sufficient gain is provided by the QD active region.

The characteristics of lasers of the 1.44–1.46-μm optical range grown on GaAs substrates using a metamorphic buffer are studied. The active region of the laser contains 10 rows of InAs/In0.4Ga0.6As/In0.2Ga0.8As quantum dots. It is shown that the use of special selective high-temperature annealing along with the application of short-period In0.2Ga0.8As/In0.2Al0.3Ga0.5As short-period superlattices makes it possible to substantially decrease the density of threading dislocations in the active region. A threshold current density of 1300 A cm–2, external differential quantum efficiency of 38%, and maximal pulsed-mode output power of 13 W are attained for a laser with a broad area 3 mm in length.

The emission-line width for 850-nm single-mode vertical-cavity surface-emitting lasers based on InGaAs/AlGaAs quantum wells is studied. The width of the emission line for a laser with a 2-μm oxide current aperture attains it minimum (~110 MHz) at an output power of 0.8 mW. As the optical output power is further increased, anomalous broadening of the emission line is observed; this is apparently caused by an increase in the α-factor as a result of a decrease in the differential gain in the active region under conditions of increased concentration of charge carriers and of high internal optical losses in the microcavity. The α-factor is estimated using two independent methods.

The studies of the emission linewidth for single-mode near-IR vertical-cavity surface-emitting lasers with an active region based on InGaAs/AlGaAs quantum wells and different optical microcavity design. For low mirror loss, lasers with a 1λ cavity and carrier injection through distributed Bragg reflectors demonstrate a linewidth of 70 MHz and its growth to 110 MHz with increasing mirror loss (corresponding differential of efficiency ∼0.65 W/A). The design of the optical cavity with carrier injection through intracavity contacts and low-Q composition Bragg lattices reduces the linewidth to 40 MHz in spite of high mirror loss (corresponding differential efficiency of ∼0.6 W/A).

The electron transport in superlattices based on GaAs/AlAs heterostructures with a small number of periods (6 periods) is calculated by the Monte Carlo method. These superlattices are used in terahertz diodes for the frequency stabilization of quantum cascade lasers in the range up to 4.7 THz. The band structure of superlattices with different numbers of AlAs monolayers is considered and their current–voltage characteristics are calculated. The calculated current–voltage characteristics are compared with the experimental data. The possibility of the efficient application of these superlattices in the THz frequency range is established both theoretically and experimentally.

We report on room-temperature generation at the 4.8-μm wavelength in a lattice-matched structure of a quantum cascade laser (QCL) grown on indium phosphide (InP) substrate. Laser heterostructures grown by molecular beam epitaxy (MBE) comprised 30 cascades and were designed to generate at the 4.80 μm wavelength corresponding to an atmospheric transparency window. Experiments demonstrated effective lasing at temperatures from 80 to 300 K on a wavelength coinciding with the calculated value, which confirmed the high quality of interfaces, high precision of layer thicknesses, and high accuracy of active region doping.

Small-signal experiments with a 2.5 mm-long quantum dot narrow ridge-waveguide laser on silicon show a modulation bandwidth of 1.6 GHz. For the first time, we report key high-speed parameters such as the differential gain and the gain compression factor.

This paper presents theoretical and experimental studies of ultrabright internal second harmonic during femtosecond superradiant emission generation in multiple sections GaAs/AlGaAs laser structures at room temperature. Experimentally measured conversion efficiencies are by 1-2 orders of magnitude greater than expected. To explain this fact, a model based on one-dimensional nonlinear Maxwell curl equations without taking into consideration the slowly-varying envelope approximation has been developed. It has been demonstrated that strong transient periodic modulation of e-h density and refraction index dramatically affects the process of superradiance in semiconductor media and can explain the ultrastrong internal second harmonic generation.

Studies aimed at optimization of the design of a dielectric distributed Bragg reflector (DBR) produced by the reactive magnetron sputtering method for applications in near-IR vertical-cavity surface-emitting lasers with intracavity contacts (ICC-VCSELs) are carried out. It is shown that the reflectivity of the dielectric DBRs based on SiO2/TiO2 decreases due to the polycrystalline structure of the TiO2 layers, which causes diffusive scattering of light. In contrast, amorphous Ta2O5 layers is characterized by a low surface roughness and low fluctuation in the refractive index. Single-mode ICC-VCSELs in the 980-nm spectral range with dielectric DBR based on SiO2/Ta2O5 with a threshold current less than 0.27 mA, electric resistance of less than 200 Ω, and differential efficiency of more than 0.8 W/A are demonstrated.

The fundamental possibility of achieving temperature stability of laser emitters of 1.3-μm spectral range exhibiting a vertical microcavity and an active region based on InAs/InGaAs quantum dots (QDs) is investigated. It is demonstrated that using an undoped hybrid vertical optical microcavity formed by a lower undoped semiconductor and an upper distributed dielectric Bragg reflectors allows obtaining laser oscillation up to a temperature of ~100°C at nearly constant threshold optical pump power for an active region consisting of QD layers under optimal spectral mismatch between the position of maximum gain of the QD ground state and the resonance wavelength.

The polarization characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts and a rhomboidal oxide current aperture are studied. It is found that radiation polarization is always directed along the minor diagonal of the rhomboidal aperture (along the [ $$\overline 1 $$ 10] direction) for all single-mode VCSELs. The numerical simulation of carrier transport does not reveal the significant anisotropy of carrier injection to the active region. Furthermore, an analysis of the spatial distribution of the fundamental mode for two orthogonal polarizations within an effective waveguide model shows close transverse optical-confinement factors. Optical loss anisotropy in the asymmetric microcavity and/or gain anisotropy in the strained active region are the most likely mechanisms responsible for fixing the polarization.

The first small-signal modulation experiments with monolithic single transverse mode InAs/GaAs lasers on Si demonstrate a 3dB bandwidth of 1.6 GHz. By fitting the modulation response curves, we extract high-speed laser parameters allowing an insight into the intrinsic laser dynamics.

© 1983-2012 IEEE. We report the first demonstration of gain-switched optical pulses generated by continuous-wave 1.3 μm InAs/GaAs quantum dot (QD) broad-area lasers directly grown on silicon. The shortest observed pulses have typical durations between 175 and 200 ps with peak output powers of up to 66 mW. By varying the drive current pulsewidth and amplitude systematically, we find that the peak optical power is maximized through sufficiently long high-amplitude drive pulses, whereas shorter drive pulses with high amplitudes yield the narrowest achievable pulses. A three-level rate equation travelling-wave model is used for the simulation of our results in order to gain a first insight into the underlying physics and the laser parameters responsible for the observed behavior. The simulations indicate that a limited gain from the InAs QDs and a very high gain compression factor are the main factors contributing to the increased pulsewidth. As the optical spectra of the tested broad-area QD laser give a clear evidence of multitransverse-mode operation, the laser's dynamic response could be additionally limited by transversal variations of the gain, carrier density, and photon density over the 50 μm wide laser waveguide.

The spectral characteristics of a laser with an active region based on a ten-layer system of In(Ga)As/GaAs vertically correlated quantum dots with 4.5-nm GaAs spacer layers between InAs quantum dots are studied under the conditions of spontaneous and stimulated emission, depending on the current and the duration of pump pulses. Data obtained by transmission electron microscopy and electroluminescence and absorption polarization anisotropy measurements make it possible to demonstrate that the investigated system of tunnel-coupled InAs quantum dots separated by thin GaAs barriers represents a quantum-dot superlattice. With an increase in the laser pump current, the electroluminescence intensity increases linearly and the spectral position of the electroluminescence maximum shifts to higher energies, which is caused by the dependence of the miniband density-of-states distribution on the pump current. Upon exceeding the threshold current, multimode lasing via the miniband ground state is observed. One of the lasing modes can be attributed to the zero-phonon line, and the other is determined by the longitudinal-optical phonon replica of quantum-dot emission. The results obtained give evidence that, under conditions of the laser pumping of an In(Ga)As/GaAs quantum-dot superlattice, strong coupling between the discrete electron states in the miniband and optical phonons takes place. This leads to the formation of quantum-dot polarons, resulting from the resonant mixing of electronic states whose energy separation is comparable to the optical-phonon energy.

© 2016 Kvantovaya Elektronika and Turpion Ltd. The emission of anomalously bright blue light under internal doubling of the frequency of femtosecond superradiance pulses in the active medium of semiconductor GaAs/AlGaAs laser heterostructures has been experimentally found. The efficiency of the internal second-harmonic generation is an order of magnitude higher than in the conventional lasing regime. This effect is due to the formation of a transient ordered state of electrons and holes under superradiance, occurrence of dynamic coherent population lattices, and periodic modulation of the nonlinear susceptibility of the medium.

Single-spatial-mode semiconductor vertical-cavity surface-emitting lasers (VCSELs) with a non-planar upper (output) dielectric distributed Bragg reflector (DBR) for the 850 nm spectral region are fabricated. The suggested design provides stable single-mode generation in the entire range of working currents, limited by overheating of the active region. Devices with intracavity contacts and a comparatively large current-aperture diameter (5–6 μm) exhibit single-mode lasing at a wavelength of 840–845 nm in the continuous-wave mode at room temperature with threshold currents of 1.2–1.3 mA, a differential efficiency of 0.5–0.55 mW mA−1, and anoutput power of up to 2 mW.

The coherence properties of a transient electron – hole state developing during superradiance emission in semiconductor laser structures have been studied experimentally using a Michelson interferometer and Young's classic double-slit configuration. The results demonstrate that, in the lasers studied, the first-order correlation function, which quantifies spatial coherence, approaches unity for superradiant emission and is 0.2 – 0.5 for laser emission. The supercoherence is due to long-range ordering upon the superradiant phase transition.

Vertical-external-cavity surface-emitting lasers (VECSEL), or semiconductor disk lasers (SDL), are attractive laser source for a wide range of applications owing to unique possibility to combine high output power with an excellent beam quality [1]. The intrinsic features of InAs quantum dots (QD) can offer low threshold, broad wavelength tunability, fast carrier dynamics and low temperature sensitivity. Recently, continuous wave (CW) operation of QD-based VECSEL emitting at 1.25 μm with output powers reaching multi-watt levels were achieved at room temperature [2]. However, extending the emission wavelength to 1.3 μm and beyond becomes more challenging. To date, QD-based VECSEL with optical power greater than 0.5 mW at 1305 nm has been demonstrated [3]. Here, we present a record-high power InAs/InGaAs QD-based VECSEL operating at the wavelength of 1.3 μm.

Basic technology for the fabrication of submicron surface reliefs in epitaxial GaAs structures with thin AlGaAs stop layers has been developed using electron-beam lithography. High sensitivity of the characteristics of vertical-cavity surface-emitting lasers (VCSELs) with respect to the level of optical losses allows this technology to be used for controlling the mode composition and stabilizing the polarization of VCSEL radiation.

We develop an analytical theory of high-power passively mode-locked lasers with a slow absorber; the theory is valid at pulse energies well exceeding the saturation energy. We analyze the Haus modelocking master equation in the pulse-energy-domain representation, approximating the intensity profile function by a series in the vicinity of its peak value. We consider the high-power operation regime of subpicosecond blue–violet GaN mode-locked diode lasers, using the approach developed.

Terahertz and near-infrared photoluminescence under conditions of interband stimulated emission are studied in n-GaAs/AlGaAs quantum well laser structure. The observed terahertz emission is related to the optical transitions of nonequilibrium electrons from the first electron subband and excited donor states to donor ground states in quantum wells. The opportunity to increase the intensity of impurity-assisted terahertz emission due to interband stimulated emission with the participation of impurity centres is demonstrated.

Parameters of external-cavity semiconductor lasers, when the stationary lasing becomes unstable, were analysed within the framework of a theoretical model of self-starting mode locking. In this case, a train of ultrashort pulses can be generated due to intrinsic nonlinearities of the laser medium. A decisive role of the transverse optical field nonuniformity, pump rate, and gain spectral bandwidth in the development of the instability of stationary lasing was demonstrated.

The laser-diode parameters at which the steady-state regime of generation becomes unstable are analyzed within the framework of the mode-locking model. The crucial role of the transverse inhomogeneity of the field, pumping intensity, and spectrum width in developing the instabilities of the steady-state regime of generation is demonstrated. The calculated values of the instability threshold are shown to be consistent with the experimental results.

The optical properties of heterostructures comprising InAs/InGaAsN quantum wells in strain-compensated GaAsN/InGaAsN superlattices have been studied. It is demonstrated that, using such superlattices of various design and thickness and with additional InAs monolayer spacers, it is possible to control the wavelength of room-temperature emission from InGaAsN quantum wells within 1.3–1.6 μm without deteriorating the output radiation characteristics, which opens additional prospects for the development of lasers on GaAs substrates for telecommunication applications.

A theoretical model of the optical gain in asymmetric GaAs/AlGaAs quantum-well lasers is developed. It is demonstrated that the emission spectrum of asymmetric GaAs/AlGaAs quantum-well lasers is much broader than that of standard quantum-well lasers. The experimental samples of such lasers and superluminescent diodes with the emission bandwidth exceeding 50 nm are fabricated. Wavelength tunable ultrashort pulses with duration of 1?2 ps at repetition rates of 0.4?1 GHz are obtained by active mode locking of an external cavity laser.

Under study are temperature dependences of laser characteristics of a GaAs/(AlGa)xOy microdisk of 6 μm in diameter, fabricated using optical lithography, ion milling with a beam of Ar+ ions, and selective oxidation of the Al0.97Ga0.03As layer which forms the microdisk base. In As/InGaAs QDs are used as the microdisk active region. Room-temperature lasing in the 1.3-μm range is observed, with the threshold optical pumping power of 160 μW. The quality factor of microdisk modes is about 104.

1.5 µm-range laser diodes based on InAs/InGaAs quantum dots (QDs) grown on metamorphic (In, Ga, Al)As layers, which were previously deposited on GaAs substrates using a defect reduction technique (DRT), are studied. More than 7 W total output power operation in the pulsed mode is shown in broad area lasers. It is shown that the narrow stripe lasers operate in the continuous wave (CW) and the single transverse mode at current densities up to 22 kA cm−2 without significant degradation. CW output power in excess of 220 mW at 10 °C heat sink temperature is demonstrated. 800 mW single-mode output power in the pulsed regime is obtained. It is also shown that the lasers demonstrate the absence of beam filamentation up to the highest current densities studied. First studies on the dynamics of the lasers show a modulation bandwidth of ~3 GHz, limited by device heating. Eye diagrams at 2.5 Gbit s−1 and room temperature (RT) have been performed. Aging tests demonstrate >800 h of CW operation at ~50 mW at 10 °C heat sink temperature and >200 h at 20 °C heat sink temperature without decrease in optical output power. The results indicate the high potential of metamorphic growth using the DRT for practical applications, such as 1500 nm GaAs vertical cavity surface emitting lasers (VCSELs).

Metamorphic InAs–InGaAs quantum dot (QD) lasers grown on GaAs substrates by molecular beam epitaxy have been studied. The lasing wavelength of about 1.5 µm and the threshold current density of 1650 A cm−2 for a 2 mm cavity laser diode have been observed. The characteristic temperature of 66 K has been shown in the temperature range from 30 to 80 °C. The analysis of spontaneous emission efficiency corroborates the high contribution of non-radiative recombination in the total recombination current, even at high current densities. The possibility of achieving modal gain as high as 190 cm−1 has been demonstrated.

Light-current, spectral, and temperature characteristics of long-wavelength (1.46–1.5 µm) lasers grown on GaAs substrates, with an active area based on InAs-InGaAs quantum dots, are studied. To reach the required lasing wavelength, quantum dots were grown on top of a metamorphic InGaAs buffer layer with an In content of about 20%. The maximum output power in pulsed mode was 7 W at room temperature. The differential efficiency of the laser, which had a 1.5-mm-long cavity, was 50%. The temperature dependence of the threshold current is described by a characteristic temperature of 61 K in the temperature range 10–73°C.

In the present work we report on the optimization of MBE growth conditions and design of metamorphic In(Al)(Ga)As/GaAs heterostructures. This results in a strong decrease in the density of threading dislocations in the upper (active) layers and the improvement of surface morphology. Room-temperature mobility in metamorphic modulation-doped InGaAs/InAlAs heterostructures was 8100?cm2?V?1?s?1, which is comparable to that of InP-based structures and noticeably superior to pseudomorphic GaAs-based structures. InAs quantum dots formed in a metamorphic InGaAs matrix on a GaAs substrate were used for lasers with promising characteristics (emitting wavelengths of 1.46??m, with threshold current densities of 1.4?kA?cm?2).

The temperature behavior of the operation characteristics of low-threshold (the threshold current density is below 100 A/cm2) high-efficiency (differential quantum efficiency is as high as 88%) injection laser heterostructures is studied. The active region of structures emitting in the range from 1.25 to 1.29 µm included two, five, and ten layers of InAs-GaAs quantum dots. It is shown that both the threshold current density and the external differential quantum efficiency become N-shaped functions of temperature as the distribution of carriers in the active region changes from nonequilibrium to equilibrium one.

Design and technology problems in the fabrication of vertical-cavity surface-emitting lasers (VCSELs) equipped with nonconducting distributed Bragg reflectors (DBRs) and fabricated using molecular-beam epitaxy are considered. VCSELs with an active region were formed on the basis of InGaAs quantum wells and incorporated an AlGaAs/GaAs bottom DBR and an oxidized AlGaO/GaAs top DBR; the diameter of the oxidized aperture was equal to 7-12 µm. The devices exhibit a continuous-wave lasing at room temperature with threshold currents of 0.5-1.5 mA, a differential efficiency as high as 0.5 mW/mA, and a highest output power of 3 mW.

A new method for the epitaxial formation of 1.3-µm injection lasers on GaAs substrates is reported. A metamorphic heterostructure with an In content of about 20% is deposited onto an intermediate buffer layer intended for mismatch strain relaxation. The laser active region is formed by quantum wells with a higher In content (about 40%). Lasers with 100-µm-wide stripes demonstrate room-temperature lasing at 1.29 µm with a minimum threshold current density of 3.3 kA cm2 (0.4 kA cm2 at T=85 K).

Near-1.3-μm lasers based on multiple layers (2, 5 and 10) of InAs/InGaAs/GaAs quantum dots with high performance have been grown by molecular beam epitaxy. A record differential efficiency as high as 88% was achieved in laser based on 10 QD layers. Threshold current density of 100–150 A/cm2 and differential efficiency of 75–80% were achieved simultaneously in the same device. Characteristic temperature of 150 K in 20–50°C temperature range was demonstrated for the laser based on 5 QD layers. A steep increase in internal loss with decreasing cavity length was found to limit the highest mirror loss possible for ground state lasing.

Two designs of vertical-cavity surface-emitting lasers (VCSELs) for the 1.3 µm spectral range on GaAs substrates with active regions based on InAs/InGaAs quantum dots and InGaAsN quantum wells are considered. The relationship between the active region properties and optical microcavity parameters required for lasing has been investigated. A comparative analysis is made of VCSELs with active regions based on InAs/InGaAs quantum dots or on InGaAsN quantum wells, which are fabricated by MBE and demonstrate room-temperature CW operation. Optimization of the vertical microcavity design provides single-pass internal optical losses lower than 0.05%.

The propagation losses in the fundamental mode of a bicone made of highly reflecting metal or a dielectric of large refraction were approximately estimated using Leontovich's boundary condition. A 400-fold concentration of the energy flux density has been obtained in a cross section which is much smaller than λ. Here, the losses are 2.5% at λ=550 nm in an Ag bicone and 12% in a semiconductor bicone with a band gap of ≈1 eV forhv larger than the band gap. The excitation efficiency of a bicone has been estimated. While not too large, it can be increased significantly using the method proposed in the present paper. The application of the optical bicone for the multiplication of a semiconductor-laser frequency is discussed. The results obtained are also of use in scanning near-field optical microscopy and in experiments on focusing laser pulses of ultrahigh power.

A theoretical model of superradiant pulse generation in semiconductor laser structures is developed. It is shown that a high optical gain of the medium can overcome phase relaxation and results in a built-up superradiant state (macroscopic dipole) in an assembly of electron-hole pairs on a time scale much longer than the characteristic polarisation relaxation time T{sub 2}. A criterion of the superradiance generation is the condition {alpha}c{sub m}T{sub 2}>1, where {alpha} is the gain coefficient and c{sub m} is the speed of light in the medium. The theoretical model describes both qualitatively and quantitatively the author's own experimental results. (physical basis of quantum electronics)

An analysis is made of the conditions for the generation of superfluorescence pulses in an inverted medium of electron—hole pairs in a semiconductor. It is shown that strong optical amplification in laser semiconductor amplifiers characterised by αL 1 (α is the small-signal gain and L is the amplifier length) leads to suppression of phase relaxation of the medium during the initial stages of evolution of superfluorescence and to formation of a macroscopic dipole from electron—hole pairs. Cooperative emission of radiation in this system results in generation of a powerful ultrashort pulse of the optical gain, which interacts coherently with the semiconductor medium. It is shown that coherent pulsations of the optical field, observed earlier by the author in Q-switched semiconductor lasers, are the result of superfluorescence and of the coherent interaction between the optical field and the medium.

We report 4ps and 8ps pulse generation from a two-section monolithic InGaN/GaN laser by hybrid and passive mode-locking, respectively. Pulse trains at a repetition rate of 28.6GHz and an emission wavelength of 422nm are generated.

We have studied the effect of high-temperature annealing on the properties of a laser heterostructure with InAs quantum dots in AlAs/GaAs superlattice. By increasing the time of annealing at 700°C, it is possible to provide for a smooth variation of the lasing wavelength from 1290 to 916 nm at a constant threshold current density (250 A/cm2 at T0=110 K). By annealing the structure at 750°C, the lasing wavelength can be reduced to 845 nm.

Single-mode lasers operating in the 1.3 μ m wavelength range have been obtained with the active region based on InAs/AlGaAs/GaAs quantum dot heterostructures. A minimum threshold current of about 1.4 mA is reached, which is a record value for ridge waveguide lasers. The maximum efficiency and maximum output power in the cw lasing mode are 0.73 W/A and 120 mW, respectively.

The possible mechanisms of the polarization control in single-mode intracavity- contacted vertical-cavity surface-emitting lasers (IC-VCSELs) with the rhomboidal selectively- oxidized current aperture were investigated. It was found that the lasing emission polarization of all single-mode VCSELs is fixed along the minor diagonal of the rhomboidal-shape aperture (the [110] direction). Numerical modelling of carrier transport did not reveal any sufficient injection anisotropy in the laser active region, while the transverse optical confinement factors calculated for the fundamental mode with two orthogonal polarizations are identical. Optical loss anisotropy and/or gain anisotropy are the most likely mechanisms of inducing the polarization fixation.

Dicke superradiance from a two-section violet GaN/InGaN semiconductor laser diode is demonstrated for the first time. In the superradiance regime, optical pulses with peak powers in excess of 2.8 W and durations as short as 1.4 ps are generated at repetition rates of up to 10 MHz at the emission wavelength of 408 nm. The properties of superradiant pulse generation from these GaN/InGaN laser diodes are very similar to those reported for infrared AlGaAs/GaAs laser diodes.

A novel explanation of observed enhanced longitudinal mode spacing in InGaN semiconductor lasers has been proposed. It has been demonstrated that e-h plasma oscillations, which can exist in the laser active layer at certain driving conditions, are responsible for mode clustering effect. The resonant excitation of the plasma oscillations occurs due to longitudinal mode beating. The separation of mode clusters is typically by an order of magnitude larger that the individual mode spacing., 3 pages, 2 figures