The mode of generation of picosecond optical pulses in the spectral range near 1064 nm by semiconductor lasers with distributed feedback and active region based on an InGaAs/GaAs quantum well has been studied. In the gain-modulation mode, the width of laser pulses decreases from 150 to 35 ps as the temperature increases from 5 to 50°C. It was demonstrated that there is a temperature range in which the pulse width is at a minimum, 35 ps, at a full spectrum width at half-maximum of 70 pm. The laser was mounted in a hermetically sealed butterfly case, which enabled a temperature tuning of the wavelength within 3 nm in the generation mode of pulses with width less than 45 ps. The peak output power was 0.4 W at the outlet of a single-mode fiber, with the polarization preserved.

Picosecond optical pulses generation by 1064nm InGaAs/GaAs quantum well distributed feedback lasers was investigated. In the gain-switching regime the duration of laser pulses decreased from 150 to 35 ps with temperature increase from 5 to 50 degrees. The minimal pulses duration 35 ps and spectral width 70 pm was achieved in the optimal temperature range. The laser was placed in sealed butterfly package, which made it possible to obtain wavelength temperature tuning of 3 nm where the pulses duration was less than 45 ps. The output peak power was 0.4 W from single-mode polarization maintaining fiber.

Numerical modelling of electron wavefunctions in a one-dimensional superlattice was conducted. The obtained series of wavefunctions were used to calculate matrix elements of dipole transitions and light emission probabilities. The transitions between distant Stark states were shown to be of high probability together with conventional transitions between neighbor states dubbed Bloch oscillations. Distant transitions have emission probabilities with the same dependence on the applied field and somewhat smaller probabilities.

We study Tamm plasmon structure based on GaAs/Al0.95GaAs distributed Bragg reflector covered by thin silver layer, with active area formed by InAs quantum dots. We have measured the spectral and angular characteristics of photoluminescence and performed theoretical calculation of the spontaneous emission rate (modal Purcell factor) in the structure by using S-quantization formalism. We show that for Tamm plasmon mode the spontaneous emission can be enhanced by more than an order of magnitude, despite absorption in metallic layer.

It was theoretically and experimentally demonstrated that in metal/semiconductor Tamm plasmon structures the probability of spontaneous emission can be increased despite losses in metal, and theoretical analysis of experimental results suggested that the enhancement could be as high as one order of magnitude. Tamm plasmon structure with quantum dots has been fabricated and the emission pattern has been measured. Electromagnetic modes of the structure have been analyzed and modification of spontaneous emission rates has been calculated showing a good agreement with experimentally observed emission pattern.

Получение ультракоротких мощных оптических импульсов

Fiber-coupled semiconductor lasers are studied under pumping with high-power short current pulses. Appropriate parameters of the current pumping make it possible to substantially reduce the output pulse duration to 80 ps for a single-mode laser and 120 ps for a wide-stripe multimode laser at a pump pulse duration of 1 ns and to 40 ps for the single-mode laser at a pump pulse duration of 0.5 ns.

Исследованы полупроводниковые лазеры с выводом излучения через оптическое волокно при их накачке мощными короткими импульсами тока с длительностью 5 ns и передним фронтом импульса меньше 1 ns. Показано, что при такой накачке удается получить существенное обострение оптического выходного импульса: менее 80 ps для одномодового лазера и 120 ps для широкополоскового многомодового лазера с высокой выходной пиковой оптической мощностью: 1.5 W для одномодового и 27 W для многомодового соответственно.

A turn on of a quantum dot (QD) semiconductor laser simultaneously operating at the ground state (GS) and excited state (ES) is investigated both experimentally and theoretically. We find experimentally that the slow passage through the two successive laser thresholds may lead to significant delays in the GS and ES turn ons. The difference between the turn-on times is measured as a function of the pump rate of change ɛ and reveals no clear power law. This has motivated a detailed analysis of rate equations appropriate for two-state lasing QD lasers. We find that the effective time of the GS turn on follows an ɛ^{-1/2} power law provided that the rate of change is not too small. The effective time of the ES transition follows an ɛ^{-1} power law, but its first order correction in ln(ɛ) is numerically significant. The two turn ons result from different physical mechanisms. The delay of the GS transition strongly depends on the slow growth of the dot population, whereas the ES transition only depends on the time needed to leave a repellent steady state.

Fiber-coupled semiconductor lasers have been studied when pumped by high-power short electrical pulses of 5 ns width and leading front duration below 1 ns. In this pumping regime, it is possible to ensure significant sharpening of output pulses, the duration of which decreases below 80 ps for a single-mode laser and below 120 ps for a broad aperture multimode laser at an output peak optical power as high as 1.5 and 27 W, respectively.

We study InGaAs QD laser operating simultaneously at ground (GS) and excited (ES) states under 30ns pulsed-pumping and distinguish three regimes of operation depending on the pump current and the carrier relaxation pathways. An increased current leads to an increase in ES intensity and to a decrease in GS intensity (or saturation) for low pump range, as typical for the cascade-like pathway. Both the GS and ES intensities are steadily increased for high current ranges, which prove the dominance of the direct capture pathway. The relaxation oscillations are not pronounced for these ranges. For the mediate currents, the interplay between the both pathways leads to the damped large amplitude relaxation oscillations with significant deviation of the relaxation oscillation frequency from the initial value during the pulse.

We examine the response of a pulse pumped quantum dot laser both experimentally and numerically. As the maximum of the pump pulse comes closer to the excited-state threshold, the output pulse shape becomes unstable and leads to dropouts. We conjecture that these instabilities result from an increase of the linewidth enhancement factor α as the pump parameter comes close to the excitated state threshold. In order to analyze the dynamical mechanism of the dropout, we consider two cases for which the laser exhibits either a jump to a different single mode or a jump to fast intensity oscillations. The origin of these two instabilities is clarified by a combined analytical and numerical bifurcation diagram of the steady state intensity modes.

Turn-on experiments are important for the characterization of the laser dynamical response. We study the turn-on of a quantum dot (QD) laser when lasing occurs at both ground (GS) and excited (ES) states. Depending on the amplitude of the current pulse, the laser may either turn-on simultaneously at both states or with a significant nanosecond-scale delay between GS and ES outputs. We address this effect to the slow passage through the GS and ES bifurcation transitions as the pump current increases. Scaling laws are determined experimentally and analytically from rate equations for either small or large pump currents.

Semiconductor quantum dot lasers are attractive for multiple technological applications in biophotonics. Simultaneous two-state lasing of ground state (GS) and excited state (ES) electrons and holes in QD lasers is possible under a certain parameter range. It has already been investigated in steady-state operations and in dynamical regimes and is currently a subject of the intensive research.

The focusing of multimode laser diode beams is probably the most significant problem that hinders the expansion of the high-power semiconductor lasers in many spatially-demanding applications. Generally, the 'quality' of laser beams is characterized by so-called 'beam propagation parameter' M-2, which is defined as the ratio of the divergence of the laser beam to that of a diffraction-limited counterpart. Therefore, M-2 determines the ratio of the beam focal-spot size to that of the 'ideal' Gaussian beam focused by the same optical system. Typically, M-2 takes the value of 20-50 for high-power broad-stripe laser diodes thus making the focal-spot 1-2 orders of magnitude larger than the diffraction limit. The idea of 'superfocusing' for high-M-2 beams relies on a technique developed for the generation of Bessel beams from laser diodes using a cone-shaped lens (axicon). With traditional focusing of multimode radiation, different curvatures of the wave-fronts of the various constituent modes lead to a shift of their focal points along the optical axis that in turn implies larger focal-spot sizes with correspondingly increased values of M-2. In contrast, the generation of a Bessel-type beam with an axicon relies on 'self-interference' of each mode thus eliminating the underlying reason for an increase in the focal-spot size. For an experimental demonstration of the proposed technique, we used a fiber-coupled laser diode with M2 below 20 and an emission wavelength in similar to 1 mu m range. Utilization of the axicons with apex angle of 140deg, made by direct laser writing on a fiber tip, enabled the demonstration of an order of magnitude decrease of the focal-spot size compared to that achievable using an 'ideal' lens of unity numerical aperture.

Turn-on delay of laser diodes with quantum-sized active media is investigated both theoretically and experimentally. In this research we show the striking difference in turn-on delay of quantum dot and quantum well laser diodes: With quantum-well lasers turn on delay tends to zero in the limit of high pumping, while with quantum dot lasers turn-on delay has the non-vanishing component which is independent of pumping.

A turn-on of a quantum dot semiconductor laser is analyzed in detail both theoretically and experimentally. We show that quantum dot lasers have a nonlinear damping rate which strongly affects laser turn-on dynamics due to the non-instantaneous capture of carriers to a dot. It results in nonvanishing turn-on delay even at very high pumping in good agreement with experiment.