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A simple model is presented for carrier heating in semiconductor lasers from which the temperature dynamics of the electron and hole distributions can be calculated. Analytical expressions for two new contributions to the nonlinear gain coefficient, in are derived, which reflect carrier heating due to stimulated emission and free carrier absorption. In typical cases, carrier heating and spectral holeburning are found to give comparable contributions to nonlinear gain suppression. The results are in good agreement with recent measurements on InGaAsP laser diodes. >

We estimate homogeneous broadening and shift of optical transition lines in self-assembled quantum dots (SAQD) caused by elastic Coulomb collisions of carriers in wetting layer with carriers in the SAQD. In particular, we demonstrate that the dephasing time for lasing transitions can be similar to 0.1-1 ps at carrier densities in wetting layer similar to 10(15) m(-2). (C) 1999 American Institute of Physics. (DOI: 10.1063/1.124068)

We present theoretical study of fast and slow light in a chirp-compensate semiconductor optical amplifier scheme. We obtain excellent match with experimental results. Using this model, we predict that a delay-bandwidth product of 33 can be attained with properly chosen parameters.

Theoretically predicted "dipole lasing" as spontaneous excitation of coherent oscillations of dipole momentum of metal nano-particles placed inside or near the surface of the medium with optical amplification. It has close analogy with ordinary lasing, but the polarization of nano-particles stands for the optical cavity mode. Oscillations of polarization cause coherent radiation from nano-particles acting as "nano-antennas". Optical cavity is not necessary, so that the minimum size of the dipole laser can be on the nano-scale. Dipole laser frequency corresponds to the localized plasmon resonance of nano-particles. The manifestation of the dipole lasing is in the divergence of the nano-particle polarisability, that is a second-order phase transition. Threshold conditions, enhancement of the spontaneous emission and optical bistability is dipole lasers are found.

We present excellent agreement of theoretical simulation and experimental results of THz fast and slow light using a novel chirped-pulse technique. A large timeshift of 8.7 pulses is demonstrated with minimum broadening and distortion.

We introduce a new type of electroplasmonic interfacing component to electrically generate surface plasmons. Specifically, an electron-fed optical tunneling gap antenna is integrated on a plasmonic waveguiding platform. When electrical charges are injected in the tunneling barrier of the gap antenna, a broad-band radiation is emitted from the feed area by a process identified as a thermal emission of hot electrons. Part of the emitted photons couples to surface plasmon modes sustained by the waveguide geometry. The transducing optical antenna is thus acting as a localized electrical source of surface plasmon polaritons. The integration of electrically-activated optical antennas into a plasmonic architecture mitigates the need for complex coupling scheme and proposes a solution for realizing nanoscale units at the interface between nano-electronics and photonics.

Polarization dependence of fast light in semiconductor optical amplifiers is studied. For a 630 fs pulse propagating through the SOA, an advance of 2.7 pulses is achieved for TE polarisation while TM polarisation gives an advance of 2.3 pulses.

We demonstrate fast light advance of 2.7 pulse widths for sub-picosecond pulses in a single semiconductor optical amplifier. Two such pulses, separated by 7 ps, can also be advanced more than 1.8 pulse widths each.

Electrically tunable delays and advances for 600fs pulses are achieved using ultra-fast nonlinearities in SOAs. Feasibility of cascading multiple SOAs to achieve higher delays is confirmed using a novel scheme that uses a single SOA. (Slow and Fast Light, 2007) Article not available.

The change in group index in a semiconductor optical amplifier due to carrier heating and spectral hole burning dominates in short pulse shaping, resulting in fast/slow light.

Electrically tunable delays and advances for 600fs pulses are achieved using ultra-fast nonlinearities in SOAs. Feasibility of cascading multiple SOAs to achieve higher delays is confirmed using a novel scheme that uses a single SOA.

We analyze a self-assembled quantum-dot laser where lasing levels are pumped purely through Auger carrier capture. Analysis shows that Auger carrier capture and Auger transport of carriers between quantum dots can provide effective laser pumping and fast modulation at least up to 10 GHz. Auger carrier transport decreases spectral hole burning, which together with dot-barrier hole burning can damp relaxation oscillations.

We establish rate equations to describe Auger carrier capture kinetics in quantum dot structures, calculate Auger capture coefficients for self-assembled quantum dots, and analyze Auger capture kinetics using these equations. We show that Auger capture times can be of the order of 1–100 ps depending on barrier carrier and dot densities. Auger capture rates depend strongly on dot diameters and are greatest at dot diameters of about 10–20 nm.

Ultrafast carrier dynamics is examined in a quantum-dot (QD) semiconductor optical amplifier with a rate equation model which includes two-photon absorption (TPA) and gain bleaching during the propagation of 120 fs optical pulses at the wavelength near telecommunication wavebands. The TPA-generated carriers in the bulk region of the waveguide relax to the QDs via the wetting layer, which occurs synchronously in time and space with QD carrier depletion. This leads to efficient enhancement of the rate of carrier capture into the QDs, reducing the pattern effects for ultra high-speed optical signal processing.

This study discusses the phase-amplitude coupling of semiconductor quantum dot lasers. A plot of the phase/amplitude modulation index ratio as a function of frequency is presented. In particular, the ratio of the phase and intensity modulation indices do not necessarily converge at high frequency due to the carrier capture dynamics.

We perform simple link analysis simulations to assess the performance of an SOA generating slow and fast light via four wave mixing. Power penalty is calculated for various alpha parameter values and bit rates.

We investigate ultrafast gain-dynamics in a quantum-dot (QD) semiconductor optical amplifier where two-photon absorption (TPA) occurs in the bulk region of the waveguide during propagation of a sub-picosecond optical pulse, and gain bleaching occurs in the QD active region. Our calculation reveals that TPA provides optical pumping which is quasi-synchronous in time and space with QD carrier depletion, leading to enhancement of carrier capture into the QDs on an ultrafast timescale. The TPA-induced optical pumping, which is qualitatively different from electrical pumping, changes qualitatively carrier recovery dynamics, reducing pattern effects when a train of optical pulses is injected at the ultra-high speed.

Both optically and electrically controllable slow and superluminal light are demonstrated via four-wave mixing in semiconductor optical amplifiers. Tunable delays up to 1.2 ns are achieved for 0.5 GHz, corresponding to a RF phase change of 1.2 p.

Ultrafast intraband carrier dynamics strongly influence many important characteristics in bulk and quantum well lasers and amplifiers through Spectral-Hole Burning (SHB) leading to nonlinear gain effects. In Quantum Dot (QD) devices, where the inter-level relaxation times can be even longer than the intraband relaxation times in conventional devices, SHB effects should also be substantial. A number of promising applications of QD amplifiers in high-speed optical processing (Cross-Gain Modulation, for instance) are based on features of the carrier dynamics in QD structures. In the present paper, based on a density matrix approach, we develop a theory of SHB-based nonlinear gain in QD lasers and amplifiers, which can affect such important characteristics as the modulation bandwidth in QD lasers and the saturation power and pulse energy in QD amplifiers. We give an expression for the nonlinear gain in QD devices, and show how it depends, particularly, on the capture/escape and relaxation/excitation rates.

The line-width enhancement factor and the relative intensity noise spectrum of quantum dot semiconductor lasers were measured. The sensitivity to optical feedback of quantum dot semiconductor lasers was compared to quantum well semiconductor lasers. A reduced sensitivity of 20 dB compared to quantum well semiconductor lasers was observed. Rate equations describing the capture of carriers from the quantum well into the dots was used as basis in providing an explanation for the reduced sensitivity to optical feedback.

We have developed a theory of the nonlinear refractive index in Quantum Dot (QD) Semiconductor Optical Amplifiers (SOAs) due to Spectral Hole Burning (SHB). Estimates show that this SHB nonlinear refractive index can be of order of 4x10 -16 m 2 /W that is by four orders higher than the nonlinear refractive index in silica, and offers the possibility of an efficient ultrafast Cross-Phase-Modulation (XPM) in QD SOAs. The opportunity of XPM without patterning effects via this refractive index nonlinearity is discussed. The Pattern-Effect-Free (PEF) XPM is possible in QD SOAs at high pumps, when maximal (constant) gain is achieved in SOAs, and the linear and nonlinear refractive indices also become independent of the total carrier density in the QD structure. In whole, use of the ultrafast refractive index nonlinearity in the regime of maximum gain in QD SOAs can lead to the development of a new generation of nonlinear interferometers for ultrafast optical switching.

We analyse the sensitivity of quantum dot semiconductor lasers to optical feedback. While bulk and quantum well semiconductor lasers are usually extremely unstable when submitted to back reflection, quantum dot semiconductor lasers exhibit a reduced sensitivity. Using a rate equation approach, we show that this behaviour is the result of a relatively low but nonzero line-width enhancement factor and strongly damped relaxation oscillations.

We have developed a theory of high-speed operation of quantum dot (QD) semiconductor optical amplifiers (SOAs), and showed that pattern-effect-free amplification of pulse trains, cross gain modulation (XGM) and cross phase modulation (XPM) can take place in QD SOA in the regime with maximum gain. Formulas, which relate the maximum bit-rate for the pattern-effect-free operation and the average SOA output power to the SOA pump current density, were derived. XGM without pattern effect can be realized in the regime with maximum gain due to spectral hole burning effects. Possibility of ultrafast frequency conversion and demultiplexing of data pulse streams through this nonlinearity is illustrated. Expression for the nonlinear refractive index η nl due to spectral hole burning in QD structure was obtained. The value of η nl in QD SOAs can be by 4-5 orders larger than η nl in silica; and efficient ultrafast XPM without pattern effects can be carried out in QD SOA through this nonlinearity. In whole, usage of the regime with maximum gain in QD SOAs can lead to development of new generation of high-speed devices for ultrafast optical processing and communications.

We analyse the sensitivity of quantum dot semiconductor lasers to optical. While bulk and quantum well semiconductor lasers are usually extremely unstable when submitted to back reflection, quantum dot semiconductor lasers exhibit a reduced sensitivity. Using a rate equation approach, we show that this behaviour is the result of a relatively low but nonzero line-width enhancement factor and of strongly damped relaxation oscillations.

The carrier-induced refractive index in quantum dot (QD) structures due to optical transitions from QD levels to continuum states is considered. It is shown that, for large photon energies, the refractive index change is given asymptotically by the Drude formula. Calculations of the linewidth enhancement factor, alpha, show that alphasimilar to1 due to this contribution to the total refractive index. Furthermore, for highly localized QD states, the absorption coefficient at the photon energies similar to0.8-1.0 eV due to these transitions can be on the order of 10(3) m(-1). (C) 2004 American Institute of Physics. (DOI: 10.1063/1.1639933)

Summary form only given. Significant progress has been obtained on quantum dot (QD) lasers, but the possible advantages of QD amplifiers are not yet clear. We show here that a relatively slow coupling between the optically active QD carrier states and the surrounding carrier reservoir can lead to efficient gain modulation suitable for ultrafast signal processing. The basis of this property is that the process of spectral hole burning (SHB) can become very effective. We consider a traveling wave optical amplifier consisting of the dot states, which interact with the optical signal (no inhomogeneous broadening included), and the wetting layer (WL), where current is injected. Time evolution is described by two coupled rate equations. Carrier capture from WL to dots is characterized by the capture time /spl tau//sub 0/.

We calculate carrier capture rates into cone- and truncated-cone-shaped quantum dots mediated by Auger processes. It is demonstrated that the capture rates depend strongly on both dot size and shape. The importance of phonon-mediated versus the Auger-mediated capture processes is discussed.

We identify operation conditions under which quantum dot semiconductor optical amplifiers can amplify optical data signals at high bit-rates without significant patterning effects. Simple expressions for the critical bit-rate are derived.

Pump‐probe measurements in GaAs/GaAlAs waveguide saturable absorbers reveal an ultrafast transient in the absorption recovery dynamics, and a second slower signal before the final recovery. We present a model of the differential transmission measurements which includes high field and space charge effects in addition to the spectral hole burning and carrier heating typically found in semiconductor amplifiers. The results of the model indicate that field‐induced carrier heating strongly influences the absorption dynamics in saturable absorbers used for mode‐locked diode lasers.

Highly nondegenerate four‐wave mixing processes in bulk semiconductor optical amplifiers are analyzed by comparing experimental data at detuning frequencies up to 3 THz with numerical calculations based on semiclassical density‐matrix equations. Carrier heating and spectral holeburning are found to be dominant in mediating wave mixing in the THz region and lead to comparable contributions to nonlinear gain suppression in semiconductor lasers.

Summary form only given. The results of a model of differential transmission measurements in GaAs-GaAlAs waveguide saturable absorbers indicate that high field effects, spectral hole burning and carrier heating are important mechanisms governing absorption dynamics.

Highly non-degenerate four-wave mixing processes in semiconductor optical amplifiers are analyzed by comparing experimental data at detuning frequencies up to 3 THz with numerical calculations based on microscopic density matrix equations.

Multiphonon capture processes are investigated theoretically and found to contribute efficiently to the carrier injection into quantum dots. It is shown that two-phonon capture contributes where single-phonon capture is energetically inhibited and can lead to electron capture times of a few picoseconds at room temperature and carrier densities of 10(17) cm(-3) in the barrier.

Mechanisms of pure dephasing in quantum dots due to Coulomb correlations and the dynamics of carrier capture and emission are suggested, and a phenomenological model for the dephasing is developed. It is shown that, if the rates of these capture and emission processes are sufficiently high, significant homogeneous line broadening of the order of several meV can result.

Summary form only given. We investigate capture of carriers from states in the continuous part of the energy spectrum into the discrete states of self-assembled InAs/GaAs QDs via emission of one or two phonons. We are not aware of any other investigations of two-phonon mediated capture processes in QDs, but we show that this may be an efficient capture mechanism. The phonons are assumed to be bulk GaAs LO phonons with zero dispersion. The QD was modelled by a finite confinement potential well in the effective-mass approximation.

The effects of carrier cooling on the saturation characteristics of quantum well absorbers are theoretically investigated. A comprehensive many-body model is employed, and both excitonic effects and bandgap renormalization are shown to play a significant role. The detailed interplay between band-filling and many-body effects at low carrier temperatures is shown to lead to saturation characteristics that are highly spectrally dependent, and that cannot in general be identified by a linear saturation characteristic. In addition, a spectral regime of enhanced fast saturation is identified at or slightly below the exciton peak energy, which may provide a mechanism for previously observed mode-locking behavior.

Interpretation of experiments on quantum dot (QD) lasers presents a challenge: the phonon bottleneck, which should strongly suppress relaxation and dephasing of the discrete energy states, often seems to be inoperative. We suggest and develop a theory for an intrinsic mechanism for dephasing in QD's: second-order elastic interaction between quantum dot charge carriers and LO-phonons. The calculated dephasing times are of the order of 200 fs at room temperature, consistent with experiments. The phonon bottleneck thus does not prevent significant room temperature dephasing., 4 pages, 1 figure, accepted for Phys. Rev. Lett

The dual pump four wave mixing (FWM) in semiconductor optical amplifiers (SOAs) has been proposed as a promising method to achieve high efficiency and signal to background noise ratio (SBR), specially for large wavelength shifts. In the present work experimental study and theoretical modeling of the mixing processes generating the converted signal will be presented. Moreover, the operation of the dual pump converter in a 10 Gb/s experiment will be demonstrated.

Carrier heating in quantum dot (QD) devices, which accompanies Auger capture of carriers from a carrier reservoir to discrete QD levels, is considered for the first time. Equations for carrier dynamics of QD structures are formulated and analyzed by taking into account the carrier heating. A numerical example shows that heating of carriers in a carrier reservoir of a QD structure can be much higher than that of bulk and quantum well devices. Auger capture carrier heating in QD devices can lead to a longer (more than a factor of 2 for the 90%-recovery time) relaxation time from a carrier reservoir to QDs.

Theoretically predicted ''dipole lasing'', i.e., spontaneous excitation of coherent metal nano-particle dipole oscillations through interaction with a quantum-dot two-level system subject to population inversion is demonstrated. Equations for dipole lasing are the same as equations for ordinary laser, where the dipole momentum of nano-particle stands for the electromagnetic field cavity mode. Dipole lasing frequency corresponds to the localized plasmon resonance of the nano-particle. Dipole momentum of nano-particle leads to coherent dipole radiation. Optical cavity is not necessary, the size of the dipole laser can be smaller than the optical wavelength, i.e. it is dipole nano-laser. Threshold conditions and optical bistability in dipole nano-lasers are considered.

Carrier dynamics of a 1.3 mu m InAs/GaAs quantum dot amplifier is studied using heterodyne pump-probe spectroscopy. Measurements of the recovery times versus injection current reveal a power law behavior predicted by a quantum dot rate equation model. These results indicate that Auger processes dominate the carrier dynamics. (c) 2007 American Institute of Physics. (DOI:10.1063/1.2715115)

Ultra fast non-linear processes are used to achieve an advance of 2 ps for a 600 fs pulse propagating through two SOAs in series. This corresponding 3.3-pulse advance is tuned continuously by changing the current applied to the devices. We propose an experimental scheme that uses a single SOA in a loop to emulate the propagation of pulse through multiple cascaded SOAs.

An effective mechanism to achieve slow and superluminal light can be achieved in semiconductor optical amplifiers via wave mixing processes due to nonzero linewidth enhancement factor.

The sensitivity of quantum-dot semiconductor lasers to optical feedback is analyzed with a Lang-Kobayashi approach applied to a standard quantum-dot laser model. The carriers are injected into a quantum well and are captured by, or escape from, the quantum dots through either carrier-carrier or phonon-carrier interaction. Because of Pauli blocking, the capture rate into the dots depends on the carrier occupancy level in the dots. Here we show that different carrier capture dynamics lead to a strong modification of the damping of the relaxation oscillations. Regions of increased damping display reduced sensitivity to optical feedback even for a relatively large alpha factor.

Picosecond pulse propagation through a field-enhanced waveguide bulk semiconductor saturable absorber is studied numerically. Fast switching from unsaturated absorption to delayed strong saturation and gain, as well as the predicted dependence of saturation energy on electric field, is based on intraband carrier kinetics and electric-field dynamics in the absorber and can lead to improved, controllable pulse shaping.

An investigation was made of the visible radiation emitted by planar metal–barrier–metal structures as a result of decay of plasma oscillations. A method was found for increasing the intensity of the output radiation using a barrier in the form of a multilayer insulator consisting of different oxides evaporated consecutively. It was found experimentally that the efficiency of emission by these structures was twice that of structures with a simple barrier. The rise time of an optical response of such metal–barrier–metal structures to a single short voltage pulse was at least 4 nsec. The output radiation intensity increased under the additional action of a microwave field of frequency up to 1.2 GHz. This property could be used for the purpose of fast-response visualization of microwave fields with a sensitivity threshold of ~1 mW/cm2.

Some results are reported on coherent propagation of optical pulses. In particular, a solution is presented of the Maxwell-Bloch equations for the case of amplification of high-power pulses with varying carrier frequency but with constant number of photons in the pulse.

A theoretical investigation is made of the optical properties of quantum-well tunnel semiconductor structures. It is shown that resonant tunneling accompanied by the absorption and emission of electromagnetic radiation quanta makes it possible, in particular, to amplify light in such structures and the gain profile may be tunable by the application of a voltage.