Showing papers on "Semiconductor optical gain published in 2008"
TL;DR: By using strong optical injection locking, resonance frequency enhancement in excess of 100 GHz in semiconductor lasers is reported, showing the broad applicability of the technique and that the coupling Q is the figure-of-merit for Resonance frequency enhancement.
Abstract: By using strong optical injection locking, we report resonance frequency enhancement in excess of 100 GHz in semiconductor lasers. We demonstrate this enhancement in both distributed feedback (DFB) lasers and vertical-cavity surface-emitting lasers (VCSELs), showing the broad applicability of the technique and that the coupling Q is the figure-of-merit for resonance frequency enhancement. We have also identified the key factors that cause low-frequency roll-off in injection-locked lasers. By increasing the slave laser's DC current bias, we have achieved a record intrinsic 3-dB bandwidth of 80 GHz in VCSELs.
185 citations
Patent•
10 Jan 2008
TL;DR: In this paper, a semiconductor optical amplifier (SOA) in a laser ring is chosen to provide low polarization-dependent gain (PDG) and a booster SOA, outside of the ring, is selected to provide high PEG.
Abstract: In one embodiment of the invention, a semiconductor optical amplifier (SOA) in a laser ring is chosen to provide low polarization-dependent gain (PDG) and a booster semiconductor optical amplifier, outside of the ring, is chosen to provide high polarization-dependent gain. The use of a semiconductor optical amplifier with low polarization-dependent gain nearly eliminates variations in the polarization state of the light at the output of the laser, but does not eliminate the intra-sweep variations in the polarization state at the output of the laser, which can degrade the performance of the SS-OCT system.
143 citations
TL;DR: In this paper, it was shown that when an electron relaxes from an excited state, it generates not one but two photons, which has been seen in atomic systems, but never in semiconductors, until now.
Abstract: It is possible that when an electron relaxes from an excited state, it generates not one but two photons. Such two–photon emission has been seen in atomic systems, but never in semiconductors, until now. The experimental observation could have intriguing implications for quantum optics.
140 citations
TL;DR: It is found that operation at high bias currents optimizes the performance for nonlinear cross-gain signal processing if a low chirp is required.
Abstract: Gain and phase dynamics in InAs/GaAs quantum dot semiconductor optical amplifiers are investigated. It is shown that gain recovery is dominated by fast processes, whereas phase recovery is dominated by slow processes. Relative strengths and time constants of the underlying processes are measured. We find that operation at high bias currents optimizes the performance for nonlinear cross-gain signal processing if a low chirp is required.
105 citations
TL;DR: A new semiconductor laser structure with digitally switchable wavelength is proposed, which comprises two coupled cavities with different optical path lengths, which form V-shaped branches with a reflective 2x2 half-wave optical coupler at the closed end to produce synchronous power transfer functions.
Abstract: A new semiconductor laser structure with digitally switchable wavelength is proposed. The device comprises two coupled cavities with different optical path lengths, which form V-shaped branches with a reflective 2x2 half-wave optical coupler at the closed end. The reflective 2x2 coupler is designed to have a pi-phase difference between cross-coupling and self-coupling so as to produce synchronous power transfer functions. High single-mode selectivity is achieved by optimizing the coupling coefficient. The switchable wavelength range is greatly increased by using Vernier effect. Using deep-etched trenches as partial reflectors, additional waveguide branch structures are used outside the laser cavities to form a complete Mach-Zehnder interferometer, allowing space switching, variable attenuation, or high speed modulation to be realized simultaneously. Detailed design principle and numerical results are presented.
97 citations
TL;DR: In this article, the authors present a review of the external cavity tunable laser systems with edge emitting diode (EDD) diode lasers set-up in a hybrid configuration.
Abstract: External cavity tunable lasers have been around for many years and now constitute a large group of semiconductor lasers featuring very unique properties. The present review has been restricted to the systems based on the edge emitting diode lasers set-up in a hybrid configuration. The aim was to make the paper as concise as possible without sacrificing, however, most important details. We start with short description of the fundamentals essential for operation of the external cavity lasers to set the stage for explanation of their properties and some typical designs. Then, semiconductor optical amplifiers used in the external cavity lasers are highlighted more in detail as well as diffraction gratings and other types of wavelength-selective reflectors used to provide optical feedback in these lasers. This is followed by a survey of designs and properties of various external cavity lasers both with mobile bulk gratings and with fixed wavelength selective mirrors. The paper closes with description of some recent developments in the field to show prospects for further progress directed towards miniaturization and integration of the external cavity laser components used so far to set-up hybrid systems.
86 citations
TL;DR: Femtosecond time-resolved pump-probe measurements are employed to investigate the nature of the transport through the laser structure via the dynamics of the gain to find the gain recovery in quantum cascade lasers.
Abstract: Quantum cascade lasers are semiconductor devices based on the interplay of perpendicular transport through the heterostructure and the intracavity lasing field. We employ femtosecond time-resolved pump-probe measurements to investigate the nature of the transport through the laser structure via the dynamics of the gain. The gain recovery is determined by the time-dependent transport of electrons through both the active regions and the superlattice regions connecting them. As the laser approaches and exceeds threshold, the component of the gain recovery due to the nonzero lifetime of the upper lasing state in the active region shows a dramatic reduction due to the onset of quantum stimulated emission; the drift of the electrons is thus driven by the cavity photon density. The gain recovery is qualitatively different from that in conventional lasers due to the superlattice transport in the cascade.
85 citations
TL;DR: Numerical propagation modeling of the optical Stark effect confirms that this mechanism is able to form the pulses that are generated directly by an optical Stark passively mode-locked semiconductor disk laser at a 1 GHz repetition rate.
Abstract: We report on 260 fs transform-limited pulses generated directly by an optical Stark passively mode-locked semiconductor disk laser at a 1 GHz repetition rate. A surface recombination semiconductor saturable absorber mirror and a step-index gain structure are used. Numerical propagation modeling of the optical Stark effect confirms that this mechanism is able to form the pulses that we observe.
74 citations
TL;DR: In this paper, an analytical model for semiconductor lasers with injection (pump) of spin-polarized electrons, allowing them to systematically investigate different operating regimes, is presented. And the maximum threshold reduction by electrically pumped spin-Polarized carriers is larger than previously thought possible and can be enhanced by ultrafast spin relaxation of holes.
Abstract: We formulate an analytical model for semiconductor lasers with injection (pump) of spin-polarized electrons, allowing us to systematically investigate different operating regimes. We demonstrate that the maximum threshold reduction by electrically pumped spin-polarized carriers is larger than previously thought possible and, surprisingly, can be enhanced by ultrafast spin relaxation of holes. We reveal how different modes of carrier recombination directly affect the threshold reduction. Neither spin-up nor spin-down electron populations are separately clamped (pinned) near the threshold, where such lasers can act as effective nonlinear filters of circularly polarized light, owing to their spin-dependent gain.
67 citations
TL;DR: A wafer fused high power optically pumped semiconductor disk laser incorporating InP-based active medium fused to a GaAs/AlGaAs distributed Bragg reflector is reported, revealing the essential advantage of the wafer fusing technique over monolithically-grown all-InP- based structures.
Abstract: We report a wafer fused high-power optically-pumped semiconductor disk laser incorporating InP-based active medium fused to a GaAs/AlGaAs distributed Bragg reflector. A record value of over 2.6 W of output power in a spectral range around 1.57 µm was demonstrated, revealing the essential advantage of the wafer fusing technique over monolithically-grown all-InP-based structures. The presented approach allows for integration of lattice-mismatched compounds, quantum-well and quantum-dot based media. This would provide convenient means for extending the wavelength range of semiconductor disk lasers.
56 citations
TL;DR: In this article, a theoretical analysis of slow and fast light effects in semiconductor optical amplifiers based on coherent population oscillations and including the influence of optical filtering is presented, which is shown to enable a significant increase of the controllable phase shift experienced by an intensity modulated signal traversing the waveguide.
Abstract: A theoretical analysis of slow and fast light effects in semiconductor optical amplifiers based on coherent population oscillations and including the influence of optical filtering is presented. Optical filtering is shown to enable a significant increase of the controllable phase shift experienced by an intensity modulated signal traversing the waveguide. The theoretical model accounts for recent experimental results and is used to analyze and interpret the dependence on material and device parameters. Furthermore analytical approximations are derived using a perturbation approach and are used to gain a better physical understanding of the underlying phenomena.
TL;DR: Transform-limited pulses as short as 290 fs at 1036 nm are generated by a diode-pumped semiconductor disk laser that employs a graded-gap-barrier design in the gain section.
Abstract: Transform-limited pulses as short as 290 fs at 1036 nm are generated by a diode-pumped semiconductor disk laser. The all-semiconductor laser employs a graded-gap-barrier design in the gain section. A fast saturable absorber mirror serves as a passive mode-locker. No further elements for internal or external dispersion control are required.
TL;DR: In this paper, a strain-compensated InGaN quantum well with tensile AlGaN barriers is analyzed as improved gain media for laser diodes emitting at 420-500 nm.
Abstract: Strain-compensated InGaN quantum wells with tensile AlGaN barriers are analyzed as improved gain media for laser diodes emitting at 420–500 nm. The band structure is calculated using the 6-band k ·p formalism, taking into account valence band mixing, strain effect, and spontaneous and piezoelectric polarizations. The optical gain analysis exhibits significant improvement in the peak optical gain and differential gain for the strain-compensated structures. The calculation also shows a significant reduction of threshold carrier density and current density for diode lasers employing the strain-compensated InGaN–AlGaN QW active regions.
TL;DR: Bohringer et al. as mentioned in this paper proposed a full-time-domain approach to spatio-temporal dynamics of semiconductor laser systems, which can reveal the dynamical balance between carrier generation due to pumping into high energy states, momentum relaxation of carriers and stimulated recombination from states near the band edge.
TL;DR: Measurements of saturated amplified spontaneous emission-spectra of quantum dot semiconductor optical amplifiers demonstrate efficient replenishment of the quantum-dot ground state population from excited states and proposes optimization of the SOA operating parameters for high speed applications.
Abstract: Measurements of saturated amplified spontaneous emission-spectra of quantum dot semiconductor optical amplifiers demonstrate efficient replenishment of the quantum-dot ground state population from excited states. This saturation behavior is perfectly modeled by a rate equation model. We examined experimentally the dependence of saturation on the drive current and the saturating optical pump power as well as on the pump wavelength. A coherent noise spectral hole is observed with which we assess dynamical properties and propose optimization of the SOA operating parameters for high speed applications.
TL;DR: This work investigates both theoretically and experimentally the stochastic switching between two counterpropagating lasing modes of a semiconductor ring laser and proposes a topological approach based on a two-dimensional dynamical system.
Abstract: We investigate both theoretically and experimentally the stochastic switching between two counterpropagating lasing modes of a semiconductor ring laser. Experimentally, the residence time distribution cannot be described by a simple one-parameter Arrhenius exponential law and reveals the presence of two different mode-hop scenarios with distinct time scales. In order to elucidate the origin of these two time scales, we propose a topological approach based on a two-dimensional dynamical system.
TL;DR: In this article, a transverse-magnetic (TM)-mode dominated gain at the 1.5μm wavelength in semiconductor optical amplifiers with columnar quantum dots (QDs) was demonstrated.
Abstract: We demonstrated transverse-magnetic (TM)-mode dominated gain at the 1.5μm wavelength in semiconductor optical amplifiers (SOAs) with columnar quantum dots (QDs). We show that we can control the polarization dependence of optical gain in QD-SOAs by changing the height and tensile-strained barrier of columnar QDs. The TM mode gain is 17.3dB and a gain of over 10dB was attained over a wide wavelength range of 200nm. The saturation output power is 19.5dBm at 1.55μm.
TL;DR: These picosecond optical-pulse sources suitable for multiphoton microscopy based on mode-locked semiconductor lasers were employed successfully for nonlinear-optic bio-imaging using two-photon fluorescence, second-harmonic generation, and sum-frequency generation of synchronized two-color pulses.
Abstract: We developed picosecond optical-pulse sources suitable for multiphoton microscopy based on mode-locked semiconductor lasers. Using external-cavity geometry, stable hybrid mode locking was achieved at a repetition rate of 500 MHz. Semiconductor optical amplifiers driven by synchronized electric pulses reached subharmonic optical-pulse repetition rates of 1-100 MHz. Two-stage Yb-doped fiber amplifiers produced optical pulses of 2 ps duration, with a peak power of a few kilowatts at a repetition rate of 10 MHz. These were employed successfully for nonlinear-optic bio-imaging using two-photon fluorescence, second-harmonic generation, and sum-frequency generation of synchronized two-color pulses.
TL;DR: In this paper, the authors demonstrate temperature-independent output characteristics of an optically pumped semiconductor disk laser (SDL) based on quantum dots (QDs) grown in the Stranski-Krastanow regime.
Abstract: We demonstrate temperature-independent output characteristics of an optically pumped semiconductor disk laser (SDL) based on quantum dots (QDs) grown in the Stranski-Krastanow regime. The gain structure consists of a stack of 7×3 QD layers, each threefold group being located at an optical antinode position. The SDL emits at 1210nm independent of the pump power density. Threshold and differential efficiency do not dependent on heat sink temperature. Continuous-wave operation close to 300mW output power is achieved using the ground-state transition of the InGaAs QDs.
TL;DR: Detailed numerical studies of the dynamics of three semiconductor lasers when interacting in a linear chain through the mutual injection of their optical fields are presented, focusing on the synchronization properties of the coupling-induced dynamics and the role of the delay in the interaction between the lasers.
Abstract: We present detailed numerical studies of the dynamics of three semiconductor lasers when interacting in a linear chain through the mutual injection of their optical fields. In particular, we focus on the synchronization properties of the coupling-induced dynamics and the role of the delay in the interaction between the lasers. The recently experimentally and numerically demonstrated zero-lag synchronization Fischer et al., Phys. Rev. Lett. 97, 123902 2006 between the outer lasers in the chain is here further analyzed in detail along with a study of the robustness of this phenomenon. In addition, the propagation properties of perturbing pulses and of harmonic modulation are discussed. DOI: 10.1103/PhysRevE.78.066202
27 May 2008
TL;DR: In this article, the spectral broadening of high power semiconductor laser arrays is studied and the spectral accuracy of the pump diode is increased by reducing the spectral width of the diode, which enables the system designer to improve the laser system compactness, efficiency, power, and beam quality.
Abstract: High power semiconductor laser arrays have found increased applications in pumping of solid state laser systems for industrial, military and medical applications as well as direct material processing applications such as welding, cutting, and surface treatment. Semiconductor laser array products are required to have narrow spectral width for applications. Increasing the spectral accuracy by reducing the spectral width of the pump diode enables the laser system designer to improve the laser system compactness, efficiency, power, and beam quality while at the same time reducing thermal management cost in the system. Spectral width is one of the key specifications of laser array products and it is very important to improve the spectral performance to improve production yield, reduce cost and gain competitiveness. In this paper, we study the mechanisms of spectral broadening in high power semiconductor laser arrays.
TL;DR: In this article, the authors derived and discussed a theory for the (coupled) spatio-temporal light-field and carrier dynamics of novel semiconductor lasers, combining a density matrix description of the optoelectronic properties of quantum well gain media with the full-time-domain Maxwell equations for the electromagnetic (i.e. the coupled electric and magnetic) field dynamics.
TL;DR: In this article, the InGaN∕AlGaInN quantum well with zero internal field was investigated by using the non-Markovian gain model with many-body effects.
Abstract: Electronic and optical properties of InGaN∕InAlGaN quantum well with zero internal field were investigated by using the non-Markovian gain model with many-body effects. The In composition x in the well to give zero internal field is shown to increase with the In composition y in the barrier. The InGaN∕AlGaInN system has much larger optical gain than the conventional InGaN∕GaN system because the optical matrix element is largely enhanced due to disappearance of the internal field. The peak gain is shown to decrease with increasing In composition for both systems. The decrease in the optical gain for the InGaN∕AlGaInN system is mainly due to the reduction in quasi-Fermi-level separation while that for the InGaN∕GaN system is due to the reduction in the matrix element.
TL;DR: In this article, the modal properties of semiconductor ring lasers and the wavelength jumps that occur in connection with directional switching above a threshold were analyzed experimentally and theoretically, and the authors also theoretically analyzed the modulation properties of ring laser.
Abstract: We have experimentally and theoretically analyzed the modal properties of semiconductor ring lasers and the wavelength jumps that occur in connection with directional switching above the threshold.
TL;DR: In this paper, a cavity-length study was conducted to determine the temperature variation of the internal loss and gain per unit current density in a ten-stage interband cascade laser that operated cw up to 269K with an emission wavelength of 4.05μm.
Abstract: We employ a cavity-length study to determine the temperature variation of the internal loss and gain per unit current density in a ten-stage interband cascade laser that operated cw up to 269K with an emission wavelength of 4.05μm. The characteristic temperature for the gain per unit current density is 39K, which is slightly lower than T0 of the threshold current and is consistent with dominance by Auger recombination. The internal loss for the 150-μm-wide mesa devices increased from 11cm−1 at 78Kto28cm−1 at 275K.
TL;DR: In this paper, the magnitude of threshold reduction in a semiconductor laser with electron spin injection is shown to depend on such intrinsic properties of the active region as the dominant recombination mechanism, the ratio of hole-to-electron densities of states, the active-region doping, and the available material gain as well as cavity properties such as the optical loss.
Abstract: The magnitude of threshold reduction in a semiconductor laser with electron spin injection is shown to depend on such intrinsic properties of the active region as the dominant recombination mechanism, the ratio of hole-to-electron densities of states, the active-region doping, and the available material gain as well as cavity properties such as the optical loss. The threshold reduction is expected to be greatest when the laser’s active region is undoped, the recombination is strongly dominated by Auger processes, and the threshold gain is low. It can approach a factor of 3.5 for fully spin-polarized electrons in the active region.
TL;DR: In this paper, the authors study light emission patterns from stadium-shaped semiconductor (GaAs) microcavity lasers theoretically and experimentally and demonstrate that the averaging by low-loss modes, such as those realized in multimode lasing, generates an emission pattern in good agreement with the ray model's prediction.
Abstract: We study light emission patterns from stadium-shaped semiconductor (GaAs) microcavity lasers theoretically and experimentally. Performing systematic wave calculations for passive cavity modes, we demonstrate that the averaging by low-loss modes, such as those realized in multimode lasing, generates an emission pattern in good agreement with the ray model's prediction. In addition, we show that the dependence of experimental far-field emission patterns on the aspect ratio of the stadium cavity is well reproduced by the ray model.
TL;DR: In this paper, the authors illustrate the utilization of the nonlinear dynamics of single-mode semiconductor laser by focusing on the period-one oscillation for its applications in tunable photonic microwave generation, AM-to-FM conversion, and dual-frequency precision Doppler lidar.
Abstract: With a proper perturbation, even a single-mode semiconductor laser can exhibit highly complex dynamical characteristics ranging from stable, narrow-linewidth oscillation to broadband chaos. In recent years, three approaches to invoke complex nonlinear dynamical states in a single-mode semiconductor laser have been thoroughly studied: optical injection, optical feedback, and optoelectronic feedback. In each case, the nonlinear dynamics of the semiconductor laser depends on five intrinsic laser parameters and three operational parameters. The dynamical state of a given laser can be precisely controlled by properly adjusting the three operational parameters. This ability to control the dynamical behavior of a laser, combined with the understanding of its characteristics, opens up the opportunity for a wide range of novel applications. This paper illustrates the utilization of the rich nonlinear dynamics of single-mode semiconductor lasers by focusing on the period-one oscillation for its applications in tunable photonic microwave generation, AM-to-FM conversion, and dual-frequency precision Doppler lidar.
TL;DR: In this paper, the authors showed that the nonuniform near field leads to regions of inefficient clamping of the carrier density in the laser stripe, resulting in increased power conversion efficiency.
Abstract: Etching microstructures into broad area diode lasers is found to lead to more uniform near field and increased power conversion efficiency, arising from increased slope. Self-consistent device simulation indicates that this improvement is due to an increase in the effective internal injection efficiency above threshold—the nonuniform near field leads to regions of inefficient clamping of the carrier density in the laser stripe. Measurements of spontaneous emission through the substrate confirm the predicted carrier profile. Both experiment and theory show that improved overlap between carrier and power distributions correlates with improved slope.
TL;DR: This work reports on directional mode switching in semiconductor ring lasers through optical injection co-propagating with the lasing mode through the particular structure of a two-dimensional asymptotic phase space.
Abstract: We report on directional mode switching in semiconductor ring lasers through optical injection co-propagating with the lasing mode. The understanding of this novel feature in ring lasers is based on the particular structure of a two-dimensional asymptotic phase space. Our theoretical results are verified numerically and experimentally.