This PDF file contains the front matter associated with SPIE Proceedings Volume 7211, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The thermoelectric properties of AlGaN and InGaN semiconductors are analyzed. In our analysis, the thermal conductivities, electrical conductivities, Seebeck coefficients, and figure of merits (Z*T) of AlGaN and InGaN semiconductors are computed. The electron transports in AlGaN and InGaN alloys are analyzed by solving Boltzmann transport equation, taking into account the dominant mechanisms of energy-dependent electron scatterings. Virtual crystal model is implemented to simulate the lattice thermal conductivity from phonon scattering for both AlGaN and InGaN alloys. The calculated Z*T is as high as 0.15 for optimized InGaN alloy at temperature around 1000 K. For optimized AlGaN composition, the Z*T of 0.06-0.07 can be achieved. The improved thermoelectric performance of ternary alloys over binary alloys can be attributed to the reduced lattice thermal conductivity.

This paper investigates sensitivity of semiconductor lasers to external optical signals. Bifurcation analysis of ordinary rate equations, describing noise-free lasers with pure coherent external signal, reveals that adjusting the extend and type of externally-induced bifurcations and chaos to desired state is possible by tailoring of the laser active medium and resonator configurations. Extending the analysis to stochastic rate equations, which describe lasers with spontaneous emission noise and noisy external signal, reveals a dramatic impact of phase-fluctuations (incoherence) in the external signal on induced bifurcations and chaos. A nonlinear optics approach is proposed where the strong sensitivity of laser instabilities to the intensity and coherence of external signal are used to detect ultra low levels of laser radiation.

Characteristics of the frequency-locked states generated by nonlinear dynamical behaviors of semiconductor lasers under periodical optical injection are investigated experimentally. The periodic optical waveforms used for injection, including repetitive pulses and sine oscillations, are generated from a laser (master laser) through self optoelectronic feedback and direct current modulation, respectively. Under proper operational conditions, namely the repetition frequency and injection strength of the injected light, microwave frequency combs are observed at the output of the injected laser (slave laser). In generating the microwave frequency combs, the pulse injection scheme shows the best performance compared to the sine modulation and cw optical injection schemes. The potential applications of these microwave frequency combs in frequency division and multiplexing are demonstrated.

The microwave domain modulation response of an injection-locked laser system is analyzed in the context of a Quantum Dash Fabry-Perot laser. This work demonstrates the applicability of a newly-derived modulation response function by using it to least-squares fit data collected on an injection-locked system with a Quantum-Dash Fabry-Perot semiconductor slave laser. The maximum injection strength, linewidth enhancement factor, coupled phase between the master and slave, and field enhancement factor characterizing the deviation of the locked slave laser from its freerunning value are extracted by least-squares fitting the collected data with the function. The extracted values are then compared with theoretically expected values under the given detuning conditions. The correlation between the frequency of the resonance peak of the modulation response at the positive frequency detuning edge and a pole in the modulation response function under this detuning condition is illustrated. The calculation of the injection strength based on the experimental operating conditions is verified by applying the modulation response function to the experimental data. With the modulation response function, injection-locked behaviors can be accurately simulated in the microwave domain and used to predict operating conditions ideal for high-performance RF links.

The dramatic variation in the linewidth enhancement factor (α_Η-factor) that has been reported for quantum dot lasers makes them an interesting subject for optical feedback studies. A low α_Η-factor combined with a high damping factor is especially interesting because it should increase the tolerance to optical feedback in these devices and may offer potential advantages for direct modulation. In the particular case of QD lasers, the carrier density is not clearly clamped at threshold. The lasing wavelength can switch from the ground state (GS) to the excited state (ES) as the current injection increases meaning that a carrier accumulation occurs in the ES even though lasing in the GS is still occurring. The filling of the ES inevitably enhances the α_Η-factor of the GS above threshold as experimentally and numerically shown. Consequently, this strong variation of the GS α_Η-factor in comparison to QW devices, should theoretically produce a significant variation in the onset of coherence collapse due to feedback. This coherence collapse regime, in which the laser is subject to instabilities, is incompatible with data transmission because of the induced high bit-error rate. One method to investigate the tolerance to optical feedback is to compare experiment with the theoretical work introduced by Petermann. It will be presented that under specific conditions, i.e., in the case of a strong enhancement in the α_Η-factor, the feedback sensitivity of the laser can vary by as much as 10dB within the same device.

Scientists throughout the world are seeking to enhance the capabilities of satellite-to-satellite tracking laser interferometer-based optical systems used to measure the alterations in earth's gravitational field that indicate critical changes in the environment. These systems must be able to measure infinitesimal fluctuations in the relative velocities of two satellites, using a light source that oscillates at a level of frequency stability rated better than 10-13 in the square root of the Allan variance. In our experiments, semiconductor laser frequency stabilization that typically requires a brief direct modulation of the laser injection current to obtain an error signal, was accomplished using the Faraday effect of Rb absorption lines. This effectively modulates the reference frequency of the stabilization system, i.e., the Rb absorption line, by modulating the magnetic field applied to the Rb absorption cell, instead of the oscillation frequency of the laser diode. Most recently, we used the Faraday method, in conjunction with a precision temperature controller. For present purposes, we also use the PEAK method, to obtain the most accurate signal possible, comparing it with saturated absorption spectroscopic readings, to determine the noise-source.

We present a practical theoretical framework for describing quantum light-matter interactions and photon transport in photonic crystal chips. The semiconductor chips can include quantum dots, waveguides, coupled cavities, and integrated output couplers. Practical designs for efficient single photon sources and entangled photon sources are introduced, and the limitations, challenges, and exciting potential of developing on-chip quantum light sources are discussed.

A quantum dot strongly coupled to a photonic crystal resonator is used to investigate cavity quantum electro- dynamics phenomena in solid state physics. Nonlinear optical phenomena such as photon blockade and photon induced tunneling are observed in this system. The nonlinearity of this system is sensitive to intra-cavity photon numbers close to unity, and it has been used to demonstrate conditional phase shifts of 28° at a single photon level and a second order auto-correlation of g²(0) = 0.9 in the photon blockade regime.

We present an electrically driven single quantum dot emitter that is adapted for operation at room temperature. Epitaxially grown CdSe quantum dots were embedded between ZnSSe/MgS barriers optimized with respect to both, high quantum efficiency and efficient current injection at elevated temperatures. Most important, electroluminescence from one single quantum dot is observed even at room temperature with a surprisingly low driving voltage of 2.6 V. This might be a key step for a single photon emitter operating under ambient conditions.

Site-selective epitaxy and standard electron beam lithography techniques are employed to spatially couple small InAs/InP quantum dot ensembles to 2D photonic crystal membrane cavities. The small InAs quantum dot ensembles, consisting of just a few dots, are localized to areas 100x100nm² at predetermined positions dictated by a nanotemplate consisting of InP pyramids. The dots are embedded in a 2D membrane using a planarization growth step and single missing-hole defect cavities are fabricated in the membrane with the defect sites centered on the dot ensembles. This spatially couples the ensembles to the χ-dipole mode of the cavities. Emission from the cavities shows the expected mode structure, with quality factors of 2000.

We present the on-demand coupling of single NV- defect centers in nanodiamonds to a polystyrene microspherical resonator. From an ensemble on a coverslip we select out single nanodiamonds containing a single defect proven by a pronounced antibunching dip. With the help of a scanning near-field probe we can attach these nanodiamonds to a microsphere resonator one-by-one. A clearly modulated fluorescence spectrum demonstrates coupling of the single defect centers to high- whispering-allery modes. Our experiments establish a toolbox to assemble complex systems consisting of single quantum emitters and (coupled) microresonators.

Incorporating quantum wells into multi-junction III-V solar cells provides a means of adjusting the absorption edge of the component junctions. Further, by using alternating compressive and tensile materials, a strain-balanced stack of quantum well and barrier layers can be grown, defect free, providing absorption-edge / lattice parameter combinations that are inaccessible using bulk materials. Incomplete absorption in the quantum wells has been addressed using a distributed Bragg reflector, extending the optical path length through the cell and enabling photon recycling to take place. State of the art single-junction quantum well solar cells have now reached an efficiency of 27.3% under 500X solar concentration and are projected to reach 34% in a double junction configuration.

Successions of dilute nitride-based III-V semiconductor staircase like superlattice structures are incorporated in the intrinsic region of common III-V p-i-n solar cells. The choices of material system and energy band design are tuned towards facilitating the collection of all photo-generated carriers while minimizing recombination losses. Band structure calculations including strain effects, band anti-crossing models and transfer matrix methods are used to theoretically demonstrate optimum conditions for enhanced vertical transport. High electron quantum tunneling escape probability, together with a free movement of quasi-3 D holes, is predicted here to result in enhanced PV device performance. Furthermore, the increase in electron effective mass due to the incorporation of N translates in enhanced absorptive properties, ideal for PV application.

Fluorescent solar collectors represent an alternative to flat plate photovoltaic arrays. With the emphasis on minimizing the use of silicon, the collector is usually composed of a mixture of fluorescent dyes embedded in a transparent medium. The absorbed incoming sunlight is re-emitted at a longer wavelength. A large fraction of fluorescence is totally internally reflected and transported to the edge of the collector, where the solar cell is placed. The key requirements for efficient fluorescent collectors are a good photon transport and a broad absorption of sunlight. The fundamental parameter that determines the efficiency of photon transport is the probability of reabsorption. Based on experimental results and ray-tracing simulations carried out with "TracePro", this publication illustrates the use of ray tracing to model reabsorption in collectors with different shapes as well as inhomogeneous structures, and to assess the validity of the traditional analytical approach. We show that, contrary to expectations, some novel structures (for example, "thin film" or "waveguide" collectors) do not represent an improvement over their corresponding homogeneous collectors and that any variation of the film refractive index on a glass substrate leads to an efficiency drop.

We employ our simulation framework TDKP/AQUA to investigate bulk, planar quantum-well and V-groove quantum-wire light-emitting diodes. Carrier transport and spontaneous light emission are calculated self-consistently for all degrees of quantization. The simulation is based on a semi-coherent picture of drift and diffusion along unquantized directions whereas confinement and luminescence are calculated from a multiband Schroedinger equation in the confined directions. The three structures with different quantization degrees are compared with respect to light conversion efficiency and overall output power. It is shown that carrier confinement greatly improves the radiative conversion efficiency but at the same time limits output power and enhances carrier leakage into the minority regions due to a reduced density of states.

A scheme to realize fiber-based all-optical Boolean logic functions including XOR, AND, OR and NOT based on a semiconductor optical amplifier with a closely stacked Stranski-Krastanow InAs/GaAs quantum dot layers is proposed. Rate equations is given to describe the population dynamics of the carrier in the device, as well as the nonlinear dynamics including carrier heating and spectral hole-burning. The model is used to simulated the cross gain and cross phase modulation in the device that are related to the logic processes. Results show with QD excited state serving as a carrier reservoir, this type of QD device is suitable for high speed operations with ultra fast carrier and phase relaxation. All optical logic operation can be carried out at up to 250 Gb/s.

This paper investigates the electrostatics and carrier transport in nanowires with double heterostructures (DH). The particular interests include strong fringing field and weak screening effects resulting from the increased surface to volume ratio in nanowires. A general device simulator, PROPHET, is employed for a model nanowire structure with Al_0.2Ga_0.8N/GaN DH. Our simulations show that in general, the junction depletion width in the active region increases for nanowire based DH devices. The impacts of such effect on carrier injection in nanowire devices as well as the roles of forward biasing and material compositions are also investigated.

We have investigated the intensity distribution through metallic nano double slit and nano double box by two dimensional finite-difference time-domain (FDTD) method based on Drude model. In particular, we find that there is an 'intermediate region' between near-field and far-field regions which varies with thickness and width of double slit. We will present the local fields propagating along and perpendicular to metal surface and their spatial distributions to verify the existence of the intermediate region.

Semiconductor microring resonators are excellent fundamental building blocks for the development of opto-electronic integrated circuits (OEICs), due to their large third-order nonlinearities enhanced by the resonance effect and compactness which leads to monolithic integration capability. A wide range of potential applications is presented and analyzed and the applicability of microring based devices as low-cost fundamental units in access/metro optical networks is discussed.

We show for the first time to our knowledge, synchronization between two bulk semiconductor lasers onto an erratic train of pulses. They occurred erratically at different times, following a Poisson statistical law over a nanosecond scale. These pulses are due to excitability and are obtained using an optically injected bulk semiconductor laser. For the first time to our knowledge, two semiconductor lasers showing an erratic train of pulses are synchronized by cascading two optical injection schemes. The degree of correlation between the two signal outputs is analyzed following the detuning and the injected power. This correlation is related to the standard map obtained in the detuning-injected power chart for an optically injected laser, seeded by a non continuous wave. The synchronization on a single pulse is studied as well as on a regular temporal train of pulses.

In this paper, we propose a novel sensor structure based on the rectangular ring resonator with the photonic crystal microcavity (PCM), and optimize the structure using finite-difference time-domain (FDTD) method. This sensor consists of the rectangular resonator with total internal reflection mirror and the PCM, which can be placed at the nearby optical waveguide of the rectangular ring resonator. The PCM is composed of a defect cavity with different holes on the center of it. The Q-factor of the PCM can be significantly enhanced when the PCM has the resonance wavelength. The PCM can be evanescently coupled to a side waveguide arm of the rectangular ring resonator. The sensitivity of the ring resonator in the presence of gas or biomolecules composition was calculated using the FDTD method. When the injected gas or biomolecules pass through the PCM, the variation of effective index due to their concentration affects the resonance condition of the rectangular ring resonator. We have investigated how the shift of the resonance peak in the resonance wavelengths depends on the gas or biomolecules concentration. We also have optimized the sensor structure for the waveguide width and length, the hole radius, and the number of hole on the PCM. The optimum lattice constants, hole radius, and cavity length are 370, 100, and 580 nm, respectively. The rectangular ring resonator sensor with microcavity significantly enhances the quality factor and the sensitivity compared to the directional coupler sensor with PCM. The change of normalized output power in rectangular ring resonator with PCM is approximately twice larger than the change in directional coupler with PCM.

We present the development of theoretical model based on multi-population rate equation to assess the broadband lasing emission in addition to the derivative optical gain and chirp characteristics from the supercontinuum InGaAs/GaAs self-assembled quantum-dot (QD) interband laser. The model incorporates the peculiar characteristics such as inhomogeneous broadening of the QD transition energies due to the size and composition fluctuation, homogeneous broadening due to the finite carrier lifetime in each confined energy states, and the presence of continuum states in wetting layer. We showed that the theoretical model agrees well with the experimental data of broadband QD laser. From the model, the broadband lasing characteristics can be ascribed to the large dispersion of QD with varying energy sub-bands and the change of de-phasing rate. These interesting characteristics can be attributed to the carrier localization in different dots that result in a system without a global Fermi function and thus an inhomogeneously broadened gain spectrum. Furthermore, our simulation results predict that the linewidth enhancement factor (α = 2) from the ground state (GS) in this new class of semiconductor lasers is slightly larger but in the same order of magnitude as the values obtained in conventional QD lasers. The calculated gain spectrum shows similar magnitude order of material differential gain (~10^-16 cm²) and material differential refractive index (~10^-20 cm³) as compared to conventional QD lasers. The comparable derivative characteristics of broadband QD laser shows its competency in providing low frequency chirping as well as a platform for monolithic integration operation.

Quantum dot (QD) lasers exhibit many useful properties such as low threshold current, temperature and feedback insensitivity, chirpless behavior, and low linewidth enhancement factor. The aim of this paper is to investigate the lasing spectra behaviour of InAs/InP(311B) QD lasers. In order to reach the standards of long-haul transmissions, 1.55μm InAs QD lasers grown on InP substrate have been developed. More particularly, it has been demonstrated that the use of the specific InP(113)B substrate orientation when combined with optimized growth techniques allows the growth of very small (4 nm high) and dense (up to 1011cm^-2) QD structures. Consequently, a model based on the multi-population rate equations (MPRE) taking into account many cavity longitudinal modes for the calculation of the entire emission spectrum has been developed. In order to include the inhomogeneous gain broadening of the QD ensemble, various dot populations, each characterized by a ground state (GS) and an excited state (ES) average energy level have been considered. It will be shown that the numerical results are in good agreement with the experimental ones, both for the case of the double laser emission and for the effects of the homogeneous broadening on the lasing spectra. This numerical investigation based on carrier dynamics is of prime importance for the optimization of low cost sources for optical telecommunications as well as for a further improvement of QD laser performances at 1.55-μm on InP substrate, as already demonstrated for InAs-GaAs QD lasers emitting at 1.3-μm.

We have compared the gain dynamics of the ground state excitonic transition between undoped and p-doped electrically-pumped InGaAs quantum-dot optical amplifiers, for temperatures from 300 K to 20 K. A pump-probe differential transmission technique in heterodyne detection with sub-picosecond time resolution was used. The comparison shows that in the gain regime at high temperatures the recovery dynamics of the p-doped sample is slower than in the undoped device operating at the same modal gain, due to a reduced electron reservoir in the excited states. Conversely, at 20 K the initial gain dynamics is faster in the p-doped device due to hole-hole scattering.

A model to study four-wave mixing (FWM) wavelength conversion in InAs-GaAs quantum-dot semiconductor optical amplifier is proposed. Rate equations involving two QD states are solved to simulate the carrier density modulation in the system, results show that the existence of QD excited state contributes to the ultra fast recover time for single pulse response by serving as a carrier reservoir for the QD ground state, its speed limitations are also studied. Nondegenerate four-wave mixing process with small intensity modulation probe signal injected is simulated using this model, a set of coupled wave equations describing the evolution of all frequency components in the active region of QD-SOA are derived and solved numerically. Results show that better FWM conversion efficiency can be obtained compared with the regular bulk SOA, and the four-wave mixing bandwidth can exceed 1.5 THz when the detuning between pump and probe lights is 0.5 nm.

Lifetimes, Auger coefficients, and internal losses were deduced for 25 different type-II "W" interband cascade laser structures, from correlations of the experimental threshold current densities and slope efficiencies with calculated threshold carrier densities and optical gains. The room-temperature Auger coefficients for a number of lowthreshold devices emitting at wavelengths from 2.9 μm to 5.2 μm fall in the narrow range 3-11 × 10^-28 cm⁶/s, which represents a much stronger suppression of Auger decay than was implied by most earlier experiments and theoretical projections. The estimated internal loss is lowest at intermediate wavelengths, and the most recent designs display additional reduction to as little as 8 cm^-1 at 300 K.

Tunnel junctions have been widely used in the fabrication of Vertical Cavity Surface Emitting Lasers since it allows fabrication of low electrical resistance as well as low optical absorption Bragg mirrors. The basic idea is to inject holes through a highly doped reverse biased n+/p+ tunnel junction. We present in this paper a review of the different materials that can be used for various wavelength applications ranging from UV (GaN) to IR (GaSb). We have elaborated a new modelling tool that has been validated for homo-junctions. The results show that the injection efficiency is directly linked to the energy gap of the material and to the effective mass of the electrons and light holes. The first important discussion is related to the condition on doping levels to get the material degenerate. Low band gap materials such as InAs or GaSb semiconductors are well appropriate to realise tunnel junctions with moderate doping levels. At the opposite large band-gap materials as GaN or AlN require very high doping levels to reach the tunnelling condition. GaSb based VCSELs emitting in the infrared region (2-3 μm) can use very efficiently such electrical injection scheme. On the other side, it will be much less beneficial to use it for surface emitting laser emitting in the ultra violet wavelength range. Comparison with published papers will be discussed as well as preliminary work done in the case of hetero junctions.

We report on the modeling, epitaxial growth, fabrication, and characterization of 830-845 nm vertical cavity surface emitting lasers (VCSELs) that employ InAs-GaAs quantum dot (QD) gain elements. The GaAs-based VCSELs are essentially conventional in design, grown by solid-source molecular beam epitaxy, and include top and bottom gradedheterointerface AlGaAs distributed Bragg reflectors, a single selectively-oxidized AlAs waveguiding/current funneling aperture layer, and a quasi-antiwaveguiding microcavity. The active region consists of three sheets of InAs-GaAs submonolayer insertions separated by AlGaAs matrix layers. Compared to QWs the InAs-GaAs insertions are expected to offer higher exciton-dominated modal gain and improved carrier capture and retention, thus resulting in superior temperature stability and resilience to degradation caused by operating at the larger switching currents commonly employed to increase the data rates of modern optical communication systems. We investigate the robustness and temperature performance of our QD VCSEL design by fabricating prototype devices in a high-frequency ground-sourceground contact pad configuration suitable for on-wafer probing. Arrays of VCSELs are produced with precise variations in top mesa diameter from 24 to 36 μm and oxide aperture diameter from 1 to 12 μm resulting in VCSELs that operate in full single-mode, single-mode to multi-mode, and full multi-mode regimes. The single-mode QD VCSELs have room temperature threshold currents below 0.5 mA and peak output powers near 1 mW, whereas the corresponding values for full multi-mode devices range from about 0.5 to 1.5 mA and 2.5 to 5 mW. At 20°C we observe optical transmission at 20 Gb/s through 150 m of OM3 fiber with a bit error ratio better than 10^-12, thus demonstrating the great potential of our QD VCSELs for applications in next-generation short-distance optical data communications and interconnect systems.

An efficient modular approach is used to develop components for a 3D simulator for complex semiconductor LED and laser structures. In this approach, only drift transport is simulated in bulk regions, while the active region is simulated with models of varying complexity. The approach is tested using a basic vertical-cavity surface emitting laser (VCSEL) structure, and comparisons are made with experimental data. This approach is advantageous for fast simulation of complex photonic crystal LEDs and VCSELs, for which 2D simulation is inadequate.

We present a new simulation technique for Distributed Feedback lasers in 2D. The method is based on recently developed Trigonometric Finite Wave Elements (TFWEs) that approximate oscillating and internally reflected optical waves. Since our method is derived from the Transfer Matrix Method (TMM), the TFWE method provides exactly the same results as the TMM for 1D problems but it can be extended to higher dimensions and to time-dynamic simulations. Therefore, large laser structures and the influence of the injected current can be simulated time-dynamically. Furthermore, the wavelengths of the competing modes can be detected using the Fast Fourier Transformation.

Mode-locked lasers (MLLs) and semiconductor optical amplifiers (SOAs) based on quantum dot (QD) gain material will impact the development of next generation networks like the 100Gb/s Ethernet. Hybrid mode-locked lasers consisting of a monolithic two section device presently already generate picosecond pulse trains at 40 GHz with an extremely low jitter in the range of 200 fs under optimum operating conditions. A detailed chirp analysis which is prerequisite for optical time division multiplexing applications is presented. QD SOAs are showing superior performance for linear amplification as well as nonlinear signal processing. Wavelength conversion via cross-gain modulation is shown to have a small signal bandwidth beyond 40 GHz under high bias current injection. This makes QD SOAs much superior to conventional SOAs.

Monolithic InAs quantum dash 1.58-micron passively mode-locked lasers grown on an InP substrate are reported. A repetition rate of up to 18.5 GHz has been realized. The dashes-in-a-well (DWELL) active region consists of 5 stacks of InAs quantum dashes embedded in compressively strained Al_0.20Ga_0.16In_0.64As quantum wells separated by 30-nm undoped tensile-strained Al_0.28Ga_0.22In_0.50As spacers on both sides of the DWELL. 4 micron-wide ridge waveguides with cavity lengths in the range of 2.3 to 4 mm were fabricated with multiple electrically-isolated anode contacts. The modal gain and loss spectra of the InAs active region were then measured through the improved segmented contact method, and the characteristics that make InAs quantum dash materials system desirable for semiconductor mode-locked lasers were identified. The segmented waveguides were then reconfigured into mode-locked lasers by wire bonding the segments together to form separate gain and absorber regions utilizing the same DWELL active region. A highly reflective coating (95%) was applied to the mirror facet next to the absorber while the other facet was cleaved. To assist in the cavity design and to determine the relative length of the absorber and gain sections, a model for the cavity geometry of the twosection passively mode-locked lasers was studied and is based on a microwave photonics perspective. A new set of theoretical equations was used to find the optimal device layout using the measured modal gain and loss characteristics as input data.

We study nonequilibrium carriers (electrons and holes) in an intrinsic graphene at low temperatures under farand mid-infrared optical pumping in a wide range of its power densities. The energy distributions of carriers are calculated using a quasiclassic kinetic equation which accounts for the energy relaxation due to acoustic phonons and the radiative generation-recombination processes associated with thermal radiation and the carrier photoexcitation by incident radiation. It is found that the nonequilibrium distributions are determined by an interplay between weak energy relaxation on acoustic phonons and generation-recombination processes as well as by the effect of pumping saturation. Due to the effect of pumping saturation, the carrier distribution functions can exhibit plateaus whose width increases with increasing pumping power density. The graphene steady-state conductivity as a function of the pumping power density exhibits a pronounced nonlinearity with a sub-linear region at fairly low power densities. As shown, at certain pumping power density the population inversion as well as the dynamic negative conductivity can take place in terahertz and far-infrared frequencies, suggesting the possibility of utilization of graphene under optical pumping for optoelectronic applications, in particular, lasing at such frequencies.

We simulated the evolution of self-similar parabolic pulses (similaritons) in a normally dispersive fiber amplifier. The rate of development of a Gaussian pulse into the asymptotic parabolic regime has been studied. The model has been applied to an optical transmission system with a fiber amplifier. By calculating the Q-factor, we numerically determined the signal to noise performance of the pulse train along fiber length. For the parameters we used, a 6m long fiber amplifier with 20 dB gain is capable of amplifying 200Gb/s initial chirp-free Gaussian pulses of duration 0.4ps with no distortion and additional noise. The trade-off between pulse width and amplifier length has been studied.

For III-nitride compound materials, the existence of spontaneous and piezoelectric polarizations results in strong electrostatic fields, which might strongly affect the optical properties of 405-nm InGaN laser diodes. In this work, for polarization-free purpose, the use of polarization-matched AlGaInN electron-blocking layer and barrier layer in the violet InGaN multiple-quantum-well laser diodes is proposed. The laser performance and optical characteristics of the violet laser diodes are numerically evaluated by using the LASTIP (abbreviation of LASer Technology Integrated Program) simulation program. The simulation results show that, when the original Al_0.20Ga_0.80N electron-blocking layer is replaced by the polarization-matched Al_0.39Ga_0.49In_0.12N electron-blocking layer, the laser performance is slightly improved. However, on the other hand, when compared to the original InGaN laser diode, the violet InGaN laser diode with a polarization-matched Al_0.33Ga_0.45In_0.22N barrier layer possesses an increase of the threshold current and a decrease of the slope efficiency. It is presumably due to the fact that the effective potential height of conduction band at the interface of barrier and electron-blocking layer is reduced, and the electron leakage current is correspondingly enhanced when the polarization-matched barrier layer is utilized.

Effect of polarization on optical characteristics of blue InGaN LEDs with staggered QW are numerically investigated in this article by using APSYS simulation program. Specifically, band diagram, carrier distribution, and output power have been discussed. According to the simulation results, the structure of staggered QW is proposed to reduce the polarization-related effect; furthermore, the staggered QW structure together with thinner well width is beneficial for improvement of the output power of the blue InGaN SQW LEDs. In this work, the best optical performance is obtained when the quantum-well structure is designed as In_0.20Ga_0.80N (0.9 nm)-In_0.26Ga_0.74N (1.1 nm) owing mainly to the enhanced overlap of electron and hole wavefunctions inside the QW.