Simulation on Gain Recovery of Quantum Dot Semiconductor Optical Amplifiers by Rate Equation

The gain recoveries in quantum dot semiconductor optical amplifiers are numerically studied by rate equation models. Similar to the optical pump-probe experiment, the injection of double optical pulses is used to simulate the gain recovery of a weak continuous signal for the QD SOAs. The gain recoveries are fitted by a response function with multiple exponential terms. For the pulses duration of 10 ps, the gain recovery can be described by three exponential terms with the time constants, and for the pulse with the width of 150 fs, the gain recovery can be described by two exponential terms, the reason is that the short pulse does not consume lot of carriers.

Design and Simulation Analysis of Spot-Size Converter in Silicon-On-Insulator

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simulation and interaction of fluid dynamics

In the fluid simulation, the fluids and their surroundings may greatly change properties such as shape and temperature simultaneously, and different surroundings would characterize different interactions, which would change the shape and motion of the fluids in different ways. On the other hand, interactions among fluid mixtures of different kinds would generate more comprehensive behavior. To investigate the interaction behavior in physically based simulation of fluids, it is of importance to build physically correct models to represent the varying interactions between fluids and the environments, as well as interactions among the mixtures. In this paper, we will make a simple review of the interactions, and focus on those most interesting to us, and model them with various physical solutions. In particular, more detail will be given on the simulation of miscible and immiscible binary mixtures. In some of the methods, it is advantageous to be taken with the graphics processing unit (GPU) to achieve real-time computation for middle-scale simulation.

MEASUREMENT AND SIMULATION OF THE TURN-ON DELAY TIME JITTER IN GAIN-SWITCHED SEMICONDUCTOR-LASERS

The turn-on delay time jitter of four different unbiased gain-switched laser types is determined by measuring the temporal probability distribution of the leading edge of the emitted optical pulse. One single-mode 1.5-mu-m distributed feed-back laser and three multimode Fabry-Perot lasers emitting at 750 nm and 1.3-mu-m are investigated. The jitter is found to decrease for all lasers with increasing injection current. For multimode lasers it decreases from 8 ps excited slightly above threshold down to below 2 ps at three times the threshold current. The jitter of the distributed feedback (DFB) laser is a factor of 3-5 larger than the jitter of the three multimode lasers. A new model to predict the turn-on delay time jitter is presented and explains the experiments quantitatively.

THE STUDY OF MICROSTRUCTURE IN IRON-DOPED AND SULFUR-DOPED INP CRYSTALS BY MEANS OF HREM AND COMPUTER-SIMULATION

The microstructures in iron- and sulphur-doped InP crystals were studied using both electron microscopy and electron diffraction. A modulated structure has been found in S-doped InP crystal, where the commensurate modulations corresponded to periodicities of 0.68 nm and 0.7 nm in real space and were related to the reflections of the cubic lattice in [111] and [113BAR] directions; they were indexed as q111* = 1/2(a* + b* + c*) and q113BAR* = 1/4(-a* - b* + 3c*), respectively. Single atomic layers of iron precipitate were observed, with preferred orientations along which precipitates are formed. Simulated calculations by means of the dynamical theory of electron diffraction using models for the precipitate structure were in good agreement with our experimental results. The relation between the modulated structure and the precipitates is also discussed.

PHYSICAL VAPOR TRANSPORT AND CRYSTAL-GROWTH OF GESEXTE1-X SOLID-SOLUTIONS

Physical vapor transport studies of GeSe(x)Te1 - x (x = 0.1, 0.2, 0.3, and 0.4) solid solutions demonstrated, that individual, large single crystals of these materials can be grown in closed ampoules. A compositional analysis of the grown crystals revealed, that the mass transport (crystal growth) process under steady-state conditions is pseudo-congruent and controlled by diffusion processes in the source material. From these experiments, the degree of non-stoichiometry (Ge-vacancy concentrations) of GeSe(x)Te1 - x single crystals could be estimated. The effects of the cubic to rhombohedral phase transformation during cooling on the microstructure and morphology of the grown mixed crystals are observed. This work provides the basis for subsequent defect studies and electrical measurements on these crystals.

PHYSICAL BEHAVIOR OF RUTHENIUM IN SILICON

We report the physical behavior of Ru atom in silicon in this paper. Two energy levels E(0.58) and H(0.34) were observed. The pure substitutional Ru in silicon was responsible for the H(0.34), and the E(0.58) was introduced by a complex of a Ru atom and a vacancy (or vacancies). By use of scattered wave-X-alpha (SW-X-alpha) cluster method the theoretical calculation of electronic states for substitutional Ru atom in silicon has been performed. The results obtained were compared with those of experimental measurements.

Ab initio calculations for the neutral and charged O vacancy in sapphire

The energetics, lattice relaxation, and the defect-induced states of st single O vacancy in alpha-Al2O3 are studied by means of supercell total-energy calculations using a first-principles method based on density-functional theory. The supercell model with 120 atoms in a hexagonal lattice is sufficiently large to give realistic results for an isolated single vacancy (square). Self-consistent calculations are performed for each assumed configuration of lattice relaxation involving the nearest-neighbor Al atoms and the next-nearest-neighbor O atoms of the vacancy site. Total-energy data thus accumulated are used to construct an energy hypersurface. A theoretical zero-temperature vacancy formation energy of 5.83 eV is obtained. Our results show a large relaxation of Al (O) atoms away from the vacancy site by about 16% (8%) of the original Al-square (O-square) distances. The relaxation of the neighboring Al atoms has a much weaker energy dependence than the O atoms. The O vacancy introduces a deep and doubly occupied defect level, or an F center in the gap, and three unoccupied defect levels near the conduction band edge, the positions of the latter are sensitive to the degree of relaxation. The defect state wave functions are found to be not so localized, but extend up to the boundary of the supercell. Defect-induced levels are also found in the valence-band region below the O 2s and the O 2p bands. Also investigated is the case of a singly occupied defect level (an F+ center). This is done by reducing both the total number of electrons in the supercell and the background positive charge by one electron in the self-consistent electronic structure calculations. The optical transitions between the occupied and excited states of the: F and F+ centers are also investigated and found to be anisotropic in agreement with optical data.

Numerical simulation of quantum directional couplers

A numerical analysis of a quantum directional coupler based on Pi-shaped electron waveguides is presented with use of the scattering-matrix method. After the optimization of the device parameters, uniform output for the two output ports and high directivity are obtained within a wide range of the electron momenta. The electron transfer in the device is found more efficient than that in the previously proposed structures. The study of the shape-dependence of transmission for the device shows that the device structure with smooth boundaries exhibits a much better performance.

Verification of EL2 electronic absorption effect on charge transfer in semi-insulating GaAs

The electronic absorption of EL2 centers has been clarified to be related to the electron acid hole photoionizations, and the transition from its ground state to metastable state, respectively. Under an illumination with a selected photon energy in the near infrared region, these three processes with different optical cross sections will show different kinetics against the illumination time. It has recently been shown that the photosensitivity (measured under 1.25 eV illumination) of the local vibrational mode absorption induced by some deep defect centers in SI-GaAs is a consequence of the electron and hole photoionizations of EL2. This paper directly measures the kinetics of the electronic transition associated with EL2 under 1.25 eV illumination, which implies the expected charge transfer among different charge states of the EL2 center. A calculation based on a simple rate equation model is in good agreement with the experimental results.

Simulation of a Monolithic Integrated CMOS Preamplifier for Neural Recordings

A monolithic integrated CMOS preamplifier is presented for neural recording applications. Two AC-coupied capacitors are used to eliminate the large and random DC offsets existing in the electrode-electrolyte interface. Diode-connected nMOS transistors with a negative voltage between the gate and source are candidates for the large resistors necessary for the preamplifier. A novel analysis is given to determine the noise power spectral density. Simulation results show that the two-stage CMOS preamplifier in a closed-loop capacitive feedback configuration provides an AC in-band gain of 38.8dB,a DC gain of 0,and an input-referred noise of 277nVmax, integrated from 0. 1Hz to 1kHz. The preamplifier can eliminate the DC offset voltage and has low input-referred noise by novel circuit configuration and theoretical analysis.

Analysis and Simulation of S-shaped Waveguide in Silicon-on-insulator

The simulation and analysis of S-shaped waveguide bend are presented.Bend radius larger than 30 mm assures less than 0.5 dB radiation loss for a 4-μm-wide silicon-on-insulator waveguide bend with 2-μm etch depth.Intersection angle greater than 20° provides negligible crosstalk (＜-30 dB) and very low insertion loss.Any reduction in bend radius and intersection angle is at the cost of the degradation of characteristics of bent waveguide and intersecting waveguide, respectively.