A 10 Gb/s Directly-Modulated 1.3 mu m InAs/GaAs Quantum-Dot Laser

We demonstrate 10 Gb/s directly-modulated 1.3 mu m InAs quantum-dot (QD) lasers grown on GaAs substrates by molecular beam epitaxy. The active region of the QD lasers consists of five-stacked InAs QD layers. Ridge-waveguide lasers with a ridge width of 4 mu m and a cavity length of 600 mu m are fabricated with standard lithography and wet etching techniques. It is found that the lasers emit at 1293 nm with a very low threshold current of 5 mA at room temperature. Furthermore, clear eye-opening patterns under 10 Gb/s modulation rate at temperatures of up to 50 degrees C are achieved by the QD lasers. The results presented here have important implications for realizing low-cost, low-power-consumption, and high-speed light sources for next-generation communication systems.

on a class of pseudorandom sequences from elliptic curves over finite fields

Following the idea of Xing et al., we investigate a general method for constructing families of pseudorandom sequences with low correlation and large linear complexity from elliptic curves over finite fields in this correspondence. With the help of the tool of exponential sums on elliptic curves, we study their periods, linear complexities, linear complexity profiles, distributions of r-patterns, periodic correlation, partial period distributions, and aperiodic correlation in detail. The results show that they have nice randomness.

Controllable negative and positive group delay in transmission through a single quantum well at finite magnetic fields

We investigate the controllable negative and positive group delay in transmission through a single quantum well at the finite longitudinal magnetic fields. It is shown that the magneto-coupling effect between the longitudinal motion component and the transverse Landau orbits plays an important role in the group delay. The group delay depends not only on the width of potential well and the incident energy, but also on the magnetic-field strengthen and the Landau quantum number. The results show that the group delay can be changed from positive to negative by the modulation of the magnetic field. These interesting phenomena may lead to the tunable quantum mechanical delay line. (c) 2007 Elsevier B.V. All rights reserved.

Coherent laser control in attosecond sum-frequency polarization beats using twin noisy driving fields

Based on the phase-conjugate polarization interference between two-pathway excitations, we obtained an analytic closed form for the second-order or fourth-order Markovian stochastic correlation of the V three-level sum-frequency polarization beat (SFPB) in attosecond scale. Novel interferometric oscillatory behavior is exposed in terms of radiation-radiation, radiation-matter, and matter-matter polarization beats. The phase-coherent control of the light beams in the SFPB is subtle. When the laser has broadband linewidth, the homodyne detected SFPB signal shows resonant-nonresonant cross correlation, a drastic difference for three Markovian stochastic fields, and the autocorrelation of the SFPB exhibits hybrid radiation-matter detuning terahertz damping oscillation. As an attosecond ultrafast modulation process, it can be extended intrinsically to any sum frequency of energy levels. It has been also found that the asymmetric behaviors of the polarization beat signals due to the unbalanced controllable dispersion effects between the two arms of interferometer do not affect the overall accuracy in case using the SFPB to measure the Doppler-free energy-level sum of two excited states.

Magnetoexcitonic optical absorption in semiconductors under strong magnetic fields and intense terahertz radiation in the Voigt configuration

The magnetoexcitonic optical absorption of a GaAs bulk semiconductor driven by a terahertz (THz) field is investigated numerically. The method of the solution of the initial-value problem, in combination with the perfect matched layer technique, is used to calculate the optical susceptibility, with Coulomb interaction, Landau quantization, and THz fields involved nonperturbatively. It shows that there appear replicas and sidebands of magnetoexciton of different Landau levels, which greatly enrich the magneto-optical spectrum in the presence of a driving THz field. Copyright (C) EPLA, 2008.

COHERENT MODEL FOR RESONANT-TUNNELING OF ELECTRONS IN DOUBLE-QUANTUM WELLS UNDER ELECTRIC-FIELDS

Taking the inhomogenous broadening of the electron energy levels into account, a coherent model of the resonant tunneling (RT) of electrons in double quantum wells is presented. The validity of the model is confirmed with the experiments [M. Nido et al., Proc. SPIE 1268, 177 (1990)], and shows that the tunneling process can be explained by the simple coherent theory even in the presence of the carrier scattering. We have discussed the dependence of resonant tunneling on the barrier thickness L(B) by introducing the contrast ratio LAMBDA and the full width at half depth of the RT valley, and found that LAMBDA first increases with increasing barrier thickness, reaches a maximum, and then decreases with a further increase of L(B), in striking contrast to the Fabry-Perot model where a monotonic increase of the peak-to-valley ratio is predicted. We attribute the reduction of LAMBDA with large L(B) to the energy broadening resulting from the carrier scattering. A monotonic decrease of the full width at half depth of the RT valley with an increase of L(R) is also found.