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This paper presents a theoretical study of the high-speed modulation response of Fabry-Pérot (FP) and distributed-feedback (DFB) quantum-dot lasers based on the rate equation models, making reference to available experimental data. We show that the K-factor-limited maximum modulation bandwidth increases with the maximum optical gain and that there is an optimum cavity loss to maximize the bandwidth at a given maximum gain, enabling us to design the bandwidth of FP lasers as well as DFB lasers with and without a phase shift. We present modulation wave forms of FP quantum-dot lasers to indicate that the maximum modal gain of 30–40 cm-1 is sufficient for 10 Gbit/s eye opening, which explains the recent success of 10 Gbit/s modulation of the quantum-dot laser with ten dot layers in the active region having the maximum modal gain of 35 cm-1. We show a design for low-driving-current 10 Gbit/s operation by shortening the cavity length with the optimum cavity loss maintained by the high-reflectivity coating. [ABSTRACT FROM AUTHOR]

In order to evaluate the large third-order optical nonlinearity of materials accurately, the influence of the irradiance (I[sub 0]) and sample thickness (L) on the Z-scan transmittance of PbO-containing glass as a representative material was investigated using simple and conventional Z-scan experiments and analyses. The transmittance difference between the peak and valley (ΔT[sub p–v]) in the Z-scan curve resulting from nonlinear refraction and the difference between the baseline (1.0) and valley (ΔT[sub 1-v]) due to nonlinear absorption deviated from a linear relationship at increased I[sub 0] and L. It was found that an analysis based on the linear relationship at large I[sub 0] and L underestimated the third-order optical nonlinearity due to saturation. Taking into consideration the saturation of ΔT[sub p-v] and ΔT[sub 1-v] with L under moderate irradiance, the intrinsic nonlinear refractive index (γ) and nonlinear absorption coefficient (β) of the present glass were calculated to be 1.58×10[sup -17] m[sup 2] W[sup -1] and 7.75 cm GW[sup -1], respectively. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The authors have studied Nb λ/2 coplanar-waveguide (CPW) resonators whose resonant frequencies are 10–11 GHz. The resonators have different film thicknesses, t=0.05, 0.1, 0.2, and 0.3 μm. They measured at low temperatures, T=0.02–5 K, one of the scattering-matrix element, S21, which is the transmission coefficient from one port to the other. At the base temperatures, T=0.02–0.03 K, the resonators are overcoupled to the input/output microwave lines, and the loaded quality factors are on the order of 103. The resonant frequency has a considerably larger film-thickness dependence compared to the predictions by circuit simulators which calculate the inductance of CPW taking into account Lg only, where Lg is the usual magnetic inductance determined by the CPW geometry. By fitting a theoretical S21 versus frequency curve to the experimental data, they determined for each film thickness the phase velocity of the CPW with an accuracy better than 0.1%. The large film-thickness dependence must be due to the kinetic inductance Lk of the CPW center conductor. They also measured S21 as a function of temperature up to T=4–5 K, and confirmed that both thickness and temperature dependence are consistent with the theoretical prediction for Lk. [ABSTRACT FROM AUTHOR]

We present a method that improves the emission efficiency of InAs quantum dots (QDs) fabricated by antimony surfactant-mediated metal organic chemical vapor deposition. This process consists of removing the excess segregated antimony from the surface of InAs/Sb:GaAs QDs by applying a high arsenic pressure before capping. In such a way, one benefits from the advantages of InAs/Sb:GaAs QDs (high density, low coalescence) without the formation of antimony-induced nonradiative defects. Finally, we show that this better QD interface quality results in a strong decrease of the threshold current densities of InAs/Sb:GaAs QD lasers in the 1.3 μm band. [ABSTRACT FROM AUTHOR]

Analyzes the carrier recombination coefficient of quantum well laser structures. Parameter of semiconductor lasers; Combination of two-level ambipolar rate equations and a carrier diffusion equation; Factors determining the recombination coefficient.