998 resultados para Semiconductor doping


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We have demonstrated an electroabsorption modulator (EAM) and semiconductor optical amplifier (SOA) monolithically integrated with novel dual-waveguide spot-size converters (SSCs) at the input and output ports for low-loss coupling to planar light-guide circuit silica waveguide or cleaved single-mode optical fiber. The device is fabricated by means of selective-area MOVPE growth (SAG), quantum well intermixing (QWI) and asymmetric twin waveguide (ATG) technologies with only three steps low-pressure MOVPE growth. For the device structure, in SOA/EAM section, double ridge structure was employed to reduce the EAM capacitances and enable high bit-rate operation. In the SSC sections, buried ridge stripe (BRS) were incorporated. Such a combination of ridge, ATG and BRS structure is reported for the first time in which it can take advantage of both easy processing of ridge structure and the excellent mode characteristic of BRS. At the wavelength range of 1550-1600 nm, lossless operation with extinction ratios of 25 dB DC and more than 10 GHz 3-dB bandwidth is successfully achieved. The beam divergence angles of the input and output ports of the device are as small as 8.0 degrees x 12.6 degrees, resulting in 3.0 dB coupling loss with cleaved single-mode optical fiber. (c) 2005 Elsevier B.V. All rights reserved.

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The scattering matrix method is used to analyze the multiple reflection effect between the laser diode facet and the fiber grating facet by considering the fiber grating external cavity laser diode (FGECL) as a four-mirror cavity laser. When neglecting other important parameters such as butt-coupling distance between the diode and the fiber facets, coupling efficiency, external cavity length, it is shown that low reflectivity is not a crucial factor for the laser characteristics such as SMSR. Experimentally high SMSR fiber grating external cavity laser is fabricated with a relatively large residual facet reflectivity (about 1%), which is coincident with our simulation results.

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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.

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Radiant heat conversion performance dominated by the active layer of Ga0.84In0.16As0.14Sb0.86 diode has been systematically investigated based on an analytic absorption spectrum, which is suggested here by numerically fitting the limited experimental data. For the concerned diode configuration, our calculation demonstrates that the optimal base doping is 3-4 x 10(17) cm(-3), which is less sensitive to the variation of the external radiation spectrum. Given the scarcity of the alloy elements, an economical device configuration of the 0.2-0.6 mu m emitter and the 4-6 mu m base would be particularly acceptable because the corresponding conversion efficiency cannot exhibit discouraging degradation in comparison to the one for the optimal structure, the thickness of which may be up to 10 mu m. More importantly, the method we suggested here to calculate alloy absorption can be easily transferred to other composition, thus bringing great convenience for design or optimization of the optoelectronic device formed by these alloys.

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The thin films of TiO2 doped by Mn non-uniformly were prepared by sol-gel method under process control. In our preceding study, we investigated in detail, the effect of doping mode on the photocatalytic activity of TiO2 films showing that Mn non-uniform doping can greatly enhance the activity. In this study we looked at the effect of doping concentration on the photocatalytic activity of the TiO2 films. In this paper, the thin films were characterized by UV-vis spectrophotometer and electrochemical workstation. The activity of the photocatalyst was also evaluated by photocatalytic degradation rate of aqueous methyl orange under UV radiation. The results illustrate that the TiO2 thin film doped by Mn non-uniformly at the optimal dopant concentration (0.7 at %) is of the highest activity, and on the contrary, the activity of those doped uniformly is decreased. As a comparison, in 80 min, the degradation rate of methyl orange is 62 %, 12 % and 34 % for Mn non-uniform doping film (0.7 at %), the uniform doping film (0.7 at %) and pure titanium dioxide film, respectively. We have seen that, for the doping and the pure TiO2 films, the stronger signals of open circuit potential and transient photocurrent, the better photocatalytic activity. We also discusse the effect of dopant concentration on the photocatalytic activity of the TiO2 films in terms of effective separation of the photon-generated carriers in the semiconductor. (C) Versita Warsaw and Springer-Verlag Berlin Heidelberg. All rights reserved.

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The nonlinear optical properties of semiconductor quantum wells driven by intense in-plane terahertz electric fields are investigated theoretically by employing the extended semiconductor Bloch equations. The dynamical Franz-Keldysh effect of the optical absorption near the band edge is analyzed with Coulomb correlation among the carriers included. The in-plane terahertz field induces a variety of behavior in the absorption spectra, including terahertz replicas of the (dark) 2p exciton and terahertz sidebands of the 1s exciton. The dependence of these interesting features on the intensity, frequency, and phase of the terahertz field is explored in detail.

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The nonlinear optical absorption in a three-subband step asymmetric semiconductor quantum well driven by a strong terahertz (THz) field is investigated theoretically by employing the intersubband semiconductor-Bloch equations. We show that the optical absorption spectrum strongly depends on the intensity, frequency, and phase of the pump THz wave. The strong THz field induces THz sidebands and Autler-Townes splitting in the probe absorption spectrum. Varying the pump frequency can bring not only the new absorption peaks but also the changing of the energy separation of the two higher-energy levels. The dependence of the absorption spectrum on the phase of the pump THz wave is also very remarkable.

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A photoconductive semiconductor switch (PCSS) would work in a nonlinear mode under high biased electrical field. The experimental results of nonlinear critical state have shown that both the biased voltage and the laser energy may have working thresholds to turn on the nonlinear modes. The relation between the biased voltage (aid the laser energy is inverse ratio, i.e., higher biased field need lower laser energy for nonlinear mode, and vise versa. At the nonlinear critical point, the output of PCSS is unstable, as both the linear and nonlinear pulse may occur. As the laser energy and biased field increase, the PCSS would work in the nonlinear mode steadily. (C) 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 56-59 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOT 10.1002/mop.24001