987 resultados para Functional gain
Resumo:
Mode gain spectrum is measured by the Fourier series expansion method for InAs/GaAs quantum-dot (QD) lasers with seven stacks of QDs at different injection currents. Gain spectra with distinctive peaks are observed at the short and long wavelengths of about 1210 nm and 1300 nm. For a QD laser with the cavity length of 1060 mu m, the peak gain of the long wavelength first increases slowly or even decreases with the injection current as the peak gain of the short wavelength increases quickly, and finally increases quickly before approaching the saturated values as the injection current further increases.
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An InGaA1As multiquantum well (MQW) has been successfully overgrown on the absorptive InGaAsP corrugation for fabricating the 1.3 mu m gain coupled distributed feedback (DFB) lasers. The absorptive InGaAsP corrugation was efficaciously preserved during the overgrowth of the InGaA1As MQW active region. The absorptive InGaAsP corrugation has a relatively high intensity around the PL peak wavelength in comparison with that of the InGaA1As MQW. The fabricated DFB laser exhibited a side mode suppression ratio of 40 dB together with a high single-mode yield of 90%.
Resumo:
In this work a practical scheme is developed for the first-principles study of time-dependent quantum transport. The basic idea is to combine the transport master equation with the well-known time-dependent density functional theory. The key ingredients of this paper include (i) the partitioning-free initial condition and the consideration of the time-dependent bias voltages which base our treatment on the Runge-Gross existence theorem; (ii) the non-Markovian master equation for the reduced (many-body) central system (i.e., the device); and (iii) the construction of Kohn-Sham master equations for the reduced single-particle density matrix, where a number of auxiliary functions are introduced and their equations of motion (EOMs) are established based on the technique of spectral decomposition. As a result, starting with a well-defined initial state, the time-dependent transport current can be calculated simultaneously along with the propagation of the Kohn-Sham master equation and the EOMs of the auxiliary functions.
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Effect of rapid thermal annealing on photoluminescence (PL) properties of InGaAs, InGaNAs, InGaAsSb, and InGaNAsSb quantum wells (QWs) grown by molecular-beam epitaxy was systematically investigated. Variations of PL intensity and full width at half maximum were recorded from the samples annealed at different conditions. The PL peak intensities of InGaAs and InGaNAs QWs initially increase and then decrease when the annealing temperature increased from 600 to 900 degrees C, but the drawing lines of InGaAsSb and InGaNAsSb take on an "M" shape. The enhancement of the PL intensity and the decrease of the full width at half maximum in our samples are likely due to the removal of defects and dislocations as well as the composition's homogenization. In the 800-900 degrees C high-temperature region, interdiffusion is likely the main factor influencing the PL intensity. In-N is easily formed during annealing which will prevent In out diffusion, so the largest blueshift was observed in InGaAsSb in the high-temperature region. (c) 2006 American Institute of Physics.
Resumo:
A technique based on the integrations of the product of amplified spontaneous emission spectrum and a phase function over one mode interval is proposed for measuring gain spectrum for Fabry-Perot semiconductor lasers, and a gain correction factor related to the response function of the optical spectrum analyzer (OSA) is obtained for improving the accuracy of measured gain spectrum. The gain spectra with a difference less than 1.3 cm(-1) from 1500 to 1600 nm are obtained for a 250-mum-long semiconductor laser at the OSA resolution of 0.06, 0.1, 0.2, and 0.5 nm. The corresponding gain correction factor is about 9 cm(-1) at the resolution of 0.5 nm. The gain spectrum measured at the resolution of 0.5 nm has the same accuracy as that obtained by the Hakki-Paoli method at the resolution of 0.06 nm for the laser with the mode interval of 1.3 nm.
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Based on the band-anticrossing model, the effect of the strain-compensated layer and the strain-mediated layer on the band structure, the gain, and the differential gain of GaInNAs-GaAs quantum well lasers have been investigated. Different band-filling mechanisms have been illustrated. Compared to the GaInNAs-GaAs single quantum well with the same wavelength,, the introduction. (if the strain-compensated layer and the strain-mediated layer increases the transparency carrier density. However, these multilayer structures help to suppress the degradation of the differential gain.
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To improve the accuracy of measured gain spectra, which is usually limited by the resolution of the optical spectrum analyzer (OSA), a deconvolution process based on the measured spectrum of a narrow linewidth semiconductor laser is applied in the Fourier transform method. The numerical simulation shows that practical gain spectra can be resumed by the Fourier transform method with the deconvolution process. Taking the OSA resolution to be 0.06, 0.1, and 0.2 nm, the gain-reflectivity product spectra with the difference of about 2% are obtained for a 1550-nm semiconductor laser with the cavity length of 720 pm. The spectra obtained by the Fourier transform method without the deconvolution process and the Hakki-Paoli method are presented and compared. The simulation also shows that the Fourier transform method has less sensitivity to noise than the Hakki-Paoli method.
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A polarization insensitive gain medium for optical amplifiers has been fabricated. The active layer is a structure with alternate tensile and compressive strain quantum wells. The waveguide is made into a taper with angled facets. In the experiment we found that the structure can suppress the lasing and decrease the polarization sensitivity. The gain imbalance between transverse electric and transverse magnetic gains is small, and 0.1 dB is obtained at a driving current of 100 mA. The full-width at half-maximum of amplified spontaneous emission is 40 nm within large current. (C) 2002 Elsevier Science Ltd. All rights reserved.
Resumo:
The present status and future prospects of functional information materials, mainly focusing on semiconductor microstructural materials, are introduced first in this paper. Then a brief discussion how to enhance the academic level and innovation capability of research and development of functional information materials in China are made. Finally the main problems concerning the studies of materials science and technology are analyzed, and possible measures for promoting its development are proposed.
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The deep centers of high electron mobility transistor (HEMT) and pseudomorphic-HEMT (P-HEMT) functional materials of ultra-high-speed microstructures grown by MBE are investigated using deep level transient spectroscopy (DLTS) technique. DLTS spectra demonstrate that midgap states, having larger concentrations and capture cross sections, are measured in n-AlGaAs layers of HEMT and P-HEMT structures. These states may correlate strongly with oxygen content of n-AlGaAs layer. At the same time, one can observe that the movement of DX center is related to silicon impurity that is induced by the strain in AlGaAs layer of the mismatched AlGaAs/InGaAs/GaAs system of P-HEMT structure. The experimental results also show that DLTS technique may be a tool of optimization design of the practical devices.
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The relations between the gain factor, defined as the ratio of modal gain to material gain, and the optical confinement factor are discussed for the TE and TM modes in slab waveguides. For the TE modes, the gain factor is larger than the optical confinement factor, due to the zigzag propagation of the modal light ray in the core layers. For the TM modes, the existence of a nonzero electric field in the propagation direction results in a more complicated relation of the gain factor and the confinement factor. For an air-Si-SiO2 strong slab waveguide, the numerical results show that the modal gain can be larger than the material gain and the higher-order transverse mode can have an even larger modal gain than the fundamental mode, The efficiency of waveguiding photodetectors can be improved by applying the modal gain or loss characteristics in strong waveguides.
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The atomic structures and electronic properties of small Ti-N (N=2-10) clusters have been studied by using the density-functional theory with a local spin density approximation. We find that the inner-shells (3s3p) of the titanium atom plays an important role in the formation of the small clusters. We have obtained the ground state of titanium clusters, Ti-7 is found to be a magic cluster, which is in good agreement with the experimental results. Starting with Ti-8 cluster some features of the electronic structure of the titanium bulk have been developed. The ionization potentials and magnetic moments for these small titanium clusters are also presented. (C) 2000 American Institute of Physics. [S0021- 9606(00)30544-X].
Resumo:
Monomers of methacrylate with various pi -conjugated pendants were designed and prepared in our laboratory, The monomer with suitable end-group was successfully assembled with nano-scale inorganic particles to form an orderly-aligned structure that showed special optical properties, both absorption and emission band were much red-shifted compared with the monomer, A new type of organic/inorganic hybrid materials was obtained by in situ polymerization of the assembly, The hybrid materials could also show special optical properties as the assembly, This might open a new route to tune the emission color.
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A new algorithm, representing an important advance in determination of the functional relationship, is first reported here. The algorithm is very useful and convenient for analyzing the incorporation of impurities. To show how the algorithm works, two early and well-known vapor phase epitaxy (VPE) experiments-Ashen's (Ashen, D. J.; Dean, P. J.; Hurle, D. T. J.; Mullin, J. B.; Royle, A.; White, A. M. Gallium Arsenide and Related Compounds, Institute of Physics Conference Series 24, 1974; Institute of Physics: London, 1975; p 229.), involving the doping of silicon and DiLorenzo's (DiLorenzo, J. V. J. Cryst. Growth 1972, 17, 189.), involving the mole fraction effect-are calculated to find the functional relationship between the Si contamination and the partial pressure of HCl. The calculated curves agree with the experimental results. A conclusion that the calculated values are greater than the true values has been drawn.
Resumo:
The electronic band structures and optical gains of InAs1-xNx/GaAs pyramid quantum dots (QDs) are calculated using the ten-band k . p model and the valence force field method. The optical gains are calculated using the zero-dimensional optical gain formula with taking into consideration of both homogeneous and inhomogeneous broadenings due to the size fluctuation of quantum dots which follows a normal distribution. With the variation of QD sizes and nitrogen composition, it can be shown that the nitrogen composition and the strains can significantly affect the energy levels especially the conduction band which has repulsion interaction with nitrogen resonant state due to the band anticrossing interaction. It facilitates to achieve emission of longer wavelength (1.33 or 1.55 mu m) lasers for optical fiber communication system. For QD with higher nitrogen composition, it has longer emission wavelength and less detrimental effect of higher excited state transition, but nitrogen composition can affect the maximum gain depending on the factors of transition matrix element and the Fermi-Dirac distributions for electrons in the conduction bands and holes in the valence bands respectively. For larger QD, its maximum optical gain is greater at lower carrier density, but it is slowly surpassed by smaller QD as carrier concentration increases. Larger QD can reach its saturation gain faster, but this saturation gain is smaller than that of smaller QD. So the trade-off between longer wavelength, maximum optical, saturation gain, and differential gain must be considered to select the appropriate QD size according to the specific application requirement. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3143025]