The third subband population in modulation-doped InGaAs/InAlAs heterostructures

We have observed the population of the third (n=3) two-dimensional electron subband of InGaAs/ InAlAs modulation-doped structures with very dense sheet carrier density by means of Fourier transform photoluminescence (PL). Three well-resolved PL peaks centered at 0.737, 0.908, and 0.980 eV are observed, which are attributed to the recombination transitions from the lowest three electron subbands to the n=1 heavy-hole subband. The subband separations clearly exhibit the features of the stepped quantum well with triangle and square potential, consistent with numerical calculation. Thanks to the presence of the Fermi cutoff, the population ratio of these three subbands can be estimated. Temperature and excitation intensity dependence of the quantum well luminescence intensity is also analyzed. (C) 1997 American Institute of Physics.

Characterization of high-speed optoelectronics devices based optical and electrical spectra analyses - art. no. 68380Q

In this paper, we presents the characterization technique of high-speed optoelectronics devices based electrical and optical spectra, which is as important access to the devices performance as the prevalent vector network analyzer (VNA) sweeping method. The measurement of additional modulation of laser and frequency response of photodetector from electrical spectra, and the estimation of the modulation indexes and the chirp parameters of directly modulated lasers based on optical spectra analysis, are given as examples.

Single-negative negative index metamaterials with broad bandwidth - art. no. 683109

The theoretical method to design negative refractive index metamaterials by single negative permittivity metamaterials is presented. By designing the electric and magnetic response metamaterials separately, the complexity of the design work can be simplified a lot. For the magnetic response metamaterials, the metallic post structure is adopted. Varying the height of the post, the response wavelength can be adjusted linearly. For electric metamaterials, wire-mesh structure is adopted. The effective material parameters, including refractive index, impedance, permittivity and permeability are given. Such a structure has negative refractive index during a broad frequency band and easy to design.

Design and Realization of Index-Coupled DFB Laser with Sampled Grating

An index-coupled distributed feedback laser with the sampled grating has been designed and fabricated. The +1(st) order reflection of the sampled grating is utilized for laser single mode operation, which is 1.5329 mu m in the experiment. The sampled grating is formed by a conventional holographic exposure combined with the usual photolithography. The typical threshold current of DFB laser with the sampled grating is 25mA, and the optical output is about 10mW at the injected current of 100mA.

Subtraction of S-parameters for adiabatic small-signal modulation characteristics of laser diode - art. no. 60201V

An extended subtraction method of scattering parameters for characterizing laser diode is introduced in this paper. The intrinsic small-signal response can be directly extracted from the measured transmission coefficients of laser diode by the method. However the chip temperature may change with the injection bias current due to thermal effects, which causes inaccurate intrinsic response by our method. Therefore, how to determine the chip temperature and keep the laser chip adiabatic is very critical when extracting the intrinsic response. To tackle these problems, the dependence of the lasing wavelength of the laser diode on the chip temperature is investigated, and an applicable measurement setup which keeps the chip temperature stable is presented. The scattering parameters of laser diode are measured on diabatic and adiabatic conditions, and the extracted intrinsic responses for both conditions are compared. It is found that the adiabatic intrinsic responses are evidently superior to those without thermal consideration. The analysis indicates that inclusion of thermal effects is necessary to acquire accurate intrinsic response.

Temperature-dependent modulation characteristics for 1.3 mu m InAs/GaAs quantum dot lasers

Temperature-dependent modulation characteristics of 1.3 mu m InAs/GaAs quantum dot (QD) lasers under small signals have been carefully studied at various bias currents. Based on experimental observations, it is found that the modulation bandwidth significantly increases when excited state (ES) lasing emerges at high temperature. This is attributed to additional photons emitted by ES lasing which contribute to the modulation response. A rate equation model including two discrete electron energy levels and the level of wetting layer has been used to investigate the temperature-dependent dynamic behavior of the QD lasers. Numerical investigations confirm that the significant jump for the small signal modulation response is indeed caused by ES photons. Furthermore, we identify how the electron occupation probabilities of the two discrete energy levels can influence the photon density of different states and finally the modulation rate. Both experiments and numerical analysis show that the modulation bandwidth of QD lasers at high temperature can be increased by injecting more carriers into the ES that has larger electron state degeneracy and faster carrier's relaxation time than the ground state.

MULTIPLE PERIODIC SOLUTIONS OF ASYMPTOTICALLY LINEAR HAMILTONIAN SYSTEMS VIA CONLEY INDEX THEORY

In this paper we study the existence of periodic solutions of asymptotically linear Hamiltonian systems which may not satisfy the Palais-Smale condition. By using the Conley index theory and the Galerkin approximation methods, we establish the existence of at least two nontrivial periodic solutions for the corresponding systems.

基于重叠分块的FM-index性能研究与分析

FM-index压缩查询方法结合压缩技术和索引技术,其最大优势是能够在不解开压缩文件的情况下对源文件进行查询。该文通过理论分析和详细的测试数据研究重叠分块对FM-index压缩查询性能的改善。对改进后的FM-index和压缩软件Winrar在压缩时间和文件占用空间上进行分析和比较,进一步证明了重叠分块对FM-index压缩查询性能的改善。

FM-index分块并行算法及其实现

查询海量数据有压缩和索引两种方法来提高速度,该文结合这两种方法提出了压缩查询的方法.FM-index是一种自索引的全文查询算法,存在内存占用过大的问题,对于复杂的查询效率也不理想.该文提出分块FM-index算法,在分块的基础上采用MPI对算法进行并行化,解决了内存占用过多的问题,达到了较好的并行效率.