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861.
S. P. Ahrenkiel M. H. Bode M. M. Al-Jassim H. Luo S. H. Xin J.K Furdyna 《Journal of Electronic Materials》1995,24(4):319-325
Molecular beam epitaxial growth of the ZnSe1-xTex (x=0.44-0.47) alloy on vicinal (001) GaAs substrates tilted four, six, and nine degree-[111]A or B results in partial phase separation of the alloy with a vertical modulation between different compositions. Transmission electron microscopy images of samples grown on four degree-tilted substrates showed superlattice-like structures, with periods in the range 13.4-28.9Â. Lattice images reveal diffuse interfaces between light and dark bands. Period variations were detected in isolated regions of some samples. We present evidence that the modulation develops at the growth surface, and remains stable in the bulk at temperatures up to 450°C. Satellite spot pairs with approximate indices (h k 1 + δ) were present near the zinc-blende spots in electron diffraction patterns and x-ray diffraction data, as expected from material with a sinusoidal composition profile. The orientation of the spots reveals that the modulation vector is parallel to the growth direction, rather than to [001]. The [111]A- and B-tilted samples showed significant modulation, while the five degree-[110] and on-axis material showed no detectable modulation. The modulation wavelength did not strongly depend on growth temperature in the range examined (285–335°C). Samples showing composition modulation did not exhibit significantly altered low-temperature luminescence spectra from material with no modulation. 相似文献
862.
本文对如何提高国产1.55μmInGraAspDFB-LD组件直接高速调制速率以及国产PIN-FET组件的频响带宽进行了理论与实验研究。在实验测量的基础上建立了国产LD组件小信号等效电路模型,对其调制响应速率的主要限制因素进行了分析,研制了高速DFB-LD组件,将其调制速率提高到3.2GHz。同时,在对谐振式PIN-FET光接收机进行噪声分析的基础上,采用微波混合集成工艺研制了一个串联谐振式PIN-FET光接收组件,有效地提高了PIN-FET的频响带宽。 相似文献
863.
In this paper, the interaction between two solitons has been studied by the perturbation approach in the presence of synchronized amplitude modulation and synchronized phase modulation. The results show : the combined role of synchronized amplitude modulation and synchronized phase modulation can suppress effectively the interaction. 相似文献
864.
This paper proposes a new implementation for DFT based on delta modulation which isdifferent from the conventional PCM implementation.The hardware structure of the method is multiplier-free,simple and low in cost.Theoretical analyses show that its SNR can approach conventional one's,forinstance,FFT.Computer simulations demonstrate that for deterministic signals,the results agree withtheoretical analyses.For handlimited Gaussian signals,we can still get results similar to the conventionalDFT's if selecting the step size suitably.A hardware structure which simply consists of ROM,an adder andother auxiliary circuits is also given. 相似文献
865.
以调制技术为主线 ,介绍有线电视系统中模拟调制技术、光调制技术和数字调制技术的基本原理。随着有线电视的快速发展 ,调制技术正在经历电到光、模拟到数字的不断发展和全面融合的过程 相似文献
866.
The aim of the present paper is to examine the effect of a quasi-periodic gravitational modulation on the onset of convective instability in Hele-Shaw cell. The quasi-periodic modulation considered here consists in a modulation having two incommensurate frequencies. This study is an extension of a previous work by Aniss et al. [Asymptotic study of the convective parametric instability in Hele-Shaw cell, Phys. Fluids 12 (2) (2000) 262-268] in which only a periodic gravitational modulation was considered. We have shown that for Pr=O(1) or Pr?1, the gravitational modulation has no effect on the convective threshold as expected. However, for Pr=O(ε2), it turns out that a modulation with two incommensurate frequencies has a stabilizing or a destabilizing effect strongly depending on the frequencies ratio. 相似文献
867.
868.
Tsu-Chiang Yen Jer-Wei Chang Jenn-Ming Lin Rong-Jyh Chen 《Optics Communications》1998,150(1-6):158-162
This work examines the feasibility of using incoherent optical feedback to generate high-frequency optical signals in a semiconductor laser. At a roundtrip feedback distance of 30 cm, a signal appears at around 1 GHz while the laser output is kept in single longitudinal mode and single polarization. The proposed method does not use any external modulation or saturable absorber. Some of the signal's properties are discussed as well. 相似文献
869.
870.
Slimane Mechahougui Harry Ramenah Jacques Harthong Patrick Meyrueis 《Optical Review》1996,3(2):96-100
We were mainly concerned here with multiple exposure gratings that allow interactions and coupling between gratings. We started the study of interactions and coupling with five gratings recorded in dichromated gelatin (DCG). Having determined experimentally the characteristic parameters of these five gratings, we used a method developed by Oxford University to synthesize the modulation profile. Entering these parameters of each grating into our computing programs (based on the alternative theory of diffraction in modulated media) and by varying the amplitude modulation, the latter was deduced by adjusting the numerical curve to the experimental one. We then extended the study to nine multiplexed gratings. This study allowed us to know the range of the amplitude modulation such that a certain number of angular multiplexing can be done in DCG. Several undesirable effects which we had experimentally observed appeared then during the reconstruction of any one of the multiplexed images, such as cross-talk effect. We noted the good concordance between experimental and theoretical results. We finally illustrated cross-talk effect in a diffractive memory where, if the amplitude modulation was first calculated, the number of multiplexing for an angular range could then be determined and the angular separation achieved to avoid cross-talk. 相似文献