共查询到20条相似文献,搜索用时 125 毫秒
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分析了湍流大气光传输特性,讨论了光信号闪烁对宽带光无线通信误码率的影响及解决方案。从湍流大气的经典功率谱模型与修正功率谱模型出发,分析了Rytov指数与光场波长的变化关系,讨论了其对传输光场强度起伏的影响,以及分别在球面波与平面波时的差异。从实验上模拟考察了湍流大气对宽带光通信的影响,提出了一种新的从光链路上矫正波前畸变、减弱信号闪烁进而降低通信系统误码率的技术方案。该方案基于遗传算法和无模型盲优化的方式,以Zernike多项式系数为向量,对波前畸变进行编码,根据畸变波前的Zernike多项式的系数实现波前重构。其特点是没有预先测量波前相位畸变信息,而是采用施特列耳比作为遗传算法的适应度评判标准,通过优化达到最佳的波前畸变补偿效果。分析结果表明,该方案对中等强度以下的湍流大气光传输具有明显改善效果。 相似文献
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为了提高传统随机并行梯度下降 (Stochastic Parallel Gradient Descent, SPGD) 算法校正波前畸变的性能,提出了一种基于AdaBelief优化器的新型SPGD优化算法。该算法将深度学习中AdaBelief优化器的一阶动量和二阶动量集成到SPGD算法中以提高算法的收敛速度,并使得算法能够自适应地调整增益系数。 此外,对实际增益系数进行自适应动态裁剪以避免因实际增益系数出现极端值而造成的震荡。仿真结果表明:在37单元变形镜 (Deformable Mirror, DM)下,新型SPGD优化算法能够对不同湍流强度下的波前畸变实现有效校正,不同波前畸变经过校正后的斯特列尔比(Strehl ratio, SR)分别提升至0.83、0.47和0.31。此外,该算法在不同湍流强度下的SR仅仅需要149、229和230次迭代达到阈值,与传统SPGD算法及其他优化算法相比有更快的收敛速度,且在稳定性和参数调节方面也具有一定的优越性。 相似文献
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基于MEMS技术的分立式微变形镜校正能力研究 总被引:1,自引:0,他引:1
针对基于微型机电系统技术的分立式微变形镜,从镜面面形特点出发分析了方形和蜂窝形阵列变形镜适配能力,并利用ZEMAX软件建立畸变波前和变形镜模型,仿真分析两种分立式微变形镜的校正能力.研究表明在近似子单元数情况下,蜂窝形阵列微变形镜对畸变波前的校正能力更好. 相似文献
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《中国激光》2015,(12)
在波前校正过程中,变形镜(DM)在强激光连续辐照(CW)下会产生热形变,进而对入射光引入附加波前畸变,从而制约了变形镜的波前校正效果,致使光束质量改善效果变差。从变形镜热形变面形的Zernike多项式分解出发,建立了强激光连续辐照下变形镜的热形变预估模型,根据预估所得的热形变面形,模拟计算得到了变形镜的驱动器控制信号参数,进而驱动变形镜对其自身的热形变面形进行了实时补偿。仿真结果表明,该自校正方法能有效补偿变形镜自身的热形变面形,减小变形镜热形变对其校正能力的影响;采用局部换热方式只能在一定程度上减小变形镜形变面形引起的平移相差和离焦相差,对光束质量的改善效果也比较有限,而该自校正方法能有效减小热形变引起的光程差,从而对光束质量起到明显的改善作用。 相似文献
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High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET > PDMAT > TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center. 相似文献
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In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal (200) (2d = 0.4027 nm) is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line(w), the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line(x), the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines(y), the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line(z) in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line(q) in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution(λ/△ 2) is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy. 相似文献
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This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors. 相似文献
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YUXiao-hua XIANGYu-qun 《半导体技术》2005,30(2):30-32,37
An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB. 相似文献
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The epi material growth of GaAsSb based DHBTs with InAlAs emitters are investigated using a 4 × 100mm multi-wafer production Riber 49 MBE reactor fully equipped with real-time in-situ sensors including an absorption band edge spectroscope and an optical-based flux monitor. The state-of-the-art hole mobilities are obtained from 100nm thick carbon-doped GaAsSb. A Sb composition variation of less than ± 0.1 atomic percent across a 4 × 100mm platen configuration has been achieved. The large area InAlAs/GaAsSb/InP DHBT device demonstrates excellent DC characteristics,such as BVCEO>6V and a DC current gain of 45 at 1kA/cm2 for an emitter size of 50μm × 50μm. The devices have a 40nm thick GaAsSb base with p-doping of 4. 5 × 1019cm-3 . Devices with an emitter size of 4μm × 30μm have a current gain variation less than 2% across the fully processed 100mm wafer. ft and fmax are over 50GHz,with a power efficiency of 50% ,which are comparable to standard power GaAs HBT results. These results demonstrate the potential application of GaAsSb/InP DHBT for power amplifiers and the feasibility of multi-wafer MBE for mass production of GaAsSb-based HBTs. 相似文献
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We calculate the Langevin noise sources of self-pulsation laser diodes, analyze the effects of active region noise and saturable-absorption region noise on the power fluctuation as well as period fluctuation, and propose a novel method to restrain the noise effects. A visible SIMULINK model is established to simulate the system, The results indicate that the effects of noise in absorption region can be ignored; that with the increase of DC injecting current, the noise effects enhance power jitter, and nevertheless, the period jitter is decreased; and that with external sinusoidal current modulating the self-pulsation laser diode, the noise-induced power jitter and period jitter can be suppressed greatly. This work is valuable for clock recovery in all-optical network. 相似文献
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Large-scale synthesis of single-crystal CdSe nanoribbons is achieved by a modified thermal evaporation method, in which two-step-thermal-evaporation is used to control CdSe sources' evaporation. The synthesized CdSe nanoribbons are usually several micrometers in width, 50 nm in thickness, and tens to several hundred micrometers in length. Studies have shown that high-quality CdSe nanoribbons with regular shapes can be obtained by this method. Room-temperature photolumines-cence indicates that the lasing emission at 710 nm has been observed under optical pumping (266 nm) at power densities of 25-153 kW/cm^2. The full width half maximum (FWHM) of the lasing mode is 0.67 nm 相似文献
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TANG Bin JIANG Xing-fang LIU Zhi-min 《光电子快报》2008,4(1):78-80
By using the expansion of the aperture function into a finte sum of complex Gaussian functions, the corresponding analytical expressions of Hermite-cosh-Gaussian beams passing through annular apertured paraxially and symmetrically optical systems written in terms of ABCD matrix were derived, and they could reduce to the cases with squared aperture. In a similar way, the corresponding analytical expressions of cosh-Gaussian beams through annular apertured ABCD matrix were also given. The method could save more calculation time than that by using the diffraction integral formula directly. 相似文献
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Tian-hua Xu Feng Tang Wen-cai Jing Hong-xia Zhang Da-gong Ji Chang-song Yu Ge Zhou Yi-mo Zhang 《光电子快报》2008,4(4):292-294
Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited. 相似文献
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《中国通信》2014,(9)
正Communications—VLSI Researches and industries of telecommunications have been growing rapidly in the last 20 years and will keep their high growing pace in the next decade.The involved researches and developments cover mobile communications,highway and last-mile broadband communication,domain specific communications,and emerging D2D M2M communications.Radio communication steps into its 相似文献