Littrow型光栅外腔半导体激光器的输出特性分析

在讨论光栅外腔半导体激光器理论的基础上.对影响Littrow型光栅外腔半导体激光器输出功率和线宽压窄的各种因素进行了数值模拟分析.研制了单纵模高质量激光输出的Littrow型光栅外腔半导体激光器,在工作电流为400 mA时,连续输出功率达到180 mW,线宽优于1 MHz.     

窄线宽的外腔半导体激光器

介绍了使用闪耀光栅作为光反馈元件,与原始线宽大于1200GHz的半导体激光器构成的Littrow型外腔半导体激光器,极大地改善了激光器的性能。实验得到了功率恒定、模式单一稳定、线宽优于1.2MHz的激光输出,压窄线宽比为106,并针对Littrow型外腔结构提出了简洁、紧凑的复合型外腔方式。     

光纤光栅外腔半导体激光器的线宽特性研究

通过构建外腔半导体激光器的等效腔模型,并在修正的肖洛-汤斯线宽公式中引入外腔压窄因子,系统模拟了光纤光栅外腔半导体激光器的电流阈值特性和线宽特性.以等效腔模型为基础,综合考虑外腔压窄因子,利用修正后的肖恩-汤斯公式,使用Matlab对外腔激光器的阈值和线宽特性进行了系统的模拟.模拟结果表明:通过增加外腔反射率,可有效增加光子寿命并降低阈值载流子浓度,进而获得较低的阈值电流,对于0.81的外腔等效反射率,阈值电流低至3.83 mA;通过增加外腔反射率、耦合效率和外腔长度,可显著压窄线宽至千赫兹量级;此外,合理限制增益芯片尺寸也会压窄线宽.激光器工作电流为60 mA时,当外腔光栅反射率由0.1提高至0.9可使阈值电流由9.04 mA降低至4.01 mA,线宽由95.27 kHz降低至1.34 kHz;当外腔长度由2 cm增加至6 cm时,激光器线宽由3.20 kHz降低至0.36 kHz.     

浅析元件参数对外腔半导体激光器输出谱宽影响

半导体抽运碱金属蒸气激光器（DPAL）需大功率窄线宽泵浦源,但市售半导体激光器输出线宽远远大于碱金属原子吸收谱宽,难以实现有效泵浦,因此需采用Littrow 外腔法压窄半导体激光器输出谱宽。Littrow 外腔系统中元件参数的选择直接影响大功率半导体激光器输出谱宽。为此文中沿入射光线方向构建外腔压窄模型,利用球面镜替代柱面镜,分析了微柱透镜阵列、光学系统和光栅元件对外腔输出谱宽的影响,模拟结果为微柱透镜阵列焦距越小、光栅刻线越密、球面镜焦距越大,外腔输出谱宽越窄,实验结果符合理论模型。     

外腔半导体激光器动态模稳定性的研究

为了研究调谐过程中外腔半导体激光器的模稳定性,采用多光束干涉理论推导Littrow结构外腔半导体激光器的腔增益,并模拟其模结构。分析了光栅面和转臂不在同一平面的情形下,在光栅转动调谐时,通过匹配光栅的反馈波长变化率与外腔波长变化率,推导出最佳的初始外腔长度,并研究了动态模稳定（无跳模调谐）的范围;采用严格的耦合理论和光线变换矩阵分析了准直（耦合）透镜的位置对系统后向耦合效率的影响。结果表明,系统后向耦合效率最大可达99%,极大地压窄了中心波长为780nm半导体激光器的线宽,外腔半导体激光器的理论线宽为未加外腔时的0.96%,动态模稳定范围可达6.8nm。     

准直透镜失调对Littman-Metcalf光栅外腔激光器线宽的影响

以光栅外腔半导体激光器的理论知识为基础,对Littman-Metcalf型外腔半导体激光器的工作原理进行了说明,并详细地讨论了外腔半导体激光器的线宽压窄以及模式选择机制,采用严格的耦合理论和光线变换矩阵推导了系统结构参数对光场耦合效率影响的计算公式。同时,对影响Littman-Metcalf外腔激光器输出激光线宽的几个重要因素进行了分析,重点讨论了系统中准直透镜位置失调导致的线宽变化规律。计算结果表明:合理地控制Littman-Metcalf光栅外腔半导体激光器的外腔参数可以将中心波长为785 nm半导体激光器的本征线宽压窄四个数量级,该外腔系统中准直透镜位置失调会影响系统出射光场与经外腔反馈光场之间的耦合效率,进而影响光栅外腔半导体激光器的输出线宽。     

405nm波段光栅外腔窄线宽蓝紫光半导体激光器

自由运行的半导体激光器由于谱线较宽而无法满足如拉曼散射等对线宽有要求的应用需求,因此获得线宽较窄、波长稳定的半导体激光器十分必要。采用反射式全息光栅作为谱线窄化元件,研究了在Littrow布局下的405 nm外腔半导体激光器。反射式全息光栅的加入,使得光栅面和半导体激光器的输出面组成耦合外腔,这在很大程度上改善了405 nm半导体激光器的线宽性能。实验结果表明,通过加入2400 line/mm的反射式全息光栅形成外腔反馈,半导体激光器的阈值电流由31 m A下降到22 m A,谱线宽度从自由运行时的1 nm减小到0.03 nm以下,实现了窄线宽输出,并且在工作电流为100 m A时,得到窄线宽半导体激光器的输出功率为28 m W,为自由运行半导体激光器输出功率的31.7%。此外,通过调节反馈光栅的角度,实现了较大电流范围的激光波长的连续调谐,最大调谐范围达3.5 nm。     

光反馈对光纤光栅外腔半导体激光器特性的影响

主要研究了外加光反馈对光纤布拉格光栅外腔半导体窄线宽激光器特性的影响。在研究温度对光纤光栅外腔半导体激光器激射波长影响的基础上,设计了强度可调的外加光反馈系统,并利用延时自外差法测试外腔半导体激光器的线宽,从实验上分析了不同强度的外加光反馈对外腔半导体激光器线宽和噪声的影响。实验结果表明,在外加光反馈强度逐渐增强的过程中,激光器线宽逐渐变窄。当反馈比为-22dB时,激光器线宽被压窄至原始线宽的15%。与此同时,在相同的反馈变化下,激光器的相对强度噪声开始无明显变化,直到反馈比达到-27dB。再继续增大反馈强度,相对强度噪声显著增大,激光器内部发生相干崩塌。     

紧凑型光栅外腔可调谐半导体激光器

研制了一台结构紧凑的窄线宽、可调谐半导体激光器.采用光栅外腔Littrow结构,将光栅和平面反射镜置于同一个旋转平台上,并使光栅衍射平面和平面镜反射平面的交线与平台旋转轴重合,通过旋转平台实现光栅外腔选取单纵模、压窄线宽和波长调谐,并保证输出光的方位不发生改变,同时用棱镜将输出光斑压缩成为类方形.该激光器的尺寸为110 mm×80 mm×35 mm,中心输出波长为653 nm,谱宽0.07 nm,调谐范围4.6 nm,可连续稳定运转4小时以上.     

宽调谐范围光栅外腔窄线宽405nm蓝紫光半导体激光器研究

自由运行的半导体激光器通常为多纵模光谱输出,谱线宽度较大,不能满足拉曼散射等对光源线宽有要求的应用。为得到稳定输出的窄线宽激光,通过使用反射式全息光栅,有效地窄化了405 nm波段激光二极管的谱线宽度。使用高分辨率单色仪检测了Littrow布局下光栅外腔半导体激光器的输出光谱,并通过输出功率和光谱特性研究了光栅外腔半导体激光器的阈值和调谐特性。实验发现,通过使用2400 l/mm和3600 l/mm刻线密度的反射式全息光栅,激光二极管的阈值电流由30.0 m A分别下降到19.7 m A和21.3 m A,谱线宽度也从自由运行时的1 nm左右下降到0.03 nm以内,在标称的工作电流范围内得到了窄线宽激光输出,并且分别实现了5.45 nm和5.33 nm宽度的波长调谐。这一结果有利于推动蓝紫光激光二极管的光谱应用。     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.     

New insert layer structure OLEDs

An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.