Conventional and modified Schwarzschild objective for EUV lithography: design relations

The design criteria of a Schwarzschild-type optical system are reviewed in relation to its use as an imaging system in an extreme ultraviolet lithography setup. Both the conventional and the modified reductor imaging configurations are considered, and the respective performances, as far as the geometrical resolution in the image plane is concerned, are compared. In this connection, a formal relation defining the modified configuration is elaborated, refining a rather naïve definition presented in an earlier work. The dependence of the geometrical resolution on the image-space numerical aperture for a given magnification is investigated in detail for both configurations. So, the advantages of the modified configuration with respect to the conventional one are clearly evidenced. The results of a semi-analytical procedure are compared with those obtained from a numerical simulation performed by an optical design program. The Schwarzschild objective based system under implementation at the ENEA Frascati Center within the context of the Italian FIRB project for EUV lithography has been used as a model. Best-fit functions accounting for the behaviour of the system parameters vs. the numerical aperture are reported; they can be a useful guide for the design of Schwarzschild objective type optical systems.     

轴对称综合孔径光学系统的调制传递函数和成像性质

综合分析目前各种综合孔径光学系统的结构和成像特征,并对它们作了比较。使用数值模拟方法,对单环轴对称综合孔径光学系统和双环结构的轴对称系统进行分析,研究了轴对称综合孔径光学系统的结构形式及其调制传递函数(MTF),并对其成像性质作了评估与比较。讨论了一种4+2双环结构的轴对称综合孔径系统的结构形式,对其成像特点作了详细描述,最后运用图像复原维纳滤波器对系统成像图做了处理,以使这种轴对称综合孔径系统具有更理想的成像效果。     

稀稀疏孔径等边六孔径结构研究

对光学稀疏孔径子孔径空间分布结构与系统成像特性的基本关系进行了讨论.提出了一种新的子孔径分布结构——等边六孔径结构并给出了该结构的具体分布形式和光瞳函数.对等边六孔径结构的成像特性进行分析,把它与MMT型和Golay6型六孔径结构的调制传递函数进行了仿真实验和比较.     

Design of a Thin-Film-Based Optical Filter for Broadband Multichannel Communication Systems

This paper is concerned with the design of an optical filter, based on thin-film interference, for multichannel optical communication systems with Ta₂O₅ and MgF₂ materials for 1550 nm operation. The performance of the filter configuration is analyzed and the numerical results of the optimization parameters, such as central wavelength, 3-dB bandwidth, figure of merit and ripple in the passband, are reported. The variation of these parameters is also studied for various modified filter configurations. The angular performance of the filter is investigated in terms of the polarization-dependent loss and spectral shift of transmittance towards shorter wavelengths.     

Backward pumping kilowatt Yb3+-doped double-clad fiber laser

A ytterbium-doped double-clad fiber laser generating up to 1026 W of continuous-wave output power at 1085 nm with a slope efficiency of 74% by single-ended backward pumping configuration is reported. The core diameter was 20 μm with a low numerical aperture of 0.06, and a good beam quality (BPP < 1.8 mm mrad) is achieved without special mode selection methods. No undesirable roll-over was observed in output power with increasing pump power, and the maximum output power was limited by the available pump power. The instability of maximum output power was better than ±0.6%. Different pumping configurations were also compared in experiment, which shows good agreements with theoretical analyses.     

Effects of End-Face Tilt Angle on Numerical Aperture for Straight and Bent Plastic Optical Fibers

Numerical aperture (NA) is an important parameter of optical fibers. The larger it is, the greater the amount of light input into the fiber and, hence, the greater the achievable transmission distance. In this article, analytical functions are given for numerical aperture of an angle-ended plastic optical fiber in terms of the tilt angle of its input/output face. This tilt may be intentional, as in biomedical spectroscopic sensors, or otherwise when exploiting the quick interconnectivity potential of plastic fibers. The influence of fiber curvature on its numerical aperture has also been quantified as the functions given cover both straight and curved fiber configurations.     

Fluorescence microscopy with 3D resolution in the 100 nm range

We propose a combination of 4Pi and Theta microscopies to improve the resolution of fluorescence microscopy by using six microscope objectives in a configuration we call Multiple Objective Microscopy (MOM). A resolution in the 100 nm range is obtained in the three dimensions using low numerical aperture, long working distance objectives. The obtained results not only show that high resolution is not restricted to high numerical aperture objectives, but also open the possibility of exploring large volumes with a very good resolution.     

拼接式望远镜主镜衍射效应研究

拼接式主镜的设计使超大口径望远镜的构想成为现实。为了研究拼接式望远镜的成像性能,精确分析和量化了拼接式主镜构型、平移误差、倾斜误差对衍射效应的影响,从拼接式光学系统的成像原理出发,基于齐次坐标变换建立了拼接式主镜的光瞳模型,并仿真分析了拼接主镜构型对衍射效应的影响。分析结果表明:对于不同构型的拼接主镜,其衍射效应受拼接主镜的填充因子和孔径间隔共同影响,填充因子越高,孔径间隔越小,系统成像质量越好。以典型的拼接主镜构型为例,分别仿真分析了单个子镜平移误差、倾斜误差和拼接主镜整体平移误差、倾斜误差对衍射效应的影响。分析结果表明:对于单个子镜,平移误差对远场衍射的影响具有周期性;对于拼接主镜整体,当子镜piston误差的均方根值小于0.039λ时,斯特列尔比大于0.95;当子镜tip-tilt误差的均方根值小于0.036λ时,斯特列尔比大于0.95。分析结果为拼接式望远镜的成像性能分析、主镜的构型设计、平移误差和倾斜误差的检测与调整等提供了依据。     

Comparison of NETD performance of staring and partial-scanning infrared focal plane arrays

The NETD performance of two main configurations are compared: a staring matrix and a partial-scanning system in which a number of vectors, equally-spaced along the image width, are scanning in parallel with a smaller amplitude. The comparison is systematically derived and is valid for both the hybrid and monolithic approaches. The derivation leads to an optimal design procedure for the partial-scanning configuration, based on the optimization of the direct integration time. Several numerical examples relevant to current technologies are presented. In cases characterized by high photon flux levels or 2-D cold shield with low efficiency, the partial-scanning configuration may yield better NETD values compared to a staring system. In addition, it usually has a better spatial resolution and hence may result in superior MRTD performance.     

Fabry–Perot effect on dimer nanoantennas

In this work, we investigate the interaction between a single quantum emitter and dimer nanoantennas through a Fabry–Perot structure composed of an appropriate combination of two dielectric layers. This type of dielectric configuration is well known in the microwave region to increase the antenna performance, such as directivity, radiation efficiency, and radiation resistance. Here, the Fabry–Perot concept is transposed to the optical domain. The single emitter couples to the antenna through the dielectric structure, giving rise to a wide aperture field on top of the dielectrics with the same polarization of the emitter. This purely polarized aperture field can be used to excite one or more conveniently spaced nanoantennas. We demonstrate by 3D numerical calculations that the directivity and excitation rate of a single dimer is highly increased. Also, we show that multiple dimers arranged in an array configuration can be enhanced due to the wide aperture field generated by a single emitter.     

LCoS背投光学引擎中变焦投影物镜设计

设计出变焦投影物镜，能满足相同光学引擎、相同屏幕位置下不同屏幕尺寸的需要。考虑到所设计的系统为大相对孔径、中等视场和小变焦比，从变焦理论出发，采用正组补偿的机械补偿法，对变倍组进行合理的倍率选段，求出了高斯解；然后分组元选用合理的初始结构，利用ZEMAX光学设计软件进行优化设计，解决了变焦系统畸变难以控制的问题，并使用调制传递函数对整个系统进行了综合评价。设计结果表明：该变焦投影物镜系统的光学性能和成像质量均满足设计指标要求，能应用于101.6～177.8cm的大屏幕电视。     

Improving the performance of three level code division multiplexing using the optimization of signal level spacing

In order to optimize the performance of three level code division multiplexing (3LCDM) at 2×20 Gb/s data rate, signal level spacing technique is investigated in this paper. The 3LCDM performance is improved considerably using both electrical and optical level spacing optimization configurations. The results demonstrate that by optimization, in conditions of the optical signal-to-noise ratio, an improvement of around 4.5 dB can be achieved in both approaches as well as 3.3 dB in the electrical configuration and 3.5 dB in the optical configuration can be accomplished for the 3LCDM in terms of the receiver sensitivity.     

长焦距超高倍率变焦距光学系统设计

为设计一套焦距17～1 700mm的长焦距、超高倍率变焦距光学系统,首先在合理选择初始结构基础上,通过比较高斯光学计算结果找出高斯解对系统性能的影响规律,从而确定系统的关键参量;然后通过分析各组元相对孔径和像差特点选定结构形式,并进行系统像差的校正和优化.设计结果系统光学总长760mm,各焦距位置全视场50lp/mm处MTF>0.3,各项指标满足系统要求.     

光突发交换的交换控制策略和光缓存配置

光突发交换是面向下一代互联网的光交换模式.讨论了异步光突发交换系统的交换控制策略以及相应光缓存的优化配置策略.除了传统预约模式的交换策略,还研究了非预约和改进型预约模式,它们的性能评估由计算机仿真给出.结果表明:在条件相当情况下,改进型预约模式具有最低的丢包率.同时光缓存的配置对上述几类交换控制策略的性能都有很大影响,仿真结果指出:光缓存的粒度对系统性能具有重要影响,所讨论的几类交换模式都存在最佳时延粒度,研究结果对光交换矩阵的设计有指导意义.     

光阑对非线性折射光限幅效果影响的理论研究

分析和计算了光阑在两种典型光路系统的光限幅中对限幅效果的影响,包括光阑的大小和位置.两种典型系统分别为理想望远系统和理想聚焦系统.计算模型基于Z扫描理论及其改进公式,限幅机理为非线性折射.对每种情况下光阑的影响进行了定性分析和计算,并取得了相应的理论曲线.研究结果对于光限幅结构中光阑的选取和优化有重要的参考意义.     

LED based fiber optic surface plasmon resonance sensor

Modeling of a miniaturized fiber optic sensor based on surface plasmon resonance utilizing a broad band diffuse source is presented. Attenuated total internal reflection with Kretschmann configuration is the basis of the theoretical model. For simulation both meridional and skew rays are considered. The performance of the sensor is evaluated in terms of sensitivity, detection accuracy and signal to noise ratio. Effects of the numerical aperture of the fiber, core diameter and length of the sensing region on the performance parameters of the sensor are studied. The results are obtained for gold and silver metallic layer on the core of the fiber. The theoretical results obtained are compared with SPR based fiber optic sensor utilizing focused beam on the end face of the fiber from a collimated source. The advantages of using broadband LED (diffuse source) source for launching light in the fiber are the miniaturization, compactness and low cost of the sensor.     

陡化前沿Marx发生器的重频运行研究

 将10级陡化前沿Marx发生器由电阻隔离型改造成为电感隔离型,以便对其开展重频特性研究。通过恒压源充电的单次实验发现,发生器在氮气(N₂)中工作时,两种隔离方式的输出脉冲波形基本一致,然而在六氟化硫(SF₆)气体中工作时,电感隔离型相对于电阻隔离型的输出脉冲前沿较慢;对其原因做出了初步分析。在利用恒流充电装置充电的重频实验过程中,通过采用提高充电电流的方法,解决了发生器恒流充电时的充电脉动问题,进而开展了重复频率运行实验研究。实验结果表明,在不对开关进行吹气的情况下,当充电30 kV时,发生器可以在8.2 Hz的重频下稳定工作,输出脉冲的重叠一致性比较好,输出电压约为150 kV,电流约为1.8 kA,脉冲前沿为十几ns。     

Modified synthetic transmit aperture algorithm for ultrasound imaging

The modified synthetic transmit aperture (STA) algorithm is described. The primary goal of this work was to assess the possibility to improve the image quality achievable using synthetic aperture (SA) approach and to evaluate the performance and the clinical applicability of the modified algorithm using phantoms. The modified algorithm is based on the coherent summation of back-scattered RF echo signals with weights calculated for each point in the image and for all possible combinations of the transmit-receive pairs. The weights are calculated using the angular directivity functions of the transmit-receive elements, which are approximated by a far-field radiation pattern of a narrow strip transducer element vibrating with uniform pressure amplitude over its width. In this way, the algorithm takes into account the finite aperture of each individual element in the imaging transducer array. The performance of the approach developed was tested using FIELD II simulated synthetic aperture data of the point reflectors, which allowed the visualization (penetration) depth and lateral resolution to be estimated. Also, both simulated and measured data of cyst phantom were used for qualitative assessment of the imaging contrast improvement. The experimental data were obtained using 128 elements, 4 MHz, linear transducer array of the Ultrasonix research platform. The comparison of the results obtained using the modified and conventional (unweighted) STA algorithms revealed that the modified STA exhibited an increase in the penetration depth accompanied by a minor, yet discernible upon the closer examination, degradation in lateral resolution, mainly in the proximity of the transducer aperture. Overall, however, a considerable (12 dB) improvement in the image quality, particularly in the immediate vicinity of the transducer’s surface was demonstrated. The modified STA method holds promise to be of clinical importance, especially in the applications where the quality of the “near-field” image, that is the image in the immediate vicinity of the scanhead is of critical importance such as for instance in skin- and breast-examinations.     

Nanoscale plasmonic devices for dynamically controllable beam focusing and scanning

We have performed simulations to investigate the variable focusing and scanning capability of metallic nano-slit configurations. In a symmetric nanorod configuration inside an aperture with adjustable offset of the center rod, the focal position is found to be variable in the 0.5–3.5 μm range. In a ladder configuration of the rods, the transmitted beam is found to be deflected up to 23°. Horizontal displacement of rods allows for finer control of angular scanning up to 4°. Such slit geometries offer the potential to be controlled by using nano-positioning systems for applications in dynamic beam shaping and scanning on the nanoscale.