Gaussian optical design of a submillimeter-wave and far-infrared laser sideband heterodyne spectrometer

A submillimeter-wave/far-infrared (SMM/FIR) laser sideband heterodyne spectrometer has been built for molecular rotational spectroscopy application in the frequency range of 600–3000 GHz. Based on Gaussian optics, optical system of the spectrometer is designed to be quasi-achromatic and low losses. In this article the optical design and the performance of the spectrometer are presented.     

边耦合光腔用于远红外FEL的分析

 模拟了边耦合输出用于FIR FEL 的可实用性，证明这种输出方式适合于远红外FEL。分析且模拟了光腔各种输出参数（如输出功率、腔增益、耦合效率等）随输出镜尺寸及位置的变化规律，找出了最佳的输出镜尺寸及位置。并对谐振腔有漂移管和无漂移管两种情况进行了比较。通过移动或者更换输出镜（输出反射镜），改变输出镜尺寸和位置，可以灵活地选择和调节光腔的Q值。能适应实验不同阶段的需要：例如在实验初期可以提高Q值，增大净增益；而在做饱和实验时可以增大输出，使输出功率最大。     

剪切电子散斑平移棱镜相移方法研究

在剪切电子散斑干涉中,由于错位的二物光束同向传播,很难将二物光分开引入附加相位的方法来实现相移.平移棱镜相移法可以在二束物光不分开的情况下实现相移.本文对平移棱镜相移法进行了理论分析,证明平移棱镜可以引入稳定、线性的附加相位,给出了附加位移与附加相位之间的关系式.利用周边固定、中心加载的圆盘进行实验,给出了实验结果,证明平移棱镜相移法可以有效地从干涉条纹中定量提取位移导数信息.     

利用电子散斑相移技术测量物体三维面形的方法

为了获得准确的面形测量,提出了一种相移电子散斑干涉技术测量物体面形的测量方法.利用电子散斑干涉产生载波条纹,该载波条纹受到物体表面高度的调制变得弯曲,引起载波条纹相位的变化,可运用相移技术提取物体的相位信息,最后根据高度和相位之间的关系得到物体的面形.介绍了该方法的原理,利用该方法对球冠物体进行了面形测量,证明该方法测量物体面形是可行性的.由于是采用散斑干涉的方法产生干涉条纹,因此该方法测量物体面形具有灵敏度高的优点.     

Cross-spectral density matrix of the far field generated by a blackbody source

An expression is derived for the cross-spectral density matrix, valid in the paraxial region of the far field, generated by a planar blackbody source. With the help of it we determine the spectral degrees of polarization and of cross-polarization of the far field.     

Phase profile analysis of transparent objects through the use of a two windows interferometer based on a one beam splitter configuration

In this research we implemented a two windows interferometer based on polarization phase shifting and grating interferometry techniques in order to retrieve the phase data profile of the object in a single capture. The optical configuration has two optical beams with circular polarization in opposite directions, and it is coupled with a 4-f system. An amplitude grid is used as a filter which is placed at the Fourier plane to obtain replicas of each beam which can properly interfere, depending on the separation between beams. The interferometer presents the capability of changing the beam separation in order to make different orders interfere properly. The interference patterns produced can be separately modulated through the operation of linear polarizer's placed on each interference replica. In order to present the capabilities of the system we will select four interferograms result of contiguous orders interference.     

Enhancement of free space optical link in heavy rain attenuation using multiple beam concept

Free space optics (FSO) has attracted a lot of attention for a variety of applications in telecommunications area, and it is dream of every researcher and telecommunication society to make it a real alternative solution for the last mile problem, to replace fiber optics. FSO is much preferred because of its low maintenance cost and deployment time. FSO with single-beam system is vulnerable to atmospheric attenuation, so to overcome this, a multiple-beam FSO transceiver system has become prominent and is usually used. In this paper, average rain attenuation is evaluated from the collected rain intensity data which are collected for a period of seven months, and implemented in the study concerning results relating link distance, and received optical power of using multiple-beam FSO system in tropical rainy weather. Comparison is made in terms of received optical power, geometrical losses, atmospheric losses, and bit error rate (BER) on using different number of optical beams, based on simulation at data rate of 1 Gb/s. From the results it is clear that the quality of received power is improved by using up to four beams, along with link distance up to 1141.2 m as compared to one-beam, two-beam, and three-beam, with link distances 833.3 m, 991.0 m, 1075.4 m, respectively.     

First demonstration of a temporal coherence analysis through a parametric interferometer

We analyze the temporal coherence of an optical infrared radiation in the visible domain by using a Mach-Zehnder interferometer and a wavelength conversion stage in each arm. We exploit a sum frequency generation process in bulk PPLN crystal to convert the infrared radiation at 1.55 μm into 0.63 μm before the interferometric mixing. The applicability of the Wiener-Kintchine theorem through up-conversion processes is here demonstrated by direct comparisons among visible and infrared measurements.     

单幅对称变形相位图分离二维变形分量的相移电子散斑干涉技术

提出了利用相移电子散斑干涉测量物体二维变形分量的方法.单光束照明的传统电子散斑干涉技术,测量得到的是一幅物体变形的混合相位场.当物体具有对称变形时,可由这一幅相位图求得二维变形分量.方法是将该相位图镜像翻转得到第二幅相位图,通过二幅相位图的叠加、复位和分离运算,获得物体的二维变形场的分量值.利用三点加载的简支梁进行了实验,给出了实验结果,并与对称光照明实验结果进行了对比,验证了该方法的正确性.     

Theoretical analysis of pattern effect suppression in semiconductor optical amplifier utilizing optical delay interferometer

The ability of an optical delay interferometer (ODI) to suppress the pattern effect that is inherently present in a straightforward, solitary semiconductor optical amplifier (SOA) whose dynamic response is slower than the period of its driving high-speed return-to-zero (RZ) data signal is theoretically investigated. For this purpose an existing comprehensive model that simulates and links the operation of these two elements is methodically applied to their concatenated configuration. In this manner an extensive set of curves is numerically obtained, which allow to analyze and assess the impact of the input pulse energy and width as well as of the SOA carrier lifetime, linewidth enhancement factor and small signal gain on the amplitude modulation of the transmitted sequence at the output of each one of these block units. Their thorough study and interpretation reveals that the employment of the ODI can significantly reduce the value of this quality metric resulting from a single SOA only. The main offered benefit, however, is that any technical restrictions regarding the involved critical parameters can be considerably relaxed while at the same time their useful operational range can be extended. These important findings highlight the necessity of placing this passive device after the SOA and exploiting it in order to effectively alleviate the detrimental pattern-dependent degradation. This fact in conjunction with its overall practicality renders it a promising candidate for enhancing, within the frame of the proposed scheme, the performance of SOAs that are employed as pure amplification elements in fiber-optic communication systems and networking applications.     

Theoretical analysis of all-optical 2R regeneration in a SOA-based Mach–Zehnder interferometer

All-optical 2R regeneration in a semiconductor optical amplifier-based Mach–Zehnder interferometer is theoretically analyzed. It is shown that the chirp of the regenerated signal is positive, while the input signal has no chirp. The peak extinction ratio (ER) of the regenerated signal is associated with the input wavelength and there exists an input wavelength corresponding to the largest ER of the output signal. The output peak ER is also found influenced by the input power, with lower input power getting higher peak ER.     

Feasibility analysis of solid immersion lens-based dual-layer near-field recording optics with a numerical aperture of 1.84

A dual-layer near-field recording (NFR) optical system with a high numerical aperture (NA) of 1.84 was designed by appropriate cover and spacing layer selection, using layers with refractive indices of 2.0. The designed aplanatic imaging optics exhibited additional aberrations in the multi-layered stack, mainly due to the air-gap and spacer layer. Given optics designed only to compensate for aberrations caused by a 2-μm-thick cover-layer, a 3-μm-thick spacer layer induces 96.2 mλ_rms and 6.5 mλ_rms of spherical aberration and defocus, respectively. A complete electric field calculation analysis for the inside of the multi-layer stack verified that diffraction-limited spot quality can be ensured on the recording layer with phase-only correction. As the aberration caused by the multi-layered stack cannot be corrected perfectly, due to the high oscillation of the aberration function along the radial direction in the exit pupil, three different types of liquid crystal (LC) electrodes were considered for practical implementation. Of the three phase-correction methods, the approximate linear phase-correction method was the most tolerant of axis decenter from the optical axis, providing acceptable diffraction-limited correction performance.     

Real‐space analysis of radiation‐induced specific changes with independent component analysis

A method of analysis is presented that allows for the separation of specific radiation‐induced changes into distinct components in real space. The method relies on independent component analysis (ICA) and can be effectively applied to electron density maps and other types of maps, provided that they can be represented as sets of numbers on a grid. Here, for glucose isomerase crystals, ICA was used in a proof‐of‐concept analysis to separate temperature‐dependent and temperature‐independent components of specific radiation‐induced changes for data sets acquired from multiple crystals across multiple temperatures. ICA identified two components, with the temperature‐independent component being responsible for the majority of specific radiation‐induced changes at temperatures below 130 K. The patterns of specific temperature‐independent radiation‐induced changes suggest a contribution from the tunnelling of electron holes as a possible explanation. In the second case, where a group of 22 data sets was collected on a single thaumatin crystal, ICA was used in another type of analysis to separate specific radiation‐induced effects happening on different exposure‐level scales. Here, ICA identified two components of specific radiation‐induced changes that likely result from radiation‐induced chemical reactions progressing with different rates at different locations in the structure. In addition, ICA unexpectedly identified the radiation‐damage state corresponding to reduced disulfide bridges rather than the zero‐dose extrapolated state as the highest contrast structure. The application of ICA to the analysis of specific radiation‐induced changes in real space and the data pre‐processing for ICA that relies on singular value decomposition, which was used previously in data space to validate a two‐component physical model of X‐ray radiation‐induced changes, are discussed in detail. This work lays a foundation for a better understanding of protein‐specific radiation chemistries and provides a framework for analysing effects of specific radiation damage in crystallographic and cryo‐EM experiments.     

Elimination of environmental noise in interferometric wavelength shift demodulation for dynamic fiber Bragg grating sensor array

We present a novel reference compensation method for eliminating environmental noise in interferometric wavelength shift demodulation for dynamic fiber Bragg grating (FBG) sensors. By employing a shielded wavelength-division-multiplexed reference FBG in the system, the environmental noise is measured from the reference channel, and then subtracted from the demodulation result of each sensor channel. An approximate 40 dB reduction of the environmental noise has been experimentally achieved over a frequency range from 20 Hz to 2 kHz. This method is also suitable for the elimination of broadband environmental noise. The corresponding FBG sensor array system proposed in this paper has shown a wavelength resolution of .     

Design and analysis of Si-based arch-shaped gate-all-around (GAA) tunneling field-effect transistor (TFET)

In this work, a Si-based arch-shaped gate-all-around (GAA) tunneling field-effect transistor (TFET) has been designed and analyzed. Various studies on III–V compound semiconductor materials for applications in TFET devices have been made and we adopt one of them to perform a physical design for boosting the tunneling probability. The GAA structure has a partially open region for extending the tunneling area and the channel is under the GAA region, which makes it an arch-shaped GAA structure. We have performed the design optimization with variables of epitaxy channel thickness (t_epi) and height of source region (H_source) in the Si-based TFET. The designed arch-shaped GAA TFET based on Si platform demonstrates excellent performances for low-power (LP) applications including on-state current (I_on) of 694 μA/μm, subthreshold swing (S) of 7.8 mV/dec, threshold voltage (V_t) of 0.1 V, current gain cut-off frequency (f_T) of 12 GHz, and maximum oscillation frequency (f_max) of 283 GHz.     

用于双层存储的SIL近场分析

固体浸没透镜 (SIL)用于光存储光学系统增大了光学头物镜的数值孔径 ,利用近场倏逝波读写 ,减小了光斑的直径 ,提高了存储密度。文中建议 :(1)将半球SIL分割成两部分 ,其中一部分由存储媒质的保护层充当 ,避免直接污染记录层 ;(2 )在半球SIL单层读写的基础上 ,再将第一层记录媒质作为SIL的一部分形成超半球齐明SIL ,以实现双层存储。并对此时的近场进行了解析分折     

一种硅基SiO2波导耦合器的设计与分析

波导耦合器是组成光纤传感系统和光纤通信系统光收发组件及模块的重要元器件,是实现光收发模块一体化光电集成的基础。给出了一种用光纤陀螺系统的X型四端口波导耦合器的工作原理,采用有效折射率法和BPM(Beam propagation method)法建立了耦合器的数学模型,计算并分析了耦合器尺寸在尽可能小的情况下和在满足单模传输的条件下耦合器的耦合系数、有效耦合长度、分光比以及回波损耗等参数之间的关系,并对其关键技术进行了系统的研究。仿真结果表明,所设计的波导耦合器在低损耗情况下分光比可达到50%∶50%,耦合器全长为33.5mm,输入输出波导间距为410μm,芯层截面积为6μm×6μm。     

Theoretical analysis and performance investigation of ultrafast all-optical Boolean XOR gate with semiconductor optical amplifier-assisted Sagnac interferometer

A comprehensive theoretical model of an ultrafast all-optical Boolean XOR gate implemented with a semiconductor optical amplifier (SOA)-assisted Sagnac interferometer is presented. The model accounts for the SOA small signal gain, linewidth enhancement factor and carrier lifetime, the switching pulses energy and width and the Sagnac loop asymmetry. By undertaking a detailed numerical simulation, the influence of these key parameters on the metrics that determine the quality of switching is thoroughly investigated and simple design rules are extracted for their proper selection so as to ensure optimum operation. The obtained results are in good agreement with the published experimental measurements and confirm the feasibility of realizing the gate at 10 Gb/s with fairly high performance. The model can be extended for studying more complex all-optical circuits of enhanced functionality in which the XOR gate is the basic building block.     

人体腿部四层结构的红外热成像有限元分析

为研究人体红外热成像和体内肿瘤热源的关联,本文构建了包括骨层、肌肉层、脂肪层、皮肤层的人体腿部有限元模型。根据体内温度沿径向分布的特点,给出了各区域内动脉血液灌注热生成率随径向坐标变化的情况,解决了有限元建模中动脉血灌注热生成率随温度变化的非线性问题。进而用有限元方法数值计算了不同尺寸和不同深度的体内肿瘤所带来的温度变化。结果表明：在所研究的肿瘤尺寸范围内,肿瘤尺寸越小,体内温度提升越高,体表的峰值温度越高,体表温度分布半峰宽越窄,温度变化越陡峭。对于特定尺寸的肿瘤,肿瘤越深,体内峰值温度越高,体表的峰值温度越低,体表温度分布半峰宽越宽,温度变化越平缓。     

空间太阳望远镜在轨自动调焦的最小图像熵判据

由于复杂的发射状态和动态在轨空间环境以及高达0 1″的角分辨率,所以自动调焦技术已成为太阳空间望远镜在轨图像处理中的关键技术。在分析图像离焦时的状态特性的基础上,提出了一种新的更适用于空间相机的离焦判据———最小图像熵判据。最小图像熵合焦判据更适合于低对比度的天体目标。利用计算机仿真程序演示了给定目标经系统成像的过程,计算了不同离焦状态下的图像熵。这一技术将应用于2005年发射的太阳空间望远镜中。