基于分数泰伯效应的双波长微距分束的研究

微距光谱分束是红外领域小型双波段成像系统的关键技术之一。利用菲涅耳衍射理论和角谱理论,研究了双波长和宽角度入射光场通过阶梯光栅在分数泰伯距离下的衍射特性。建立了基于阶梯光栅的双探测阵列成像模型,数值模拟了入射波长分别为4 m和4.5 m的光束在-30~30入射角度范围的光栅分束结果,获取了探测面上的发光强度、能量和信噪比等参数值。此文的研究成果可为构建微型双波段成像装置及设计精密光谱分束器件提供理论支持。     

Level-set-based artery-vein separation in blood pool agent CE-MR angiograms

Blood pool agents (BPAs) for contrast-enhanced (CE) magnetic-resonance angiography (MRA) allow prolonged imaging times for higher contrast and resolution. Imaging is performed during the steady state when the contrast agent is distributed through the complete vascular system. However, simultaneous venous and arterial enhancement in this steady state hampers interpretation. In order to improve visualization of the arteries and veins from steady-state BPA data, a semiautomated method for artery-vein separation is presented. In this method, the central arterial axis and central venous axis are used as initializations for two surfaces that simultaneously evolve in order to capture the arterial and venous parts of the vasculature using the level-set framework. Since arteries and veins can be in close proximity of each other, leakage from the evolving arterial (venous) surface into the venous (arterial) part of the vasculature is inevitable. In these situations, voxels are labeled arterial or venous based on the arrival time of the respective surface. The evolution is steered by external forces related to feature images derived from the image data and by internal forces related to the geometry of the level sets. In this paper, the robustness and accuracy of three external forces (based on image intensity, image gradient, and vessel-enhancement filtering) and combinations of them are investigated and tested on seven patient datasets. To this end, results with the level-set-based segmentation are compared to the reference-standard manually obtained segmentations. Best results are achieved by applying a combination of intensity- and gradient-based forces and a smoothness constraint based on the curvature of the surface. By applying this combination to the seven datasets, it is shown that, with minimal user interaction, artery-vein separation for improved arterial and venous visualization in BPA CE-MRA can be achieved.     

CO2 laser stabilization to 0.1-Hz level using externalelectrooptic modulation

We have developed a frequency stabilization scheme for CO₂ lasers using only external modulation via an electrooptic modulator (EOM). One of the two laser sidebands which are generated by the EOM and frequency-modulated is set in resonance with a Fabry-Perot cavity, itself filled with OsO₄ as an absorber. The saturation signal of an OsO₄ line detected in transmission of the Fabry-Perot cavity is used for stabilization. We obtained a stability of 0.1 Hz (Δν/ν=3.5 10^-15) on a 100-s time scale, and a reproducibility up to 10 Hz with the strongest OsO₄ reference lines. These results largely improve the performance of our previous setup for which modulation was applied through piezoelectric transducers. Further, the stabilized laser is not frequency-modulated and is easily tunable     

Pixelless imaging device using optical up-converter

A pixelless imaging device based on optical wavelength conversion was designed and fabricated. The up-converter consisted of an integrated InGaAs/InP PIN photodetector and an InGaAsP/InP light-emitting diode (LED) epitaxially grown on a single InP substrate. Incoming 1.5 /spl mu/m optical radiation was absorbed by the p-i-n detector and generated a photocurrent. The resultant photocurrent was used to bias the LED that emitted at 1 /spl mu/m, which could be detected by conventional silicon charge coupled device. Pixelless imaging by the device has been demonstrated at room temperature.     

光参量振荡器中的多频振荡

在双谐光参量振荡器中,首次在信号和空闲波段同时记录下多于一个“群”的振荡,并观察到输出频率的跳变,从实验上证实了“群集效应”。     

Blind signal separation from optical imaging recordings with extended spatial decorrelation

Optical imaging is the video recording of two-dimensional patterns of changes in light reflectance from cortical tissue evoked by stimulation. We derived a method, extended spatial decorrelation (ESD), that uses second-order statistics in space for separating the intrinsic signals into the stimulus related components and the nonspecific variations. The performance of ESD on model data is compared to independent component analysis algorithms using statistics of fourth and higher order. Robustness against sensor noise is scored. When applied to optical images, ESD separates the stimulus specific signal well from biological noise and artifacts.     

Three-dimensional surface reconstruction using optical flow formedical imaging

The recovery of a three-dimensional (3-D) model from a sequence of two-dimensional (2-D) images is very useful in medical image analysis. Image sequences obtained from the relative motion between the object and the camera or the scanner contain more 3-D information than a single image. Methods to visualize the computed tomograms can be divided into two approaches: the surface rendering approach and the volume rendering approach. In this paper, a new surface rendering method using optical flow is proposed. Optical flow is the apparent motion in the image plane produced by the projection of real 3-D motion onto the 2-D image. The 3-D motion of an object can be recovered from the optical-flow field using additional constraints. By extracting the surface information from 3-D motion, it is possible to obtain an accurate 3-D model of the object. Both synthetic and real image sequences have been used to illustrate the feasibility of the proposed method. The experimental results suggest that the proposed method is suitable for the reconstruction of 3-D models from ultrasound medical images as well as other computed tomograms     

采用光学处理方法的被动太赫兹波综合孔径成像

综合孔径技术对于提高被动太赫(THz)成像系统的分辨率、减小系统体积有着重要的意义.研究了一种基于电光调制和空间光干涉成像的THz综合孔径成像技术.在该成像方法中,天线阵列接收目标辐射的THz信号,通过混频和电光调制将信号振幅和相位信息加栽到激光载波上,由光纤传输该激光信号并在光纤末端形成天线缩比阵列结构,最终利用光纤阵列输出光束的空间互相干在透镜焦平面上获得目标成像.分析了该成像方法的原理,以及成像中的信号变换与光学干涉处理的关键技术,并利用0.5 THz超导体一绝缘体一超导体(SIS)接收机进行了电光调制和干涉实验.结果表明:该方法能够应用于被动THz综合孔径成像.     

光纤中光脉冲的直线平移及幅度衰减振荡特性

为了探索初始1阶相位调制对高斯光脉冲光纤中长距离传输特性的影响规律,从光纤中的非线性光演化方程出发,采用分步傅里叶算法,数值研究了初始1阶相位调制的高斯光脉冲在光纤中传输时的形状、幅度、时间轨道的演化特性。结果表明,高斯脉冲在长距离传输中,一方面其幅度呈现出衰减的振荡行为,另一方面其时间轨道则因为1阶相位调制的存在而发生直线平移;直线平移的大小和方向分别取决于相位调制参量的绝对值和正负号。该工作可扩展非孤子脉冲的长距离传输特性研究,并可用于脉冲时间轨道的直线调控。     

Microwave indirect holographic imaging using an adaptation of optical techniques

Indirect holography provides a quick and inexpensive three-dimensional (3-D) imaging technique at optical frequencies which has not been directly adapted to microwave imaging. This letter describes a technique whereby a radiated offset reference plane wave can be electronically synthesized allowing this technique to be used at microwave frequencies. In this letter, this technique has been applied to the problem of determining antenna radiation patterns and reconstructing complex near fields. Early experimental results compare favorably with results taken using traditional methods.     

Image deblurring using derivative compressed sensing for optical imaging application

The problem of reconstruction of digital images from their blurred and noisy measurements is unarguably one of the central problems in imaging sciences. Despite its ill-posed nature, this problem can often be solved in a unique and stable manner, provided appropriate assumptions on the nature of the images to be recovered. In this paper, however, a more challenging setting is considered, in which accurate knowledge of the blurring operator is lacking, thereby transforming the reconstruction problem at hand into a problem of blind deconvolution. As a specific application, the current presentation focuses on reconstruction of short-exposure optical images measured through atmospheric turbulence. The latter is known to give rise to random aberrations in the optical wavefront, which are in turn translated into random variations of the point spread function of the optical system in use. A standard way to track such variations involves using adaptive optics. Thus, for example, the Shack-Hartmann interferometer provides measurements of the optical wavefront through sensing its partial derivatives. In such a case, the accuracy of wavefront reconstruction is proportional to the number of lenslets used by the interferometer and, hence, to its complexity. Accordingly, in this paper, we show how to minimize the above complexity through reducing the number of the lenslets while compensating for undersampling artifacts by means of derivative compressed sensing. Additionally, we provide empirical proof that the above simplification and its associated solution scheme result in image reconstructions, whose quality is comparable to the reconstructions obtained using conventional (dense) measurements of the optical wavefront.     

Two and three level optical PCM transmitter design for multigigabit systems using a relaxation oscillation technique

A theoretical method based on gain switching of semiconductor lasers is described which optimizes the bandwidth and modulated output power from a given laser for application in optical PCM systems. Both two- and three-level systems are considered. The type of laser used to demonstrate the technique is typical of an AlGaAs BH laser. A three-level optical system based on only two electrical drive levels is evaluated. Numerical results based on the single-mode rate equations, including a diffusion term, predict bit rates of 5 Gbit/s for a two-level system and 8 Gbit/s for the three level system. The technique was also applied to short cavity and quaternary lasers. For a short-cavity (100-μm) laser bit rates of 9 and 14 Gbit/s were predicted for the two- and three-level systems, respectively. For an In-GaAsP etched mesa BH laser bit rates of 10 and 16 Gbit/s were predicted for the two- and three-levels systems, respectively. The bandwidth was found to be limited by the laser parameters and catastrophic mirror damage which limits the maximum allowed drive current.     

将成像光学系统用于激光发射的设计与分析

为减轻卫星载荷质量和应对各种突发状况,将成像光学系统同时用作激光发射天线的共口径设计具有重要意义。因此根据特定的成像光学系统给出了共口径设计方法,针对其中基于EDFA功放技术的发射单元与成像系统相匹配的耦合镜头进行了分析与设计,基于此研究了发射高斯光束在该共口径系统中的传输及出射光束的场分布,讨论并仿真分析了耦合镜头与成像主次镜距离的改变对出射光束性能的影响。结果表明,共口径设计满足激光发射要求,并且微调耦合镜头与成像主次镜的距离可以改变出射光束的束腰和远场光强峰值能量从而满足不同的通信需求,且对出射光束的总能量没有明显影响。     

全息透镜阵列实焦点成像实现PS光互连

利用２＊２全息透镜阵列的实焦点成像方式实现２Ｎ＊２Ｎ输入的ＰＳ光互连,分析指出,由于实点点成像对输入 的交错,必须在秀镜阵列后添加一个成像透镜才能获得ＰＳ互连变换;     

174-nm mode spacing in dual-wavelength semiconductor laser using nonidentical InGaAsP quantum wells

A very wide tuning range of dual-wavelength semiconductor lasers with properly designed nonidentical InGaAsP quantum wells is reported. As the external cavity of reflected-type grating telescope configuration is well aligned, the dual-wavelength operation can be achieved with a record wavelength separation as large as 174 nm (25 THz). The wide separation of two wavelengths is possible due to a proper modification of the external-cavity configuration and reduced gain competition of laser modes.     

Optical imaging of anatomical maps derived from magnetic resonanceimages using time-independent optical sources

Presents a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed     

L-band fiber laser with wide tuning range based on dual-wavelength optical bistability in linear overlapping grating cavities

A new mechanism to tune an erbium-doped fiber laser in the L-band is presented. The technique is based on the dual-wavelength bistability in overlapping linear cavities, which allows two lasing lines to be switched from one to another by a triggering pulse superimposed to the dc bias current applied to the pump source. The two wavelengths can be independently tuned to give the laser a total tuning range of 33 nm that covers the whole L-band, while the tuning range of either of the tunable fiber Bragg gratings (FBGs) used is only half of that range. An output dynamic range of 7 dB, and a maximum output power of up to 11 dBm with high optical signal-to-noise ratios are obtained. A study of the switching transient responses shows that the typical switching time is about 4 to 12 ms, depending on the dc bias current applied to the pump source. Moreover, our wide tuning technique is implemented by only applying ordinary commercial tunable FBGs which normally would have given rise to only about half of the tuning range; no additional filtering mechanisms are required to achieve almost uniform outputs.     

Picosecond pulse generation in semiconductor lasers using resonance oscillation

Narrow pulses below 100 ps (f.w.h.m.) have been generated by applying 100 or 300 ps current pulses to a wide-stripe double heterostructure laser. The modulation current was increased to minimise the pulse width.     

Compound noise separation in digital circuits using blind source separation

Analysis of individual noise sources in pre-nanometer circuits cannot take into account the evolving reality of multiple noise sources interacting with each other. Noise measurement made at an evaluation node will reflect the cumulative effect of all the active noise sources, while individual and relative severity of various noise sources will determine what types of remedial steps can be taken, pressing the need for development of algorithms that can analyze the contributions of different noise sources when a noise measurement is available. This paper addresses the cocktail-party problem inside integrated circuits with multiple noise sources. It presents a method to extract the time characteristics of individual noise source from the measured compound voltage in order to study the contribution and properties of each source. This extraction is facilitated by application of blind source separation technique, which is based on the assumption of statistical independence of various noise sources over time. The estimated noise sources can aid in performing timing and spectral analysis, and yield better circuit design techniques.     

Differential amplitude imaging in scanning optical microscope

A differential amplitude scanning optical microscope (DASOM) is described. The system, which uses a simple optical and electronic arrangement, is capable of detecting variations in optical reflectivity of 9 × 10?6 in a 10kHz bandwidth. Results of surface studies of polished stainless steel and of natural diamond are presented.