Two-Dimensional Alignment-Free Optical Interconnect Using Micro Optical Bench Scheme

In this paper, we have proposed and demonstrated a novel packaging method involving a vertical cavity-surface emitting laser (VCSEL) array. The concept is based on micro optical bench (MOB) placing a laser sub-mount and two-dimensional optical fiber array to match the reference plane of MOB to provide an alignment free optical interconnect. No degradation of I-V and I-L characteristics of the packaged VCSELs was found after use of the proposed packaging process. The coupling loss was about 0.9 dB for λ = 1.55 μm and the loss deviation among channels was less than 0.5 dB in a 2 x 4 ch coupling module between planar microlens and multi-mode fibers.     

Invariant Optical Recognition of Color Range Patterns Using Image Encoding

Correlation methods for recognition of polychromatic range images are presented. First, polychromatic range images are described. The correlation can be performed using either a single channel compressing both the range and the color images or a multichannel approach. The advantages of both methods are discussed. Translation invariant recognition along the x, y, and z axis is obtained. In the single channel approach, the range and the hue are combined using phase and amplitude coding. Then the double-channel approach is considered using sine-coding for the input image and phase-coding for the reference image. Finally, both channels are combined in order to improve the discrimination capability of the system. Optical implementation is performed.     

非均匀偏振光场的应力工程及应用

光场偏振态的空间不均匀性对光束聚焦、传播、照明、成像等方面具有奇异的效应。本文将举例说明在光学元件的外周施加确定的应力可以用于对波束传播的基本特性的研究,而且还能获得一些应用,比如旋光器件等。     

Measurements of Time-Varying Characteristics of Optical Signals and Inhomogeneities of Tested Substances with Additional Phase Modulation

The problem of investigation of the amplitude and phase structure of a time-varying probing optical signal and the structure of time-varying inhomogeneities of a substance tested by this signal is considered. The analysis is concerned, in particular, with determination of the structure of signals and processes with resolution in the pico- and femtosecond range. The scheme used for the analysis is based on registration of four spatially separated spectra of the studied radiation. The spectra are formed in a four-channel scheme with a twin-wave Michelson interferometer and a spectral device. Modulators based on electrooptical crystals (perovskites) are placed in the channels. The sum spectra are formed: without modulators, with the effect of either of the modulators, and with both of them affecting the radiation. The effect of the studied substance implies either modulating the radiation (in this case it is described by multiplication) or redistributing the radiation (then it is described by convolution).     

非均匀光栅的振幅分布和光强特性分析

从光栅自身的空间结构出发,用菲涅尔衍射公式推导了非均匀光栅的振幅分布公式(θi)和光强特性公式I(θi),用Maple程序给出了算例之不规则光栅衍射光强I(θi)随sinθi变化曲线,得到了非均匀光栅的衍射特性。一维透射平面光栅的振幅分布(θ)和光强分布I(θ)不仅与非均匀光栅的平均光栅常量有关,还与每个单元单缝的缝宽a有关。这一特性,补充完善了平面光栅衍射性质,同时,也为通过调整光栅空间结构,设计、研制、测试非线性光栅提供了理论依据。     

激光输入光纤环形腔内相位调制输出功率谱分析

从理论上详细分析了光纤环形腔有内相位调制时的输出光电流功率谱密度函数，该理论对任意相干长度的输入激光光源都是有效的。理论结果和实验数据表明，过快的相位调制能够平坦光电流功率谱上由于环形腔谐振特性而形成的周期性小峰，而弱相位调制对环形腔输出功率谱则影响不大。     

Two-Dimensional Near-Field Optical Spectroscopy in Magnetic Fields up to 4 T

We have developed a magnetic-field-type scanning near-field optical microscopy (SNOM) system, which enables us to obtain two-dimensional near-field images under magnetic fields up to 4 T. We have performed two-dimensional near-field scanning optical spectroscopy on (Cd,Mn) Te self-assembled quantum dots with this system.     

一种新颖的实现冷原子或冷分子囚禁的可控制光学四阱及其二维光学晶格

原子光学晶格为精确操控中性原子和研究某些基本物理问题提供了一种方法。提出了一种利用单光束照明余弦型振幅光栅与透镜组合系统实现冷原子或冷分子囚禁的可控制光学四阱新方案,计算了四阱的光强分布,讨论了从光学四阱到双阱或单阱的演化过程,并导出了光学四阱的几何参量、光强分布、强度梯度及其曲率与光学透镜系统参量间的解析关系,获得了四阱间距与光栅空间频率的关系。研究表明通过改变余弦光栅的空间频率即可实现从光学四阱到双阱或单阱的连续双向演化。     

Two-Dimensional Correlation Analysis of Temperature-Dependent FT-IR Spectra of Oleic Acid

ABSTRACT

In the present study, variable temperature FT-IR spectroscopic investigations were used to characterize the spectral changes in oleic acid during heating oleic acid in the temperature range from ?30°C to 22°C. In order to extract more information about the spectral variations taking place during the phase transition process, 2D correlation spectroscopy (2DCOS) was employed for the stretching (C?O) and rocking (CH₂) band of oleic acid. However, the interpretation of these spectral variations in the FT-IR spectra is not straightforward, because the absorption bands are heavily overlapped and change due to two processes: recrystallization of the γ-phase and melting of the oleic acid. Furthermore, the solid phase transition from the γ- to the α-phase was also observed between ?4°C and ?2°C. Thus, for a more detailed 2DCOS analysis, we have split up the spectral data set in the subsets recorded between ?30°C to ?16°C, ?16°C to 10°C, and 10°C to 22°C. In the corresponding synchronous and asynchronous 2D correlation plots, absorption bands that are characteristic of the crystalline and amorphous regions of oleic acid were separated.     

Scattering of a Generic Two-Dimensional Field by Cylindrical Structures in the Presence of a Plane Interface

A new method for treating the scattering of a two-dimensional electromagnetic field, expressed by means of its plane-wave spectrum, by an arbitrary configuration of circular cylinders in the presence of a plane interface between two different media, is presented. The proposed method allows us to solve the problem for both polarizations and to calculate the scattered field both in the near and in the far zone. Numerical results relevant to vacuum-dielectric interfaces are presented and compared with previous known results.     

Spectrum Invariance for a Particular Class of Optical Fields Propagated in Far Zone

This paper describes invariance of the normalized optical spectrum for a particular class of optical fields propagated in the far zone from a secondary, spatially, partially coherent source. The optical field across the secondary planar source is inhomogeneous to give the complex degree of spectral coherence such that μ = h(αω(ρ₁–ρ₂))exp(iɛω(ρ₁²–ρ₂²)), where α, ɛ are constants, ω is optical frequency, and ρ₁, ρ₂ denote two points in the secondary source. This expression for μ is the same as obtained in the Fresnel zone from a primary, spatially incoherent source. The invariance law does not hold for the spectrum of the light propagated from the primary source.     

Longitudinal Optical Fields in Light Scattering from Dielectric Spheres and Anderson Localization of Light

Recent research has shown that coupling between point scatterers in a disordered medium by longitudinal electromagnetic fields is harmful for Anderson localization of light. However, it has been unclear if this feature is generic or specific for point scatterers. The present work demonstrates that the intensity of longitudinal field outside a spherical dielectric scatterer illuminated by monochromatic light exhibits a complicated, nonmonotonous dependence on the scatterer size. Moreover, the intensity is reduced for a hollow sphere, whereas one can adjust the parameters of a coated sphere to obtain a relatively low longitudinal field together with a strong resonant scattering efficiency. Therefore, random arrangements of structured (hollow or coated) spheres may be promising three‐dimensional disordered materials for reaching Anderson localization of light.     

用基于磁场的改进型有限差分法分析光波导的全矢量本征模

提出一种改进的有限差分法,用以求解全矢量磁场波方程,分析光波导承载的全矢量本征模.离散交叉项时,采用与波导结构无关的六点差分格式,考虑磁场分量的导数在芯包分界处的不连续性,比传统四点差分格式有更高的计算精度.分析阶跃型光纤、矩形和脊形光波导的全矢量本征模问题,给出全矢量基模的磁场分布及其归一化传播常数,揭示全矢量本征模的混合特性,所得结果与解析法、高精度模横向谐振法的结果吻合,验证了方法的收敛性与计算精度.     

光学腔内两正交偏振模振幅和相位的补偿

本文开展了光学腔内两正交偏振模振幅和相位补偿的实验研究。通过采用特殊腔型和两个λ/2波片,补偿腔内反射镜对水平偏振模和垂直偏振模的反射率差异,使两个偏振模的输出振幅相等。利用一组λ/4-λ/2-λ/4波片补偿光学腔内水平偏振模和垂直偏振模的相位差,使两个模的输出重合。通过上述的振幅和相位补偿方法,可实现任意偏振光经过环形腔后偏振不变,为任意偏振比特在腔内冷原子系综中的高效率高保真度存储提供了实验基础。     

Third-Order Optical Nonlinearity in Two-Dimensional Transition Metal Dichalcogenides

We present a detailed calculation of the linear and nonlinear optical response of four types of monolayer twodimensional (2D) transition-metal dichalcogenides (TMDCs), having the formula MX₂ with M=Mo, W and X=S, Se. The calculations are based on 6-band tight-binding model of TMDCs, and then performing a semi-classical perturbation analysis of response functions. We numerically calculate the linear χ_μν⁽¹⁾ (-ω;ω) and nonlinear surface susceptibility tensors χ_μνζη⁽³⁾(-ω_Σ; ω_r; ω_s; ω_t) with ω_Σ=ω_r+ω_s+ω_t. Both non-degenerate and degenerate cases are studied for thirdharmonic generation and nonlinear refractive index, respectively. Computational results obtained with no external fitting parameters are discussed regarding two recent reported experiments on MoS₂, and thus we can confirm the extraordinarily strong optical nonlinearity of TMDCs. As a possible application, we demonstrate generation of a π/4-rotated squeezed state by means of nonlinear response of TMDCs, in a silica micro-disk resonator covered with the 2D material. Our proposed method will enable accurate calculations of nonlinear optical response, such as four-wave mixing and highharmonic generation in 2D materials and their heterostructures, thus enabling study of novel functionalities of 2D photonic integrated circuits.     

Optical Differentiation Phase Measurement Using the Bias Shifting Method

A new optical phase measurement method using a differentiation filter is proposed. The new method uses two images obtained by shifting the filter. This method has an advantage in that non-uniformity of the wavefront intensity does not produce errors. We present herein the theory of the newly proposed method and verify the theory by computer simulation. The effects of non-uniformity of the wavefront intensity, noise, and bias shifting length for errors are discussed. The system has been demonstrated for a plane wave and a spherical wave. For the proposed method, although the number of errors due to noise increases, the number of errors due to non-uniformity decreases. Therefore, the proposed method is useful for the phase measurement of a wavefront for which the intensity is not uniform. In addition, it improves the accuracy of the phase measurement system using a differentiation filter.     

Two-Dimensional Phase Unwrapping by Direct Elimination of Rotational Vector Fields from Phase Gradients Obtained by Heterodyne Techniques

Noting the analogy between electro-magnetic fields and the vector fields of phase gradients obtained by heterodyne techniques, we propose a new algorithm for least-squares phase unwrapping. Instead of solving a Poisson equation for the unwrapped phase map or using Green’s formulation, we directly remove singular points or residues from the measured phase map by superposing sign-reversed vortex fields which cancel out the rotational vector fields associated with the phase singular points.     

Measurement of Zeeman Shift of Cesium Atoms Using an Optical Nanofiber

Nanofibers have many promising applications because of their advantages of high power density and ultralow saturated light intensity. We present here a Zeeman shift of the Doppler-broadened cesium D2 transition using a tapered optical nanofiber in the presence of a magnetic field. When a weak magnetic field is parallel to the propagating light in the nanofiber, the Zeeman shift rates for different circularly polarized spectra are observed.For the +component, the typical linear Zeeman shift rates of = 3 and = 4 ground-state cesium atoms are measured to be 3.10(±0.19) MHz/G and 3.91(±0.16) MHz/G. For the -component, the values are measured to be-2.81(±0.25) MHz/G, and-0.78(±0.28) MHz/G. The Zeeman shift using the tapered nanofiber can help to develop magnetometers to measure the magnetic field at the narrow local region and the dispersive signal to lock laser frequency.     

基于线性光放大器的全光逻辑异或门理论分析

基于速率方程建立了线性光放大器(LOA)的数值模型,模拟了线性光放大器的增益钳制特性。与对称结构马赫曾德尔干涉仪(MZI)的传输矩阵相结合,构建了线性光放大器马赫曾德尔干涉仪全光逻辑异或门模型,实现了两路40Gbit/s信号的异或运算。与传统的半导体光放大器(SOA)构成的马赫曾德尔干涉仪型异或门进行了比较,从器件结构上对两种异或门运算结果的差异给出了解释。结果表明,线性光放大器具有平坦的增益特性,对输入信号的扰动具有不敏感性,垂直光场缩短了载流子恢复时间;线性光放大器马赫曾德尔干涉仪结构可以实现异或运算;利用差分相位法可以解决载流子恢复时间对信号处理速度的限制,合理地选择延迟时间能获得较好的运算结果;输出信号具有眼图张开度大、消光比高、峰值啁啾小、对波长变化不敏感等优点。     

Experimental Analysis of Optical Trapping System Using Tapered Hemispherically Lensed Optical Fiber

We describe the operation and performance of an optical fiber trap realized using a tapered hemispherically lensed optical fiber. Axial and transverse trapping forces exerted on a microsphere are experimentally analyzed to corroborate the optical trapping using an optical fiber. Experimental results are as follows. (i) Transverse force F_tr acting on a sphere is a restoring force that acts to pull the microsphere back to the center of trap. (ii) Axial force F_ax always acts to push a sphere in the direction of the beam away from the trapping fiber end. (iii) Vector sum of F_tr and F_ax acting on a sphere gives a restoring force directed back to the stable point. (iv) Transverse force F_tr plays a significant role in trapping a micro-sized object by means of an optical fiber.This paper was originally presented at the 5th International Conference on NEAR FIELD OPTICS and RELATED TECHNOLOGIES (NFO-5), which was held on December 6–10, 1998 at Coganoi Bay Hotel, Shirahama, Japan, in cooperation with the Japan Society of Applied Physics and Mombusho Grant-in Aid for Scientific Research on Priority Areas “Near-field Nano-optics” Project, sponsored by Japan Society for the Promotion of Science.