Polarisation-independent optical circulator consisting of two fibre-optic polarising beam splitters and two YIG spherical lenses

A novel polarisation-independent optical circulator, which employs two fibre-optic polarising beam splitters and two yttrium-iron-garnet (YIG) spherical lenses, is reported. The present structure has the advantage of low-loss splicing with other single-mode fibres. The insertion loss was 2.5 dB at 1.30 ?m wavelength, and was almost independent of the incident polarisation angle. The backward attenuation was more than 18 dB.     

Design of a compact photonic-crystal-based polarizing beam splitter

A compact polarizing beam splitter based on a photonic crystal (PC) directional coupler with a triangular lattice of air holes is designed and simulated. In the employed PC structure, transverse-electric (TE) light is confined with the photonic bandgap effect, while transverse-magnetic (TM) light is guided through an index-like effect. Due to the different guiding mechanisms, TM and TE light have strikingly different beat lengths, which is utilized to separate the two polarizations in a directional coupler no longer than 24.2 /spl mu/m. The two-dimensional finite-difference time-domain method of computation is used to evaluate the device performance. The extinction ratios are found to be around 20 dB for both TE and TM polarized light.     

Scattering of a beam wave by a spherical object

The theoretical analysis of the scattering of a beam wave by a small spherical object, which exists at the neighborhood of the beam waist on the propagation axis, is treated. In this analysis, the property of a spherical object is generalized so as to have anr-dependent dielectric constant. Through numerical calculations for the case of the conducting sphere, the difference between the scattering of a beam wave and that of a plane wave are discussed.     

贝塞尔-高斯光束经球差透镜的聚焦特性

利用广义惠更斯-菲涅耳衍射积分推导了一种涡漩光束——贝塞尔-高斯光束经球差透镜聚焦后的光场表达式,并利用数值计算分析了球差系数对聚焦光束光强剖面分布的影响。研究表明,通过改变球差系数,可以改变零阶贝塞尔-高斯光束轴上光强最大值点的位置,球差的存在使轴上光强最大值减小。零阶贝塞尔-高斯光束经球差透镜聚焦后不能保持其传输不变性,在几何焦面上光强剖面类似于高斯形分布,而实际焦点所在面上的分布则仍具有零阶贝塞尔函数的特征。对于一阶贝塞尔—高斯光束,球差的存在会改变其横向光强分布。     

Radiation pattern computation of a spherical lens using Mie series

The radiation pattern of a sphericai layered dielectric lens is computed using eigenfunction expansions. The method is an adaptation of the well-known classical solution for plane wave scattering from a layered sphere but uses the less well-known vector addition theorem for spherical wave functions to represent the off-center sources. The usefulness of this formulation is that the solution is analytical and "exact," and is an efficient tool for investigating spherical lens radiation properties. The method is illustrated for a typical Luneburg lens.     

Optical frequency shifting of a mode-locked laser beam

An optical frequency shifter making use of the electro-optic effect in LiNbO3was built to shift the Fourier spectrum of a mode-locked He-Ne laser; the shift was continuously adjustable from -45 GHz to +45 GHz about the central optical frequency of 473.61 THz. Shifted Fourier spectra recorded with a scanning Fabry-Perot interferometer were found to be in excellent agreement with theory.     

超高斯光束通过球差透镜后的传输特性研究

利用广义惠更斯－菲涅尔衍射积分,并考虑球差的影响,对超高斯光束通过球差透镜后的传输特性作了数值计算和讨论。本文所得主要结果对实际光学系统的设计是在用的。     

Spectral shift of a Gaussian Schell-model beam beyond a thin lens

We give a comprehensive representation of the Wolf effect in propagation both in free space and after a lens for an outstanding class of partially coherent beams, namely Gaussian Schell-model beams. We characterize the correlation-induced spectral changes, throughout the whole space, by means of isoshift lines and transverse shift profiles. The maximum value of the frequency blueshift, occurring on the optical axis, is also calculated     

圆柱面镜用于端面抽运光束整形误差分析

为了简化二极管端面抽运固体激光器的快轴准直,建立了圆柱面镜和聚焦镜作为二极管快轴准直系统的模型,给出了系统设计方法和关键参数的控制方法,通过仿真论证了以圆柱面镜做二极管激光器快轴校准的可行性,抽运光腰斑的大小和位置可以通过选择柱面镜半径、光源到柱面镜的距离、柱面镜到聚焦镜的距离及聚焦镜焦距来控制.结果表明,当柱面镜半径3mm、光源到柱面镜的距离0.7mm、柱面镜到聚焦镜的距离及聚焦镜焦距5mm时,抽运YAG晶体可以得到大于47%的光-光效率.     

用圆柱透镜准直半导体激光光束的分析

根据光线传输的基本原理 ,讨论了半导体激光器快轴方向发散光束通过圆柱透镜后的准直特性以及光强分布的改变 ,为正确认识和使用微圆柱透镜改善半导体激光快轴方向光束的发散提供了理论依据     

Optical design of a Butterfly lens for a street light based on a double-cluster LED

We construct a precise optical model of the cluster LED and propose a design of a peanut form lens to achieve an optical utilization factor of 45% and uniformity of 1/2.7. Then we propose a new design of so-called Butterfly lens with unequal tilt design aimed to serve a double-cluster LED but with a tightened size. The optical utilization factor of the Butterfly lens is about 43.8%, the uniformity is around 1/2.7, and an averaged illuminance of 14 lx, which could meet almost all types requested by IESNA. The design of the Butterfly lens is proven workable for a double-cluster LED.     

Analysis and design of a new type NRD-guide E-plane Y-junction circulator

A new type of E-plane Y-junction circulator has been developed based on the nonradiative dielectric waveguide (NRD-guide) in Ka- band. First, the circulation principle has been analysed by the theory of polarization wave. The field components in the nonreciprocal Y-junction zone and the conclusion of 60° phase difference between clockwise and counterclockwise rotating polarization modes has been obtained. And then, the resonant frequency of the non-dc biased triangle ferrite sample has also been calculated. This kind of structure is benefit to enlarge the bandwidth of the Y-junction circulator. As an example, we had designed and fabricated a circulator in Ka-band. Its operating frequency is 35. 1GHz, the 1.5dB insertion loss and 20dB isolation bandwidth is about 1. 0GHz.     

宽光谱、长焦距准直物镜光学设计

介绍了大视场、宽光谱、长焦距微光准直物镜的光学设计.重点讨论了宽谱段准直物镜的二级光谱校正及像差平衡问题,并用Zemax软件,进行了光学设计.设计结果:系统的二级光谱为0.1 mm,其他像差也达到了像质要求.     

Properties of a Four-Port Nonreciprocal Circuit Utilizing YIG on Stripline--Filter and Circulator

Experimental results of the 4-port nonreciprocal band-stop-pass filter and the tunable resonance type circulator with the properties of the 4-port filter are reported, and the theory of the new nonreciprocal circuit is discussed. The filter operates over a two-octave frequency range and the over about a one-octave frequency range.     

Optical measurement of silicon membrane and beam thickness using areflectance spectrometer

An optical technique for measuring the thickness of silicon membranes and beams such as those used in micromechanical devices is presented. The measurement, based on reflectance spectrometry, is rapid and nondestructive. The reflectance-spectrometry technique can be used to measure silicon membrane thickness in the range from 0.1 to 5 μm     

Analysis and design of a novel leaky YIG film guided wave opticalisolator

A guided wave optical isolator using a four layered leaky yttrium iron garnet (YIG) waveguide with a YIG guiding layer is proposed and analyzed through a transfer matrix formulation. The dependence of isolation characteristics on different waveguide parameters are discussed. It is shown that for four layered structures an isolation ratio of about 24 dB can be achieved with YIG films having large gyrotropy. It is also shown that by replacing the single guiding YIG film with multilayers of YIG with compensated walls and proper permittivity, high isolation ratio can be achieved even with currently available YIG films having low gyrotropy     

Observation and analysis of noise due to birefringence modulation in a fibre-optic gyroscope

The noise due to the birefringence modulation of a nonideal phase modulator in a fibre-optic gyroscope is investigated. Theoretical analysis and experimental observation show that there is a definite ?/2 phase difference between this noise and the Sagnac signal at the modulation frequency.     

Optical phase-front inscription over optical fiber end for flexible control of beam propagation and beam pattern in free space

We report a novel compact all-fiber technique to control the beam propagation and beam pattern in free space. By coating an azo-polymer thin film layer on the optical fiber end surface, various surface relief grating (SRG) structures were inscribed over the film using a single step direct exposure of interference patterns to form a novel organic/inorganic composite fiber optics beam shape converter. The linear and concentric SRGs were experimental characterized along with numerical simulations.