Distributed measurement of birefringence dispersion in polarization-maintaining fibers

A new method to measure the birefringence dispersion in high-birefringence polarization-maintaining fibers is presented using white-light interferometry. By analyzing broadening of low-coherence interferograms obtained in a scanning Michelson interferometer, the birefringence dispersion and its variation along different fiber sections are acquired with high sensitivity and accuracy. Birefringence dispersions of two PANDA fibers at their operation wavelength are measured to be 0.011 ps/(km nm) and 0.018 ps/(km nm), respectively. Distributed measurement capability of the method is also verified experimentally.     

Dispersion of birefringence and differential group delay in polarization-maintaining fiber

We present an interferometric technique for measurement of the dispersion of birefringence in polarization-maintaining fibers. The approach yields measurements over a broad spectral range from analysis of single interferograms obtained in a tandem inteferometer. The technique is demonstrated to measure first-, second-, and third-order dispersion of the differential propagation constant, corresponding to differential group delay (DGD) and its dispersion to second order; measurements are immune to asymmetry in the interferomgram that is being processed. The technique is further applied to measurement of the temperature dependence of DGD and its first-order dispersion.     

Interference method of measuring the extinction coefficient of birefringent optical fibers

The extinction coefficient of a birefringent optical fiber (the ratio between the radiation power output of the polarization mode and the radiation power transferred from this mode to another one) characterizes the capability of a birefringent fiber to retain the polarization state of the radiation. In relatively short birefringent fibers (1–100 m), the extinction coefficient may reach 10⁴–10⁶. Such high values of the extinction coefficient are difficult to measure by standard techniques (excitation of one polarization mode by an incoherent source with subsequent recording of the light intensity at the output of the analyzer). An interference method of measuring the extinction coefficient of birefringent fibers is suggested. It is based on using a coherent source and measuring interference oscillations caused by an additional phase modulation at the input of the fiber. This method does not require precise polarization matching between the laser source and fiber and considerably loosens requirements for the polarizer-analyzer extinction and resolution of the photodetector. As a result, using simple standard components (semiconductor laser, film polarizer, and photodetector), one can measure extinction coefficient as high as 10⁶. The suggested interference method of measuring the extinction coefficient of birefringent fibers receives a theoretical analysis, and experimental data obtained for 2- to 1000-m-long fibers are presented.     

High group birefringence in air-core photonic bandgap fibers

A numerical investigation of group birefringence is carried out on a recently reported highly birefringent hollow-core photonic bandgap fiber by use of an efficient vector finite-element method. The hollow fiber core has an area as large as that of approximately four airholes in the cladding region and assumes a rhombic shape with round corners, and the airholes in the cladding region are hexagonal and provide a high air-filling fraction. Numerical results show very high group birefringence of the order of 10(-2) and phase birefringence of the order of 10(-3).     

Weak mode coupling measurement with EMD-based method in polarization-maintaining fibers

The intensity and position of coupling points in polarization-maintaining fibers (PMFs) caused by force and twist can be effectively detected by Polarization Coupling Measurement (PCM). The sensitivity of detection will decrease due to the movement of scanning Michelson interferometer. To detect the weak coupling point, an EMD-based method is proposed in this paper. The experimental results illustrate that the EMD-based method can suppress the noise and improve the SNR effectively. The DWT method is also performed for a comparative study. The results show that the EMD-based method is effective and applicable for PCM and the coupling point can still be detected when the intensity is as weak as ? 70 dB.     

Hybrid immersion-polarization method for measuring birefringence applied to spider silks

A technique for accurate measurement of the principle refractive indices and birefringence for silklike samples is presented. It is based on rotating the linear polarization of the illuminating light on a silk immersed in reference liquid to achieve index matching at the silk/liquid interface. The technique was used to measure the principal refractive indices of a P. eburnus radial silk at different strains. This in turn allows the calculation of strain-optic coefficients. The first measurement of the strain-optic coefficients of spider silk is presented. The technique is more generally applicable to strain-optic study of birefringent micro-optic samples.     

极大值法测量表面张力系数

测量金属薄片从液体中拉出过程中液膜高度和拉力的关系,分析其产生的原因,给出液体表面张力系数的准确测量方案.     

Improved design of polarization-maintaining photonic crystal fibers

We propose the realization of single-polarization operation in highly birefringent photonic crystal fibers. The suppression of one of the polarization states is realized by introducing index-matched cladding defect waveguides. The leakage loss of the index-matched polarization state can be enhanced by nearly 4 orders of magnitude. In particular, polarization-dependent loss larger than 2.97 dB/m with transmission loss lower than 0.03 dB/m in a wavelength region ranging from 1.54 to 1.566 microm can be realized in one such fiber.     

Finite element analysis on stress-induced birefringence of polarization-maintaining optical fiber

Influence of thermal-mechanical properties on the features of the panda polarization-maintaining optical fiber (PMF) in fabrication process is studied in detail by finite element method (FEM). The stress birefringence is 2.13443×10-4 obtained by the static analysis and 2.1269×10-4 by dynamic analysis. The difference in simulation by two methods is around 0.4%. The non-uniformity of stress birefringence in the fiber core is about 1.6%. Predicted results demonstrate that effect of the thermal conductive parameter on fiber thermal stress dominates. The high and uniform stress birefringence in the fiber core is obtained by appropriately selecting suitable stress region area and position.     

Radiation-induced effects in polarization-maintaining optical fibers for interferometric gyroscope

Radiation-induced attenuation (RIA) in four types of polarization-maintaining optical fibers for interfer-ometric fiberoptic gyroscope (IFOG) at 1310 nm is measured. The measurements are conducted during and after steady-state γ-ray irradiation using a 60 Co source in order to observe significantly different RIA behavior and recovery kinetics. Mechanisms involving dopants and manufacturing process are introduced to analyze the RIA discrepancy as well as to guide the choice and hardening of optical fibers during the design of IFOG. Medium-accuracy IFOG using Ge–F-codoped fiber and pure silica core fiber can survive in the space radiation environment.     

测量单模光纤模场直径的一种新方法

本文根据单模光纤模场直径的横向位移定义,提出了一种测量模场直径的新方法——远场高斯掩模匹配法.讨论了几种测量及数据处理方法.最后给出了初步的实验结果.     

计算机辅助测量不良导体的导热系数

介绍了计算机数据采集及处理技术在不良导体导热系数测量实验中的应用及取得的结果．     

A diffraction method for measuring the diameter of ultrathin metal fibers

The problem of diffraction of a plane electromagnetic wave by a metal fiber with a circular cross section is considered for the case in which the diameter of the fiber differs only slightly from the radiation wavelength. Relations between the positions of the first diffraction minima and the fiber diameter are derived. The formulas obtained are used to determine the diameter of an ultrathin fiber.     

I-scan thermal lens experiment in the pulse regime for measuring two-photon absorption coefficient

We present a new pump-probe mode-mismatched thermal lens method for pulse excitation aimed to the measurement of nonlinear absorption coefficient in optical materials. We develop a theoretical model based on the Fresnel diffraction approximation and their predictions are verified experimentally with samples of Rhodamine 6G and Rhodamine B in ethanol solution. The principal advantage of this technique is that it does not require any mechanical movement during measurement. Below we perform the new type of thermal lens experiment in the pulse regime for the measurement of nonlinear absorption coefficient in transparent samples and we demonstrate the validity of theoretical predictions using an alternative method to the classical thermal lens technique.     

A cutback method for measuring low linear fibre birefringence using an electro-optic modulator

A new cutback method based on the use of phase discrimination is proposed for low-linear-fibre-birefringence measurement. In this destructive method, a detection scheme for determining the phase difference between two readily obtained signals is used to give the phase retardation of the test fibre directly. The detection scheme mainly consists of two wave plates, two sections of fibre and an electro-optic modulator. The features of this measurement scheme are two-fold. First, the aforementioned phase difference between two detected signals, and, accordingly, linear fibre birefringence, can be determined in a simple manner, compared with the conventional cutback method. Second, the test fibre can be short in length despite the existence of fibre cladding modes. Experiments show that the proposed method can give a reliable measurement of linear fibre birefringence.     

近场影响消除法测量声吸收系数

本文采用数值模拟方法理论研究了活塞式辐射器的辐射近场和采用“大”尺寸接收器接收对声场的平滑作用以及近场(及其过渡区域)对测量声吸收系数的影响.计算表明,在近场及其附近,用通常的方法测量声吸收系数将产生很大的误差.通过分析误差产生的原因,本文提出了近场影响消除法测量声吸收系数,并对a/λ=3、9,b=0、0.5a、a(a,b分别是辐射器和接收器半径)几种情况进行了数值模拟计算,结果表明,采用这种方法不仅能在近场区域进行测量,而且具有较高的测量精度。     

Autocollimation polarimeter for measuring two-dimensional distribution of birefringence

Optics and Spectroscopy - A device for studying samples with nonuniform distribution of birefringence and corresponding measurement techniques are proposed. The optical arrangement of a polarimeter...     

转筒黏度计测量液体黏度方法研究

用黏性流体力学理论求得测量装置中旋转液体径向速度梯度的理论公式,进而得到转筒法测量黏度的较精确公式.指出了国内的一些教材和文献在推导中使用近似公式的错误,用参数估计的方法求得测量装置的摩擦阻力力矩,使测量结果得到进一步校正.实验研究表明:按照近似公式与精确公式计算求得的径向速度梯度之差可达到13.1%,求得的液体黏度之差可达到28.6%;在蓖麻油的温度为25.5℃时测得测量装置的摩擦阻力力矩为9.482×10-5 N·m,相当于0.540克重物产生的力矩.     

探讨测量液体表面张力系数的优化方法

针对用拉脱法测液体表面张力系数的系统误差较大的系列问题,提出了自动降拉双π丝补偿法.用自动化降拉代替手动提拉,提高了操作过程的稳定性;用双π丝代替π丝,消除了拉膜丝的不光滑点;用突变初态和补偿态作为测量状态,有效地排除了浮力、膜重以及侧丝上的表面张力对实验结果的影响.自动降拉双π丝补偿法得到的实验结果,其精度比拉脱法提高3%.