Complex Faraday rotation in microstructured magneto-optical fiber waveguides

Magneto-optical glasses are of considerable current interest, primarily for applications in fiber circuitry, optical isolation, all-optical diodes, optical switching and modulation. While the benchmark materials are still crystalline, glasses offer a variety of unique advantages, such as very high rare-earth and heavy-metal solubility and, in principle, the possibility of being produced in fiber form. In comparison to conventional fiber-drawing processes, pressure-assisted melt-filling of microcapillaries or photonic crystal fibers with magneto-optical glasses offers an alternative route to creating complex waveguide architectures from unusual combinations of glasses. For instance, strongly diamagnetic tellurite or chalcogenide glasses with high refractive index can be combined with silica in an all-solid, microstructured waveguide. This promises the implementation of as-yet-unsuitable but strongly active glass candidates as fiber waveguides, for example in photonic crystal fibers.     

Analysis of a low-finesse Fabry-Perot sensing interferometer illuminated by a multimode optical fiber

A model of the reflected fringe system for an ideal plane-parallel, low-finesse Fabry-Perot (FP) cavity illuminated by a multimode optical fiber has been developed and experimentally validated. This showed that the phase dispersion within the cavity arising from the divergent nature of the incident illumination significantly degrades the visibility of the reflected fringes. Departures from the ideal FP cavity are also examined. The effect on fringe visibility when the plane of the FP cavity is tilted with respect to the fiber axis and when the cavity surfaces are no longer perfectly parallel to each other has been explored. The analysis described is relevant to the design and the optimization of multimode optical-fiber sensors that use FP sensing cavities.     

Temperature dependence of the Faraday effect in As-S glass fiber

Temperature dependence of the Faraday effect is investigated for As2S3 fiber at 3.39 microm, obtaining a Verdet constant V of 1.62 x 10(-2) min/cm x G at room temperature and a temperature-dependence term coefficient of 10.67 min x K/cm x G in the experiments. The V value obtained at 25 degrees C is consistent with the theoretical estimates based on the first derivative of known refractive indices with respect to the wavelength. The temperature-dependent term is also discussed theoretically.     

A glass helium cryostat for optical and magneto-optical studies

A glass helium cryostat with copper shield for optical and magneto-optical studies is described. The shield-insert placed in the nitrogen dewar without hindering visual observation at the liquid helium level, prevents scattering of light by the bubbles of boiling nitrogen.     

Ice structure monitoring with an optical fiber sensing system

Ice has been used as an effective and economical material for constructions of roads and platforms in cold regions. However, the practical applications of this brittle material are limited by the fact that ice structures can suddenly crack due to low tensile strength, be crushed due to excessive compression, melt and become soften as temperature elevates. In this paper, an early warning system is proposed to monitor the strain state and damage characteristic of ice structures. Firstly, both fiber Bragg grating (FBG) and Brillouin optical time domain analysis/reflectometry (BOTDA/R) sensors were installed in an ice block and an ice beam to understand their axial and flexural behaviors under a concentrated load. Secondly, the solution for strain state and damage process of ice structures was derived analytically under test conditions. Finally, an outdoor ice road test bed was built and continuously monitored for 34 h to validate the early warning system and understand the early stage behavior of ice structures. The experimental results agreed well with their corresponding theoretical predictions. The early warning system with optical sensors is effective and practical for long-term monitoring for ice structures.     

Suspended core tellurite glass optical fibers for infrared supercontinuum generation

We report the fabrication and characterization of tellurite TeO₂-ZnO-Na₂O (TZN) microstructured suspended core optical fibers (MOFs). These fibers are designed for infrared supercontinuum generation with zero dispersion wavelength (ZDW) at 1.45 μm. The measured losses at this wavelength are approximately 6 dB/m for a MOF with a 2.2 μm diameter core. The effective area of a particular fiber is 3.5 μm² and the nonlinear coefficient is calculated to be 437 W⁻¹km⁻¹. By pumping a 20 cm long fiber at 1.56 μm with a sub-nJ femtosecond laser source, we generate a supercontinuum (SC) spanning over 800 nm in the 1-2 μm wavelength range.     

光纤传感用激光光源技术

光纤传感系统离不开激光光源,作为被测量信号载体的光波,激光光源本身的性能,如激光器的功率稳定性、线宽、相位噪声等参数对光纤传感系统的探测距离、探测精度、灵敏度以及噪声特性起决定性的作用,因此发展优质激光光源已成为近些年的研究热点。本文简要论述了激光光源在光纤传感领域的发展状况;重点介绍了窄线宽激光光源、可调谐激光光源以及宽带白光光源在光纤传感技术领域中的应用需求;概括了现有激光光源在光纤传感中所面临的主要限制因素和关键技术。为了进一步提高光纤传感系统的性能指标,获得可在任意波段、任意时刻实现的超窄、超稳理想激光光源将是未来光纤传感的一个主要研究方向。

     

Single glass block Faraday effect current sensor with homogeneous isotropic closed optical circuit

A new scheme is proposed for achieving a closed, homogeneous, and isotropic optical circuit necessary for high-accuracy optical-current sensors. It makes use of a single solid polygonal solid with reflection surfaces coated by quarter-wavelength dielectric thin-film layers for the Faraday cell. We derive the design principle and show numerically its applicability in various Faraday materials. The cross talk with the surrounding current is investigated in particular detail both theoretically and experimentally. In the example experiment with a SF57 Faraday material, a low cross talk is demonstrated for nearby currents.     

Analysis of sensing coil polarization properties' effect on performance of fiber optical gyroscope

The mechanism of fiber coil polarization properties' effect on the performance of a fiber optical gyroscope (FOG) is investigated with analysis of secondary wave trains' polarization evolution and interference in the fiber coil. Based on the optical model, the simulation demonstrates that the bias error varies nonlinearly with the fiber coil polarization crosstalk, and the experiment verifies the analysis and simulation result, so some measures are promoted to reduce the bias' dependence on the fiber coil's polarization properties, which is significant for improving environmental adaptability and long-term stability of the FOG.     

Generation of femtosecond current pulses using the inverse magneto-optical Faraday effect

A new method of generating ultrashort current pulses is proposed that is based on the optical pumping of a mesoscopic structure comprising a metal ring with a core made of a material possessing giant magneto-optical susceptibility. The main dynamic characteristics of the proposed device are calculated.     

Surface-relief fiber Bragg gratings for sensing applications

We present a new type of fiber Bragg grating (FBG) in which we etch the grating into the flat surface of a D-shaped optical fiber. Instead of being written in the core of the fiber, as are standard FBGs, these surface-relief FBGs are placed in the cladding above the core. These gratings are a viable alternative to standard FBGs for sensing applications. We describe the fabrication process for etching Bragg gratings into the surface of D-fibers and demonstrate their performance as temperature sensors.     

Comprehensive comparison on optical properties of samarium oxide (micro/nano) particles doped tellurite glass for optoelectronics applications

Rare-earth oxides microparticles doped tellurite-based glass have been studied extensively to improve the capability of optoelectronic devices. We report a detailed comparison between two sets of glass series containing samarium microparticles and nanoparticles denoted as ZBTSm-MPs and ZBTSm-NPs, respectively. The two sets of glass have been successfully fabricated via melt-quenching technique with chemical formula {[(TeO₂)_0.70 (B₂O₃)_0.30]_0.7 (ZnO)_0.3}_1?y (Sm₂O₃ (MPs/NPs))_y with y?=?0.005, 0.01, 0.02, 0.03, 0.04 and 0.05 mol fraction. The TEM analysis confirmed the existence and formation of nanoparticles in ZBTSm-NPs glasses. The density of ZBTSm-NPs glasses was found higher than ZBTSm-MPs glasses due to the distributions of nano-scale particles in tellurite glass network. There was a linear trend of increment in the refractive index in both sets of glass series along with the concentrations of dopants. The refractive index of ZBTSm-NPs glasses was found higher than ZBTSm-MPs glasses due to the shift in compactness of glass structure with nano-scale particles. In comparison, the absorption peaks of ZBTSm-MPs glasses were greater than ZBTSm-NPs glasses which were mainly due to the restriction of electrons mobility in glass network with nano-scale particles. The optical band gap energy in ZBTSm-NPs glasses was found greater than ZBTSm-MPs glasses which correspond to the widening of forbidden gap with nano-scale particles. The polarizability of ZBTSm-NPs and ZBTSm-MPs was found in non-linear trends along with dopant concentrations. Based on these findings, the improvement of optical properties has been made by introducing samarium oxide nanoparticles in tellurite glass which is beneficial for optoelectronic devices.

     

Holmium-doped optical fiber for filter applications

We consider the properties of holmium-doped fibers in filter applications. We give spectral properties and model filter characteristics. Experiments on filtering of Raman spectra are presented. The fiber filters exhibit strong rejection in the stop band and sharp absorption cutoffs.     

The structure and optical dispersion of the refractive index of tellurite glass

The structure and optical properties of a 80TeO₂-(20−x)Li₂O-xTiO₂ glass system where x = 0, 5, 10, and 15 mol% has been investigated using FTIR spectroscopy and Brewster angle measurements. The sample preparation, linear refractive index and density measurements, and infrared spectroscopic analysis are described. The refractive index and density of the studied tellurite glass samples increase when the amount of Ti in the glass is increased. The dispersion of the phase refractive index was analyzed using Wemple’s model. The dispersion energy E_d is significantly affected by the addition of Ti to TeO₂-based glass. The analysis of FTIR spectra indicate a Te coordination change that is in agreement with the increase of the Te coordination number determined from dispersion data using Wemple’s equation.     

Vortex optical Magnus effect in multimode fibers

A theoretical and experimental analysis is made of the optical Magnus effect in multimode optical fibers excited by a laser beam whose wavefront has a pure screw dislocation and carries the topological charge ±l, where l is the azimuthal quantum number. It is found that the angular rotation of the plane of propagation of a local wave depends on the magnitude and sign of the topological charge and changes qualitatively when the circulation of the polarization is reversed. The phase mechanism is attributed to spin-orbit interaction in the photon ensemble. It is demonstrated experimentally that the optical Magnus effect in a few-mode fiber for the CP₁₁ mode at the beat length is observed as a rotation of the axis of the pure edge dislocation field through an angle proportional to the beat length. Pis’ma Zh. Tekh. Fiz. 23, 76–81 (August 26, 1997)     

Improving the precision of multimode optical fiber attenuationmeasurements/

To improve the precision of attenuation measurements for multimode optical fibers, the different measurement errors are analyzed and an error equation is established. This is used to quantify total error by inserting relevant parameters taken from a recent Chinese nationwide interlaboratory comparison of multimode optical fiber attenuation measurements. It is suggested that the measurement error of the attenuation of a multimode optical fiber be expressed in both the error for the total loss of the entire length of the fiber, and the error of the loss per unit length, rather than the usual way of only expressing it per unit length     

Colloidal gold-modified optical fiber for chemical and biochemical sensing

A novel class of fiber-optic evanescent-wave sensor was constructed on the basis of modification of the unclad portion of an optical fiber with self-assembled gold colloids. The optical properties and, hence, the attenuated total reflection spectrum of self-assembled gold colloids on the optical fiber changes with different refractive index of the environment near the colloidal gold surface. With sucrose solutions of increasing refractive index, the sensor response decreases linearly. The colloidal gold surface was also functionalized with glycine, succinic acid, or biotin to enhance the selectivity of the sensor. Results show that the sensor response decreases linearly with increasing concentration of each analyte. When the colloidal gold surface was functionalized with biotin, the detection limit of the sensor for streptavidin was 9.8 x 10(-11) M. Using this approach, we demonstrate proof-of-concept of a class of refractive index sensor that is sensitive to the refractive index of the environment near the colloidal gold surface and, hence, is suitable for label-free detection of molecular or biomolecular binding at the surface of gold colloids.     

Embedded corrugated long-period fiber gratings for sensing applications

We demonstrate a method to make possible the mass production of corrugated long-period fiber gratings (C-LPFGs) by utilizing imprint lithography on polycarbonate (PC) substrates. For such C-LPFGs whose working principle is based on photoelastic effect, pretensile tension is required to be applied to inducing periodical refractive index variation. We then present an attempt to use PC as embedding material for providing internal compressive stress for C-LPFGs to have a photoelastic effect. This type of LPFG, termed embedded corrugated long-period fiber gratings (EC-LPFGs), is obtained after reimprinting the C-LPFGs into other PC substrates. Since compressive stress is retained due to the materials of different coefficients of thermal expansion (CTE), unlike C-LPFGs, EC-LPFGs can serve as strain, bending, and temperature sensors without the need of pretensile strain. The two most troublesome problems, the fragility of an etched fiber grating and the requirement of pretensile strain, can be simultaneously alleviated or solved by EC-LPFGs.