Optical fiber modulator derivates from hollow optical fiber with suspended core

A fiber optic integrated modulation-depth-tunable modulator based on a type of hollow optical fiber with suspended core is proposed and investigated. We synthesized magnetic fluid containing superparamagnetic Fe(3)O(4) nanoparticles and encapsulated it in the hollow optical fiber as the cladding layer of the suspended core by fusing the hollow optical fiber with the multimode optical fibers. The light with a wavelength of 632.8 nm is coupled in and out of the modulating element by a tapering technique. Experimental results show that the light attenuation in the system can be greatly influenced by only 2.0×10(-2) μL of the magnetic fluid under different magnetic field strengths. The saturated modulation depth is 43% when the magnetic field strength is 489 Oe. The response time of the system is <120 ms. Significantly, this work presents information for the development of all-fiber modulators, including other integrated electro-optic devices, such as optical switch, optical fiber filter, and magnetic sensors utilizing the special structure of this hollow optical fiber with suspended core and superparamagnetic magnetic fluid.     

Magneto-optic fiber Sagnac modulator based on magnetic fluids

A magneto-optic modulator with a magnetic fluid film inserted into an optical fiber Sagnac interferometer is proposed. The magnetic fluid exhibits variable birefringence and Faraday effect under external magnetic field that will lead to a phase difference and polarization state rotation in the Sagnac interferometer. As a result, the intensity of the output light is modulated under the external magnetic field. Moreover, the modulator has a high extinction ratio and can easily be integrated in a single-mode fiber system. The performance of the modulator is not affected by ambient temperature variation from room temperature to 40 °C.     

Magneto and Electro-Optic Intensity Modulator Based on Liquid Crystal and Magnetic Fluid Filled Photonic Crystal Fiber

We propose a novel light intensity modulator based on magnetic fluid and liquid crystal(LC) filled photonic crystal fibers(PCFs). The influences of electric and magnetic fields on the transmission intensity are theoretically and experimentally analyzed and investigated. Both the electric and magnetic fields can manipulate the molecular arrangement of LC to array a certain angle without changing the refractive index of the LC. Therefore, light loss in the PCF varies with the electric and magnetic fields whereas the peak wavelengths remain constant. The experimental results show that the transmission intensity decreases with the increase of the electric and magnetic fields. The cut-off electric field is 0.899 V/um at 20 Hz and the cut-off magnetic field is 195 m T. This simple and compacted optical modulator will have a great prospect in sensing applications.     

基于插入损耗的光纤信号调制器

基于光纤连接的横向偏移造成的插入损耗研制了一种的新型的光纤信号光调制器。调节对接光纤的横向偏移,可以调节对接光纤间的光耦合效率,利用调制信号调制横向偏移可实现对光纤传输光信号的调制。实验中,将调制电信号放大并加载于压电陶瓷使其振荡,由此控制对接光纤的横向偏移与调制信号同步变化,实现了对下一级光纤输出端光强的调制。这种光纤信号调制器主要针对光的振幅调制,实验中获得调制度优于95%,信噪比约为20dB,带宽约为200kHz。具有价格低廉、调制度高的特点,可应用于光纤传输信号的调制及信号斩波等。     

新型缓变锥型PCF结构接口耦合损耗特性

提出一种新型的缓变锥型光纤接口器件。该接口器件是一个长度为150mm左右的缓变锥型光子晶体光纤。利用有限元方法对模场直径差别较大的不同光纤进行拼接时的损耗问题进行研究。研究结果表明:在模场直径分别为9μm和10.4μm的光纤之间加入锥型光纤后可以有效降低耦合损耗,并且在不同波长下耦合损耗都维持在一个较低水平。因此,该接口器件能够实现光纤拼接时物理结构的过渡和不同模场直径的转换,从而使拼接损耗降到最低。     

Polarization maintaining fibers for application in magnetic field measurements

Optical fibers may be applied in measurements of electrical current, particularly as so-called optical current transformers. Electric current sensors, in which optical fibers are used are small, light, cheap and safe. Their sensitivity is, however, due to the restricted magnetootpic properties of optical fibers, rather small. Moreover, these sensors are susceptible to deformations of the optical fiber. An increase of their sensitivity consists in lengthening the distance of optical fiber on which the magnetic field acts. However, this can lead to an increase of disturbances caused by changes of internal stresses. The negative effects can be reduced by applying optical fibers with a higher magnetooptic sensitivity and a lower susceptibility to mechanical stresses and deformations. The present paper deals with side-hole optical fibers with a decreased birefringence reducing the susceptibility to deformations. The optical fibers consist of a multicomponent glass with a higher value of the refractive index, thanks to which the sensitivity to the effect of the external magnetic field is increased. In future such optical fibers are planed to be applied in magnetooptic sensors.     

多孔芯光子晶体光纤及其偏振特性

强激光与气体的长距离相互作用能产生许多新奇的物理效应,而自由空间光束的自聚焦、衍射、散射等问题限制了该科技领域的发展。本文提出了一种新型多孔芯光子晶体光纤,纤芯亚波长、低折射率空气孔可以传光,具有宽带、低损耗、单模传输特性。利用倏逝波耦合效应,研究了纤芯亚波长空气孔束缚光的原理。根据光波传输的电磁场理论,分析了低折射率空气孔中的光强增大效应。强光在空气孔中长距离传输,为光与物质的相互作用提供了新条件,可以用于气体传感、非线性光学、高集成光子技术、原子操控等。由于纤芯空气孔可以传光,改变空气孔的大小,直接影响模场分布,进而可以获得很高的结构双折射。通过光纤结构参数的合理设计,分别获得了B=4×10^-2的高双折射、纤芯直径5 μm的大模场高双折射、大模面积单偏振单模特性,在光纤偏振器、光纤滤波器、光开关及光纤传感等领域有广泛的应用前景,为新型光场调控提供了新方法。     

梯度磁场作用下光纤中磁流体光透射特性研究的建模与分析

对光纤中磁流体在梯度磁场作用下的光透射特性进行了研究,提出光纤中磁流体的光透射率变化主要来源于梯度磁场引起的磁流体密度分布变化。根据郎之万函数和流体理论,推导了光纤中磁流体在梯度磁场作用下的密度分布,并根据Beer-Lambert定律,得到磁流体光功率透射衰减和纳米粒子局部密度的关系,从而建立光纤中磁流体在梯度磁场作用下光透射特性的理论模型。进而对光纤中磁流体在不同梯度磁场作用下的光透射功率进行数值分析,得到不同磁场强度和磁场梯度下光纤中磁流体透射功率的变化规律。最后将数值分析的结果和实验数据进行对比,验证了模型的合理性, 同时也验证了梯度磁场作用下磁流体光透射功率的变化主要来源于磁流体密度分布变化的推论。     

基于白光扫描干涉法的光纤折射率分布的测量

提出了一种光纤折射率分布的测量方法,采用白光扫描干涉技术,并在参考镜上构造与光纤样品相同的结构来克服白光相干长度短的限制,优化了光路,提高了干涉条纹间的对比度。采用与白光干涉信号的包络线呈高斯分布的Morlet小波作为小波变换的母小波进行拟合处理,得到光纤与已知折射率的匹配液之间的相对高度。通过计算获得光纤的折射率分布,并对获得的数据采用光纤折射率分布的经典函数进行拟合,得到多模光纤和单模光纤的决定系数分别为0.997 2和0.996 4。最后将实验获得的结果与官方参数进行比较,误差为0.01%,表明该种方法测量的精度较高,完全可以用来测量光纤的折射率。     

基于酒精与磁流体填充的单模-空芯-单模光纤结构温度磁场双参数传感器

提出了一种基于空芯光纤模间干涉原理的环境温度和磁场双参数传感器,为了使光入射进空芯光纤壁中,将空芯光纤与单模光纤错位熔接,传感部分用毛细玻璃管封装,空芯光纤内外分别填充酒精和磁流体.除了光纤材料的热光效应和热膨胀效应外,环境温度变化会引起两种溶液折射率的变化,而磁场变化仅引起空芯光纤外的磁流体折射率变化.理论计算可知空芯光纤壁中可支持多个模式传输并相互干涉,各模式传输相位对内外溶液折射率变化灵敏程度不同.因此,干涉谱中两个含有不同模式成分的波谷,即波谷1和波谷2,它们的漂移可以作为指示信号,通过建立敏感矩阵可同时解调出周围环境温度与磁场的变化.实验中,在28—58℃范围内,温度传感灵敏度可达-468 pm/℃;在0—169 Oe范围内磁场传感灵敏度可达82 pm/Oe.该传感器具有高灵敏度与高机械强度,并且能够实现温度与磁场的同时测量,有效消除了温度波动对磁场测量信号的干扰.     

Study on magnetic fluid optical fiber devices for optical logic operations by characteristics of superparamagnetic nanoparticles and magnetic fluids

We propose two optical fiber-based schemes using two magnetic fluid optical fiber modulators in series or in parallel for optical logic signal processing and operation. Here, each magnetic fluid optical fiber modulator consists of a bare multimode fiber surrounded by magnetic fluid in which the refractive index is adjustable by applying external magnetic fields amplifying the input electrical signal to vary the transmission intensity of the optical fiber-based scheme. The physical mechanisms for the performances of the magnetic fluid optical fiber devices, such as the transmission loss related to Boolean number of the logic operation as well as the dynamic response, are studied by the characteristics of superparamagnetic nanoparticles and magnetic fluids. For example, in the dynamic response composed of the retarding and response sub-procedures except the response times of the actuation coil, the theoretical evaluation of the retarding time variation with cladding magnetic fluids length has good agreement with the experimental results.     

Polarization-independent magnetic control of the light phase in a chiral optical fiber

The proposition is made to fine-tune the phase of an unpolarized guided mode in a chiral optical waveguide, or fiber, by a static magnetic field applied in the direction of the light propagation. The core of the fiber should consist of randomly oriented chiral molecules, and the magnetic field-induced change of the refractive index would be due to the magnetochiral effect [1]. Although the magnetochiral birefringence is very small for magnetic field strengths obtainable under routine laboratory conditions, the induced phase shift for a given magnetic field should be maximized by increasing the pathlength of light inside the field. This would be technically achievable by winding the optical fiber axially many times around the electric solenoid that generates the magnetic field, in such a way that the path of the light inside the fiber follows closely and over a distance as long as possible the magnetic induction lines.     

High-resolution, large dynamic range fiber length measurement based on a frequency-shifted asymmetric Sagnac interferometer

We propose and experimentally demonstrate a single-mode fiber length and dispersion measurement system based on what we believe to be a novel frequency-shifted asymmetric Sagnac interferometer incorporating an acousto-optic modulator (AOM). By sweeping the driving frequency of the AOM, which is asymmetrically placed in the Sagnac loop, the optical length of the fiber can be determined by measuring the corresponding variation in the phase delay between the two counterpropagating light beams. Combined with a high-resolution data processing algorithm, this system yields a dynamic range from a few centimeters to 60 km (limited by our availability of long fibers) with a resolution of approximately 1 part per million for long fibers.     

微纳结构光纤光谱学

微纳结构光纤光谱学是指以空芯微结构或微纳光纤为样品池,光和物质在纤芯内部或表面进行相互作用的光谱学技术。本文回顾空芯和微纳光纤导光的基本原理,介绍气体、液体样品池构建的理论和方法,综述基于光谱吸收、光热、光声、荧光、拉曼等效应的微纳结构光纤光谱学的最新进展及今后可能的发展方向。微纳结构光纤对光场的束缚能力强、模场能量在空气中的比例高,可实现光和物质在其中的高效、长距离相互作用。微纳结构光纤样品池的采用,可提升传统光谱学系统的性能或构建新型的光谱学系统;应用传输光纤与其他光学元器件进行柔性连接,可促进光谱学仪器和传感器的小型化和实用化。     

Magneto-controlled illumination with opto-fluidics

Imaging of micro- and nanofluidics is a challenge since the size of the channels is so small that the installment of additional optical and mechanical switches is very difficult. The size of the device and associated increase in viscous dissipation constitute another constraint. In response to these limitations, this work proposes and demonstrates the manipulation of light by adding a functional lens to control the light on demand. In the present work, this lens is realized by filling a hollow fiber with a colloid of superparamagnetic Fe₃O₄ nanoparticles. When the propagation of light is perpendicular to the magnetic field, this lens stretches the circular beam into a ribbon yielding a larger visible area. Potentially, one can apply a rotating magnetic field thus illuminating a larger spot size or creating other beam geometries. Such composite fibers might also be of value for Faraday isolation and other magneto-optic effects in optical fibers.     

Optical properties of modified Bragg fiber-optic waveguides

A modified form of optical fibers with varying cross section is proposed. A Bragg optical fiber with an additional conic layer between the core and periodic cladding is considered. Oscillating scattering of light through the side surface of such a fiber is predicted. It is shown that the optical properties of spicules of marine glass sponges Hyalonema sieboldi can be explained by the conic shape of the near-axis layer.     

干涉法测量掺铒光纤的非线性折射率

本文提出一种测量掺铒光纤非线性折射率的方法,该方法使氩离子激光通过一根掺铒光纤和另一根并排的普通光纤产生干涉.由掺铒光纤的非线性折射率导致的位相差变化将使干涉条纹发生位移,通过位移的测量可以得出光纤的非线性折射率.     

Selective polarization mode excitation in InGaAs/GaAs microtubes

We report on selective polarization mode excitation in InGaAs/GaAs rolled-up microtubes. The microtubes are fabricated by selectively releasing a coherently strained InGaAs/GaAs quantum dot layer from its host GaAs substrate. An optical fiber abrupt taper is used to pick up the microtube, while an adiabatically tapered optical fiber is used to couple light into the resonant optical modes of the microtube. By varying the polarization of the light in the adiabatically tapered fiber both transverse electric and transverse magnetic modes are observed in the microtube. We also show that the microtube can be used as a red (0.6?μm) to infrared light (1.5?μm) optical-optical modulator taking advantage of the thermal-optical effect.     

电光调制在被动综合孔径成像探测中的应用

介绍了一种新型被动综合孔径成像探测方法:视场辐射信号被接收和放大后,通过电光幅度调制将其幅度和相位信息加载到光波上,经光纤传输在末端形成阵列,通过光学系统直接成像,将视场实时恢复出来.该方法可实现工作在微波、毫米波和太赫兹波段的高分辨力实时成像探测的目的.深入分析了电光调制器在综合孔径成像探测中的应用,建立电光调制模型,讨论了在小信号调制下的电光幅度调制近似理论.通过数值计算与仿真分析,得到综合孔径成像探测中电光调制器的调制信号强度限制的有关结论.结果表明,利用上变频电光调制技术和光信息处理,所得到的成像仿真图的半峰全宽和信噪比性能都优于传统的基于下变频技术的成像仿真结果.     

Time Domain Optical Spectrometry with Fiber Optic Waveguides

Abstract

The transit time, τ, of a light pulse in a fiber optic waveguide is a function not only of the fiber length but also of the frequency content of the pulse and, to some extent, the electric and magnetic field distributions within the fiber. Thus, we can write τ = τ(L, γ, μ, v) where L is the fiber length and γ is the wavelength. The integers and v index the mode of propagation which is excited. The purpose of this article is to review a number of ways the various transit time effects in optical fibers can be used to measure optical spectra in the time domain. Conventional spectrometers disperse the light spatially. The spectrum is measured either with an array of detectors or, if a single detector is used, by mechanically scanning some element of the spectrometer. The instruments described in this review use optical fibers to selectively delay the wavelength components of a modulated light source so that these components arrive sequentially at a single detector. If the light source is already pulsed, these instruments have the same inherent capability as a multiple detector spectrometer in terms of measurement time or signal-to-noise ratio. For a steady source, special modulation schemes can be used to improve the signal collection and reduce the effective dead time required to measure the dispersed light.