Influence of the irregularity of twisting of the birefringence axes of single-mode optical fibers on the polarization nonreciprocity of fiber ring interferometers

A particular example of the so-called minimum-configuration fiber ring interferometer whose loop comprises two different-length segments of a single-mode optical fiber with the same linear birefringence but different twisting is used to show that even in the case where the birefringence axes at the loop input coincide with the polarizer transmission direction, the phenomenon of polarization nonreciprocity of the fiber ring interferometer can emerge. It is shown that polarization nonreciprocity can be eliminated by the proper adjustment of the axes of a single-mode optical fiber, but the above adjustment should be changed if the waveguide temperature is changed. It is also shown that polarization nonreciprocity is a function of the light wavelength and the polarization nonreciprocity value in a fiber ring interferometer varies quasiperiodically in response to the temperature change in an optical fiber with random irregularities.     

基于低双折射光子晶体光纤Sagnac干涉仪的超低温度系数扭曲传感器

研究了低双折射光子晶体光纤中由光纤扭曲造成的圆双折射效应,并应用Sagnac干涉仪结构设计了扭曲传感器.在Sagnac环中的光子晶体光纤上施加机械压力引入初始线双折射并产生正弦干涉光谱,再扭曲光纤产生圆双折射使干涉光谱随扭曲角度移动.光谱峰值波长随扭曲角度变化符合Sinc函数关系,理论分析与实验相符.传感器灵敏度为1....     

超低温度系数的光子晶体光纤Sagnac压力传感器

 提出了一种基于光子晶体光纤Sagnac干涉仪的横向压力传感器。使用的光子晶体光纤为低双折射光纤,首先预先在Saganc环中的光子晶体光纤上施加初始压力,使Sagnac干涉仪产生正弦干涉光谱,然后再将被测物体放在光子晶体光纤上,由于被测物体重力的作用,Saganc干涉仪输出的光谱产生移动,实现横向压力传感测量。传感器具有高灵敏度0.529 nm/(N·mm)及超低的温度系数-0.4 pm/℃,其环境温度的影响可以忽略。     

A Novel Method for Measuring Photo-Induced Birefringence of Photosensitive Fibers

In this paper, we report a novel method for accurately measuring the photo-induced birefringence of photosensitive fiber by using Mach-Zehnder interferometer. The results indicate that the normalized birefringence can attain 10-5.     

基于Sagnac原理的单轴分布式光纤传感系统偏振态分析

针对Sagnac干涉型单轴分布式光纤传感器中使用单模光纤作为传感器件时,由于传输光偏振态在双折射影响下所带来的干涉信号“偏振诱导衰落”问题,运用琼斯矩阵分析法,建立了该型传感器系统在传感光纤双折射和外部事件共同作用下,传输光的偏振态对系统功率传输系数影响的数学模型;仿真分析了在传感光纤线性双折射和圆双折射共同作用下,传输光的偏振态对系统功率传输系数的影响;提出了使用法拉第旋转镜提高系统抗偏振能力的改进方法.仿真结果表明,该方法能很好地消除光纤线性双折射和圆双折射.     

Measurement of photo-induced birefringence in germanosilicate fibers

In this paper, we report a novel method for accurately measuring the photo-induced birefringence of germanosilicate fibers by using an all fiber Mach-Zehnder interferometer. The results indicate that the photo-induced normalized birefringence of C₅98-302(s) germanosilicate fiber can attain 10⁻⁵ and is multi-decaying-exponentially proportional to the UV exposure.      

基于低双折射光子晶体光纤Sagnac干涉仪的超低温度系数扭曲传感器

研究了低双折射光子晶体光纤中由光纤扭曲造成的圆双折射效应,并应用Sagnac干涉仪结构设计了扭曲传感器.在Sagnac环中的光子晶体光纤上施加机械压力引入初始线双折射并产生正弦干涉光谱,再扭曲光纤产生圆双折射使干涉光谱随扭曲角度移动.光谱峰值波长随扭曲角度变化符合Sinc函数关系,理论分析与实验相符.传感器灵敏度为1.00 nm/°,分比率为0.01°,并具有超低的温度系数-0.5 pm/℃.     

Non-contact detection of laser-generated surface acoustic waves using fiber optic Sagnac interferometer

A high powered Q-switched Nd:YAG laser was used to excite the surface waves, and an optical fiber sensor was used to detect the out-of-plane displacements due to the propagating waves. This sensor is based on the fiber optic Sagnac interferometer, which has the path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence in an optical path using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. The performance of the fiber optic Sagnac interferometer was investigated, and laser-generated surface wave signals were detected using this fiber optic sensor. The developed fiber optic sensor configured in this study is very simple and is effective for non-contact detection of ultrasonic waves.     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: XII. Dependence of the zero drift in fiber ring interferometers in orthogonal polarization modes on the range of temperature variation in an optical fiber

Temperature dependences of the zero drift in a fiber ring interferometer (FRI) without a polarizer in the presence of random inhomogeneities in a single-mode optical fiber in the FRI loop are obtained by numerical simulation. The results are compared with known experimental data. It is shown that FRIs using a superluminescent diode as a source of nonmonochromatic radiation and a loop made of a single-mode optical fiber with weak linear birefringence can find application as low-accuracy fiber-optic gyroscopes and FRIs with a loop made of a single-mode optical fiber with strong linear birefringence can be used as medium-accuracy fiber-optic gyroscopes.     

一种新型侧漏型光子晶体光纤的研制及其传输特性研究

通过引入椭圆掺锗芯和侧向泄露通道, 提出并研制出一种侧漏型光子晶体光纤(photonic crystal fiber, PCF). 应用结构重构全矢量有限元数值分析法分析了设计结构和实际研制的侧漏型PCF的传输特性. 研制的侧漏型PCF, 在波长1550 nm处基模的平均模场直径为9.275 μm, 与G652标准单模光纤具有很好的适配性, 模式双折射为0.837× 10^-4, 群双折射约为1.508× 10^-4. 基于研制的侧漏型PCF光纤构建了Sagnac干涉仪, 对其群双折射进行了测量. 测量结果表明:当侧漏型PCF光纤达到一定长度时, 在1450–1750 nm波长范围内, 二阶模在光纤中不能成为有效传输模式, 光纤可以实现单模传输; 另外, 研制的侧漏型PCF群双折射实验的测量平均值, 与数值分析结果相符合. 侧向泄露通道的引入, 增强了侧漏型PCF光纤对外界参量变化的敏感性, 提高了其在扭转、弯曲、压力等参量的光纤传感和高性能光纤激光器构建等方面的应用潜能. 关键词： 光子晶体光纤 侧向泄露通道 双折射 Sagnac干涉仪     

Spectral analysis of the temperature dependence of the nonreciprocal phase difference of counterpropagating waves in a fiber ring interferometer

Using the method of the Fourier analysis, we obtain spectral-density distributions of the dependence of the nonreciprocal phase difference of counterpropagating waves at the output of a fiber ring interferometer on the temperature of a single-mode fiber lightguide of the interferometer circuit. It is shown that the main role in measuring the nonreciprocal phase difference is played by the temperature variation in the difference of the optical-path in slow and fast birefringence axes of the single-mode fiber lightguide between the circuit ends and random irregularities. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 5, pp. 452–459, May 2008.     

Influence of radiation coherence on the effects of polarization nonreciprocity of fiber ring interferometers

In this paper, we consider the effects of polarization nonreciprocity taking into account coherence or partial coherence of radiation at the output of a fiber ring interferometer (FRI) and discuss the possibility of occurrence of additional effects of polarization nonreciprocity at the output of an FRI with a broadband radiation source due to the coherent component of radiation resulting from the coupling of orthogonal modes at the output segments of the fiber. Allowing for the coherence, we estimate the temperature instability of the interferometer signal related to the polarization nonreciprocity. The features of the polarization nonreciprocity effects for a fiber ring interferometer with polarizer or dichroism are considered. It is shown that if the conditions of conventional reciprocity theorem (no rotation) are satisfied for the interferometer, then the polarization nonreciprocity effects become hidden and cannot be detected in the interference signal without a priori information on the character of birefringence and on the orientation of anisotropic elements of the fiber loop of the interferometer and polarizer.     

Twist sensor based on Sagnac single-mode optic fiber interferometer

An optical fiber twist sensor based on Sagnac single-mode optic fiber interferometer is proposed. The stress-induced birefringence of single-mode optical fiber is obtained by applying a transverse force against a short length of singlemode fiber. A high sensitivity and resolution of the twist angle measurement of 0.19 nm/° and 0.002° is achieved experimentally, respectively. The proposed sensor is more convenient and simple than that of standard polarization-maintaining fibers.     

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.     

波长可选择高双折射光纤干涉滤波器

为了实现具有全光纤结构和波长可选择滤波器,设计并从理论上计算和分析了一种基于双折射光纤的干涉滤波器.该滤波器具有很好的选频特性,不同的偏振角自由组合使得该滤波器具有更灵活的调节性.该滤波器提高了双折射光纤的使用效率,用12 m高双折射光纤可以产生等同于在Sagnac环形腔中用16 m同样光纤时的滤波效果.这种高效波长可选择滤波器还具有较好的光频隔离效果,并很容易用光纤或光波导制作出来.     

Jones matrix analysis for a polarization-sensitive optical coherence tomography system using fiber-optic components

We present an analysis for polarization-sensitive optical coherence tomography that facilitates the unrestricted use of fiber and fiber-optic components throughout an interferometer and yields sample birefringence, diattenuation, and relative optic axis orientation. We use a novel Jones matrix approach that compares the polarization states of light reflected from the sample surface with those reflected from within a biological sample for pairs of depth scans. The incident polarization alternated between two states that are perpendicular in a Poincaré sphere representation to ensure proper detection of tissue birefringence regardless of optical fiber contributions. The method was validated by comparing the calculated diattenuation of a polarizing sheet, chicken tendon, and muscle with that obtained by independent measurement. The relative importance of diattenuation versus birefringence to angular displacement of Stokes vectors on a Poincaré sphere was quantified.     

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.     

Increase in the correlation length of nonmonochromatic radiation during propagation in a single-mode optical fiber containing random inhomogeneities and the influence of this increase on the operation of a fiber ring interferometer

An analysis is made of the conditions under which the coupling of orthogonal polarization modes at random inhomogeneities in single-mode optical fibers leads to an increase in the correlation length of a source of nonmonochromatic radiation. It is shown that when long-base fiber ring interferometers with a single-mode fiber ring system possessing weak linear birefringence are used, the correlation length of the nonmonochromatic radiation at the interferometer exit is increased, which means that the interference pattern can have satisfactory visibility even when there is an appreciable difference between the interferometer arms as a result of the Sagnac effect due to the Earth’s rotation. The calculations were made by mathematical modeling of random inhomogeneities in the fiber. Zh. Tekh. Fiz. 69, 140–143 (July 1999)     

Fiber optic sensing applications using the entangled states walk-off compensations

This paper presents a new concept of the measurement of the entangled photon states timing walk-off in fiber optic systems. The relationship between the applied physical parameter on fiber optic and timing walk-off compensation can be performed. When polarized light pulse propagates into a fiber optic length, a pair of the entangled photons introduces the change in phase difference, i.e. birefringence, which can be recovered and detected. The potential of use in applications such as quantum interferometer and fiber optic remote sensing is proposed and described. The increase in measurement resolution in terms of the entangled photon walk-off length is analyzed and discussed.     

Temperature-Induced Changes of Sensitivity in the Unbalanced Hi-Bi Fiber Sagnac Interferometer

A temperature sensor based on the unbalanced Hi-Bi fiber Sagnac interferometer is analyzed in the temperature interval 15 250 C. It is shown that the sensitivity of such a sensor exhibits irreversible changes at temperatures higher than 200 C. To achieve this, it is proposed to anneal the fiber at 200 C for 1.5 h to avoid hysteresis and extend the measured temperature interval. Measurements were done for the polymer-coating-induced birefringence and the residual stresses causing hysteresis. It is also shown that the sensor sensitivity is reduced by 27 % when stresses are removed.