一种高精度光纤陀螺用光子晶体光纤设计

为了解决光子晶体光纤陀螺中高阶模致非互易性问题,设计了一种用于高精度光纤陀螺的单模保偏光子晶体光纤。为获得光纤结构参数最优区域,基于全矢量有限元方法开展了光子晶体光纤模场分布、双折射特性和限制损耗与三个重要结构参数(归一化频率、空气填充比、大孔直径)的依赖关系数值仿真分析。以传统熊猫型保偏光纤特性为参照,确定了光子晶体光纤结构参数最优区域。采用优化的光子晶体光纤绕制了1500 m环圈并装配于陀螺,对陀螺进行了相应测试。未采用温度补偿措施下,陀螺全温零偏稳定性优于0.008 (°)/h (100 s, 1σ),表明这种光子晶体光纤适用于高精度光纤陀螺。     

五角芯型保偏光子晶体光纤(Q-PM-PCF)的双折射

提出了一种内层空气孔环含有五个空气孔的新型高双折射光子晶体光纤结构;采用全矢量有限元法进行分析,研究了该光子晶体光纤两正交偏振模的有效折射率和双折射,分别给出了该五角芯型保偏光子晶体光纤双折射随输入光波长和大空气孔半径的变化曲线.分析结果表明:该五角芯型保偏光子晶体光纤的双折射很易达到i0-3量级甚至更高,比传统保偏光纤的双折射至少高出一个数量级,合理设计光纤结构参数,该保偏光纤的双折射在1550 nm处可以达到6.5×10-3以上,甚至更高,适合应用于偏振特性及稳定性要求都较高的实际光纤传感系统,例如光纤陀螺.     

保偏光子晶体光纤的近圆形模场分布特性

在光纤陀螺中,由于保偏光纤的性能易受环境的影响,制约了光纤陀螺稳定性和精度的进一步提高。保偏光子晶体光纤的研究为光纤陀螺解决环境适应性问题提供了新思路,针对保偏光子晶体光纤与传统光纤的模场匹配问题,采用有限元方法,对保偏光子晶体光纤的保偏性能和模场分布特性进行了分析与研究。通过分析不同空气孔尺寸对保偏光子晶体光纤性能的影响,得到其保偏性能与模场分布特性存在相互制约性。提出了一种改善保偏光子晶体光纤模场分布的方法,并通过仿真分析验证了这一方法的可行性,这为光纤陀螺用光子晶体光纤的发展提供了借鉴。     

光纤陀螺用保偏光纤温度敏感性测试与分析

针对高精度光纤陀螺的温度敏感性问题,重点研究了光纤陀螺用保偏光纤温度性能。利用具有高空间分辨率的脉冲预泵浦光时域分析技术,测量不同温度点光纤的长度变化量,再根据光纤长度随温度的变化量与折射率温度系数的关系,给出光纤的折射率温度系数。试验共测量了8种国内和国外主流保偏光纤的折射率温度系数,测试结果显示:8种光纤折射率温度系数的最大值与最小值之间相差14%;某型国内保偏光纤与某型国外保偏光纤的折射率温度系数最小,量值基本相同。这种不同类型的保偏光纤折射率温度系数的差异与光纤纤芯的掺杂元素及掺杂浓度是直接相关的。该项测试技术可在基础材料层面提升光纤陀螺的温度性能;通过折射率温度系数测试,优选出更加适用于光纤环圈制作的保偏光纤,从而减小光纤陀螺温度Shupe效应误差,对于提高光纤陀螺的温度性能具有重要意义。     

高精度光子晶体光纤陀螺设计及在轨应用验证

针对空间辐照带来的光功率衰减和卫星轨道周期带来的周期性温变效应,基于光子晶体光纤单一材料特点带来的抗辐照和弱温度敏感特性,提出开展空间用高精度光子晶体光纤陀螺技术研究.通过设计实芯光子晶体光纤结构,完成损耗<1.5 dB/km、偏振串音<-24 dB/km和直径135μm的光子晶体光纤技术验证,并采用八极对称绕制技术完...     

光子晶体光纤陀螺技术及其首次空间试验

光子晶体光纤具有抗辐射、抗弯曲、抗磁场干扰和温度敏感性低等优势,是空间用光纤陀螺的理想选择.针对空间用光纤陀螺,提出了四层孔和双层孔陀螺用光子晶体光纤结构,突破了光子晶体光纤长距离拉制关键技术,批量制备了陀螺用长距离低损耗实芯光子晶体光纤与空芯光子晶体光纤,利用开发的光子晶体光纤周向散射、背向散射、温度、磁等性能测试设...     

陀螺用超细径保偏光纤机械强度评估方法

针对陀螺应用场景下超细径保偏光纤机械强度评估需求,提出一种基于可拉伸骨架的超细径保偏光纤强度评估方法,超细径保偏光纤绕制于可拉伸骨架之上形成光纤环圈可模拟出成环应力过程,采用该光纤环圈构建光纤陀螺,环圈骨架内的压电堆栈可驱动骨架带动超细径保偏光纤周期性拉伸,对超细径保偏光纤起到应力激励施加效果可激发光纤疲劳以实现光纤强度快速评估与筛选,同时在超细径保偏光纤内形成相位调制功能以实现陀螺偏置调制,陀螺信号长期输出变化情况可表征超细径保偏光纤力学特性优劣。该方法能够体现出超细径保偏光纤成环应力施加的复杂性和陀螺应用光纤长期张紧、弯曲等条件下应力长期演变性,有助于陀螺用超细径保偏光纤强度评估与筛选。     

光纤陀螺抗辐照方案

为了提高光纤陀螺的抗辐照性能,满足空间应用的各种需要,对光纤陀螺光电器件进行了大量的辐射试验,尤其是对光纤陀螺的敏感器件-保偏光纤环进行了深入分析,采用光褪色心的方案,即向保偏光纤环中注入大功率激光,通过退色心的方法降低由于辐射而引起的光纤损耗的增加,从而增加了保偏光纤环的抗辐照性能。在此基础上,在光纤陀螺重量增加不大的前提下,提出了光纤陀螺主动抗辐射方案。试验表明该方案能够有效的提高光纤陀螺的抗辐射性能,能大大提高空间应用光纤陀螺的可靠性和使用寿命,能够起到抗辐照的作用。     

光子晶体光纤的耦合技术

光子晶体光纤与普通单模光纤的低损耗熔接是影响光子晶体光纤实用化的重要技术.针对自行设计的光子晶体光纤,对其与普通单模光纤的熔接损耗机制进行了理论和实验研究.首先分析了影响熔接损耗的主要因素,然后理论计算了光子晶体光纤与普通单模光纤之间的耦合损耗,最后采用常规电弧放电熔接技术对光子晶体光纤与单模光纤的熔接损耗进行了实验研究,通过优化放电参数,使熔接损耗可以降到0.7 dB以下,满足了实际应用的要求.该方法为其他类型的光子晶体光纤与普通单模光纤的熔接提供了借鉴.     

基于超细径光纤的高精度光纤陀螺

在应用系统的牵引及光学器件技术的推动下,工程化光纤陀螺朝着小型化、轻量化、高精度方向发展,设计了一种基于新型超细径(60/100)光纤制作的高精度光纤陀螺。相比于传统细径保偏光纤,新型超细径光纤可增加光纤的抗弯曲程度,也可使光纤环圈的绕制半径减少;同时,由于光纤变细,光纤环厚度减小,当环境温度改变时,内外层光纤温度差减小,有利于改善光纤陀螺环圈全温性能,提高光纤陀螺温度特性。首先研究了新型超细径光纤纤芯、包层结构设计,在此基础上为针对性提高涂覆胶体、绕环胶体材料的可靠性,建立了胶体材料性能随时间退化的模型;随后,基于上述新型光纤和小型化宽谱ASE光源,成功搭建了高精度光纤陀螺仪样机,陀螺整机尺寸为70 mm×70 mm×35 mm,陀螺测试零偏稳定性可达0.007°/h,可以满足陀螺小型化、轻量化、高精度需求。     

Homogenization of long fiber reinforced composites including fiber bending effects

This paper presents a homogenization method, which accounts for intrinsic size effects related to the fiber diameter in long fiber reinforced composite materials with two independent constitutive models for the matrix and fiber materials. A new choice of internal kinematic variables allows to maintain the kinematics of the two material phases independent from the assumed constitutive models, so that stress–deformation relationships, can be expressed in the framework of hyper-elasticity and hyper-elastoplasticity for the fiber and the matrix materials respectively. The bending stiffness of the reinforcing fibers is captured by higher order strain terms, resulting in an accurate representation of the micro-mechanical behavior of the composite. Numerical examples show that the accuracy of the proposed model is very close to a non-homogenized finite-element model with an explicit discretization of the matrix and the fibers.     

Obtaining fiber stress-strain curves by recording fiber vibrations during electric-field measurements

A simple method for constructing tension curves of thin fibers is proposed which consists of determining the dependence of the frequencies of small transverse vibrations of thin fibers on their tensile strain. The fiber stress at these frequencies is calculated using the classical formula of string vibrations. Instead of force and strain, it is proposed to measure frequency and strain. This method has a number of advantages, in particular, it is more accurate. Resonant frequencies are determined by recording the accompanying electric field resulting from the variation in the charge distributed over the fiber surface. The effectiveness of the method is demonstrated by constructing copolymer fibers of various diameters. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 219–223, July–August, 2009.     

Numerical prediction of fiber motion in a branching channel flow of fiber suspensions

Fiber orientation and dispersion in the dilute fiber suspension that flows through a T-shaped branching channel are simulated numerically based on the slender-body theory. The simulated results are consistent qualitatively with the experimental data available in the literature. The results show that the spatial distribution of fibers is dependent on the fiber aspect ratio, but has no relation with the volume fraction of fiber. The content ratio of fibers near the upper wall increases monotonically with an increasing Re number, and the situation is reverse for the region near the bottom wall. The orientation of fibers depends on Re number, however, the function of fiber volume fraction and aspect ratio is negligible. The fibers near the wall and in the central region of the channel align along the flow direction at all times, but the fibers in the other parts of the channel tend to align along the flow direction only in the downstream region.The project supported by the National Natural Science Foundation of China (10372090) and Doctoral Program of Higher Education in China (20030335001)The English text was polished by Ron Marshall     

基于光纤环安装方式的光纤陀螺振动误差抑制方法

随着光纤陀螺的实用化,发现载体振动会引起光纤陀螺尤其是高精度光纤陀螺的测量误差增大,对光纤陀螺的性能指标造成不可忽视的影响。对干涉式数字闭环光纤陀螺,从弹光效应出发,分析了振动对光纤陀螺光路的影响机理,得出了振动影响下光纤环中反向传播的光信号非互易相移误差信号的表现形式,并针对此提出了通过合理安装光纤环,使光路满足互异性,来抑制振动情况下光纤陀螺输出信号噪声和漂移。实验结果表明,该方案有效降低光纤陀螺输出信号的噪声,抑制了由振动引起的陀螺漂移,使得陀螺振动误差减小了一个数量级。     

Stress state of a fiber composite with curved structures with a low fiber concentration

International Applied Mechanics -     

A study on validity of using average fiber aspect ratio for mechanical properties of aligned short fiber composites with different fiber aspect ratios

A closed-form solution using the actual distribution of the fiber aspect ratio is proposed for predicting the stiffness of aligned short fiber composite. The present model is the simplified form of Takao and Taya’s model and the extended version of Taya and Chou’s model, where Eshelby’s equivalent inclusion method modified for finite fiber volume fraction is employed. The validity of using average fiber aspect ratio for predicting the composite stiffness is justified in terms of the scatter of fiber aspect ratio, fiber volume fraction, and constituents‘ Young’s modulus ratio, comparing with the results by the present model. The guideline for selection of either the actual distribution or the average fiber aspect ratio is presented for the better prediction of the composite stiffness.     

Dynamical regimes of fiber spinning

An analytical solution is obtained that describes fiber spinning with a given force on the receiving bobbin. As an example, a calculation is made of the response of the final fiber section to a periodically varying draw force; a solution is constructed that describes the propagation along the fiber of a finite perturbation associated with a change in the conditions at the spinneret for a fixed draw force. The problem of the small perturbations of a fiber spun at a given rate onto a bobbin is reduced to a linear integrodifferential equation with retardation whose characteristic equation determines the region of the “draw resonance” instability. The reasons for the occurrence for the instability are elucidated.     

Elongational viscosity by fiber spinning

Isothermal melt, fiber-spinning was recently analyzed by means of a nonlinear, integral, constitutive equation that incorporates shear history effects, spectrum of relaxation times, shear-thinning, and extension thinning or thickening when either the drawing force or the draw ratio is specified. The predictions agreed with experimental data on spinning of polystyrene, low-density polyethylene, and polypropylene melts. The predicted apparent elongational viscosity along the threadline (which, as shown in this work, must be identical to that measured experimentally by fiber spinning type of elongational rheometers) is compared with the true elongational viscosity predicted by the same constitutive equation under well-defined experimental conditions of constant extension rate, independent of any strain history. It is concluded that the apparent elongational viscosity, as measured by fiber-spinning, approaches the true elongational viscosity at low Weissenberg numbers (defined as the product of the liquid's relaxation time multiplied by the extension rate). At moderate Weissenberg numbers, the two viscosities may differ by an order of magnitude and their difference grows even larger at high Weissenberg numbers.     

Theoretical research on rotational dispersion coefficient of fiber in turbulent shear flow of fiber suspension

The rotational dispersion coefficient of the fiber in the turbulent shear flow of fiber suspension was studied theoretically. The function of correlation moment between the different fluctuating velocity gradients of the flow was built firstly. Then the expression, dependent on the characteristic length, time, velocity and a dimensionless parameter related to the effect of wall, of rotational dispersion coefficient is derived. The derived expression of rotational dispersion coefficient can be employed to the inhomogeneous and non-isotropic turbulent flows. Furthermore it can be expanded to three-dimensional turbulent flows and serves the theoretical basis for solving the turbulent flow of fiber suspension.     

research on rotational dispersion coefficient of fiber in turbulent shear flow of fiber suspension

The rotational dispersion coefficient of the fiber in the turbulent shear flow of fiber suspension was studied theoretically. The function of correlation moment between the different fluctuating velocity gradients of the flow was built firstly. Then the expres- sion, dependent on the characteristic length, time, velocity and a dimensionless parameter related to the effect of wall, of rotational dispersion coefficient is derived. The derived expression of rotational dispersion coefficient can be employed to the inhomogeneous and non-isotropic turbulent flows. Furthermore it can be expanded to three-dimensional turbulent flows and serves the theoretical basis for solving the turbulent flow of fiber suspension.