Theoretical analysis of a coated single-mode fiber termination

The antireflection efficiency of a single layer coating in front of an abruptly terminated monomode optical fiber is treated analytically by means of an integral equation, that is appropriate to solve the corresponding boundary value problem. Both guided and radiation modes are taken into account, when describing the field inside the optical fiber region. Then the integral equation is solved approximately by a Neumann series procedure giving highly accurate results when the weakly guidance condition holds, which is a case of practical interest in the optical communications area. The reflection coefficient and the radiation pattern of this configuration are computed. Numerical results are given for several values of the parameters of the geometry under consideration.     

Theoretical analysis of a push-pull fiber-optic hydrophone

A push-pull fiber-optic hydrophone is analyzed theoretically by closed-form approximations. The sensor is a fiber-optic Mach-Zehnder interferometer with a single-mode optical fiber from each arm wound on a separate tube. The two tubes are coaxial, with one tube inside the other. The acoustic medium is applied to the inside (outside) of the smaller (larger) diameter tube with the fiber wound on the tube's opposite side. This configuration is desired so that the acoustic signal modulates the optical phase of the arms with equal magnitude 180° out of phase. This gives the sensor twice the sensitivity of an analogous single tube sensor. The heat sinked interferometer arms with equal and opposite sensitivities are in relative close proximity to each other. This promotes good noise rejection to achieve a low minimum detectable acoustic pressure due to the interferometer's common-mode rejection.     

Recent developments in hermetically coated optical fiber

Recent progress on the development of hermetically coated optical fiber is presented. This fiber provides improved fatigue resistance; high usable strength; and excellent resistance to hydrogen permeation, 25-90°C water, and corrosive chemicals such as hydrofluoric acid and boiling sodium hydroxide. These attributes make the hermetically coated fiber an excellent candidate for use in undersea cables and other special applications where a harsh environment prevails     

Stresses in a partially coated optical glass fiber subjected to theends off-set

A simple formula based on the elementary beam theory is obtained for the evaluation of the maximum bending stress in an optical glass fiber whose ends are clamped and experience lateral off-set. We consider a situation when the fiber is partially coated and/or partially metallized, and therefore its flexural rigidity is not constant along its span. The obtained formula can be helpful in the analysis and design of optical glass fibers and optical interconnects structures of the type in question     

光纤碳密封涂覆的工艺研究

碳密封涂覆光纤具有良好的耐疲劳性能，以及抗氯损性能，在军事及通信领域内有着重要的应用前景。本文简单介绍了碳密封涂覆光纤的研究进展，以及其应用前景，并主要分析了碳密封涂覆光纤的工艺影响因素。     

Theoretical analysis of reflectometric measurements in optical fiber links affected by polarization-dependent loss

The theory of reflectometric measurements of polarization-dependent effects in optical fiber links is generalized to the case of links with polarization-dependent losses. The results are a clean generalization of the no-loss case. In particular, a new technique for the reflectometric measurement of the mean polarization-dependent loss is proposed. Furthermore, the possibility of characterizing the local birefringence and the local dichroism of the link is discussed.     

Low temperature characteristics of UV-curable resin coated optical fiber

Transmission characteristics of coated optical fiber depend on coating materials at low temperature. Loss increase phenomena are compared for UV-curable resin coated and silicone-nylon coated fibers. Different mechanisms induce loss increase depending on coating materials. Lateral forces are caused by shrinkage and Young's modulus increase at low temperature for UV-curable resin coated fibers. These forces cause fiber microbending for correlation lengths of not more than 1 mm. However, for silicone-nylon coated fibers, axial forces cause fiber buckling for correlation lengths longer than 5 mm. The relationship between the UV-coating structure and loss increase at low temperature is also described.     

基于种子光特性优化的光纤放大器理论分析

种子光特性直接影响放大脉冲的特性,为获得高质量放大脉冲输出,文章对基于SESAM被动锁模光纤放大器中种子光的特性进行优化模拟。理论分析了锁模光纤激光器的单模光纤长度、增益光纤长度、滤波器带宽以及输出耦合比的变化对种子光特性的影响,以及种子光携带的啁啾对放大脉冲的影响。综合色散和非线性效应等对种子光的影响,得到各项参数的最优值,并进行两级放大模拟,最终获得脉冲宽度为1353 ps、光谱宽度为115nm、平均功率为61W的高质量放大脉冲。     

Simplified analysis of a polarizing optical fiber

A simplified analysis of anisotropic, polarizing fibers consisting of a circular core placed in a highly elliptical inner cladding is presented. The simplification consists of treating the problem in the scalar approximation and of letting the highly elliptical inner cladding degenerate into two semi-infinite half spaces bounded by plane surfaces. The birefringence of the fiber material is not explicitly included in the analysis. Instead, it is assumed that modes that are linearly polarized at right angles to each other `see' effectively different isotropic media. The solution yields the field distributions and dispersion curves for guided modes right to their points of cutoff. Leakage losses of modes below cutoff are estimated with low accuracy. The results are useful for designing polarization maintaining fibers or fiber polarizers     

In-line optical fiber polarizer and modulator coated withLangmuir-Blodgett films

In-line optical fiber polarizer and modulator were fabricated by depositing Langmuir-Blodgett (LB) films on polished fiber surface with gold layer. The thickness of LB film was adjusted by changing the number of monolayers, which then optimized the performance of the fiber polarizer. Good agreement was observed between the theoretically predicted conditions for efficient coupling and the experimentally determined conditions for high TM/TE extinction ratio of the optical field. By applying an electric field between the LB film, the polarization state of the lightwave in the optical fiber can be modulated     

光纤传感器中布里渊增益系数与应变关系的理论研究

布里渊功率和应变的关系是分布式布里渊光纤温度和应变传感器的基础之一,而温度和应变又是通过改变布里渊增益系数来影响布里渊信号的功率。目前许多学者认为布里渊增益系数的变化与应变呈线性关系,但是我们通过理论研究和数值模拟发现,布里渊增益系数和应变之间并非一直为线性关系。因此在测量温度和应变时如果把布里渊增益系数的变化与应变近似地当作线性关系将会产生误差。本文基于此原因,对其进行理论研究并通过数值模拟得出各参数对布里渊增益系数变化的影响。     

光纤涂碳工艺和特性研究

介绍了利用国产拉丝设备、原材料制造碳密封涂覆光纤的工艺和产品特性。涂碳工艺稳定可靠，光纤静态疲劳参数n＞100，平均断裂应力＞60N，能够满足苛刻环境对光纤长期可靠性的要求。     

A fiber-optic autocollimation refractometric method for dispersionmeasurement of bulk optical materials using a widely tunable fiber Ramanlaser

A simple and highly sensitive fiber-optic autocollimation method for refractive-index dispersion measurement of solid-state and liquid bulk optical materials is presented. The method is based on the use of a double-pass multimode fiber Raman laser which generates widely tunable emission in a broadband (0.54-1.01 μm) continuous spectral range at pumping with the second harmonic of a Q-switched Nd:YAG laser. The optical fiber is used in a specific multifunctional regime where, because of its micrometric core dimensions, it serves simultaneously as a point laser source for the formation of a collimated input emission, as a highly sensitive receiver of the autocollimation backreflectance, and as a medium for nonlinear frequency conversion and generation of a broad-band continuum spectrum. The experimental results obtained in the refractive-index dispersion measurements are fitted to the Sellmeier dispersion equation and used to determine the material dispersion and additional dispersive characteristics of the test optical material     

FDTD法研究镀纳米结构薄膜光纤探针近场分布的特性

利用时域有限差分法(finite difference time domain,FDTD),对镀纳米结构薄膜光纤探针的成像特性进行数值模拟.讨论了探针尖端纳米颗粒以及薄膜中粒间距对探针分辨率和灵敏度的影响.结果发现,镀膜中颗粒分散且针尖端20 nm内有一个纳米颗粒时,分辨率可以提高数十纳米,灵敏度提高数十倍.     

单模光纤带宽-色散关系的理论性视探

本文将理论与实践相结合，以单模光纤的带宽与色散之间关系为论题，导出了有关的公式和图形，还讨论了影咱带宽的诸因素。本文可为单模光纤系统及其优越性的研究开发利用提供理论依据。     

Theoretical and experimental investigation of rhodamine B-dopedpolymer optical fiber amplifiers

High-power (620 W) and high-gain (28 dB) amplification was achieved by a rhodamine B (RB)-doped GI polymer-optical fiber amplifier (POFA) with a l-m length. A theoretical analysis of the amplification in the RE-doped GI POFA was carried out using the rate equation for the fast three level system. The calculated gain behaviour reasonably fit the experimental data. The possibility of higher power (more than 620 W) and higher gain (more than 28 dB) amplification covering a wide range in the visible region is shown from the calculation. Absorption and emission cross sections of RE in poly(methyl methacrylate) bulk were determined and used in the calculation. The values of the cross sections (σ_{a max}=3.4·10^-20m² ,σ_{e max}=3.4·10^-20 m ²) were approximately 10,000 times larger than those of Er ³⁺ in GeO₂-SiO₂ glass     

光纤中二次谐波的产生及机理的电镜分析

本文报导了石英光纤中的二次谐波产生及用透射电子显微镜观察光纤内部物质结构变化的实验结果,观察到了已“预置”光纤中缺陷的存在.     

双轴晶两类光轴方向的理论分析

用几何作图和理论推导方法,求得在双轴晶体中光轴与光线轴方向。     

An optical fiber magnetic field sensor based on fiber spherical structure interferometer coated by magnetic fluid

A novel magnetic field sensor based on optical fiber Mach-Zehnder interferometer (MZI) coated by magnetic fluid (MF) is proposed. The MZI consists of two spherical structures formed on standard single mode fiber (SMF). The interference wavelength and the power of the sensing structure are sensitive to the external refractive index (RI). Since RI of the MF is sensitive to the magnetic field, the magnetic field measurement can be realized by detecting the variation of the interference spectrum. Experimental results show that the wavelength and the power of interference dip both increase with the increase of magnetic field intensity.     

Pressure-induced birefringence in a coated highly birefringentoptical fiber

An attempt is made to explain the pressure-induced birefringence in a birefringent fiber based on a consideration of the effect due to the difference between the elastic properties of the stress-applying regions and the cladding of the fiber. The elastic properties and the thickness of a single fiber coating are also incorporated into the analysis. Numerical results for some typical coating materials are presented and compared with existing experimental data. The implications of the results with regard to sensor applications are also discussed. A polarimetric sensor using a suitably coated highly birefringent fiber should be useful for the detection of static and low-frequency acoustic pressures