Field in Single-Mode Helically-Wound Optical Fibers

The scalar field wave equations of the fundamental mode in single-mode helically-wound optical fibers with circular cross section are obtained by using the Maxwell equations in the local orthogonal curvilinear coordinate system introduced by Tang. Two important results are brought about 1) The field in the above-mentioned fibers maintains a quasi-linear state of polarization while its orientation rotates with a rotation rate close to - tau with respect to the Serret-Frenet frame. 2) The state of polarization (SOP) of the above field changes periodically along the propagation distances from 1 to a value a little less than 1, and, for a fixed s, it changes periodically according to the incident polarized angles with a period/spl pi//2. The theoretical results have been verified by the experimental measurements.     

Degree of Polarization in Anisotropic Single-Mode Optical Fibers: Theory

The degree of polarization for propagation waves in anisotropic single-mode fibers is formulated in terms of light source spectrum, incident polarization condition, and fiber parameters. The polarization degree deterioration is based on the incident wave split into two eigenpolarization modes inherent in the fiber. Since the two eigenpolarization modes have different group velocities from each other, the degree of polarization is degraded when both of the modes are excited. Polarization degree is preserved when only one of the eigenpolarization modes is excited. The degradation is determined by the mutual correlation function gamma, between the two modes, which depends on the light source spectra, fiber polarization dispersion, and fiber length.     

Dispersion Measurement in Optical Fibers Using Supercontinuum Pulses

The chromatic dispersion of an optical fiber is measured using a time-of-flight technique, based on temporally and spectrally resolving a dispersed broadband pulse, on which a spectral fringe pattern has been imposed using an etalon. The technique employs broadband supercontinuum radiation, generated by launching picosecond pulses from a fiber laser into a photonic- crystal fiber. It allows the dispersion of highly dispersive optical fibers and components to be measured with a high spectral resolution over a wide wavelength region. The technique is demonstrated by measuring the dispersion of a dispersion-compensating module over its entire 400-nm transmission band with a subnanometer spectral resolution.     

Wave Coupling Between Parallel Single-Mode and Multimode Optical Fibers

A directional coupler composed of a single-mode optical fiber and a multimode optical fiber has been considered to be capable of serving as a drop/insert device of a node in optical fiber Iocal area networks. It should couple almost all the local transmitter power into the multimode fiber bus, while removing only a small fraction of the optical power from the bus through the single-mode fiber. In this paper, the underlying fundamental process of the power transfer between two such optical fibers is analyzed utilizing a coupled-mode theory. Numerical calculations show that wave coupling among the guided modes on the fibers is quite complicated and that the wave amplitude variations along the propagation direction are different from the sinusoidal types resulting from two-mode coupling. The theoretical results do support the expected performance of the proposed couplers and provide an important guide for the design of such devices.     

Propagation Properties of Single-Mode Liquid-Core Optical Fibers With Subwavelength Diameter

We investigate the optical wave guiding properties of subwavelength-diameter liquid-core optical fibers (LOCFs) that are filled with high-refractive-index liquids. The single-mode condition, modal fields, nonlinear coefficient gamma, group velocities, and group velocity dispersions are studied theoretically. Compared with traditional silica subwavelength-diameter wires, subwavelength-diameter LOCFs show unique interesting properties, such as more confined guided-mode electrical fields and large nonlinear parameters gamma in the visible and infrared regions.     

线双折射光纤与正交极化孤子碰撞的研究

从描述线双折射光纤中ｐｓ量级孤子脉冲的归一化ＮＬＳ方程出发,利用对称分步傅里叶变换计算方法,分析和归纳了正交极化孤子在双折射光纤中的碰撞数值特性,并对相关结论作了粗略探讨。     

Analysis of the Polarization-Mode-Dispersion Vector Distribution for Linearly Birefringent Optical Fibers

We analyze the polarization-mode-dispersion (PMD) vector distribution for linearly birefringent optical fibers. We assume the linear birefringence vector components as white Gaussian processes. From the corresponding Fokker-Planck equation, we find an asymptotic solution for the probability density function of the PMD vector. Our analysis shows that the PMD vector distribution is dependent on the polar angle during its transient and the distribution tail for the magnitude of the PMD vector is higher than the Maxwellian.     

Cross-Polarization Modulation Domain Wall Solitons for WDM Signals in Birefringent Optical Fibers

Nonlinear cross-polarization modulation between two wavelength multiplexed channels propagating in an elliptically birefringent optical fiber leads to polarization domain wall solitons. These solitons represent a switching of the polarization of both waves between two stable orthogonal states. The potential application of polarization domains to nonlinear loss-free polarizers is described.      

光学孤子在单模光纤中的非线性传输方程

人们熟知,由非线性薛定谔(NLS)方程描述的光学孤子可以在单模光纤中稳定地传输。本文在准单色近似和慢变包络近似条件下,利拥泰勒级数展开推出了这一非线性传输方程。由于推出的方程包含着高阶线性色散和光纤损耗项,因而可以用来研究短光脉冲(皮秒量级)在单模光纤传输过程中相关的非线性光学孤子效应,比如光学孤子分裂和光学孤子损耗等。     

光纤中光学高斯型脉冲的传输特性研究

应用变分法，研究了微扰对光学高斯型脉冲在光纤中非线性传输特性的影响，导出了光学高斯型脉冲参数演化的动力学方程。     

A Breather in Birefringent Fibers

The propagation properties of the breather in birefringent fibers are investigated. The breather can propagate stably in strongly birefringent fibers. The propagation law can be expected. However, random birefringence makes the propagation of the breather more complex. The breather will partly disappear and partly appear, even may split into two smaller breathers. In addition, the varying range of relative time displacement between two components of the breather becomes narrower with the effect of third-order dispersion. If third-order dispersion is too strong, the breather behavior will disappear gradually during the transmission. The breather can exist in random birefringent fiber with dispersion management rather than in strongly birefringent fiber.     

双折射光纤中损耗对孤子相互作用的影响

利用变分原理研究有损耗的情况下双折射光纤中孤子间的相互作用,发现损耗减弱了孤子间的相互作用,但同时使光纤中继间隔缩短,这为实际应用中如何控制孤子间的相互作用提供了一定的理论依据     

基于单模光纤的超短光脉冲产生及其进展

综述了基于单模光纤的超短光脉冲产生方法、原理及其进展,介绍了我们最近的研究成果,讨论了实现高效率脉冲压缩的途径。     

Polarization Holding in Ellipitical-Core Birefringent Fibers

Polarization holding in high-birefringence elliptical-core fibers is evaluated for the fiber birefringence spatial frequency range 1.5 cm/sup -1/ < Beta/sub i/ < 40 cm/sup -1/, corresponding to beat lengths from 1.6 mm to 4.2 cm. This range of spatial frequencies is spanned by making measurements with a broad-band light source on four fibers with different degrees of birefringence. In this way, the strength of the internal birefringence perturbations is mapped to give the first experimental measure of their power spectrum. It is shown that commonly available fiber jackets can significantly degrade the polarization holding. For low spatial frequencies, the strength of the perturbations decreases rapidly with increasing frequency, but this rate decreases by more than half over a one-and-a-half order of magnitude increase in spatial frequency. A possible origin of the perturbations is suggested and it is shown that the strength of these perturbations must be reduced if polarization holding to a very high degree is to be realized in elliptical-core fibers. Presently, internal perturbations limit the polarization holding to /spl les/14.4 dB over 1 km.     

双折射光纤中三阶色散对孤子稳定性的影响

本文研究了单模光纤中双折射效应和高阶色菜和效应对弧 子传输稳定性影响。研究结果表明：线性双折射所导致的两偏振孤子分离的振幅阈值三阶色散的影响而增大,如果增大脉冲 振幅的阈值以上,那么两个垂直方向的偏振孤子将锁定在一起传输。     

色散缓变光纤中的孤子效应拉曼脉冲产生

在推导描述色散缓变单模光纤负群速色散区超快受激拉曼散射过程数学模型的基础上，通过计算机模拟，对这一孤子效应拉曼脉冲产生过程进行了详细的计算和分析。发现与常规光纤中相比，在泵浦条件相同的情况下，从色散缓变光纤中获得的拉曼脉冲具有较窄的宽度和较高的峰值功率。这意味着色散缓变光纤具有比常规光纤较低的拉曼阈值。进一步研究表明，对于给定的泵浦条件，光纤色故的缓变程度存在一最佳值。     

Accurate Characterization of Twist-Induced Optical Activity in Single-Mode Fibers by Means of Polarization-Sensitive Reflectometry

The stress-optic rotation coefficient $g$, describing the twist-induced optical activity in single-mode optical fibers, has been accurately measured by means of polarization-sensitive frequency domain reflectometry. Measurements have been performed on both spun and unspun fibers and the measured values of $g$ vary between 0.14 and 0.15, with an uncertainty of less than 4%.      

Single-Mode Perfluorinated Polymer Optical Fibers With Refractive Index of 1.34 for Biomedical Applications

We demonstrate a technique for the fabrication of single-mode perfluorinated polymer optical fiber (PPOF). The PPOF preform is composed of poly-methyl-methacrylate (PMMA)-based outer cladding and a graded-index multimode PPOF as the core. A photosensitive graded-index single-mode PPOF with a core diameter of about 6.6 $ mu{hbox {m}}$ and cladding diameter of 400 $ mu{hbox {m}}$ was fabricated. The fiber has a cutoff wavelength of 854 nm and exhibits single-mode characteristics at wavelengths of 1310 and 1550 nm. The transmission loss is less than 0.2 dB/m in the wavelength range of 1410–1540 nm and less than 0.5 dB/m for wavelengths up to 1610 nm, significantly less than the typical transmission loss of $sim$100 dB/m for PMMA fiber. Another important feature of the PPOF is its low refractive index of 1.34, close to aqueous solution of biomaterials, permitting strong optical coupling for biomedical applications.      

Propagation in Doubly Clad Single-Mode Fibers

General propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer cladding index, using the two parameters inner cladding/core radii ratio and inner cladding/core index differences ratio. LP01, LP11, and LP02 cutoff conditions are examined. It is shown that dispersion properties largely differ from the singly clad single-mode fiber case, leading to large new possibilities for low-loss dispersion-free fibers at any wavelength between 1.3 and 1.7 µm.