接近无损耗传输的单模光纤

人们在谈论光纤时，一般是指一年前刚刚上市的光纤。去年，在美国安装的光纤中，单模光纤仅占4%，今年单模光纤将占绝大部分。弗吉尼亚州的大陆电话公司就是一个很好的例子。去年它安装的全是多模光纤系统。今年计划安装114个光波系统，全都用单模光纤。多模光纤将仅用于改进现有的设备。     

单模光纤测量技术(之二)单模光纤衰减的测量

一、引言单模光纤的研究和应用,促进了单模光纤测量技术的发展。由于光纤衰减是单模光纤系统最重要的参数之一,因此衰减测量技术首先得到了迅速发展。从根本上看,单模光纤的衰减测量方法与多模光纤的衰减测量方法基本相同,而且其注入条件要比多模光纤测量简单,但是鉴于下述理由,对单模光纤衰减测量的要求却高于多模光纤。 (1)单模光纤的衰减比多模光纤小,1.3μm时的典型衰减为0.4～0.7dB/km,1.55μm时的典型衰减为0.2～0.4dB/km,可见单模光纤的衰减大约为多模光纤衰减的     

单模光纤测量技术(之一)——单模光纤的色散测量方法

光纤的传输损耗和色散是限制光纤通信中传输距离的主要因素。而色散又是限制光纤通信系统传输带宽的决定性因素,因为色散使在光纤中传输的光脉冲随着传输距离的增加而展宽。在单模光纤中,脉冲展宽主要起源于折射率随波长变化所引起的模内材料色散和单个模的群速度随频率略有变化所导致的波导色散。因此单模光纤的总色散,或者说波长色散或色度色散,主要就包括这两部分。单模光纤色散的测量对于研究单模光纤的传输特性,控制和改进预制件的质量;监测单模光纤通信系统的性能具有很大的理论意义和实用价值。本文主要介绍国内外单模光纤色散测量的各种方法及其特点。     

单模光纤和单模激光器耦合理论与实践

本文对单模光纤、单模激光器的输出光束特性进行了分析,并利用高斯光束传输理论讨论了单模激光器与单模光纤、单模光纤与单模光纤之间的耦合问题。这种高斯近似分析方法,是一种简便、准确、实用的分析计算方法。     

单模光纤的测量技术

本文主要介绍光学时间畴反射仪、稳定的光源和光学验证技术。这些设备对单模纤维传输系统的使用和维修起到重要的作用。因为单模光纤的芯径为10μm,外径为125μm,纤芯和包层之间相对折射率差△为0.3 ％,单模光纤芯径和折射率差分别只有梯度折射率多模光纤的1/5和1/3。因此,激光二极管和单模光纤之间耦合效率约比多模光纤低5dB。另一方面,单模光纤不存在模的色散,因此带宽基本上不受限制。在考虑上述单模光纤特性之后,光学时间畴反射仪、稳定的光源和光学鉴别器对于大容量传输系统十分重要。     

1.32μm单模光纤OTDR实验研究

1.3μm单模光纤OTDR是最近两年发展起来的光纤测量技术。本文在对单模光纤后向瑞利散射功率分析的基础上,提出了以1.32μm Nd:YAG调Q脉冲激光器为光源的单模光纤OTDR实验系统,通过单模光纤衰减、接头损耗等初步测量,证明系统的波长、脉宽、线性度及稳定性等均能满足对单模光纤的测量及研究要求。     

普通单模光纤与掺铒单模光纤的连接损耗

本文研究了大功率时普通单模光纤与掺铒单模光纤的连接损耗，结果表明，连接损耗与功率有关。     

新一代的单模光纤设计

本文简述了单模光纤设计进展的四个阶段。从常规单模光纤开始，零色散波长于光纤通信工作的１．３１μｍ，其后激光管技术改进和光纤放大器实用化，使光纤通信工作波长转移，相应地出现零色散移位至１．５５μｍ的单模光纤。     

大型单模星形耦合器制造技术

一、引言用单模星形耦合器进行交换和分配信息的各种系统方案现正相继提出,如西柏林海茵利希·赫芝研究所修订了采用光交换技术实验方法的研究计划,在窄带业务和高速率数据业务的综合局部通信系统中采用单模星形耦合器进行光交换。单模星形耦合器的原理是以单模光纤作传输介质的LiNbO_3。光开关为依据的,但单模光纤星形耦合器的结构原理却不同于渐变型光纤星形耦合器。     

单模光纤类型和性能演进北大核心

阐述了光纤传输系统研究进展推动光纤类型与性能的演进。在强调光纤性能研究内容后,着重描述了光纤性能特点及其系统应用。最后,列举了超低损耗大有效面积单模光纤和多芯单模光纤实现超大容量传输实验实例。     

Design of a miniature lens for semiconductor laser to single-mode fiber coupling

A design method for a miniature optical lens tipped on a single-mode fiber end to improve power coupling from a semiconductor laser is described. The lens shapes studied are hemispherical, hemicylindrical, and hemiellipsoidal. The optimum coupling conditions and the obtained coupling efficiency are represented in terms of laser beam and fiber parameters. Preferable ranges of hemispherical and hemicylindrical lenses are classified according to the laser and fiber mode spot sizes. Fiber axis offset and tilt effects on coupling efficiency are also studied.     

Characteristics of a hemispherical microlens for coupling between a semiconductor laser and single-mode fiber

A hemispherical microlens is fabricated on the end of a single-mode fiber by an electric arc discharge technique. It improves coupling efficiency between InGaAsP lasers with buried heterostructure geometry and single-mode fiber. The lowest coupling loss of 2.9 dB is achieved with the optimum lens radius of 8.5 μm. This loss is 4.4 dB lower than that with a butt joint. Experimental results of coupling efficiency and alignment tolerances in coupling with different lens radii in the range of3.5-17 mum are discussed in detail. The results are in good agreement with theoretical values derived by Gaussian beam and paraxial ray approximations.     

Tapered single-mode optical fiber evanescent coupling

We describe the results of a numerical and experimental investigation of how a point source of radiation couples light to the HE ₁₁ mode of a tapered single-mode fiber. Specifically, we have investigated two different geometries of nonadiabatic, tapered single-mode optical fiber. The motivation for this study is the characterization of a single-mode tapered optical fiber biosensor. In such a device light is collected from fluorescent sources located along the cladding surface of the tapered fiber. Taper-to-taper coupling measurements and fiber mode calculations indicate the device sensitivity decreases exponentially as sources are moved away from the tip of the tapered fiber     

Distributed single-mode fiber to single-mode planar waveguidecoupler

Light transfer between a curved single-mode fiber and a single-mode planar waveguide is investigated experimentally in dependence on the refractive index and thickness of the planar waveguide and for different polishing depths. Marcuse's model is applied to treat theoretically the coupler, leading to a very good agreement with the experimental results     

SC-type single-mode optical fiber connectors

SC-type single-mode optical fiber connectors specifically developed for subscriber loop networks are discussed. The properties and design of precision zirconia ceramic ferrules which have been found to be ideal for high-performance, low-cost single-mode optical fiber connectors are described. A design approach featuring a plastic-molded rectangular connector housing using a push-pull coupling mechanism which has also been found to be suitable for durable, compact, and low-cost connectors is presented. SC connectors used with 10/125 single-mode fibers exhibit insertion loss of 0.06 dB and return loss of 38.6 dB, with no degradation during and after mechanical and environmental tests. To realize higher packaging density, duplex-ferrule connectors, quadruple-ferrule connectors and optical attenuators have also been developed on the basis of the SC connector design     

A 100-km-long single-mode optical-fiber fault location

A Raman OTDR (ROTDR) fault location for a 100-km-long single-mode optical fiber has been tested. A Ge p-i-n photodiode cooled by liquid nitrogen has been used as a backscattered light receiver. The signal-to-noise ration (SNR) improvement of the cooled Ge p-i-n photodiode from a Ge avalanche photodiode (Ge APD), which operates at room temperature, is 14 dB. Spectral Stokes light power distributions, which have been emitted from a long single-mode fiber, have been measured to estimate the maximum locatable length for a single-mode fiber. It has been shown, from the measurements and calculations, that a 100- km-long and a 30-dB total attenuation at a 1.55-μm wavelength single-mode fiber fault location can be achieved with the aid of an averaging technique. On the basis of these results, a 102-km-long single-mode fiber fault location experiment has been successfully carried out.     

Ultralow-loss fluoride-glass single-mode fiber design

The excess losses and dispersion in fluoride-glass single-mode fibers are theoretically evaluated. Microbending, splicing, coating material, and fiber stranding are considered as the causes of the excess losses. Based on these evaluations, the design for ultralow-loss fluoride-glass single-mode fibers is carried out. Relative refractive-index difference of 0.43     

Random coupling theory of single-mode optical fibers

A random coupling theory is developed for analyzing the propagation characteristics of the polarization state of light in single-mode optical fibers (including conventional and polarization maintaining fibers) under random disturbances. The basic idea is that the disturbances that a fiber suffers in practice continuously change with time and space, so time-varying coupling will occur along the fiber between two linearly polarized modes HE₁₁ that may propagate in the fiber. A coupled-mode equation of single-mode fibers under random disturbances is derived and solved rigorously with few assumptions. A random coupled-mode equation is derived considering time and space variation. Analytic solutions are obtained and used for analyzing the effect of random birefringence, polarization dispersion, polarization fluctuation, and evolution of the degree of polarization in single-mode fibers and for characterizing fiber properties     

Single-polarization single-mode optical fibers

Strictly speaking, an ordinary axially symmetrical single-mode fiber is a "two-mode" fiber because two orthogonally polarized HE11modes can be propagated in it. This fact results in the instability of the polarization state of the propagated mode when geometrical perturbation exists in the fiber, and also the so-called polarization mode dispersion. These are harmful in some applications of single-mode fibers to communication and measurement. To prevent these adverse effects, single-polarization single-mode (SPSM) optical fibers have been developed. Three basic types of the SPSM fiber are elliptical-core fiber, stress-induced birefringent fiber, and side-pit fiber. This paper describes the principles of these three types, performance obtained experimentally, theoretical approaches, and measurement techniques related to the SPSM fibers. Finally, relevant technical tasks in the future are mentioned.     

Loss mechanisms in single-mode fiber tapers

The onset of transmission loss in four single-mode tapers is shown to coincide with the taper slope exceeding the critical slope angle at which fundamental mode cutoff occurs. This implies that the primary loss mechanism in single-mode fiber tapers is cutoff of the fundamental mode from the core. A secondary loss mechanism of coupling to the modes of a coaxial outer waveguide is also observed and modeled. Implications for fused fiber couplers are discussed.