Bandpass and band-rejection filters using dispersive fibers

It is shown that bent optical fibers can have bandpass or band-rejection filter characteristics by selecting the core and cladding materials of appropriate index dispersions. The filter properties are caused by wavelength dependence on the index difference between the core and cladding. The spectral bending loss of dispersive fibres is calculated and their characteristics as in-line fibers are discussed. The magnitude of the loss depends strongly on the fiber curvature. The bending loss of curved optical fibers is evaluated to estimate the filter characteristics     

Changing multimode dispersive fibers into single-mode fibers byannealing and guided mode analysis of annealed fibers

Dispersive fibers whose refractive index differences change greatly with wavelength are fabricated from optical glasses with different index dispersions. The fibers have several guided modes, and are changed into single-mode fibers by annealing under suitable conditions. The number of guided modes is investigated by measuring the bending loss and the mode lines of annealed dispersive fibers. The annealed single-mode fibers support only the fundamental mode over broad spectral ranges and no second guided mode at any wavelength     

弯曲损耗不敏感光纤的国际标准及宏弯损耗测试

详细介绍了ITU-T和IEC有关弯曲损耗不敏感光纤标准的最新进展情况以及弯曲损耗不敏感光纤宏弯损耗的测试方法。     

Dispersion-shifted dual-shape core fibers. Optimization based onspot size definitions

Design features, for very low bend and splice losses, in dispersion-shifted dual-shape core (DSC) single-mode fibers are obtained in terms of characteristic mode spot sizes W¯ responsible for splice loss, and W_∞ responsible for bend loss. Dual-shape core fiber designs are given with W¯_∞/W lying between 1.16 and 1.33 while maintaining the mode spot size between 4 and 5 μm at the operating wavelength of 1550 nm. With this design goal it is shown that bending loss would be lower in a step-index than in a graded-index DSC fiber. Further, conventional single clad step-index or triangular-index dispersion-shifted fibers are seen to have higher bending loss than well-designed DSC fibers     

Bending losses of coated single-mode optical fibers

Peaks appear in bending losses of coated single-mode fibers due to interference between the guided mode and rays which are radiated from the guided mode and are reflected at cladding-coating boundary. This paper reports derivation of bending loss formulas for coated slab waveguides and coated fibers. Plane wave concepts are also used to explain the appearance of the loss peaks. Measurements were performed by using two coated single-mode fibers. The agreement between theory and experimental results is found to be excellent. It is possible to obtain the refractive index difference from measured peak wavelengths.     

Design and performance of Gaussian-profile dispersion-shifted fibers manufactured by VAD process

Design and manufacturing of dispersion-shifted fibers with a Gaussian profile, which is compatible to the VAD process, are studied. From the viewpoint of stable cabling, the parametric analysis is made with emphasis on the bending loss. To make the bending sensitivity of the Gaussian core fibers comparable with the conventional 1.3- μm zero-dispersion fibers, an 0.8 percent or higher index difference is required. In the experiment, the achieved loss at the 1.55-μm dispersionless wavelength is 0.21 dB/km. The effects of a ring profile around the Gaussian core on the fiber transmission characteristics also are examined. While the cutoff wavelengths are greatly lengthened by the ring, the bending sensitivity is not so affected. It is found that the index difference of the main core still dominates the bending loss of the fiber.     

标准单模光纤宏弯曲损耗的理论研究

文章给出了多包层标准单模光纤的宏弯曲损耗模型,这一损耗模型不仅适用于多包层单模光纤的宏弯曲损耗的计算,也适用于单包层单模光纤的宏弯曲损耗的计算.文章还讨论了弯曲半径及工作波长与单模光纤弯曲损耗之间的关系,并把这种关系与传统的弯曲损耗模型进行了比较,比较结果表明,单模光纤包层对弯曲损耗有很大的影响.此外,文章还运用模式耦合理论详细解释了廊(Whispering-gallery,WG)模对损耗振荡的影响.     

Effective area limit of large-mode-area solid-core photonic bandgap fibers for fiber laser applications

We investigate the bending characteristics of solid-core photonic bandgap fibers (SC-PBGFs) aiming to achieve large mode area (LMA) and effectively single-mode operation with a practically allowable bending radius for high-power Yb-doped fiber lasers and amplifiers. Through detailed numerical simulations based on the finite element method (FEM), we evaluate the impacts of the order of photonic bandgap on the bending performance and point out the limits of core size enlargement in the SC-PBGFs with a 1-cell core structure due to the increment of bending loss. In addition, under practical constraints, we find that the SC-PBGFs having a 7-cell core can achieve sufficient differential bending loss between the fundamental mode and the higher-order modes and a much larger effective area limit as compared with previously-reported index-guiding LMA fibers.     

Bending loss evaluation of single-mode fibres with arbitrary coreindex profile by far-field pattern

An evaluation of the bending loss of single-mode fibers based on the measured mode field is described. The field decay constant and the normalized field intensity in the cladding are determined. Experimental results verified the validity of this method. Its accuracy is determined by the accuracy of field measurement. The mode field is calculated from the far-field distribution measured with finite dynamic range of more than 50 dB. Far-field measurement with finite dynamic range limits the accuracy of field evaluation. Dispersion shifted fibers are easier for evaluation because of the wider far-field distribution. Bending loss and mode field diameter can be measured simultaneously, and the method is applicable to any single-mode fibers with a matched clad structure. A microbending loss formula is also determined by the decay constant and the normalized field intensity in the cladding as well as uniform bending loss     

Experimental verification of microbending theory using modecoupling to discrete cladding modes

The existence of discrete cladding modes in single-mode fibers is illustrated by inducing periodically repeated microbends along the fiber axis and performing spectral measurements of the loss are performed. In order to explain the results of the measurements, it is necessary to apply a microbending theory in which coupling between the guided mode and a number of discrete cladding modes is considered. Very good agreement between theory and measurement is achieved. The consequences of the existence of discrete cladding modes with regard to the proper choice of artificial microbending spectrum used for fiber characterization are also discussed     

A review of the environmental factors affecting optical cabledesign

The main environmental factors considered are fiber bending loss, hydrogen loss degradation, and stress corrosion. The major bending and stress corrosion mechanisms that affect fibers are first discussed. Then each of the environmental factors is examined with respect to its impact on optical cable design     

High-bandwidth, high-numerical aperture graded-index polymeroptical fiber

A new large core (0.5-1.0 mm) graded-index polymer optical fiber was proposed to solve the connection problem of the single-mode silica fiber indoor use for high speed multimedia network. The bending loss for 10-mm bending diameter was dramatically decreased from 20 dB to less than 1 dB by preparing the high numerical aperture graded-index polymer optical fiber. The bandwidth was 585.2 MHz km which was one hundred times larger than that of any existent step-index polymer optical fibers, and the attenuation was 150 dB/km at 650-nm wavelength     

红外光纤的损耗测试

一、引言近年来国际上开展了红外光纤的研制,并取得了进展。红外光纤在近期内可用于激光手术刀、红外传感器、红外摄像等。从远期看可望获得比目前石英光纤更低损耗的光纤而用于光通信。因此,正确测量和分析红外光纤损耗的工作是很必要的。二、固定波长的损耗测定我们第一步是针对二氧化碳激光治疗的应用,目前首先测定光纤在10.6μm波长的损耗,一般用切断法和插入法二种。 (1)切断法:图1是用切断法测10.6μm波长损耗的示意图。     

Study of MPI measurement conditions and MPI characteristic in BIF

We investigated the measurement conditions for measuring multipath interference (MPI) occurring between fundamental and higher order modes. We considered the sampling interval as a function of the free spectral range (FSR) as a measurement condition. We also investigated the effect of randomized polarization states when measuring the MPI characteristics. We then confirmed the MPI characteristic, which we measured using three methods with a suitable sampling interval over FSR value and a suitable number of repetitions of randomized polarization states. Furthermore, we describe the MPI characteristic of bending loss insensitive fibers (BIFs) with offset connections and tight bends. We discuss the MPI degradation factor in an access network employing BIF.     

Triple-clad single-mode fibers for dispersion shifting

A design procedure for triple-clad dispersion-shifted single-mode fibers is developed. Following this procedure, fibers are identified which have low dopant concentrations in the core compared to those of the previous dispersion-shifted fiber designs, a second-mode cutoff wavelength close to the operating wavelength, zero dispersion at 1550 nm, a small bending loss at 1550 nm (for a bend radius of 3.75 cm), and a spot size that is large enough not to compromise the splice loss. A significant advantage of these fibers is that low-dispersion is available over a wide wavelength band about the wavelength of zero dispersion     

FTTH用微结构光纤

文章描述了国外光纤到户(FTTH)用微结构光纤(MOF)的种类及其应用情况,并从弯曲损耗、衰减、熔接损耗以及寿命4个方面阐述了微结构弯曲不敏感光纤的性能.分析表明,微结构弯曲不敏感光纤适合于空间狭小、弯曲直径较小与弯曲点较多的情况下的灵活安装,可满足FTTH光网络发展的需要.     

低弯曲损耗大模场面积多芯光纤的研究

针对19芯、37芯大模场光纤提出两种降低弯曲损耗的方法,一种方法是在芯区外引入一层空气孔,另外一种方法是在芯区外引入多包层低折射率结构。理论分析表明,多芯光纤弯曲损耗存在临界弯曲半径,在大于临界半径的情况下,弯曲损耗基本不变,在小于临界半径的情况下,弯曲损耗急剧增大。引入空气孔后,当19、37芯光纤模场面积分别为516μm2和920μm2时,临界弯曲半径都从3.5 cm减小到4 mm。当引入包层数达三层以上时,多包层结构也可使19、37芯光纤的临界弯曲半径从3.5cm减小到4 mm。     

Bend-optimized dispersion-shifted single-mode designs

A bend-optimized design for a dispersion-shifted single-mode fiber with segmented-core profile is described. With this design, dispersion-shifted fibers having the highest cutoff wavelengths reported to date have been achieved. Results on dispersion, attenuation, mode radius, bending, and microbending loss for such fibers are presented and compared to alternate designs.     

Waveguide parameter design of graded-index plastic optical fibers for bending-loss reduction

The waveguide structure of graded-index plastic optical fibers (GI POFs), such as index profile, numerical aperture (NA), and core diameter, is appropriately designed for eliminating bending losses, even under a severe bending condition. The bending loss of GI POFs under a severe bending condition is drastically reduced when the core diameter is smaller than 200 /spl mu/m and when the NA is higher than 0.25. The bending loss of GI POFs even under a severe bending condition vanishes with a core diameter of 200 /spl mu/m and an NA of 0.24. It is experimentally confirmed for the first time that the mode coupling due to the bending induces the bending loss. The mode coupling strength before the fiber is bent affects the bending loss seriously. Moreover, the mode-coupling strength is evaluated by the propagation constant difference /spl Delta//spl beta/ between the adjacent modes. The /spl Delta//spl beta/ value, which is a function of the core diameter and NA, affects the bending loss. Therefore, based on the calculation of the /spl Delta//spl beta/, we propose a guideline for the appropriate design of waveguide parameters for GI POF, in order to suppress the bending loss.     

光子晶体光纤弯曲损耗特性研究

光子晶体光纤是一种新型光纤,由于它的性能优良,成为研究领域的热点。本文先对光子晶体光纤进行了介绍,分析了光子晶体光纤弯曲耗损理论,最后对光子带隙型晶体光纤的弯曲耗损进行了测试研究。结果表明光子带隙型晶体光纤抗弯曲耗损比传统的单模光子晶体光纤能力强。