Dispersion minimisation in single-mode fibres over a wide spectral range

The waveguide and material dispersion are investigated for various silica-based single-mode optical fibres with arbitrary refractive-index profiles. It is shown that in the case of the doubly clad optical fibre with an index difference between the core and the outer cladding ?1=1% and that between the inner cladding and the outer ?2=?1%, the diameter of the core 2a=7.2 ?m, and the thickness of the inner cladding t=0.3a, the total dispersion is reduced within ± 1 ps/km/nm over a wide spectral range of ?=1.35?1.67 ?m.     

Propagation model for multimode optical-fibre waveguide

Pulse dispersions of 5 ps/m have been measured in cladded-glass and liquid-core multimode fibres. A theoretical model is proposed which gives excellent agreement with measured propagation delay and pulse dispersion. In the fibres used, there is little light scattering either in the core or at the core-cladding interface.     

Influence of waveguide dispersion in fluoride glass fibres

The dispersive properties of step-index fluoride glass fibres have been evaluated using a computer model. The results show that, by a suitable choice of core diameter and index difference in these materials, the dispersion can be reduced to zero over a broad wavelength range.     

Uniform and low polarisation-mode dispersion in 100 fibre ribbonslotted core optical cable

Uniform and low polarisation-mode dispersion, 0.052 and 0.053 ps/√km on the average, has been confirmed in 100 fibre ribbon slotted core optical cable before and after installation, respectively. The cable has been manufactured with standard singlemode fibres having nearly optimised coating structure determined through finite element method analysis conducted to minimise lateral force induced birefringence     

Interference patterns from very thick samples for determining the profile of graded-index fibres

Recent studies have pointed out the need for very thin (10 ?m) fibre samples prepared for interferometric analysis of the refractive index profile of an optical fibre. We show that this is not necessary for all graded-index fibres with reasonable dispersion properties. Sample thicknesses of 125 ?m, or more, can be used for fibres with a core diameter of about 50 ?m.     

Polarisation characteristics of a side-tunnel fibre

Modal birefringence and polarisation mode dispersion in a single-mode fibre having vacuum pits beside the core are measured in the wavelength region from 0.633 ?m to 1.52?m. Both quantities monotonically increase as the operation wavelength becomes large. The magnitudes of birefringence and modal dispersion are evaluated to be 1.0 × 10?4 at 1.52?m and 148 ps/km at 1.41 ?m, respectively. These values are much less than those predicted theoretically for side-tunnel-type optical fibres.     

Tailoring zero chromatic dispersion into the 1.5?1.6 ?m low-loss spectral region of single-mode fibres

We have designed and fabricated single-mode silica fibres that have zero chromatic dispersion within the 1.5?1.6 ?m low-loss spectral region by controlling their waveguide dispersion and dopant-dependent material dispersion. These fibres have small core diameters and large core-cladding refractive-index differences, ?n = 0.018, corresponding to a 13 mole % GeO2 dopant concentration in the core. The zero-dispersion wavelength was shifted from ?0 = 1.375 ? to ?0 = 1.54 ? by decreasing the fibre core diameter from 7 ?m to 4.8 ?m. This ability to tailor the minimum dispersion wavelength to the ultra-low-loss region near 1.55 ?m is important for designing single-mode fibres for very long distance and very high capacity optical transmission.     

Evaluation of longitudinal chromatic dispersion

The relationship between changes in the refractive index along a fiber and chromatic dispersion is investigated theoretically. The variance of the chromatic dispersion along a fiber is approximately proportional to that of longitudinal structural fiber parameters. To control the dispersion to within ±1 ps/km/nm, theoretical results indicate that the longitudinal deviations of the core radius and relative index difference must be less than 0.04 μm and 0.014%, respectively, for W-type dispersion-flattened fiber. Measurements of the standard deviation of the change in the longitudinal parameter for W-type dispersion-flattened fiber fabricated by the vapour axial deposition VAD method show that chromatic dispersion deviation is mainly caused by longitudinal core radius deviation. The effective standard deviation of the core radius is estimated to be within 0.03 μm     

Dispersion-determined limits on production tolerances of single-mode fibres

For single-mode fibres the standard deviation of dispersion at the nominal zero-dispersion wavelength depends strongly on the dispersion slope. For dispersion-shifted fibres, optimum values of the slope as a function of production tolerances on core radius and index difference are found, and for dispersion-flattened fibres maximum allowable production tolerances are given.     

基于组合包层的微结构光纤的色散特性

为了获得微结构光纤的平坦色散特性,设计了一种圆形排列的微结构光纤,其包层由周期分布的空气孔构成,通过有限元数值分析法对该微结构光纤基模的色散特性进行了数值仿真,研究了色散和纤芯圆孔尺寸以及波长的关系。结果表明:内外空气孔间距和直径对微结构光纤的色散曲线都有影响,但内包层大孔间距和第一圈小空气孔的直径对色散曲线的走向起决定作用。在内圈空气孔直径为3.1μm,其他空气孔直径为1.0μm,内圈空气孔中心间距为5μm,其他空气孔中心间距为4μm时,光纤在1.3μm波长的色散为19.5ps/(nm·km),在1.6μm波长的色散为26.5ps/(nm·km),在1.3～1.6μm波长范围内,其色散值变化范围为7ps/(nm·km)。     

A numerical method for the analysis of single-mode low-dispersion graded-index fibers

A numerical integration method for the calculation of the time dispersion of optical-fiber modes is introduced and used to determine the parameters of single-mode graded-index silica-based fibers for the 1.55-μm band. The method gives an accuracy on the order of 0.001 ps/km/nm, and it was possible to quantify the error in assuming the overall time dispersion to be the sum of the material and waveguide dispersions. The analysis indicates that when large material dispersion is to be neutralized by waveguide dispersion, the outer diameter of the cladding must be increased to avoid higher microbending losses. When the difference between the refractive indices at the center of the core and in the cladding decreases, the ratio between the cladding and core diameters must be increased.     

Negative dispersion-flattened fibre suitable for 10 Gbit/s directly-modulated signal transmission in whole telecommunication band

New dispersion-flattened fibres having negative dispersion of about -8 ps/nm/km over the whole telecommunication band are developed. Transmissions with 10 Gbit/s directly modulated LDs over 51 km at 1275 nm and over 80 km at 1550 nm are realised without dispersion compensation.     

Pulse broadening in long-span dispersion-free single-mode fibres at 1.5 ?m

Dispersion-free single-mode fibres at 1.5 ?m were fabricated by controlling their waveguide dispersion and dopant-dependent material dispersion. Pulse broadening in the 20 km long fibre was measured by using a laser diode operated at 1.5 ?m. Measured pulse broadening was 1.3 ps/km nm, which is in good agreement with theoretical results. The present experiment confirms that it is beneficial to use such fibres for large-capacity and long-distance transmission media.     

新型光子晶体光纤近零平坦色散的研究

文章作者设计了一种新型的光子晶体光纤(PCF),在纤芯引入了一个小空气孔形成缺陷,并改变第一层空气孔的直径.采用平面波法研究了该PCF的色散特性,结果表明,该光纤能够得到比传统的PCF更低、更平坦的色散曲线;通过优化该光纤的结构参数,可以设计在1 350～2 010 nm波长范围内近于零的平坦色散PCF,其色散变化△D＜0.5 ps/(km·nm),在1 320～2 040 nm波长范围内色散斜率变化△D<,slope>＜0.02 ps/(km·nm<'2>).     

Design Considerations of Broadband Dual-Mode Optical Fibers

We propose and present design data for a new type of graded index fiber which has a profile and radius such that only two mode groups (LP/sub 01/ and LP/sub 11/) propagate and both propagate with virtually identical group velocities. This dual-mode fiber has a core diameter approximately twice that of a conventional step index single-mode fiber. For example, a core diameter of 16.3 mu m is attainable with relative index difference Delta=0.3 percent at 1.25-mu m wavelength. Fabrication tolerances securing a group delay difference below 100 ps/km are given by a power-law profile parameter alpha=4.85/spl plusmn/0.25 and a normalized frequency upsilon=4.45/spl plusmn/0.11. The allowable upsilon-value deviation range to keep the group delay difference within 100 ps/km is about five times as large as that of a step-index fiber, in which group delays of two mode groups are matched. Comparison with a multimode graded-index fiber, with respect to group delay characteristics and bending loss of the dual-mode fiber, are also discussed.     

Tolerance requirements for the drawing ratio of single-mode fibres with arbitrary refractive-index profile

The letter presents a simple formula for the dispersion sensitivity of single-mode fibres due to arbitrary variations of the drawing ratio. For this calculation only the requested dispersion coefficient of the ideal fibre is required without the need for data on the actual index profile. As an example the tolerance requirements of broadband fibres are investigated.     

Low-loss quadruple-clad single-mode lightguides with dispersion below 2 ps/km nm over the 1.28 ?m?1.65 ?m wavelength range

Low-loss fibres with dispersion below 2 ps/km nm over the spectral range between 1.28 ?m and 1.65 ?m have been designed and fabricated. These fibres were achieved by the use of quadruple cladding and designed with the use of a computer analysis program. They should be desirable for future wavelength-division-multiplexing applications.     

新型色散平坦光子晶体光纤设计与分析

研究了一种新改进的折射率导光光子晶体光纤的色散性能。研究表明当纤芯空气孔的孔径小于包层空气孔孔径时, 光子晶体光纤仍然通过全内反射（TIR）导光。采用全矢量平面波展开法分析光子晶体光纤的色散特性, 并设计了波长为1360 nm到1730 nm时, 色散值在-10±0.5 ps/（nm·km）之间的色散平坦光子晶体光纤, 其色散斜率在波长为1370～1740 nm时可达±0.01 ps/nm2/km。     

基于纤芯失配多模干涉的光纤折射率传感器

基于多模干涉效应的单模-多模-单模(SMS)结构光纤折射率传感器通常需要进行包层腐蚀来提高灵敏度,而且易受环境温度影响。为克服SMS结构的这些不足,提出了一种新型的基于纤芯失配多模干涉的光纤折射率传感器,由单模光纤-色散补偿光纤-单模光纤(SMF-DCF-SMF)级联光纤布拉格光栅(FBG)构成,长度不超过100mm。对其灵敏度、线性范围和温度特性等进行了测试,实验结果显示在测量折射率为1.33～1.39的折射率液时,特征波长与折射率呈线性关系,灵敏度为232.8nm,级联的FBG具有良好的温度校准功能。     

Low-dispersion fluoride glass single-mode fibres operating in twospectral ranges

Chromatic dispersion characteristics of fluoride glass single-mode fibres are investigated experimentally and theoretically. It is proposed that the quasi-single-mode operation at zero material dispersion wavelength is effective in extending the low dispersive spectral range. It is shown that total chromatic dispersion is suppressed within ±1 ps/km/nm in the two spectral ranges of 1.57-1.71 μm and 2.4-3.35 μm