Fundamental mode microbending loss in graded-index and W fibres

The microbending loss in single-mode or quasi-single-mode fibres is approximately determined from a calculation of the fundamental mode field in a fibre with constant curvature. The result of the microbending loss essentially depends on the spot size of the fundamental mode, only. The approximations are verified by studying a statistical model and by comparing the approximations with exact calculations in the case of W fibres.     

Holey optical fibres: Fundamental properties and device applications

The presence of wavelength-scale holes in the transverse profile of a holey fibre can lead to novel optical properties that cannot be achieved in more conventional forms of optical fibre. Examples of such properties include broadband single-mode guidance, the extremes of fibre nonlinearity, from fibres providing tight mode confinement to those offering large mode areas, and a range of remarkable dispersive properties, including broadband flattened dispersion, anomalous dispersion below 1.3 μm, and large normal dispersion values at 1.55 μm. Fundamentals and recent progress are reviewed, ranging from design and fabrication through to applications and devices based on this emerging fibre type. To cite this article: T.M. Monro, D.J. Richardson, C. R. Physique 4 (2003).     

Scattering in optical fibres: analysis of mode degeneration

Mode degeneration and mode conversion in multimode optical fibres are the main subjects of this work. In particular it is shown how fluctuations of the core shape can cause a rapid degeneration among the modes with the same azimuthal mode number. This allows a rigorous single variable approach to the second problem obtaining evident simplifications. The formalism proposed is applied to the study of mode distribution in the general case of microbending, of core-radius fluctuations in fibres with power law profiles and for simultaneous presence of microbending and ellipticity in parabolic fibres with differential mode attenuation.     

W型单模单偏振光纤基模截止的条件

给出了 W型单模单偏振光纤基模截止的必要条件。通过对基模截止波长的数值计算 ,分析了这个必要条件的充分性。结论是 :对于圆形内包层 W型光纤来说 ,这是必要的而又充分的条件 ;对于低椭圆度内包层 W型单模单偏振光纤来说 ,它可以在较高的精度上近似作为充分条件 ,而对于高椭圆度内包层 W型单模单偏振光纤来说 ,它仅仅只是必要条件而非充分条件     

先进光学制造技术进展

针对高功率固体激光发展的需求,总结了先进光学制造技术方面的研究进展。采用超精密制造技术提高了非球面等元件的加工精度和制造效率,并为解决低缺陷加工提供了技术途径。围绕面形误差控制,特别是中频波前误差控制,发展了多种确定性抛光技术。针对熔石英元件建立了去除-抑制模型及新的抛光技术,有效抑制了亚表面缺陷的产生。     

A technique for the study of mode cut-offs in multimode optical fibres

We describe a technique of using a variable wavelength source to study mode cut-offs up to aV value of 20 for the optical fibre by means of the radiated (scattered) power leaving the fibre. This allows the identification of individual modes in a fibre carrying up to 80 or 100 modes in all and provides a non-destructive method for the study of the length and bend dependence of the energy carried by the highest order modes.     

A new approach to investigating mode coupling phenomena in graded-index optical fibres

To study mode coupling in optical fibres a new technique is developed, based on mode selective excitation and output near-field analysis. Experimental results support decoupling of the problem into two phenomena which are effective on different scales of propagation length: azimuthal and longitudinal mode mixing. A statistical model providing a simulation of the experimental near-field patterns is developed. Comparison with measurements shows that azimuthal mixing is complete before 1 km propagation, while effects of uncomplete axial coupling are accounted for. This approach also suggests a method for measuring the steady-state distribution length, with useful system implications.     

Effects of joints on mode power distribution and losses in multimode optical fibres

The transformation of mode power distribution at a joint between two different (even elliptical) optical fibres is studied. Simple analytical expressions are obtained also in the most general coupling and mismatch configuration, provided that coupling errors and mismatch parameters are small. Detailed calculations of joint losses are performed in each case, including propagation effects in both fibres. Original results are obtained particularly in the cases of misalignment, end separation between the fibres, mismatches in index profiles and coupling between two elliptical fibres. A strong dependence on the launching conditions and the amount of mode coupling is evidenced in all cases.     

Asymmetries in optical fibres

Two methods for treating the effects of small asymmetries in the cross sections of roughly cylindrical optical fibres are described. These predict the presence of stable power distributions, ribbons for example, within the fibre core. Experimental results on actual fibres showing these effects are given. To be effectively asymmetric a fibre of elliptical cross section need have major and minor diameters differing by only 0.08 μm.     

Remote actuation by optical power transmission in fibres

Some preliminary experiments on the remote actuation of a servo-valve are described in which the power transmission medium is an optical fibre. Using a semiconductor laser or a Nd:YAG laser as the power source and silicon cells as the opto-electrical transducer, switching of the servo-valve has been observed at power levels of a few milliwatts over 800 m of fibre.     

先进光学制造技术发展研究

本文报告了高技术的牵引和市场需求推动是先进光学制造技术发展的动力。研究了先进光学制造技术分类方法。讨论了先进光学制造技术的概念，指出了继承和集成是先进光学制造技术主要特点。一大一小，一长一短，一刚一柔是其主要发展方向。     

Resonance modes in optical fibres

The weakly nonlinear boundary value problem of wave propagation in an optical fibere(for the transverse electric mode,for example)is formulated and a modified linear solution is obained.It is shown that a self-consistent theory of fibre optics should be weakly nonlinear,The mode of critical refraction that does not exist in the linear theory is obtained,showing that it is a mode consisting of resonance modes,It is shown that the signal carriers in a long fibre are of resonance modes,not normal modes,Some experimental data are given for comparison with the theoretical predictions and the agreement seems satisfactory.     

光纤偏振模色散对信号偏振度的影响

采用一种简化的线路传输模型，详细讨论了在高速光纤通信系统中，线路偏振模色散（PMD ），尤其是二阶PMD、输入信号偏振态等对信号偏振度（DOP）的影响，并指出以信号DOP做 反馈控制信号适合于一阶PMD优化补偿系统，但在较大二阶PMD的影响下，将增加控制算法的 复杂性，使系统可能陷入局部最优解. 关键词： 信号偏振度 偏振模色散 信号偏振态     

Fundamental studies on laser radiation therapy: dispersion of a laser beam passing through optical fibres

For laser internal therapy in medical applications, optical fibres are required to propagate the laser beam. The far-field pattern of the laser beam at the exit face of the optical fibre is studied using a multimode step-index fibre and a graded index Selfoc fibre. The degree of dispersion, or the output angular distribution, of the beam passing through the Selfoc fibre is much smaller than that passing through the multimode step-index fibre. Consequently, the energy density in the far-field pattern of the beam passing through the Selfoc fibre is very much larger than that for the beam passing through the multimode step-index fibre. It is concluded that the Selfoc fibre is more effective in laser internal therapy.     

Anomalous group delay in optical fibres

It is shown, by means of computation on a specific model, how pulse broadening in multimode gradedindex optical waveguides is significantly affected by the levels of excitation of the high-order modes. Pulse widths are computed as functions of the profile parameter, under conditions of equal excitation, high-order mode suppression and GaAs laser excitation.     

Polarization noise in single mode fibres and its reduction by depolarizers

Fluctuations of the state of polarization in single mode fibres due to environmental conditions such as vibrations cause intensity noise if elements with polarization-dependent loss are inserted into the fibre system. Diffraction gratings, which are key elements for wavelength division multiplex-single mode fibre systems, exhibit a strong polarization dependence of loss. The polarization noise, originating from the combination of single mode fibres and diffraction gratings, is investigated experimentally. A drastic deterioration of the signal/noise ratio is observed, which is even more severe than modal noise with multimode fibres. Depolarizing devices, which reduce this kind of noise sufficiently, are presented and examined.     

Polymer jacket stripping of optical fibres by laser irradiation

Laser jacket stripping of the two-layer polymer jacket coating of Corning SMF-28 silica fibres has been studied as an alternative approach to chemical and mechanical techniques. These polymer outer layers, although chemically similar, become discernable through laser ablation and depth per pulse experiments. Etch rate measurements using nanosecond UV excimer laser sources (F₂, ArF, KrF and XeCl lasers) reveal that, as expected, the threshold fluence (energy per unit area) for significant material removal drops as the laser wavelength becomes shorter. For some wavelengths and fluences, spontaneous cone formation has been observed, thus providing additional threshold data through apex angle determination. The possible occurrence of deleterious damage to the silica cladding has been assessed using electron microscopy and optical transmission measurements. A wide fluence range over which damage was not observed characterised all the interactions. Irradiation techniques for producing apertures in the polymer coating or complete jacket removal are demonstrated and discussed. Briefly, polymer jacket stripping using a femtosecond laser source (800 nm) has been demonstrated. PACS 42.62.Cf; 52.38.Mf