Vibration-induced polarisation modulation of light guided in single-mode optical fibres

The polarisation state of the HE11-mode in a single-mode optical fibre with a fused silica core was varied by mechanical vibrations of the fibre. The accompanying amplitude modulation is suppressed in the experimental arrangement. The influence of the plane of the incident polarisation on the signal modulation is discussed. The measurements were made with both reflecting and nonreflecting fibre endfaces.     

Characteristics of dispersion-shifted dual shape core single-mode fibers

The structural design, bending loss, and dispersion characteristics of the dual shape core (DSC) single-mode fiber with zero dispersion at 1.55 μm are described. It is clarified that the bending loss of the DSC fiber is less than one tenth of that of a step-index fiber, and that the dispersion sensitivity due to a small change of the core radius is less than half of that of a step-index fiber. The explanation for the small bending loss is presented. A greater reduction of bending loss is expected from the replacement of the center core profile with a Gaussian or triangular profile.     

Effective cutoff wavelength of the LP11mode in single-mode fiber cables

The effective cutoff wavelength of the LP11mode is investigated for nylon-coated step-index type single-mode fibers stranded in a cable. It is found from the pulse propagation experiments that the single-mode operation is effectively attained in the two-mode region up to theV-value of 3.0. It is numerically estimated that splice loss, bending loss, and absorption loss due to the OH-ion in cladding are reduced by choosing the operatingV-value as large as 3.0.     

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     

Radiation from optical waveguides: leaky-mode interpretation

Previous calculations of radiation loss from an HE11-mode propagating on a fibre with a sinusoidally perturbed core boundary are valid only for radiation directions sufficiently near 0° or 90° to the fibre axis. This letter presents a solution valid for all angles and also shows that radiation maxima are clearly associated with leaky-mode resonances.     

Modal noise in single-mode fibres operated slightly above cutoff

If a single-mode fibre is operated slightly above the theoretical cutoff frequency, at every discontinuity like a misaligned joint, a part of the LP01-mode will be converted to the LP11-mode. At a following discontinuity, the LP11-mode will be partly reconverted to the LP01-mode, e.g. a source wavelength shift will then cause modal noise.     

Fabrication of low-loss Al2O3-doped silica fibres

This letter is concerned with the alternative dopant of Al2O3 for VAD silica-based optical fibres. In order to clarify basic loss characteristics of Al2O3-doped silica glass fibres, single-mode fibres were made. The fabricated single-mode fibre shows an ideal step-index profile and a low transmission loss of 0.65 dB/km at 1.56 ?m.     

Single-mode propagation in 2-mode region of optical fibre by using mode filter

The effect of a mode filter using fibre bend has been clearly shown experimentally. The mode filter effectively removes the LP11-mode, and has a negligibly small effect on the attenuation of the LP01-mode. The single-mode propagation was attained at the V-value of 2.8 by using the filter.     

低弯曲损耗少模光纤传输特性研究

提出一种采用少模阶跃光纤与单模光纤连接的方法,实现低弯曲损耗传输的新型光纤通信系统。采用有限元法研究了在模场直径相同的情况下少模光纤纤芯半径与折射率差的关系,以及不同参数下光纤的弯曲损耗;采用光束传播法计算了少模光纤的各种模式与普通单模光纤的基模的连接损耗。证明了采用少模光纤可以利用模式间的正交性实现有效的单模传输,并具有低的弯曲损耗和连接损耗。     

Practical microbending loss formula for single-mode optical fibers

Microbending loss in a step-index single-mode fiber is formulated in an expression which provides an explicit dependence on wavelength λ and relative index difference Δ. For the permissible mean bending radiusRdaggercorresponding to a given loss,Delta^{3/2}Rdagger/lambdais the functionfof only a normalized frequency υ. This property resembles that for the uniform-bending loss. However,fin the microbending loss depends less critically on υ than in the uniform-bending loss.     

Detailed evaluation of an attainable repeater spacing for fibre transmission at 1.3 ?m and 1.55 ?m wavelengths

An attainable repeater spacing at 1.3 ?m and 1.55 ?m wavelengths using a step-index monomode fibre cable is given, after detailed consideration of total loss as well as total dispersion of an optical fibre. The longest attainable repeater spacing at 1 Gb/s is about 100 km at 1.55 ?m wavelength using a single-mode laser diode and a monomode fibre with a relatively small core-cladding refractive index difference, e.g. about 0.2%.     

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     

Macro-bending loss properties of photonic crystal fibre

Photonic crystal fibres are examined with respect to bending loss. An equivalent step-index fibre is modelled using an effective-index approach for the microstructured cladding. Measurements have been performed in a broad spectral range, and the results agree well with the calculated losses     

Minimum dispersion at 1.55 ?m for single-mode step-index fibres

The single-mode step-index fibre parameters, relative index difference and core diameter, have been predicted to achieve first-order cancellation between material and waveguide dispersions at 1.55 ?m. Our prediction by accurate solution of the characteristic equation results in fibre parameters different from those obtained by other investigators. The origin of this difference is examined.     

Dispersion-shifted convex-index single-mode fibres

The structural design of the single-mode fibre with a convex-index profile is described to achieve zero dispersion at 1.55 ?m. As a result of the fibre design, it is clarified that the bending loss of the convex-index fibre is the smallest among the losses of various index profile fibres such as step, triangular and Gaussian ones.     

Optical fiber up-tapers with high beam expansion ratios forcomponent fabrication

Optical fibre up-tapers with beam expansion ratios of 10, about twice the previously achieved value for the same taper outer diameter, have been fabricated and characterized. The increased beam expansion is achieved with a near step-index profile for the core of the taper. The excess coupling loss between two tapers is less than 0.1 dB. A lateral offset of more than 20 μm or an axial displacement of 4 mm between tapers caused an excess loss of 1 dB. The angular tolerance for this loss is a manageable 0.3°. These tapers permit, for a given beam expansion ratio, the manufacture of smaller outer diameter, more compact structures of self-aligned beam expansion. They also permit the insertion of optical elements into the expanded beam for the fabrication of inline single-mode passive fiber components     

Simple characterisation factor for practical single-mode fibres

The spot size of the HE11 mode in a practical single-mode fibre mainly depends on the numerical aperture and not on the normalised frequency. An alternative definition of spot size in terms of a matching Gaussian beam is much simpler to use.     

Bend and index insensitive long period grating in progressive three layered optical fibre

A long period fibre grating written in a progressive three-layered optical fibre is shown to exhibit an attenuation band that has a very low bending sensitivity (5.1 /spl times/ 10/sup -2/ nm m) compared to normal step-index fibre, and is also insensitive to changes in the refractive index of the surrounding medium. Applications to sensing and telecommunications are discussed.     

Experimental study of single-mode W-type optical fibre

The development and experimental study of a single-mode W-type optical fibre is described. It was found that this type of optical fibre has considerably lower bending and micro-bending losses compared with usual single-mode single-cladding fibres.     

Single-mode fibre fractional wave devices and polarisation controllers

We describe new single-mode fibre optic devices which are completely equivalent to fractional wave plates of classical optics. They employ a very simple configuration which uses the stress birefringence induced by bending the fibre. Several devices can be combined to control the polarisation inside any single-mode fibre.