Continuous measurement of optical-fibre attenuation during manufacture

An online method of continuously monitoring the attenuation of an optical fibre during its manufacture is described. It provides a complete attenuation/length profile of the fibre. The present system can measure an overall attenuation of 30 dB, and the results agree with corresponding offline differential measurements to better than ± 1 dB/km.     

Power budget optimisation of WDM network with MSCM control

The authors have experimentally demonstrated a 28.7 dB power budget for simultaneous transmission of 2.5 Gbit/s/node payload data and 80 Mbit/s/node control channels using the multichannel subcarrier multiplexing (MSCM) signalling technique. The power budget is sufficient to support a 234 node MSCM-WDM network with 2.5 Gbit/s/node 10 km radius coverage and 0.25 dB/km fibre attenuation with 0.45 dB/km attenuation, the network can support up to 93 nodes     

Low-OH-absorption fluoride glass infra-red optical fibres

Ultralow losses of 10?2 to 10?3 dB/km have been predicted in fluoride glass optical fibres between 2 and 4.5 ?m. At 2.9 ?m, in the central part of this spectral region, the OH? ion presents its fundamental stretching vibration which gives rise to a strong and broad absorption. The attenuation at 2.9 ?m in a step-index fluorozirconate glass fibre has been brought down to 58 dB/km, by reducing the OH? concentration in the glass. It is the lowest attenuation yet reported at this wavelength in any optical fibre.     

New optical fibre fabrication method

A new method for optical fibre fabrication has been found. The method is based on the so-called `sol-gel process?, which enables one to produce a core rod for optical fibre. Pure silica core fibre fabricated using this method exhibits an optical attenuation characteristic as low as 6 dB/km at a wavelength of 0.85 ?m.     

Over 300 km CPFSK transmission experiment using 67 photon/bit sensitivity receiver at 2.5 Gbit/s

A nonrepeated fibre transmission experiment over 308 km of conventional optical fibre is reported at 2.5 Gbit/s in a CPFSK heterodyne detection system. The system has a sensitivity of -46.7 dBm or 67 photons/bit at 10/sup -9/ BER and has the maximum allowable attenuation of 55.1 dB without an optical amplifier.<>     

Low-Loss single-mode fibre at the material-dispersion-free wavelength of 1.27 ?m

A GeO2-doped silica single-mode optical fibre with a low attenuation loss of 0.5 dB/km at 1.27 ?m, where the material dispersion of the silica glass falls to zero, has been made by a C.V.D. technique. Attention was paid to reducing OH absorption losses in the single-mode fibre.     

Technique for minimising effect of detector inhomogeneity on fibre attenuation measurements

In fibre attenuation measurements by the `cut-back? method, the necessity for a homogeneous detector is implicit. We have found a commonly used germanium detector to be significantly inhomogeneous, leading to an estimated attenuation discrepancy of 0.02 dB at best and 0.4 dB at worst. In the letter, we outline a method for reducing this discrepancy to levels of less than 0.004 dB.     

Fabrication of long-length high-strength single-mode silica fibres

The letter reports an alternative approach to the realisation of long, low-attenuation, high-strength single-mode optical fibres suitable for high bit-rate transmission over long distances in adverse environments. We show that low attenuation (less than 0.45 dB km) can be achieved in combination with high proof-test levels (1% ? 2% strain) in fibre lengths greater than 5 km, using natural fused-quartz tubing, and report a 15 km fibre having an attenuation of 0.44 dB km which survived a proof test at 1% strain.     

Germanium-oxide glass optical fibre prepared by VAD method

Germanium-oxide glass optical fibre doped with antimony for transmission of the 2 to 3 ?m band has been prepared by the vapour-phase axial deposition (VAD) method. An attenuation loss of 13 dB/km at 2.05 ?m and 70 dB/km at 2.4 ?m has been achieved.     

Large graded-index preforms fabricated by high-rate VAD

A large preform for 220 km of fibre was fabricated with the vapour-phase axial deposition (VAD) method. The deposition rate for the core was 1.7 g/min. Optical fibre drawn from a part of the preform had optical attenuation of 0.58 dB/km and bandwidth 500 MHz km0.9 at a wavelength of 1.3 ?m.     

12 nm FWHM 20 dB stop-band filter based on cascaded dual concentriccore fibre filters

A spectral stop-band filter with peak attenuation = 5 dB, full width at half-maximum (FWHM) = 31 nm based on a dual asymmetric concentric core optical fibre is investigated. An efficient 12 nm FWHM 20 dB peak attenuation is demonstrated at 1300 nm by cascading four filters     

Long wavelength performance of SiO2/GeO2/P2O5 core fibres with different P2O5 levels

The attenuation performance of SiO2/GeO2/P2O5 core graded index multimode fibres at 1.6 ?m has been studied in relation to changing P2O5 concentrations. Loss is related to both P2O5 doping and OH contamination levels, and reduction of both has led to a minimum fibre attenuation of 0.23 dB/km at 1.62 ?m.     

Long-period fibre grating formation with 264 nm femtosecondradiation

A new approach for producing long period fibre gratings by exposure of the optical fibre to high-intensity femosecond pulses λ = 264 nm is presented. Different types of fibres were investigated and it was found that strong attenuation peaks (16-28 dB) can be induced in H₂-loaded fibres     

Preparation of graded-index optical glass fibres in the alkali germanosilicate system

Multicomponent glass fibres with a graded refractive index have been made in the alkali germanosilicate system using the double-crucible method. The index profile is based on Na+ ? K+ ion exchange. Bulk-glass absorption losses of ?10 dB/km at 752 nm have been measured. The present minimum level of fibre attenuation is 35 dB/km.     

Spectral attenuation measurement for fluoride glass single-mode fibres by Fourier transform techniques

A new spectral attenuation measurement system using a Fourier transform spectrometer is developed. The Fourier transform spectral attenuation measurement (FT-SAM) system makes the signal acquisition time for a wide wave-length range of 1.0?4.2? much shorter than measurement with a conventional dispersive spectral attenuation measurement system. The spectral attenuation for a fluoride glass single-mode fibre, with a minimum loss of 3±1 dB/km at 2.5?m, is measured with this system.     

一种新型超低损耗大有效面光纤的技术研究

采用双包层的波导结构结合纯二氧化硅芯的技术方案,通过包层氟掺杂的设计与芯/包层之间粘度匹配的优化,实现了超低损耗大有效面积ULA-130型G.654.E光纤的制造,然后利用自行搭建的光纤非线性系数测量系统和自主设计的光纤宏弯损耗松绕设备,结合现有技术对ULA-130光纤的各项性能技术指标进行了研究。该光纤在1 550 nm波长的衰减系数为0.159 dB/km,有效面积为133 μm²,非线性系数为1.67×10^-10W^-1。理论计算与技术研究结果表明,该光纤具有优异的衰减系数和非线性性能,适用于大容量、高速率和长距离光通信骨干网传输系统,相对于常规的 G.652.D 光纤,可以显著改善系统的光信噪比,提升系统的传输性能。     

Improved chemical vapour deposition method for long-length optical fibre

The deformation of the supporting tube during the c.v.d. process for optical fibre fabrication is completely suppressed by controlling the internal pressure of the tube. A 14 km length single-mode fibre with attenuation loss of about 3.2 dB/km at 0.85 ?m was fabricated by this improved method.     

Radiation-induced effects in a highly birefringent fibre

The effect of ?-ray irradiation on a high-birefringence polarisation-holding fibre is investigated. A permanent attenuation of 2000 dB/km at a wavelength of 0.85 ?m results from a dose of 6 × 105 rad. For the same dose, there is no appreciable change in either the fibre birefringence or the polarisation-holding parameter. This indicates that no significant crosscoupling of the polarisation modes is caused by the defects induced by ionising radiation.     

Design of monomode quadruple-clad fibres

The design of quadruple-clad profiles, leading to (truly) monomode fibres is described: an explicit set of parameters is proposed. Experimental results are presented, concerning a fibre with a dispersion smaller than ±0.5 ps/km nm and an attenuation around 0.3 dB/km, over the 1.5?1.65 ?m wavelength interval.     

Rapid long-period grating formation in hydrogen-loaded fibre with157 nm F2-laser radiation

Long-period gratings were fabricated in hydrogen-loaded telecommunication fibre using 157 nm F₂-laser radiation. A >20 dB attenuation peak at 1590 nm was induced with only 5.0 J/cm² accumulated fluence, a value >250-fold smaller in comparison with fluence requirements for 248 nm KrF-laser irradiation