Radiation-hardened pure silica-core fibre optics

Transmission losses induced by ionising radiation in fibre opties having cores drawn from pure synthetic silica may be reduced by pre-exposure to large hardening doses. Characteristics of the hardened fibres are described and the necessary features of the hardening irradiations identified.     

Optical fibres coated with a UV-curable material at a speed of 12 m/s

The letter reports the successful achievement of coating silica fibre at a rate of greater than 10 m/s. We draw 125 ?m-diameter fibres from silica rods and preforms, and coated in-line with UV-curable material. All fibres were proof-tested at two different stress levels of 0.7 and 1.4 GN/m2 We also checked the transmission properties of the fibre. It is found that the optical properties of the fibre remain the same while the mechanical properties are comparable to those of the fibres coated at a low speed.     

Photochromic behaviour of thulium-doped silica optical fibres

The first observation of the photochromic effect in thulium-doped silica fibres has been presented. The fact that the particular transmissive state is permanently recorded at room temperature in these doped silica glass fibres may find useful memory applications. Also, the possibilities of making rearrangeable absorptive gratings in the bulk material or fibre look interesting     

Demonstration of spatial distribution of photodarkening in yb-doped large-mode-area fibre laser

Yb-doped silica fibres are used in lasers and amplifiers at the 1.0-1.1 mum wavelength range. Large-mode-area fibres are preferred in applications requiring high output peak powers, and are often coiled to improve beam quality. Photodarkening is a detrimental effect that under some conditions can decrease the transmittance of the Yb-doped core of the fibre, causing output power degradation. The spatial distribution of photodarkening in coiled large-mode-area fibres that are used as CW fibre laser cavities are experimentally demonstrated. Simulation results describing and supporting the results are presented.     

Low splice loss between 34 /spl mu/m core diameter Bragg fibre and G-652 fibre by using micro-optics

The splice loss at 1.55 /spl mu/m between a 34 /spl mu/m core diameter singlemode photonic bandgap fibre and a G-652 fibre has been dramatically reduced from 2.5 to 0.8 dB by using a micro-optics composed of graded-index and coreless pure silica fibres.     

Overcoming the effects of polishing induced stress when fabricating fused polished couplers

The tendency of the polished fibres to separate due to the thermal relaxation of polishing induced stress during the fabrication of fused polished couplers is overcome by depositing a thin layer of silica in the form of either a silica sol-gel or an aqueous suspension of silica powder on the parallel fibre assembly prior to the application of heat.<>     

Chemical change from diffused hydrogen gas to hydroxyl ion in silica glass optical fibres

The chemical change from hydrogen gas that diffuses into silica glass for optical fibres to hydroxyl function has been investigated. Hydrogen molecules that diffuse into GeO2-doped silica glass at 500°C easily change into OH ions by thermal energy, while this chemical change does not occur in pure silica glass at 500°C. Also, germanium-doped silica fibre, in which hydrogen gas is dissolved at room temperature, shows OH ion absorption loss increase with chemical change by heat treatment at above 100°C, while pure silica core fibre shows no OH ion absorption loss increase by the same treatment.     

A review of recent progress in holmium-doped silica fibre sources

In this paper we present a review of holmium-doped silica fibre based sources. We discuss recent demonstrations of an efficient cladding-pumped fibre geometry and the impact it has made on the power scaling of these sources. We discuss the wavelength region that is addressable by holmium-doped silica based devices and highlight the advantage over thulium-doped fibres in terms of atmospheric transmission. Finally we review the development and current status of the pulsed and CW operation of holmium fibre sources and discuss the future development potential of sources in the ns-fs pulse-width range.     

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.     

Themal spray and adhesive bonding of optical fibres to high-temperature compsie materials

Microstructural characteristic were identified for three surface-mounted optical fibre sensors which were thermal spray bonded to high-temperature composite materials. The primary objective was to determine the defect generation mechanisms that occur during thermal cycling and to make processing and testing recommendations that would optimise the sensor performance. A second objective was to identify areas of microstructural research that would have the most significant impact on the development of high-temperature smart materials. The smart material systems of the present study were comprised of (1) silica optical fibre sessors bonded to titanium matrix composites (TMCs) using a nickel-based thermal spray, (2) silica optical fibre sensors bonded to TMCs using ceramic cement and (3) sapphire optical fibre sensors bonded to titanium matrix composites (TMCs) using a nickel-based thermal spray, (2) silica optical fibre sensors bonded to TMCs using ceramic cement and (3) saphire optical fibre sensors bonded to carbon–carbon composites (CCCs) using ceramic cement. The thermal and prior to any thermal stresscycling. In combination with the non-metallic spheroidal inclusions of the titanium matrix, the microcracking provided a mechanism for disbonding the optical fibres with a subsequent loss of sensor performance. A high degree of kporosity in both systems containing ceramic cements significantly reduced the interfacial bonding area. This, combined with the inherent ceramic brittleness, caused disbonding of the optical fibres in the cemented systems.     

Low-loss high-numerical-aperture optical fibre fabricated by v.a.d. method

Low-loss high-numerical-aperture optical fibres, consisting of GeO2/P2O5-doped silica core and silica cladding, have been made by the v.a.d. method. The minimum transmission loss of the fibre with an n.a. 0.32 was 0.8 dB/km at 1.55 ?m.     

1.5 m optical transmission experiments using very low-loss single-mode fibres

By using an InGaAsP semiconductor laser emitting at 1.5 ?m, where silica fibre loss is at a minimum, single-mode fibre transmission experiments were successfully carried out at 100 Mbit/s with about 30 km repeater spacing, 400 Mbit/s transmission characteristics using 20 km fibres are also reported.     

New absorption bands in pure and F-doped silica optical fibres

Two very narrow absorption bands positioned at 765 nm and at 1273 nm have been found in pure silica and fluorinedoped silica optical fibres. Their origin is probably connected with the preform production technique. Annealing of the preform and different fibre drawing conditions did not influence the absorption bands.     

Effect of dopants on transmission loss of low-OH-content optical fibres

We formerly developed very-low-OH-content optical fibres consisting of a borosilicate cladding and a phosphosilicate core. The transmission loss of the fibre was 0.47 dB/km at 1.2 ?m. We have further investigated the effects of dopants in pure silica on the losses of fibres. The letter clarifies the effects of dopants on the loss in the near-infrared region.     

Pressure sensitivity prediction of polarisation IR fibre sensors

The pressure sensitivity evaluations of polarisation IR fibre sensors are studied in the letter. It is shown that such sensors are one to two orders of magnitude more sensitive than those on a base of silica fibres.     

Wideband near-i.r. continuum (0.7?2.1 ?m) generated in low-loss optical fibres

A wideband near-infrared continuum is obtained by nonlinear optical interactions in low-loss single-mode and multimode silica fibres pumped by pulses from a Q-switched Nd:y.a.g. laser. With 50 kW pump power coupled into a 315 m long 33 ?m core-diameter low-loss multimode fibre, a continuum spanning the spectral range 0.7?2.1 ?m with a total power of 12 kW is generated. In single-mode and low-mode-number fibres a similar continuum of lower power has been obtained. Such continuum sources are useful for measurement of fibre properties as well as for spectroscopic study of other optical materials.     

Application of UV laser induced Ge-oxygen defect fluorescence for fibre characterisation

A new technique to monitor germanium oxygen deficiency centre defects (GeODC) and their relation to the refractive index profile in Ge-Si optical fibre have been developed. This method is based on UV excited luminescence of GeODC in silica based optical fibres. The GeODC defect profiles are unique to the fibre refractive index (profile of GeO₂) and method of fibre making.     

800 Mbit/s optical transmission experiments with dispersion-free fibres at 1.5 ?m

By using dispersion-free single-mode fibres at 1.5 ?m, where silica fibres have minimum loss, an optical transmission experiment was successfully carried out at 800 Mbit/s with 20 km repeater spacing. Error rate against receiving optical level characteristics showed that the optical power penalty caused by fibre dispersion is negligible after long line transmission at 1.5 ?m.     

Angular dependence of the mode-coupling coefficient in a multimode optical fibre

We derive a simple relationship which gives the angular dependence of the mode-coupling coefficient when the steady-state radiation pattern of the fibre is known. The correlation length and the amplitude of the random bends are deduced for two naked fibres and one sheathed fibre.