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.     

Fabrication of long single-mode and multimode fluoride glass fibres by the double-crucible technique

Long single-mode and multimode fluoride glass fibres with core-clad structure are fabricated for the first time by the double-crucible technique. 500 m-long single-mode fibre and 700 m-long multimode fibre are obtained using ZrF4-BaF2-NaF-LaF3-AlF3 core and ZrF4-BaF2-NaF-LaF3-AlF3-HfF4 clad glasses.     

Fabrication of fluoride glass single-mode fibers

Single-mode optical fibers are obtained using ZrF4-based fluoride glasses. The fibers are drawn from a preform and jacketing tube. The preform with cladding/core ratio of 5.1 is made by using a built-in casting method. The cutoff wavelength of the fiber is experimentally determined to be 2.7 μm by bending loss measurement. Minimum transmission loss of the obtained fiber is 160 dB/km at a wavelength of 3.28 μm. TheV-value at this wavelength is estimated to be 2.03 from the core diameter and the refractive index difference.     

Raman amplification in fluoride glass fibres

We report on stimulated Raman multi-Stokes scattering and Raman amplification in slightly multimode fluoride glass fibres. Raman gain in excess of 40 dB has been obtained in an 18 ?m-diameter, 10 m-long fibre with a pump power in the order of 1 kW.     

OH-absorption in fluoride glass infra-red fibres

The OH fundamental peak absorption at 2.87 ?m has been reduced in fluoride fibres to less than 20 dB/km. By measuring the difference spectra between low and high peaks, the OH-peak shape has been measured over two orders of magnitude, and the results indicate that the optimum low-loss window occurs at 2.55 ?m in these materials.     

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.     

Transmission loss characteristics of fluoride glass single-mode fibre

The transmission loss spectrum of a fluoride glass single-mode fibre as obtained with a new preform fabrication technique is shown. It is clearly confirmed on the loss spectrum that the obtained fibre is a single-mode waveguide in the minimum loss wavelength range (2?4 ?m). The minimum loss of this fibre is 8.5 dB/km at 2.2 ?m and the OH excess loss is 15dB/km at 2.85 ?m. This fabrication technique is effective in eliminating OH contamination.     

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.     

Backscattering in single-mode fibres

The scattering process in single-mode optical fibres is considered in terms of wave optics rather than geometrical optics, which is inadequate in this case. Surprisingly, however, the result for the backscattering signal at the input end of the fibre is nearly the same as for multimode fibres.     

Low-dispersion single-mode silica fibre with undoped core and three F-doped claddings

The refractive-index profile of an ideal single-mode silica fibre with undoped core and three F-doped claddings was optimised by calculation to realise two zeros of the chromatic dispersion at 1.30 and 1.55 ?m where the spectral loss has its local and absolute minima, respectively. The sensitivity of the chromatic dispersion due to different scale factors for the radial co-ordinate of the refractive-index profile is considered.     

Fusion splicing of heavy metal fluoride glass optical fibres

Heavy metal fluoride (HMF) glass optical fibres were spliced by fusing the two ends of fibres using a DC arc. An average optical loss of 0.08 dB per splice and strengths of up to 600 MPa were achieved for fusion splices using an inert gas purge during splicing. Estimates are made to determine the feasibility of achieving a splice loss of 0.005 dB for single-mode (HMF) fibres.<>     

Anisotropy in spun single-mode fibres

It is shown that the dominant process for the reduction of birefringence in a spun fibre is the averaging of the local fibre anisotropy by the rapid procession of the axes of asymmetry along the fibre. No significant change in cross-sectional geometry occurs.     

Zero-mode dispersion in single-mode fibres

Near cutoff the loss of the LP11-mode in cladded optical fibres becomes very high in the presence of even slight bends. Singlemode operation can thus be achieved with zero-mode dispersion as well as zero material dispersion, thus promising enormously large bandwidths.     

Stress birefringence in single-mode fibres

The core and cladding of a glass fibre exposed to axial tension become optically uniaxial. The modified characteristic equation is presented and, for the fundamental mode, the changes in the most important propagation parameters have been calculated.     

Jointing loss in single-mode fibres

The jointing loss of single-mode fibres is mainly dependent on their numerical apertures, and is largely independent of normalised frequency and fibre diameter. The letter presents simple loss predictions as an aid for practical design work of single-mode fibre joints.     

Polarisation conservation in single-mode fibres

There exist proper orthogonal elliptical polarisation states, which are maintained over long fibre length without converting. When one of the proper polarisation states is excited, orthogonal polarisation less than ?40 dB is confirmed after 5 km single-mode fibre transmission. It is also proposed that twisted single-mode fibres show a high degree of polarisation for any incident polarisation state. The polarisation characteristics are hardly affected by external perturbations.     

Dispersion in graded single-mode fibres

The normalised frequency for zero waveguide dispersion of the HE11 mode, called VOD, is highly dependent on profile shape. The more the profile departs from a step, the greater the increase of VOD above the effective single-moded region until, for example, VOD becomes infinite for profiles that fall off at a rate greater than or equal to the parabola.     

Tee-coupler for single-mode fibres

A new concept for an end face tee-coupler with single-mode fibres is described. The outer surfaces of the two fibres are ground and polished on one side and then fixed together. A third fibre is then butt-jointed. The dividing ratio between the two fibres can be chosen arbitrarily. The total loss is about 2 dB. The coupler is polarisation-independent.     

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.