Dispersion-free single-mode doubly clad fibres with small pure bend losses

A pure bend loss formula for doubly clad profiles is used to investigate the limitations and tolerances induced in the design of dispersion-free W-fibres by keeping the radiation losses below an acceptable level.     

Polarisation mode dispersion measurements in long single mode fibres

A frequency domain determination of polarisation mode dispersion in single mode fibres is described, which allows one to obtain directly the group delay difference for long fibres. The results of such measurements are shown on a birefringent fibre with elliptical cross-section which maintains an extinction ratio between linearly polarised eigenstates greater than 10 dB over 1 km.     

Polarisation mode dispersion measurements in long single mode fibres

A new method to measure polarisation mode dispersion is described, in which the accuracy is more than 0.1 ps. 0.17 ps polarisation mode dispersion was obtained for about 1 km length of fibre. The result is compared with the retardation obtained for a short length of the fibre.     

Prediction of mode dispersion in graded-index single-mode fibres

A Cheby?shev power series method is presented for the calculation of the propagation constant of graded-index fibres. Accurate predictions of the dispersion parameters can be obtained as shown by examples of step and parabolic profiles. Measured index profiles can also be used with local index values found by linear interpolation from nearest reading points. Examples are given to demonstrate the effectiveness of this approach.     

Analysis of approximations for the mode dispersion in monomode fibres

A number of recent papers have discussed the mode dispersion in step-index, monomode fibres using formulae based on accurate approximations for the modal propagation constant. It is shown here that, since dispersion depends on the first and second derivatives of the propagation constant, the use of such formulae may often be invalid and that a different type of approximation may be more useful     

Conditions for obtaining zero polarisation mode dispersion in elliptical-core fibres

It is shown that zero polarisation mode dispersion can never be achieved in elliptical-core single-mode fibres by geometrical birefringence alone. To equalise the group delays of the two fundamental modes, stress-induced birefringence must be introduced to cancel, partly or completely, the geometrical birefringence, depending on the application.     

Wavelength dependence of polarisation mode dispersion in elliptical-core single-mode fibres

Polarisation mode dispersion in elliptical-core single-mode fibres has been measured by a spatial technique based on a visibility maximum position measurement in an interferometer. Using the technique, wavelength dependence of the modal dispersion has been measured by varying optical source wavelengths between 821 and 904 nm. As a result, contribution of geometrical and strain birefringences on the modal dispersion has been evaluated, and normalised frequency dependence of the modal dispersion has been clarified.     

Intermodal dispersion and mode coupling in perfluorinatedgraded-index plastic optical fiber

Graded-index multimode perfluorinated plastic optical fibers typically exhibit bandwidths much greater than would be expected from their index profiles. To resolve this discrepancy, we have conducted the first measurements of differential mode delay in such fibers. These measurements show intermodal dispersion that increases as the square root of fiber length, implying strong mode coupling in these fibers. Significant power transfer between modes occurs at lengths less than 20 m, so that mode coupling results in improved bandwidth on length scales relevant for local area networks. The observed coupling arises from extrinsic nonuniformities of the waveguide     

Simultaneous measurement of polarisation mode dispersion in severaloptical fibres in parallel

Polarisation mode dispersion is measured from one end of the optical fibres using a tunable optical time domain reflectometer. Four fibres are measured in parallel, and it is estimated that tens of fibres may be measured simultaneously     

Measurement of spatial distributions of mode coupling in polarisation-maintaining fibres

A new method for measuring the spatial distribution of birefringent mode coupling in polarisation-maintaining fibres is presented. By using a low-coherence laser diode and a Michelson interferometer, the mode coupling is determined by a homodyne detection scheme. The expected limit of the sensitivity and the spatial resolution are ?86 dB and 23 cm, respectively.     

Comparison of various polarisation mode dispersion measurement methods in optical fibres

The comparison of various polarisation mode dispersion (PMD) measurement methods in optical fibres, such as the interferometric method, optical pulse methods, fixed analyser method, Poincare sphere method and state of polarisation (SOP) method, are presented.<>     

Interferometric measurements of chromatic and polarisation mode dispersion in highly birefringent single-mode fibres

Interferometric measurements on highly birefringent single-mode fibres have been performed. The group delay spectrum of each polarisation mode is independently measured over the whole 1.0?1.73?m spectral range. The polarisation mode dispersion is obtained by direct subtraction of the group delay spectra.     

Production of single-mode fibres with negligible intrinsic birefringence and polarisation mode dispersion

Spinning the preform during drawing produces a fibre with a permanent twist. It is shown that such a fibre has negligible polarisation birefringence and rotation. Polarisation mode dispersion is similarly reduced.     

Modal dispersion in single-mode fibres: simple approximation issued from mode spot size spectral behaviour

We report a simple and accurate approximation of modal dispersion in single-mode optical fibres deduced from spectral behaviour of mode spot size; neither knowledge of index profile nor of maximum refractive index difference are required in this approximation.     

Measurement of polarisation mode dispersion in elliptical-core single-mode fibres at 1.3 ?m

Polarisation mode delay differences in three single-mode fibres were measured interferometrically at 1.3 ?m with a resolution below 25 fs. Polarisation mode dispersion increases strongly with core ellipticity.     

Enhancement of bandwidth and additional loss caused by controlled mode coupling in quartz fibres

Controlled mode coupling is applied to a 1 km quartz multimode fibre. Bandwidth and associated increase in loss, and the time relation between pulses with and without mode coupling, are reported.     

Profile dispersion in multimode fibres: measurement and analysis

An electronically scanned interference microscope has been used to measure the refractive-index profile and its dispersion in optical fibres. From these measurements, we find that the power-law profile that best equalises modal delays in GeO2-S1O2 fibres should have an exponent that varies between 1.9 and 2.5 in the wavelength range from 0.5 to 1.1 ?m and is close to 2 at 0.9 ?m.     

Prediction of modal dispersion in single-mode fibres from spectral behaviour of mode spot size

We report a simple calculation allowing the prediction of the modal dispersion in single-mode optical fibres from the spectral behaviour of the mode spot size and the profile index.