M. Potenza

Mode field diameter measurements in single-mode optical fibers

The role of the mode field diameter in the characterization of single-mode fibers is examined. The most relevant definitions of this parameter are reviewed, and a comparative analysis of methods for its measurement is performed. All the discussed measurement methods have reached a repeatability and reproducibility which are quite satisfying. Emphasis is given to the requirements posed by the new fiber designs, such as the polarization-maintaining structures. Most of the discussed techniques have been industrialized, and a number of instruments based on them are commercially available; however, it is predicted that the evolution of fiber design will impose new requirements on some of these instruments. >

Optical fibre amplifiers: physical model and design issues

The development of optical fibre amplifiers has caused an impressive evolution in optical telecommunications systems since the end of the 1980s. The widespread application of active fibre amplifiers requires accurate tools to design and simulate these devices in very different operating conditions. The present work describes some physical aspects of active fibre amplifiers and a numerical model for the analysis of active optical fibres that can be applied to investigate spatial and spectral properties of amplifiers for the transmission windows of optical fibre telecommunications. Finally, various design issues relevant to the investigation of optimal fibre design of silica, fluoride erbium-doped and fluoride praseodymium-doped fibres are discussed and illustrated by means of examples.

Theory of scattering in multimode optical fibres

The problem of scattering in multimode optical fibres is treated in a rigorous way by means of both a ray and a statistical approach. These two methods are interlaced and harmonized. Applications to microbending, ellipticity, core radius and maximum numerical aperture variations, and fluctuations of index profile shape are performed. Useful results about power distribution and fibre attenuation are derived in each case.

Determination Of Bending Losses From Spot-Size Measurements In Single-Mode Fibres

The determination of the sensitivity of a single-mode optical fibre to microbending and macrobending is of great importance. Two kinds of spot-size rule such a sensitivity: wn, the r.m.s. width of the near-field, and Woo the inverse of the transverse propagation constant in the cladding. While measurement techniques for wn are already known, this paper proposes an original method for woo measurements and concentrates on more plausible algorithms for macrobending and microbending loss determination from those measurements.

Application of harmonics detection to the measurement of mode field radius in single-mode optical fibers

In this paper, new techniques for the easy implementation of the measurement of the mode field radius in single-mode optical fibers are discussed. All of them are based on a dynamical filtering of the fiber output radiation and on a subsequent detection of suitable harmonic components. The capabilities of these procedures are considered, showing typical experimental results.

Scattering in optical fibres: analysis of mode degeneration

Mode degeneration and mode conversion in multimode optical fibres are the main subjects of this work. In particular it is shown how fluctuations of the core shape can cause a rapid degeneration among the modes with the same azimuthal mode number. This allows a rigorous single variable approach to the second problem obtaining evident simplifications. The formalism proposed is applied to the study of mode distribution in the general case of microbending, of core-radius fluctuations in fibres with power law profiles and for simultaneous presence of microbending and ellipticity in parabolic fibres with differential mode attenuation.

Stratification Methods in Waveguiding Structures

Stratification methods to solve waveguiding problems in planar and circular structures are presented. They are based on the approximation of the actual index profile of the guide by means of a wide class of analytically solvable curves (quartic profiles for circular fibres; quartic, Epstein and linear profiles for planar guides). The method allows to deduce accurately the propagation characteristics in the least computing time, particularly for guides with non-monotonic ndex profiles.