B. Daino

Statistical treatment of the evolution of the principal states of polarization in single-mode fibers

A simple relationship is found for the evolution of the principal states of polarization (PSPs) and their differential group delay in fiber links. A simple expression is found, using the relationship, for the probability of the differential group delay (DGD), considering the evolution of the PSPs as a Brownian motion. The theory has been verified experimentally on an optical cable composed of 12 single-mode, shifted-dispersion fibers 2.2-km long. The results show that the DGD grows as the square root of the length when the length of the fiber is far larger than the correlation length of the perturbation. The measured value of DGD can vary substantially in two fibers belonging to the same ensemble, and in the same fiber, considering two frequencies differing by more than 5 nm. >

Measurement of the group-delay difference between the principal states of polarization on a low-birefringence terrestrial fiber cable

We report some results of measurements of the frequency dependence of the state of polarization at the end of a low-birefringence long-cabled (50-km) optical fiber. The principal states of polarization and their group-delay difference were determined by making use of the Poincaré sphere representation.

New all-optical devices based on third-order nonlinearity of birefringent fibers

Exact solutions for the evolution of the state of polarization along a nonlinear single-mode birefringent fiber are given by means of the Poincare sphere representation. This approach clearly shows the possibility of realizing a new class of devices, namely, a linear coherent amplifier–mixer and an optically activated polarization switch or a phase-sensitive optical discriminator with high fanout.

Study on the Implementation of Optical Transparent Transport Networks in the European Environment—Results of the Research Project COST 239

This paper reports the main results obtained in the framework of the COST239 project on the implementation of transparent optical network schemes to connect main European cities. The investigation on transmission limitations has shown that transmission systems, for which 1662:5 Gbit/s WDM systems are used due to traf®c reasons, have a maximum range shorter than 1000 km. This condition does not allow a completely transparent network. Two solutions, the partitioned and the gridconnected network architecture, are proposed, described, and compared in the paper.

Optical multistability in a fiber-optic passive-loop resonator

Abstract The nonlinear phase-shift, unavoidably induced in an electromagnetic field circulating in a fiber-optic passive-loop resonator by the presence of the optical Kerr effect, gives rise to a multistable behavior of the input-output characteristics at relatively low optical powers.

Evolution of the bandwidth of the principal states of polarization in single-mode fibers.

The bandwidth in which the first-order approximation of the principal states of polarization of a single-mode fiber can be assumed valid is examined. The principal states of polarization and their bandwidth are found for a fiber with both constant coupling and birefringence, and the relationship with the fibers eigenmodes is examined. On the basis of these results, a fiber cascade is analyzed, and a Monte Carlo simulation provides theoretical values of the bandwidth that have been experimentally verified on a 2-km-long concatenation of single-mode dispersion-shifted fibers.

Experimental observation of time jitter in semiconductor laser turn‐on

We report an experimental study which shows how time jitter in semiconductor lasers, which arises when such sources are switched from below to above threshold, is related to the actual operating conditions. The effect is observed both in distributed feedback and in Fabry–Perot lasers, even if in the latter case it becomes more and more negligible when the output power of the final state is increased.

Speckle and Modal Noise in Optical Fibres Theory and Experiment

Modal noise has been observed in optical fibres excited by partially coherent sources. In this paper the theory of this noise is presented. Following the basic guidelines of the speckle theory, the statistical properties of the fluctuations of the power transmitted through a circular aperture of arbitrary size are evaluated. It is found that, for fibres having an α -exponent index-profile, the maximum attainable signal-to-noise ratio, when the receiving aperture area is equal to the core area, is given by the square root of the number of the guided modes. The hypotheses on which the theory is based are discussed and an experiment, confirming the theoretical results, is presented.

Speckle-pattern visibility of light transmitted through a multimode optical fiber

We show that the reduction in visibility of the speckle pattern obtained from laser light that has been passed through a step-index light guide can be found from a knowledge of the model dispersion of the guide, and the bandwidth of the laser beam.

Polarization switching in semiconductor lasers driven via injection from an external radiation

Switching between transverse electric (TE) and transverse magnetic (TM) polarization states in the output from a semiconductor laser is experimentally obtained through injection locking from an external TM polarized radiation. Switching, which is connected to the loss reduction of the TM modes caused by the injection‐locking mechanism, is faster than a few nanoseconds, the resolution limit of our apparatus.