F. Curti

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.

All-optical signal reshaping by means of four-wave mixing in optical fibers

It is experimentally demonstrated that the four-wave mixing (FWM) effect in an optical fiber can be exploited to achieve all-optical reshaping. The injection of a signal and a strong continuous-wave (CW) pump into a common dispersion-shifted fiber results in several wavelength-converted replicas of the signal. These spectral components exhibit various reshaping behaviors. Selecting low-order FWM waves, we observe a sinusoidal-like transfer function. However, unlike other reshaping devices, a step-like transfer function is obtained for higher order mixing products. A significant noise compression is observed at the converted output, starting from an input noisy nonreturn-to-zero (NRZ) signal stream.

A novel multilevel coherent optical system: 4-quadrature signaling

A novel multilevel coherent optical system is proposed. It is based on the exploitation of the property that the electromagnetic field propagating in a single-mode optical fiber can be represented by a four-dimensional vector whose components are the phase and quadrature terms of the two polarization components of the electrical field. This allows a wider use of the resources of the electromagnetic field for information transmission in order to obtain a spectrally efficient modulation format with a limited end. The net performance gain with respect to multilevel amplitude and phase modulation (N-APK) and N-PSK increases with an increase in the number of levels N. For instance, for N=32 the gain is 1.6 and 7.7 dB with respect to N-APK and N-PSK systems. The effect of laser phase noise on the system performance is evaluated. >

Phase noise and polarization state insensitive optical coherent systems

The authors present three different schemes that allow compensation of phase noise and polarisation state change by sending a reference channel that is suitably frequency shifted by using polarization modulation together with Stokes parameters detection or computing and inverting the Jones matrix that describes the fiber polarization state transformation. As a conclusion, some comparisons are made among different approaches in order to show how different systems can be tailored to different requirements both in point-to-point and in multipoint networks. >

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.

Fast tunable wavelength conversion for all-optical packet switching

We demonstrate a simple scheme to achieve fast tunable wavelength conversion over a wide spectral range. The wavelength conversion is obtained by four-wave mixing in a semiconductor optical amplifier using a double-pump scheme, 2048-bit sequences at 2.5 Gb/s, incoming at a given wavelength, are alternatively converted toward two different wavelengths for a total conversion interval of 20 nm. With this method, the time needed to change the destination wavelength is much shorter than the bit duration. This feature makes any guard-time spacing between packets unnecessary. Bit-error-rate measurements show that the process occurs with negligible penalties (less than 0.3 dB).

All-optical fiber 2+1 auxiliary carrier transponder-regenerator

The authors report simulations and experimental results about a new kind of all-optical reamplification and reshaping (2R) regenerator. The novelty is based on the principle that the ordinary four-wave-mixing process, inside a particular dispersion-shifted fiber, is able to induce input signal replicas on a third copropagating auxiliary carrier even if its state of polarization is orthogonal to that of the pump. Test results on a deployed cable showing improved 2R function and wavelength conversion capability are reported.

Wavelength converter–reshaper based on multi-wavelengths spectral components generation in optical fibre

We experimentally demonstrate a wavelength converter-reshaper, operating at 10 Gbit/s, based on multi-wavelength generation in Dispersion Shifted optical fibre due to the Kerr nonlinearity, able to generate a large number of signal replicas that permit to cover the ITU-grd. Transmission esperiments on the converted signals were also performed by using an installed cable encompassing G.652, G.653 and G.655 fibres.

Network Performance Investigation in a Wide Area Gigabit Ethernet Test Bed Adopting All-Optical Wavelength Conversion

We experimentally investigate the network performance of a wide area gigabit Ethernet test bed in which we introduced the all-optical wavelength conversion (WC) process. Such a test bed is configured to implement a quality of service (QoS) control based on the virtual private local area network service (VPLS), a technique that, according to the reported results, is well suitable to implement forwarding process based on dedicated wavelengths. We show that the all-optical WC does not degrade the QoS properties of the VPLS and it can be used with very fast switching time.