M. Romagnoli

Sideband instability induced by periodic power variation in long-distance fiber links

Periodically spaced amplifiers along a transoceanic cable provide the phase-matching condition for a four-wave mixing process owing to Kerr nonlinearity. A new kind of sideband instability, shows up in both positive and negative dispersion regimes that is similar to modulation instability. A comparison with the sideband instability that was recently discovered for solitons is carried out.

Role of third-order dispersion on soliton instabilities and interactions in optical fibers.

We analyze the role of third-order dispersion on the propagation, stability, and interactions of solitons in optical fiber transmission links and fiber lasers.

Self-induced modulational-instability laser

Summary form only given. We report a novel scheme of passive modelocking in fiber lasers that, based on modulational instability, provides continuous trains of solitons with large duty cycle and rep rates up to 130 GHz. The basic difference with the standard modelocking technique is that in configuration we are describing continuous wave operation is not inhibited as for modelocking. The train of pulses therefore originates from the forcing action of the modulational instability sidebands that lock the cavity modes. The self-induced modulational instability laser can be achieved either by including in the cavity a polarization beam splitter, which, combined with nonlinear polarization, evolution provides a power dependent transmission, or even without it. In the latter case we show that the whole cavity acts as a nonlinear gain element.

Time-domain Fourier optics for polarization-mode dispersion compensation

We report on a novel technique to compensate for all-order polarization-mode dispersion. By means of this technique, based on a suitable combination of phase modulation and group-velocity dispersion, we compensated for as much as 60 ps of differential group delay that affected a 10-Gbit/s return-to-zero data stream.

Tunable erbium–ytterbium fiber sliding-frequency soliton laser

We characterize the soliton-train emission from an Er–Yb-doped fiber loop laser. We discuss the self-starting dynamics and pulse-repetition-rate control in this sliding-frequency soliton laser. We show that the laser truly self-starts after only one cavity round trip. In the steady state the laser emits a closely spaced train of solitons. We also show that the output pulse width may be controlled by the interplay of continuous frequency shifting, bandwidth-limited amplification, and nonlinear polarization rotation of the circulating solitons. The repetition rate is fixed by means of a weak intracavity feedback. The laser is tunable by shifting of the filter wavelength through the whole spectral band of the active fiber.

BANDWIDTH LIMITS OF SOLITON TRANSMISSION WITH SLIDING FILTERS

Abstract The limitations to the maximum transmission capacity in a long distance soliton transmission system with sliding guiding filters are studied. Shown is that sliding the center frequency of the filters may substantially stabilize the soliton even in the case of strong resonance overlap with the radiation that originates from the periodic amplification. This permits a considerable reduction of both the minimum pulse width and pulse-to-pulse separation in the transmission.

Characterization and optimization criteria for filterless erbium-doped fiber lasers

The emission wavelength of a unidirectional ring erbium-doped fiber laser (EDFL) with no filters has been characterized. A measurement of the emission and the absorption erbium-doped fiber cross sections together with a theoretical model based on the solution of the rate equations for the ring laser shows that the laser emission wavelength depends on the cold-cavity losses or on the active fiber length and dopant concentration. The threshold pump power, the output power, and the slope efficiency of the EDFL have been measured and theoretically evaluated versus cold-cavity loss and active fiber length. A simple relation among loss, active fiber length, and dopant concentration that permits the design of the cavity with the maximum slope efficiency has been found.

Timing jitter in soliton transmission with sliding filters

We show that the coupling between amplitude and frequency f luctuations that is due to filter sliding significantly enhances timing jitter in soliton transmission controlled by in-line filters. This is the likely reason for the extra timing jitter observed in a recent soliton transmission experiment using sliding filters.

Role of dispersion in pulse emission from a sliding-frequency fiber laser

We present an experimental and theoretical investigation of the role of group-velocity dispersion in the generation of picosecond pulses from a sliding-frequency fiber loop laser.

High-speed DPSK coherent systems in the presence of chromatic dispersion and Kerr effect

The error probability for a single-channel coherent optical differential phase-shift keying (DPSK) transmission system based on repeaterless links in the presence of fiber chromatic dispersion and Kerr effect is evaluated. An accurate model for both the optical signal propagation and the probability distribution of the receiver decision variable is obtained by using a numerical solution of the nonlinear Shrodinger equation and the characteristic function method. The results show that the selection of an optimized IF filter bandwidth is crucial to obtaining the best system performance. When chromatic dispersion dominates, the best performance is achieved in the normal dispersion region whereas when the Kerr effect has the most limiting effect on system performances, the lowest error probability is attained in the anomalous regime. The maximum link length is limited by the presence of Kerr effect, independently of the amount of transmitted optical power, to be shorter than a threshold length if an error probability of 10/sup -9/ is to be achieved. >