Luca Banchi

Investigation of Transparency of FWM in SOA to Advanced Modulation Formats Involving Intensity, Phase, and Polarization Multiplexing

We experimentally investigate the real transparency of four-wave mixing (FWM) in semiconductor optical amplifiers to modulation formats involving intensity, phase, and polarization multiplexing. We exploit two different FWM polarization-independent schemes (that make use of two pumps) to wavelength-convert 40 Gb/s single-polarization and 80 Gb/s polarization-multiplexed signals in case of both nonreturn-to-zero ON -OFF keying (NRZ-OOK) and NRZ differential phase-shift keying modulation formats. We found that, although FWM conversion is transparent to modulation formats employing phase and intensity, polarization-multiplexed signals pose serious limitations to all-optical processing transparency.

All-Optical 10 and 40 Gbit/s RZ-to-NRZ Format and Wavelength Conversion Using Semiconductor Optical Amplifiers

We demonstrate that the cross-gain compression (XGC) in a semiconductor optical amplifier can produce effective return to zero (RZ)-to-nonreturn to zero (NRZ) format conversion. This technique is experimentally investigated at 10 and 40 Gbit/s. At 10 Gbit/s, the format adaptation allows for a very high pulsewidth increase, i.e., from 10 to 100 ps. The output 10 Gbit/s NRZ signal is transmitted on metro-like links with no chromatic dispersion compensation.

System feasibility of using stimulated Brillouin scattering in self coherent detection schemes.

We demonstrate the first self-coherent detection of 10 Gbit/s BPSK signals based on narrow-band amplification of the optical carrier by means of Stimulated Brillouin effect in a common fiber. We found that this technique is very effective only if it is combined with proper line coding and high-pass electrical filtering at the receiver. In this case we obtain OSNR-performance close to the ideal coherent receiver.

Investigation of the Effects of Chirped RZ Signals in Reducing the Transmission Impairments in R-SOA-Based Bidirectional PONs

Distributed and concentrated reflections represent the two main limitations in reflective-semiconductor optical amplifier (R-SOA)-based passive optical networks (PONs). In this paper, we experimentally discuss how the use of chirped signals in centralized light seeding bidirectional PON can increase the resilience of the system against those two types of reflections. An experimental comparison of the performance of a highly chirped return to zero (RZ) modulation format and the nonreturn to zero is given. Error-free operation is achieved down to 10 dB of signal to crosstalk ratio in presence of distributed reflection, when the upstream signal is highly chirped RZ signal. The same chirped modulation leads to a tolerance of more than -25 dB network return loss due to concentrated reflections. Finally, we assess also the system feasibility of a R-SOA-based full-duplex PON where both the upstream and the downstream are modulated signals.

Highly improved uplink transmission in bidirectional PONs by using a RZ direct-modulated R-SOA

We experimentally demonstrate unmatched resilience to carrier and signal backscattering in central light seeded PONs. By using RZ modulated R-SOA as uplink transmitter, we obtained error-free uplink communications at 10 dB signal-to-crosstalk level.

Assessing the Noise Statistics in Common Optical Transmission Systems

We experimentally investigate the probability density function (pdf) of sampled bits in common intensity-modulated direct-detection systems in linear and nonlinear regime, both single-channel and wavelength-division-multiplexed. To this aim, we use a recirculating fiber loop and selectively obtain the sample pdf for the various bits in a given sequence, which allows separating the intersymbol interference (ISI) effects. Our measurements confirm a recent theoretical simplified model, suggesting that, under the above conditions, a generalized analytic form is a good approximation of the true pdf, provided that a pattern-dependent effective noise density and noiseless signal value are assumed: all the pdfs estimated from the experimental data are indeed well fitted by this analytic form. Moreover, when nonlinear effects become dominating, the analytic form is still fitting properly the data histograms, showing, however, that the effective noise density increases. In the above regime, we clearly observe that ISI also affects the increase of the effective noise density.

BER Estimation for Performance Monitoring in High-Speed Digital Optical Signals

This paper presents a novel technique that allows easy and accurate estimation of the system bit error rate (BER) by collecting the statistical distribution of the receiver analog samples, i.e., before decision. It could be used to implement effective optical performance monitoring in real systems, with limited hardware complexity. The scheme performance is confirmed by both numerical simulations and experimental measurements. In all cases, the estimated BER is found to be very close to the real value, thus providing accurate and robust estimations. It is experimentally verified that in presence of strong intersymbol interference (ISI), or in the highly nonlinear regime, our technique works much better than the well known Q-factor approach.

Self-homodyne 10 Gbit/s PSK receiver based on stimulated Brillouin amplification and electrical filtering

We demonstrate the first self-homodyne coherent detection of 10 Gbit/s PSK signals using Brillouin amplification of the optical carrier. Performance close to the ideal homodyne receiver is obtained by using proper line coding and post-detection high-pass filtering.