Giancarlo Gavioli

Empirical modeling and simulation of phase noise in long-haul coherent optical transmission systems

An empirical phase noise channel model suitable for performance evaluation of high spectrally efficient modulations in 100G long-haul coherent optical transmission systems using polarization-division multiplexed and wavelength-division multiplexing channels is presented. The derivation of the model is worked out by exploiting the similarity between the power spectral density of the carrier extracted from the analysis of propagation measurements and the Lorentzian spectrum that is usually adopted to describe instabilities of semiconductor lasers. The proposed channel model is characterized by only two parameters: the linewidth of the carrier and the signal-to-noise ratio. We show that in the case of quadrature phase-shift keying transmission a good agreement exists between quantitative measures of performance extracted by processing experimental data and those obtained from simulations based on the use of the empirical model.

Polarization in Retracing Circuits for WDM-PON

Reflective semiconductor optical amplifier (RSOA)-based network-embedded self-tuning solutions for colorless optical network unit in wavelength-division-multiplexed passive optical network architecture suffer the device polarization-dependent gain (PDG). The Faraday-mirror-based topology proposed in the literature for low PDG RSOA is not suitable for high PDG RSOA. A polarization retracing circuit is proposed and discussed to comply with the high PDG RSOA. The polarization evolution is theoretically and experimentally analyzed in the presence of a high PDG RSOA comparing three cases: standard topology with standard mirror, the retracing circuit proposed in the literature with a Faraday rotator mirror (FRM), and the proposed retracing circuit, which includes both an FRM and a Faraday rotator.

Pilot-Symbols-Aided Carrier-Phase Recovery for 100-G PM-QPSK Digital Coherent Receivers

A feedforward pilot-symbols-aided carrier-phase recovery scheme is described. The approach relies on pilot symbols that are time-division multiplexed with the transmitted data. In the scheme, an initial coarse estimation of the optical carrier phase, exploiting the knowledge of pilot symbols, is followed by a fine nondata-aided, or blind, estimation. The main advantage of the proposed solution is that of avoiding the phase- ambiguity problem after a cycle slip. The overhead and the impact on the performance of pilot symbols are investigated for long-haul transmission of 100-Gb/s polarization-multiplexed quadrature phase-shift keying wavelength-division-multiplexing signals in different scenarios. For homogeneous transmission, the proposed scheme outperforms blind carrier recovery with differential decoding.

Routing, modulation level, and spectrum assignment in optical metro ring networks using elastic transceivers

For decades, optical networks have provided larger bandwidths than could be utilized, but with the increasing growth of the global Internet traffic demand, new optical transmission technologies are required to provide a much higher data rate per channel and to enable more flexibility in the allocation of traffic flow. Currently, researchers are investigating innovative transceiver architectures capable of dynamically adapting the modulation format to the transmission link properties. These transceivers are referred to as elastic and enable flexible allocation of optical bandwidth resources. To exploit their capabilities, the conventional fixed spectrum grid has to evolve to provide a more scalable and flexible system that can provide the spectral resources requireded to serve the client demand. The benefits of elastic transceivers with distance-adaptive data rates have been evaluated in optical core networks, but their application to metro ring networks has still not been addressed. This paper proposes methods based on integer linear programs and heuristic approaches to solve the routing, modulation level, and spectrum assignment problem in optical rings with elastic transceivers and rate-adaptive modulation formats. Moreover, we discuss how to analytically compute feasible solutions that provide useful upper bounds. Results show a significant reduction in terms of transceiver utilization and spectrum occupation.

Up to 10.7-Gb/s High-PDG RSOA-Based Colorless Transmitter for WDM Networks

The operation of a network-embedded colorless self-tuning transmitter for WDM networks is experimentally demonstrated from 2.5- up to 10.7-Gb/s data rates. Colorless operation is achieved by self-seeding an ultra-fast reflective semiconductor optical amplifier (RSOA) with the feedback signal reflected at the WDM multiplexer filter. In particular, the transmitter exploits a 2-Faraday rotators configuration to ensure polarization insensitive operation and allowing for the exploitation of high gain RSOAs, which can be designed to operate on a single polarization. The impact on the transmission of the fiber chromatic dispersion at different bit-rates and with different channel bandwidths of the WDM multiplexer filter is experimentally investigated up to 10.7 Gb/s. The tolerance to positive and negative dispersive loads is also assessed.

C- and O-band operation of RSOA WDM PON self-seeded transmitters up to 10 Gb/s [Invited]

We propose a network-embedded colorless self-tuning transmitter for wavelength division multiplexed (WDM) networks based on self-seeding in reflective semiconductor optical amplifiers (RSOAs). We compare up to a 10-Gb/s data rate in either O-band or C-band operation. In particular, the transmitter exploits a two-Faraday rotator configuration to ensure polarization-insensitive operation and allowing for the exploitation of high-gain C- and O-band RSOAs, which present a very high polarization-dependent gain. Two different multiplexers and various lengths of drop fibers constituted the network-embedded transmitters in order to evaluate various dispersion load influence on cavity buildup. Moreover, transmission over standard single-mode feeder fiber has been evaluated both at 2.5 and 10 Gb/s to compare the performance in both bands, confirming the absence of chromatic dispersion penalties for the O-band operation.

Optical ring metro networks with flexible Grid and distance-adaptive optical coherent transceivers

The utilization of distance-adaptive coherent optical transceivers in combination with a flexible finer-grained Wavelength Division Multiplexing (WDM) grid has been proposed in optical core networks to enable higher spectral efficiency and flexibility in the allocation of traffic flows. However, the application of distance-adaptive transceivers in metro networks, which are typically based on ring topologies and characterized by shorter distances and lower traffic volumes, is still an open research area both in terms of network resource savings and coherent technology requirements. This paper discusses and analyzes an optical metro ring network architecture with distance-adaptive coherent transceivers and formalizes the routing, modulation level, and spectrum assignment (RMLSA) optimization problem over such a network in order to evaluate the possible benefits introduced by the use of coherent technologies and of a spectrum grid of finer granularity in metro scenarios. Comparisons with legacy WDM systems show significant savings in terms of spectrum occupation and transceiver utilization.

Impact of Nonideal Phase Reference on Soft Decoding of Differentially Encoded Modulation

The performance of coded modulation schemes based on the concatenation of a forward-error correction (FEC) code and differentially encoded quadrature amplitude modulations (QAMs) in the presence of Wiener phase noise is considered. Log-likelihood ratios, required to perform soft decoding, are first derived for the case in which the phase of the received carrier is assumed to be perfectly known, and then used to obtain the performance for nonideal reference of phase. Simulation results of the post-FEC bit-error rate are presented for a near-Shannon limit low-density parity check code with an overhead of 20%. The performance loss, compared to ideal coherent demodulation, is evaluated for two different linewidths of the phase noise in case of quadrature-phase shift keying and 16-QAM transmission.

Self-tuning transmitter for fibre-to-the-antenna PON networks

WDM PONs offering point-to-point connectivity, independence of multiple access protocol to share the medium are good candidates for supporting the new fronthaul fibre network requirements. The necessity to allow inventory and maintenance cost reduction will favour WDM PON solutions based on colourless transceivers. We present the proposal of a network embedded self-tuning colourless transmitter, based on reflective semiconductor optical amplifier (RSOA) self-seeding architectures. We analyse the fibre-to-the-antenna network requirements and evidence the capabilities of the network embedded self-tuning colourless transmitter, showing its principle of operation, the development and the modelling of the active elements. We present and discuss recent experimental results up to 10Gbit/s, which are encouraging for the transmitter exploitation in fronthaul WDM multiplexing technology.

Self-seeded RSOAs WDM PON field trial for business and mobile fronthaul applications

GEth, CPRI and 10 Gbit/s transmissions are experimented using amplified and standard self-seeded RSOA WDM PON systems. A field trial setup was exploited to test the system performance in terms of reach and optical budget.