Armando N. Pinto

Mitigation of intra-channel nonlinearities using a frequency-domain Volterra series equalizer

We apply a frequency-domain Volterra series nonlinear equalizer to a 20 Gbaud NRZ-QPSK signal propagated over 1600 km. Using 2 samples/symbol we obtain a 2 dB improvement on the nonlinear tolerance over backward propagation split-step Fourier method.

Genetic Algorithm for the Topological Design of Survivable Optical Transport Networks

We develop a genetic algorithm for the topological design of survivable optical transport networks with minimum capital expenditure. Using the developed genetic algorithm we can obtain near-optimal topologies in a short time. The quality of the obtained solutions is assessed using an integer linear programming model. Two initial population generators, two selection methods, two crossover operators, and two population sizes are analyzed. Computational results obtained using real telecommunications networks show that by using an initial population that resembles real optical transport networks a good convergence is achieved.

Generating Realistic Optical Transport Network Topologies

We address the problem of generating physical realistic optical transport network topologies. This type of network has characteristics that differ from scale-free networks, such as the Internet. Based on the analysis of a set of real transport topologies, we identify and assess relevant characteristics. A method to generate realistic topologies is proposed. The proposed method is validated by comparing the characteristics of computer-generated and real-world optical transport networks.

Simplified Volterra Series Nonlinear Equalizer for Polarization-Multiplexed Coherent Optical Systems

Starting from a previously proposed frequency-domain Volterra series nonlinear equalizer (VSNE), whose complexity evolves as O(N3), with N being the frequency-domain block length, we derive a symmetric VSNE filter array formulation for polarization-multiplexed (PM) signals, whose full VSNE equivalent is up to 3 × more computationally efficient, with zero performance penalty. By gradually reconstructing the third-order kernel from its column/diagonal components, the full VSNE can be reduced to a restrict set of Nk frequency-domain filters, leading to O(Nk N2) complexity, associated with negligible performance loss. Finally, a simplified VSNE approach with invariant Kernel coefficients is proposed, delivering O(Nk N) complexity at the expense of controlled performance penalty. The proposed array of symmetric VSNE filters significantly increases the scalability of the previous matrix-based VSNE, providing a more flexible balance between performance and complexity, which can be freely adjusted to match the available computational resources. Performing a direct comparison between the simplified VSNE and the widely used split-step Fourier method in a long-haul 224 Gb/s PM-16QAM transmission system, we demonstrate a reduction of over 60% in terms of computational effort and 90% in terms of equalization latency.

Effect of soliton interaction on timing jitter in communication systems

Timing jitter in soliton communication systems is studied, taking into account both soliton interaction and amplifier noise. Deviations from Gordon-Haus jitter for closely spaced solitons are observed. A new analytical model for the timing jitter is proposed. The model presented considers interaction in a random sequence of solitons and the effect of the amplified spontaneous emission noise added in each amplification stage. We obtain a good agreement between the new analytical model and simulation results for practical communication systems.

Digital Postcompensation Using Volterra Series Transfer Function

We propose a noniterative digital backward propagation technique, based on an inverse modified Volterra series transfer function to postcompensate transmission linear and nonlinear impairments in the presence of optical noise. Using a single-channel 40-Gb/s nonreturn-to-zero quadrature phase-shift-keying optical signal propagated over 20 × 80 km of standard single-mode fiber, and performing digital postcompensation around the Nyquist rate, our compensation algorithm is able to surpass the maximum accuracy obtained with a symmetric split-step Fourier method, enabling us to increase the nonlinear tolerance by approximately 2 dB.

Broadband polarization pulling using Raman amplification

The Raman gain based polarization pulling process in a copropagating scheme is investigated. We map the degree of polarization, the angle between the signal and pump output Stokes vectors, the mean signal gain and its standard deviation considering the entire Raman gain bandwidth. We show that, in the undepleted regime (signal input power ~ 1 μW), the degree of polarization is proportional to the pump power and changes with the signal wavelength, following the Raman gain shape. In the depleted regime (signal input power ≳ 1 mW), the highest values for the degree of polarization are no more observed for the highest pump powers. Indeed, we show that exists an optimum pump power leading to a maximum degree of polarization.

Fully Blind Linear and Nonlinear Equalization for 100G PM-64QAM Optical Systems

We demonstrate fully blind processing and reduced-complexity nonlinear equalization (NLE) of a 100G PM-64QAM optical channel in a 50 GHz WDM grid, achieving a maximum reach of 1524 km over pure silica core fiber at a bit error rate of 2.7 × 10-2. The equalization of linear polarization-dependent effects is performed by a radius-directed constant modulus algorithm (RD-CMA), enabled by a multiradii training stage, yielding a very small penalty (<;0.1 dB in terms of Q2 factor) relatively to data-aided CMA. Applying a simplified Volterra series nonlinear equalizer (simVSNE), operating in the frequency domain, we demonstrate a reach extension of ~27% relatively to linear equalization. Due to its lower spatial resolution requirements, the simVSNE technique is shown to provide a more efficient NLE than the well-known back-propagation split-step Fourier method, both in terms of latency and number of complex multiplications per sample. The potential benefit of NLE for fully blind processing of high-order QAM optical signals is demonstrated by an incremental reduction of the RD-CMA penalty to <;0.04 dB.

Digital PDL Compensation in 3D Stokes Space

A Stokes space based technique for digital polarization-dependent losses (PDL) monitoring and compensation is proposed. The channel PDL monitoring is carried out with a resolution of 0.15 dB by computing the mean point of the signal samples represented in the three-dimensional Stokes space. The presented compensation technique is based on rotations and translations of the signal samples in the Stokes space, and provides a PDL compensation up to 2.5 dB. Error vector magnitude results show a gain of about 3 dB (assuming a PDL value equal to 1.5 dB) to a Stokes space based polarization demultiplexing technique without PDL compensation.

Adaptive 3-D Stokes Space-Based Polarization Demultiplexing Algorithm

We propose a novel polarization demultiplexing technique for complex modulated signals using the Stokes space polarization representation of the signal samples. Polarization demultiplexing of an endless time-varying SOP signal is achieved through the adaptive estimation of the inverse rotation matrix, without the calculation of a best fitting plane. Simulation results show the effectiveness of the proposed technique, with a high convergence speed, and a good response to time-varying SOP rotations. The performance of the method is assessed through EVM calculations for frequency rotations up to 15 μrad/symbol, showing a maximum penalty of 1 dB. Moreover, the technique can incorporate an additional stage for PDL compensation without penalties in terms of EVM results and algorithm complexity.