Vitor Ribeiro

Optical wireless communication for future broadband access networks

We present experimental results on ergodic channel capacity of single input single output (SISO) free-space optical (FSO) communication link. Furthermore, we present simulation results on bit error rate (BER) performance of M-ary quadrature amplitude modulation (M - QAM) considering the average received irradiance. In the simulation, effects of different parameters such as constellation size, wavelength and the refractive index which can be helpful in the adoption of adaptive modulation scheme are analyzed on system performance for different operating conditions.

Joint Iterative Carrier Synchronization and Signal Detection Employing Expectation Maximization

In this paper, joint estimation of carrier frequency, phase, signal means and noise variance, in a maximum likelihood sense, is performed iteratively by employing expectation maximization. The parameter estimation is soft decision driven and allows joint carrier synchronization and data detection. The algorithm is tested in a mixed line rate optical transmission scenario employing dual polarization 448 Gb/s 16-QAM signal surrounded by eight on-off keying channels in a 50 GHz grid. It is shown that joint carrier synchronization and data detection are more robust towards optical transmitter impairments and nonlinear phase noise, compared to digital phase-locked loop (PLL) followed by hard decisions. Additionally, soft decision driven joint carrier synchronization and detection offers an improvement of 0.5 dB in terms of input power compared to hard decision digital PLL based carrier synchronization and demodulation.

Spectrally efficient enhanced-performance bidirectional coherent PON with laserless 10 Gb/s ONU [invited]

We present and experimentally characterize a spectrally efficient, bidirectional, ultradense wavelength-division multiplexing passive optical network (PON) (2 × 120 Gb/s at 50 GHz) over 30 km standard single-mode fiber. This is achieved using a 4 GHz grid with partial spectrum overlapping, Nyquist-shaped 16-ary quadrature amplitude modulation, and digital frequency shifting. This scheme is based on a laserless, self-homodyne PON with centralized wavelength control. We achieve reduced impact of the Rayleigh back-scattering effect due to Nyquist-pulse shaping and frequency upshifting. Self-homodyne detection relaxes the laser linewidth requirement and digital signal processing complexity at the optical network unit. To demonstrate the extra benefit of the proposed PON system, we also experimentally and theoretically evaluate the impact of nonlinear Raman crosstalk in video overlay. Compared to a baseband Nyquist signal and baud rate non-return-to-zero equivalent, the proposed system improves the carrier-to-Raman crosstalk ratio of video overlay by 4 and 6 dB, respectively.

Free space optics hybrid PTMP advanced modulation bidirectional PON

We experimentally demonstrate a 12×10Gb/s bi-directional hybrid SSMF and FSO PHY PON recurring to 6.25 GHz grid, Nyquist shaping and frequency-shifting. Performance is evaluated over a 30.5 dB ODN with Hybrid splitting and coexistence with TWDM-PON.

Chromatic-Dispersion-Monitoring Scheme Using a Mach–Zehnder Interferometer and Q-Factor Calculation

In this paper we propose what we believe to be a novel method for monitoring chromatic dispersion (CD). We use radio-frequency (RF) power monitoring and Q-factor monitoring. We use a method for capturing opened eye diagrams with high-speed electro-optical sampling. This allows the calculation of the Q factor, here used to signal the correct CD. Simulation results show that with this method it is possible to have monitoring windows up to 2040 ps/nm at 40 Gbits/s, using the return-to-zero (RZ) and carrier-suppressed return-to-zero (CSRZ) modulation formats. For that to happen we just need to increase the number of iterations and the monitoring window of the variable dispersion compensator (VDC) algorithm explained further. With this method we obtain a high monitoring sensitivity of 0.3363 dB/(ps/nm).

Optical performance monitoring using the novel parametric asynchronous eye diagram

In this paper we present a novel technique, based in what we have called Parametric Asynchronous Eye Diagram (PAED). We have used a simulation scheme, which includes a differentiator and an Artificial Neural Network to monitor simultaneously several impairments such as Chromatic Dispersion, Polarization Mode Dispersion and Optical Signal to Noise Ratio. A number of modulation formats, including NRZ, RZ and QPSK is used in the computation of results. This paper also demonstrates the effectiveness of this technique in monitoring with one single device, mixed traffic, with different bit rates and On-Off Keying (OOK) modulation formats traveling through the network.

Parametric amplification with a dual-core fiber

In this paper we theoretically derive for the first time a matrix formalism for a coupled dual-core fiber optical parametric amplifier (FOPA). One of the most advantageous properties of this degenerate pump FOPA is the spectrally flat gain obtained when certain design parameters are met. This flat gain is obtained either in phase-sensitive (PS) or phase-insensitive (PI) operation of the dual-core FOPA. Properties such as maximum and minimum PS gain, along with maximum bandwidth and difference between maximum PS and PI gain are also investigated.

Parametric Asynchronous Eye Diagram for Optical Performance Monitoring

We experimentally demonstrate the novel Parametric Asynchronous Eye Diagram (PAED) applicable to Optical Performance Monitoring. Parametric Asynchronous Eye Diagram uses samples of the signal and samples of the derivative of the signal to construct a diagram similar in shape and behavior to the Synchronous Eye Diagram. This diagram allows to identify separately the impact of Chromatic Dispersion (CD), Differential Group Delay (DGD) and Optical Signal to Noise Ratio (OSNR). The technique is completely independent of the modulation format, and bit rate.

Observability of Incentive Contract and Platform Competition: OBSERVABILITY OF CONTRACT AND PLATFORM COMPETITION

As in traditional firms, owners of platforms may hire managers to reduce the marginal production cost. The managers’ contracts may be either observable or unobservable by rival platforms. This paper analyses the impact of contract observability in a two†sided market composed of symmetric indirect externalities with quantity competition and perfect information on agents’ effort. We show that, in both types of contracts, managers’ effort and platform subscription on each side of the market increase as the indirect network externality becomes more intense. However, the impact of the indirect network externality on platform profit is ambiguous. Managerial incentives, consumer surplus and social welfare are higher with observable contracts; however, platform profit is higher with unobservable contracts. Our analysis demonstrates that the disclosure of incentive information in two†sided markets implies tougher competition which unambiguously increases social welfare.

FSO for High Capacity Optical Metro and Access Networks

Free-space optic (FSO) with optical metro and access networks should couple very efficiently since they work in the same wavelengths with a transparent link. Moreover, coherent detection with advanced modulation formats can fully utilize the bandwidth and increase the transmission capacity of FSO links. This chapter considers several optical wireless systems used in metro and access networks. Advanced modulation formats and Nyquist pulse-shaping technology are discussed for future implementations of optical access networks. A fully ultra broadband optical wireless link in a building to building scenario is demonstrated. Moreover, an innovative bi-directional ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) based on advanced modulation formats and Nyquist pulse shaping in a hybrid fibre plus FSO is experimentally demonstrated.