Rui Ribeiro

Highly Linear Integrated Optical Transmitter for Subcarrier Multiplexed Systems

A highly linear optical transmitter for radio-over-fiber subcarrier-multiplexed systems is presented. An integrated dual Mach-Zehnder modulator (MZM) is utilized to combine an optical carrier suppressed signal with an optical carrier. The proposed transmitter enables more than 10-dB improvement in the carrier-to-interference ratio compared to a quadrature biased MZM, and similar results to low biased MZM considering similar insertion loss. Negligible radio-frequency power dependence with temperature-induced bias drift is reported, while the low biased MZM is penalized by more than 12 dB for a 15% bias drift. The proposed transmitter reduces the minimum error vector magnitude from 4.2% to 3.5%, when compared to quadrature biased MZM, for a 54-Mb/s orthogonal frequency-division-multiplexed signal.

Electrical dispersion compensation at 10 Gb/s optical single sideband transmission systems

We report different strategies for electrical chromatic dispersion compensation of optical single sideband transmission systems. The performance of the different compensation schemes are evaluated and compared.

Mitigation of chromatic dispersion effects on optical single sideband signals by Butterworth filtering

We present a study on the application of electrical dispersion compensation on optical single sideband signals using Butterworth filters, which are optimized for this purpose. Three schemes are studied: pre-equalization, post-equalization and dual-equalization.

Highly Linear Single Sideband Transmitter for Radio-Over-Fiber Systems

A wavelength-independent single sideband (SSB) transmitter for high-performance radio-over-fiber links is proposed. Third order intermodulation distortion improvement of 9 dB is experimentally verified in back-to-back comparing to a conventional SSB transmitter. Simulation results demonstrate dispersion-independent performance of the proposed transmitter, while the conventional transmitter is further penalized by 8 dB.

Impact of the modulation depth on self-homodyne optical single sideband systems

Simulation experiments are used to assess the feasibility of optical SSB systems using self-homodyne detection. The experiments revealed that the electrical waveforms of the drive signals, required by the transmitter modulators, play a critical role on the system performance. Particularly important is the modulation depth. The present study recommends a modulation depth of 0.2 in order to obtain the best performance. The tap delay used in the discrete approximation of the Hilbert filter was also optimized, resulting in a value of 37.5 ps.

Impact and compensation techniques of laser phase noise in ultra-dense coherent access networks

The purpose of this paper is to provide a performance comparison between two carrier phase recovery (CPR) algorithms used to mitigate the impact of the laser phase noise in an ultra-dense wavelength-division multiplexing passive optical network WDM-PON (UDWDM-PON) scenario. The algorithms used in this work are the classic non-data-aided (NDA) phase estimation (PE) algorithm based on Viterbi & Viterbi (V&V) method, and another one based on data-aided (DA) technique which makes use of pilot symbols. The performance of the algorithms is numerically assessed for Quadrature Phase Shift Keying (QPSK) and Differential QPSK (DQPSK) modulations formats. The obtained results show that the linewidths of the optical network unit (ONU) and optical line terminal (OLT) lasers play an important role in the system performance. It is shown that fine laser linewidths ofΔν.Ts = 3×10-4 are required in order to obtain low penalties.

Highly linear radio-over-fiber transmitter for subcarrier multiplexed systems

A highly linear RoF transmitter, employing a dual Mach-Zehnder modulator, is proposed and experimentally tested. Carrier to interference ratio improvement of 16 dB, compared to conventional external modulation, is reported.

External modulator linearization techniques for high performance radio over fiber transmission systems

Some of the most promising transmitter linearization techniques for high performance radio over fiber systems are reviewed and compared through simulation tests. Comparison is focused on Mach-Zehnder modulator (MZM) operated at low bias; MZM conventionally biased at quadrature, driven with low modulation depth and cascaded with a notch optical filter; optical single sideband and double sideband plus carrier (SSB / DSB + C); and carrier suppressed plus carrier (CS+C) methods. These transmitters are evaluated through carrier to interference ratio, optical insertion losses, and RF power penalty. The robustness to deviation from ideal transmitter settings is also assessed.

Laser optimization for multilevel dispersion supported transmission systems

We investigate the impact of diode laser parameters on the performance of four-level dispersion supported transmission systems and present optimization results of a 40 Gbit/s system.

Challenges in Digital Data Backhaul networks for Square Kilometre Array radio telescope

The Square Kilometre Array will be the worlds largest and most sensitive radio telescope. To meet the technical requirements demanded by the science goals, thousands of linked radio wave receptors will be located in separate arrays in Southern Africa and in Western Australia. Combining the signals from the antennas in each region will create a telescope with a collecting area equivalent to a dish with an area of about one square kilometre. A large component of the SKA will be the communications infrastructure required to interconnect a high number of antennas and other elements of the system. The design of the Digital Data Backhaul (DDBH) Networks, for Square Kilometre Array Radio Telescope, presents several technical challenges that have never been addressed before, such as a wide range of transmission rates that can exceed an aggregated transmission rate of several Tb/s in extreme environments in Southern Africa and Australia. We will present possible transport solutions for different DDBH networks in the first phase of deployment, SKA-1, to start in 2018.