Filipe Ferreira

Bio: Filipe Ferreira is an academic researcher from University College London. The author has contributed to research in topics: Multiplexing & Mode coupling. The author has an hindex of 15, co-authored 102 publications receiving 749 citations. Previous affiliations of Filipe Ferreira include University of Coimbra & Nokia Networks.

DSP complexity of mode-division multiplexed receivers

Abstract: The complexities of common equalizer schemes are analytically analyzed in this paper in terms of complex multiplications per bit. Based on this approach we compare the complexity of mode-division multiplexed digital signal processing algorithms with different numbers of multiplexed modes in terms of modal dispersion and distance. It is found that training symbol based equalizers have significantly lower complexity compared to blind approaches for long-haul transmission. Among the training symbol based schemes, OFDM requires the lowest complexity for crosstalk compensation in a mode-division multiplexed receiver. The main challenge for training symbol based schemes is the additional overhead required to compensate modal crosstalk, which increases the data rate. In order to achieve 2000 km transmission, the effective modal dispersion must therefore be below 6 ps/km when the OFDM specific overhead is limited to 10%. It is concluded that for few mode transmission systems the reduction of modal delay is crucial to enable long-haul performance.

Design of Few-Mode Fibers With M-modes and Low Differential Mode Delay

Abstract: In this paper, we investigate the design of few-mode fibers (FMFs) guiding 2 to 12 linearly polarized (LP) modes with low differential mode delay (DMD) over the C-band, suitable for long-haul transmission. Two different types of refractive index profile have been considered: a graded-core with a cladding trench (GCCT) profile and a multi-step-index (MSI) profile. The profiles parameters are optimized in order to achieve: the lowest possible DMD and macro-bend losses (MBL) lower than the ITU-T standard recommendation. The optimization results show that the MSI profiles present lower DMD than the minimum achieved with a GCCT profile. Moreover, it is shown that the optimum DMD and the MBL scale with the number of modes for both profiles. The optimum DMD obtained for 12 LP modes is lower than 3 ps/km using a GCCT profile and lower than 2.5 ps/km using a MSI profile. The optimization results reveal that the most preponderant parameter of the GCCT profile is the refractive index relative difference at the core center, Δnco. Reducing Δnco, the DMD is reduced at the expense of increasing the MBL. Regarding the MSI profiles, it is shown that 64 steps are required to obtain a DMD improvement considering 12 LP modes. Finally, the impact of the fabrication margins on the optimum DMD is analyzed. The probability of having a manufactured FMF with 12 LP modes and DMD lower than 12 ps/km is approximately 68% using a GCCT profile and 16% using a MSI profile.

Nonlinear Semi-Analytical Model for Simulation of Few-Mode Fiber Transmission

Abstract: In this letter, a nonlinear semi-analytical model (NSAM) for simulation of few-mode fiber transmission is proposed. The NSAM considers the mode mixing arising from the Kerr effect and waveguide imperfections. An analytical explanation of the model is presented, as well as simulation results for the transmission over a two mode fiber (TMF) of 112 Gb/s using coherently detected polarization multiplexed quadrature phase-shift-keying modulation. The simulations show that by transmitting over only one of the two modes on TMFs, long-haul transmission can be realized without increase of receiver complexity. For a 6000-km transmission link, a small modal dispersion penalty is observed in the linear domain, while a significant increase of the nonlinear threshold is observed due to the large core of TMF.

A Comparison of Radio Over Fiber Link Types for the Support of Wideband Radio Channels

Abstract: Three radio over fiber link types are compared to assess their relative performance for the optical transmission of next generation wireless signals having multiple wideband radio channels with high-level modulation. These links differ in their choice of modulation device; either a directly modulated laser (DML) or external modulation using a Mach-Zehnder modulator (MZM) or a reflective semiconductor optical amplifier (RSOA). The DML and RSOA link types are shown to suffer minimal degradation of the uplink wireless range compared to the baseline value without an optical link, using optimum components in terms of cost and performance. The optimum technology depends on the relative merits of simplicity (DML) or optical network architecture flexibility (RSOA).

Impact of mode coupling on the mode-dependent loss tolerance in few-mode fiber transmission

Abstract: Spatial-division multiplexing in the form of few-mode fibers has captured the attention of researchers since it is an attractive approach to significantly increase the channel capacity. However, the optical components employed in such systems introduce mode-dependent loss or gain (MDL) due to manufacturing imperfections, leading to significant system impairments. In this work the impact of MDL from optical amplifiers in few-mode fibers with either weak or strong mode coupling is analyzed for a 3x136-Gbit/s DP-QPSK mode-division multiplexed transmission system. It is shown that strong mode coupling reduces the impact of MDL in a similar manner as that polarization-dependent loss is reduced in single mode fibers by polarization-mode dispersion.

Space-division multiplexing in optical fibres

Abstract: This Review summarizes the simultaneous transmission of several independent spatial channels of light along optical fibres to expand the data-carrying capacity of optical communications. Recent results achieved in both multicore and multimode optical fibres are documented.

Space-division multiplexing: the next frontier in optical communication

Abstract: Space-division multiplexing (SDM) uses multiplicity of space channels to increase capacity for optical communication. It is applicable for optical communication in both free space and guided waves. This paper focuses on SDM for fiber-optic communication using few-mode fibers or multimode fibers, in particular on the critical challenge of mode crosstalk. Multiple-input–multiple-output (MIMO) equalization methods developed for wireless communication can be applied as an electronic method to equalize mode crosstalk. Optical approaches, including differential modal group delay management, strong mode coupling, and multicore fibers, are necessary to bring the computational complexity for MIMO mode crosstalk equalization to practical levels. Progress in passive devices, such as (de)multiplexers, and active devices, such as amplifiers and switches, which are considered straightforward challenges in comparison with mode crosstalk, are reviewed. Finally, we present the prospects for SDM in optical transmission and networking.

Radio Over Fiber Link Design for Next Generation Wireless Systems

Abstract: The performance of radio over fiber (RoF) links using low cost optoelectronic components is assessed for distributed antenna applications in next generation wireless systems Important design issues are discussed and an example link design is presented for a wireless system requiring the transmission of four radio channels per link direction, each with 100 MHz bandwidth, modulation complexity of 256-QAM and 2048 OFDM subcarriers We show that the noise introduced by the RoF links does not have a significant impact on wireless range, provided the wireless system has uplink power control Finally, we compare the cost and performance of RoF links for this application with alternative link types that use digitized radio transmission and show that RoF is the optimum choice from a cost perspective

Survey and Evaluation of Space Division Multiplexing: From Technologies to Optical Networks

Abstract: Single-mode fiber's physical capacity boundaries will soon be reached; hence, alternative solutions are much needed to overcome the multiplying and remarkably large bandwidth requests. Space division multiplexing (SDM) using multicore fibers (MCFs), multielement fibers, multimode fibers, and their combination; few-mode MCFs; or fibers based on orbital angular momentum are considered to be the propitious stepping-stones to overcome the capacity crunch of conventional single-core fibers. We critically review research progress on SDM fibers and network components, and we introduce two figures of merit aiming for quantitative evaluation of technologies such as amplifiers, fan-in/fan-out multiplexers, transmitters, switches, and SDM nodes. Results show that SDM fibers achieve a 1185-fold (18-fold) spectral–spatial efficiency increase compared with the 276-SMF bundle (single-core fiber) currently installed on the ground. In addition, an analysis of crosstalk in MCFs shows how SDM concepts can be further exploited to fit in various optical networks such as core, metro, and especially future intra-data center optical interconnects. Finally, research challenges and future directions are discussed.

Space-division multiplexing for optical fiber communications

Abstract: Research on space-division multiplexing (SDM) came to prominence in early 2010 being primarily proposed as a means of multiplying the information-carrying capacity of optical fibers at the same time as increasing efficiency through resource sharing. Proposed SDM transmission systems range from parallel single-mode fibers with shared amplifier pump lasers to the full spatial integration of transceiver hardware, signal processing, and amplification around a fiber with over 100 spatial channels comprising multiple cores each carrying multiple modes. In this paper, we review progress in SDM research. We first outline the main classifications and features of novel SDM fibers such as multicore fibers (MCFs), multimode fibers, few-mode MCFs, and coupled-core MCFs. We review research achievements of each fiber type before discussing digital-signal processing, amplifier technology, and milestones of transmission and networking demonstrations. Finally, we draw comparisons between fiber types before discussing the current trends and speculate on future developments and applications beyond optical data transmission.