Joan M. Gené

Fiber-to-the-Home Technologies

Preface. 1. Introduction. 2. Access Techniques. 3. Protocols And Standardisation. 4. Projects & Field Trials. 5. Components. 6. Transmission Impairments And Monitoring. 7. Economic Case Study. References.

Simultaneous Compensation of Polarization Mode Dispersion and Chromatic Dispersion Using Electronic Signal Processing

In this paper, we study the performance of 10.7-Gb/s nonreturn-to-zero (NRZ) and return-to-zero (RZ) on-off keying signals in the joint presence of first-order polarization mode dispersion (PMD) and chromatic dispersion (CD) based on optical signal-to-noise ratio penalty measurements. Our investigations show that the tolerance of RZ to first-order PMD is severely reduced by the presence of typical values of residual CD. Three different receiver strategies are studied: 1. unequalized threshold detection; 2. combined feed-forward and decision-feedback equalization; and 3. maximum-likelihood sequence estimation (MLSE). In all three cases, the presence of CD eliminates the advantage of RZ over NRZ in terms of PMD tolerance. For NRZ, we find that the MLSE improves the tolerance to first-order PMD by 60%-70%, even in the presence of residual CD.

Investigation of 10-Gb/s optical DQPSK systems in presence of chromatic dispersion, fiber nonlinearities, and phase noise

The impact of phase noise, chromatic dispersion, and nonlinear effects on a 10-Gb/s optical differential quadrature phase-shift keying (oDQPSK) system has been evaluated by computer simulations. Both single channel and multiple wavelength-division-multiplexing channels have been considered. The results show that the low spectral width of this format allows a reduced channel spacing as low as 25-12.5 GHz. Furthermore, the use of this format leads to an increase in dispersion tolerance together with a robustness to nonlinear effects due to the signal near constant envelope characteristics. Finally, simulations show that phase noise can be the limiting factor of oDQPSK systems.

Flex-grid/SDM backbone network design with inter-core XT-limited transmission reach

Spatial division multiplexing (SDM) has been presented as a key solution to circumvent the nonlinear Shannon limit of standard single-core fibers. To implement SDM, multi-core fiber (MCF) technology becomes a top candidate that is leveraged by the very low inter-core crosstalk (XT) measurements obtained in real laboratory MCF prototypes with up to 22 cores. In this work, we concentrate on the design of MCF-enabled optical transport networks. To this goal, we present a methodology to estimate the worst-case transmission reach of the optical signals (at different bit rates and modulation formats) across MCFs given real laboratory XT measurements. Next, we present an optimal integer linear programming (ILP) formulation for the design of a flex-grid/SDM optical transport network that makes use of the transmission reach estimations. Additionally, an effective simulated annealing (SA)-based heuristic able to solve large problem instances with reasonable execution times is presented. Once the proposed heuristic is adequately tuned and validated, we use it to compare the resource utilization in MCF-enabled network scenarios against currently available multi-fiber link solutions. Numerical results reveal very close performances with up to 19 cores/fibers in national backbone network scenarios and up to 12 cores/fibers in long-haul continental ones.

Quaternary optical transmission system combining phase and polarization-shift keying

A new optical transmission scheme which combines polarization-shift keying and differential phase-shift keying on the same optical carrier is proposed. Simulations carried out show a considerable tolerance toward different physical impairments, such as polarization-mode dispersion, nonlinear effects, and chromatic dispersion. When compared to other multilevel modulation formats, it shows the advantage of reusing the carrier power, thus, sensitivity is improved.

ISI Mitigation Capability of MLSE Direct-Detection Receivers

We explain why maximum-likelihood sequence estimation (MLSE) receivers for direct-detection optical communication systems do not achieve the single-pulse performance of threshold receivers, in which there is no intersymbol interference (ISI). For this purpose, we propose a simple and intuitive model to approximate the performance of MLSE receivers under the assumption of moderate ISI. A performance analysis of this model shows that an MLSE receiver does not reach the performance of an ISI-free threshold receiver. By simulations we evaluate the range over which the model accurately approximates the MLSE receiver.

Joint PMD and Chromatic Dispersion Compensation Using an MLSE

Experimental investigations show that maximum likelihood sequence estimation (MLSE) in a 10.7 Gb/s non return-to-zero system improves by 60-70% the tolerance to first-order polarization mode dispersion (PMD), even in the presence of residual chromatic dispersion.

Modified duobinary polarization-shift keying transmission scheme

A new version of duobinary polarization-shift keying scheme is proposed. The relocation of the duobinary filter at the receiver side and the optimization of both transmitter and receiver electrical filters offer a receiver sensitivity improvement while maintaining chromatic dispersion tolerance. The main reason for this sensitivity enhancement is the reduction of the timing jitter and the noise narrow filtering provided. Moreover, the system is more tolerant against fiber nonlinear effects.

Experimental Study of MLSE Receivers in the Presence of Narrowband and Vestigial Sideband Optical Filtering

We report on experimental investigations of real-time maximum-likelihood sequence estimation (MLSE) in the presence of narrowband optical filtering, using 10.7-Gb/s nonreturn-to-zero ON-OFF keying and a fiber grating filter with 6.25-GHz bandwidth. Compared to standard threshold detection, the MLSE eliminates a 10-3 error floor due to narrowband optical filtering and results in DFB a <2-dB optical signal-to-noise ratio penalty at a 10-3 bit-error ratio. Furthermore, we demonstrate the ability of the MLSE to simultaneously compensate for narrowband optical filtering and chromatic dispersion. Finally, we investigate the influence of narrowband filter frequency detuning and show that the well-known effect of increased filtering tolerance given by the vestigial sideband effect observed in standard threshold detection, disappears in the presence of the MLSE.

Evaluation of core-continuity-constrained ROADMs for flex-grid/MCF optical networks

To effectively keep pace with the global IP traffic growth forecasted in the years to come, flex-grid over multi-core fiber (MCF) networks can bring superior spectrum utilization flexibility, as well as bandwidth scalability far beyond the non-linear Shannons limit. In such a network scenario, however, full node switching re-configurability will require enormous node complexity, pushing the limits of current optical device technologies with prohibitive capital expenditures. Therefore, cost-effective node solutions will most probably be the key enablers of flex-grid/MCF networks, at least in the short- and mid-term future. In this context, this paper proposes a cost-effective reconfigurable optical add/drop multiplexer (ROADM) architecture for flex-grid/MCF networks, called CCC-ROADM, which reduces technological requirements (and associated costs) in exchange for demanding core continuity along the end-to-end communication. To assess the performance of the proposed CCC-ROADM in comparison with a fully flexible ROADM (i.e., a fully non-blocking ROADM, called FNB-ROADM in this work) in large-scale network scenarios, a novel lightweight heuristic to solve the route, modulation, core, and spectrum assignment problem in flex-grid/MCF networks is presented in this work, whose goodness is successfully validated against optimal ILP formulations previously proposed for the same goal. The obtained numerical results in a significant number of representative network topologies with different MCF configurations of 7, 12, and 19 cores show almost identical network performance in terms of maximum network throughput when deploying CCC-ROADMs versus FNB-ROADMs, while decreasing network capital expenditures to a large extent.