Jeroen Nijhof

Blind Adaptive Chromatic Dispersion Compensation and Estimation for DSP-Based Coherent Optical Systems

We propose an accurate and low-complexity blind adaptive algorithm for chromatic dispersion (CD) compensation and estimation in coherent optical systems. The method is based on a Frequency Domain Equalizer (FDE), a low complexity Time Domain Equalizer arranged in a butterfly structure (B-TDE) and an Optical Performance Monitoring (OPM) block in a loop configuration. The loop is such that, at each iteration, the CD value compensated by the B-TDE and estimated by the OPM is given to the FDE; according to this estimation, in the subsequent iteration, the FDE compensates also this quantity. The procedure is repeated until the majority of CD is compensated by the FDE and a small residual quantity is compensated by a low complexity B-TDE with a small number of taps. The method is extended to long haul uncompensated links exploiting the information on the mean square error (MSE) provided by the B-TDE. The proposed algorithm is then experimentally validated for a polarization multiplexed quadrature phase shift keying (PM-QPSK) signal at 112 Gbit/s propagating along 1000 km of uncompensated Z PLUS® optical fiber. A statistical analysis of the performance of the proposed solution, in terms of mean value and standard deviation of the CD estimation error, is carried out, running a set of simulations including different impairments, such as noise, polarization dependent loss, polarization mode dispersion and self-phase modulation in a line of 1000 km of uncompensated G.652 optical fiber. Our method could be used to compensate and estimate any CD quantity without increasing the number of taps in the B-TDE and exploiting devices already included in the system (TDE, FDE and OPM) arranged in a loop.

Efficient label encoding in segment-routing enabled optical networks

The currently standardized GMPLS protocol suite for packet over optical networks relies on hierarchical instances of signaling sessions. Such sessions have to be established and maintained also in transit nodes, leading to complex and weighty control plane implementations. A novel technology called Segment Routing (SR) has been recently proposed to address these issues. SR relies on the source routing paradigm to provide traffic engineering solutions. In particular, the computed route for a given request is expressed as a segment list applied as an header to data packets at the ingress node. Specific algorithms are then required to perform the path computation and express the computed path through an effective segment list encoding (i.e., label stack), minimizing the segment list depth (SLD) (i.e., the number of labels included in the segment list). So far, no algorithms have been proposed to jointly provide path and segment list computation in SR-based networks. In this study, an efficient segment list encoding algorithm is proposed, guaranteeing optimal path computation and limited SLD in SR-based networks. The algorithm also accounts for equal-cost multiple paths and multiple constraints. The proposed algorithm is successfully applied to different network scenarios, demonstrating its flexibility in several use cases and showing effective performance in terms of segment list depth and introduced packet overhead.

Path Encoding in Segment Routing

Segment Routing (SR) is emerging as an innovative traffic engineering technique compatible with traditional MPLS data plane. SR relies on label stacking, without requiring a signaling protocol. This greatly simplifies network operations in transit nodes. However, it may introduce scalability issues at the ingress node and packet overhead. Therefore, specific algorithms are required to efficiently compute the label stack for a given path. This study proposes two algorithms for SR label stack computation of strict routes that guarantee minimum label stack depth. Then, SR scalability performance is investigated. Results show that, in most of the cases, SR uses label stacks composed of few labels and introduces a limited packet overhead. However, relevant scalability issues may arise in specific cases, e.g., large planar topologies.

Generalized L-out-of-K pulse position modulation for improved power efficiency and spectral efficiency

By combining multi-pulse pulse position modulation (PPM) with polarisation-switched QPSK (PS-QPSK) one can increase the spectral efficiency over simple PPM-PS-QPSK, or both the spectral efficiency and the asymptotic power efficiency over pure PS-QPSK.

Scalable approaches for path computation

Optimal and fast approaches for path computation are of paramount importance especially for the path computation elements (PCE) of generalized multi-protocol label switching (GMPLS) networks. To overcome the computational complexity, optimality must be traded for the execution time, enabling scalable computation. This paper considers the typical routing problems addressed by PCE and compares different optimization approaches based on integer linear programming (ILP) formulation and its relaxation, with the objective of assessing optimality and scalability of the approaches.

112Gbit/s RF assisted dual-carrier DP-16-QAM in installed and new build WDM applications

The performance of a 112Gbit/s dual-carrier DP-16-QAM channel in various WDM configurations is characterized. Variations of the dispersion map, ROADM count and system length are experimentally evaluated and compared with numerical simulation.

State of the Art on Transmission Techniques

Enabling long-haul and high-speed transmission has been the premier feature of fibre optics that has rendered it an attractive and successfully deployed technology. Although optical fibres are being engaged in several applications, such as signal processing, lasers and sensors, transmission systems remain a core and continuously evolving application leading to demonstrations of several Tbit/s over hundreds of kilometres. To achieve such impressive performances, several techniques have been investigated and applied. Wavelength division multiplexing (WDM), often combined with polarisation multiplexing, offers the means to exploit the large optical bandwidth. The aggregate transmission bit rate depends on the achievable bit rate per wavelength and the number of deployed wavelengths. The simplest and most straightforward approach based on intensity modulation and direct detection (IM/DD) is giving its place to more advanced techniques based on phase modulation and coherent detection. Combination of optical fibre transmission with digital signal processing (DSP) has opened a new window in transmission systems, facilitating the use of coherent detection and the mitigation of nonlinear effects, as well as allowing the application of advanced transmission techniques such as orthogonal frequency division multiplexing (OFDM). This chapter provides an overview of the state of the art of optical fibre transmission techniques.