Herbert Haunstein

Principles for electronic equalization of polarization-mode dispersion

System performance of optical fiber transmission in the presence of polarization-mode dispersion (PMD) can be improved by various types of electronic equalizers, which will be discussed in this paper. After a brief review of equalization and detection theory, equalizer concepts are adapted to the nonlinear optical channel and the architecture is optimized for high bit rate applications. Simulation results accounting for implementation losses in state-of-the-art technologies and realistic transmission conditions indicate that these concepts provide adequate solutions for equalization in lightwave transmission systems.

Comparison of system tolerance to polarization-mode dispersion between different modulation formats

The polarization-mode dispersion (PMD) tolerance of different modulation formats is studied, including ON-OFF keyed (OOK), differential phase-shift keyed (DPSK), and carrier-suppressed return-to-zero (CSRZ) formats. It is shown that, generally, for PMD uncompensated systems, the modulation formats with larger pulsewidth have larger penalty, while the modulation formats with smaller bandwidth perform better in PMD compensated systems. It is also shown that DPSK can tolerate more PMD than OOK for both PMD uncompensated and compensated systems, and that CSRZ, because of its specific spectrum characteristics, has a different feature from return-to-zero formats.

Design of near optimum electrical equalizers for optical transmission in the presence of PMD

An adaptive Viterbi equalizer and a decision feedback equaliser (DFE) for nonlinear intersymbol interference using a state-based probabilistic approach is proposed. The Viterbi equalizer design is suitable for high data rates and outperforms other concepts for high PMD.

Coded PDM-OFDM Transmission With Shaped 256-Iterative-Polar-Modulation Achieving 11.15-b/s/Hz Intrachannel Spectral Efficiency and 800-km Reach

We propose a novel coded modulation scheme for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) to achieve high-speed transmission at spectral-efficiencies near the Shannon limit. The proposed coding scheme relies on the concept of bit interleaved coded modulation with iterative decoding (BICM-ID), low-density parity-check (LDPC) codes, and shaped iterative polar modulation (IPM). To further increase the transmission spectral efficiency, reduced guard interval (RGI) CO-OFDM is used, in which fiber chromatic dispersion (CD) is digitally compensated prior to OFDM demultiplexing at the receiver. We experimentally demonstrate the generation and forward error correction (FEC) decoding of a 231.5-Gb/s RGI-CO-OFDM signal with 256-IPM subcarrier modulation, occupying a bandwidth of 20.75 GHz. The coded 256-IPM signal offers a coding gain of 15.1-dB compared to uncoded 256-point quadrature amplitude modulation (256-QAM) at a post-FEC bit error ratio of 10- 15. Transmission was demonstrated over an 800-km ultra-large-area fiber (ULAF) link with a record intrachannel spectral efficiency of 11.15-b/s/Hz.

Influence of PMD on the performance of optical transmission systems in the presence of PDL

Polarization dependent loss and polarization mode dispersion have been treated as separate phenomena in optical transmission systems. Simulation results indicate significant penalties from interaction of these effects, which must be considered in system design.

Performance Comparison of MLSE and Iterative Equalization in FEC Systems for PMD Channels With Respect to Implementation Complexity

Advanced electronic signal processing for high-bit-rate lightwave systems has become available recently. Adaptive receiver concepts are proposed to mitigate dynamic changes in the optical channel response. In particular, two different approaches are under discussion: independent equalization and decoding, e.g., by maximum-likelihood sequence estimation followed by a separate error-correction decoder, and a combined approach by iterative decoding of the channel correlations and the error-correction code. The authors compare the two concepts with respect to their mitigation capabilities in the presence of polarization mode dispersion. Special attention is paid to hardware implementation aspects, since the application of the concepts is severely limited by memory and signal processing requirements

Integrated design and operation of a transparent optical network: a systematic approach to include physical layer awareness and cost function [Topics in Optical Communications]

The manner and exact timing of the evolution of the widely used DWDM infrastructure to a transparent optical network is judged on economic circumstances and network performance. In this context this article elaborates on a methodology developed within the Project 1ST NOBEL, for integrating cost functions and other design constraints into the planning of a DWDM network while considering this evolution perspective to a transparent optical network. This systematic approach builds upon the experience of static network design and is substantiated by specific examples in this article

Control of combined electrical feed-forward and decision feedback equalization by conditional error counts from FEC in the presence of PMD

Combined control of an adaptive 3-tap feed forward and 2-tap decision feedback equalizer employing an adjustment of coefficients by means of conditional bit error ratio (BER) estimation based on forward error correction (FEC) is proposed.

Dynamic Performance and Speed Requirement of Polarization Mode Dispersion Compensators

To study the dynamic performance of a polarizationmode-dispersion compensator (PMDC), a continuous PMD model and a dynamic PMDC model are presented. The continuous PMD model generates continuous PMD and state of polarization (SOP) variations. The statistics of the SOP variation generated by the continuous PMD model follows the Rayleigh distribution, and the SOP variation amplitude scales with the square root of sampling-time interval. The results are compared with those of a numerical and a commercial polarization scrambler, and the difference of the SOP variation characteristics between the PMD model and the polarization scramblers is explained. The continuous PMD model and the dynamic PMDC model are used to study the dynamic performance and speed requirement of a two-stage PMDC. The speed requirement of the PMDC is quantified in the SOP variation in one PMDC loop cycle. The authors found that when the SOP variation is within 3deg in one PMDC loop cycle, the dynamic PMD and SOP changes virtually does not cause any degradation in the PMDC performance

Generation and FEC-decoding of a 231.5-Gb/s PDM-OFDM signal with 256-iterative-polar-modulation achieving 11.15-b/s/Hz intrachannel spectral efficiency and 800-km reach

A 231.5-Gb/s PDM-OFDM signal with 256-iterative-polar-modulation, outperforming 256-QAM by 1.2 dB in required OSNR after soft-FEC decoding, is generated, FEC-decoded, and transmitted over a record distance of 800 km with 11.15-b/s/Hz intrachannel spectral efficiency.