Stephan Pachnicke

Physical Impairment Based Regenerator Placement and Routing in Translucent Optical Networks

A novel constraint-based routing (CBR) algorithm taking into account the dominant linear and nonlinear fiber optical transmission impairments has been analyzed. It is shown that CBR and intelligent regenerator placement decrease the blocking probability significantly.

Assessment of a constraint-based routing algorithm for translucent 10Gbits/s DWDM networks considering fiber nonlinearities

We present a constraint-based routing (CBR) approach for real-time operation considering both linear as well as nonlinear signal quality degrading effects in a heterogeneous network infrastructure. Different novel routing algorithms are assessed regarding their blocking probabilities. Furthermore, regenerator pools are placed at a limited number of nodes selected by a heuristic algorithm taking into account the physical impairments. It is shown that CBR together with intelligent regenerator placement can decrease the blocking probability significantly.

Physically constrained routing in 10-gb/s DWDM networks including fiber nonlinearities and polarization effects

Dynamic optical communication systems require fast assessment of the signal quality of the desired path through the network. This paper presents an analytical approach for describing the Q-factor due to linear (group velocity dispersion, noise, and polarization-mode dispersion) as well as the dominant nonlinear effects in 10-Gb/s nonreturn-to-zero ON-OFF keying transmission systems

Access Networks Based on Tunable Lasers

State-of-the-art, prospects, and challenges of next-generation optical access technology based on tunable lasers are discussed. These considerations can also be applied to various backhaul and mobile fronthaul applications since these have similar characteristics and requirements, and have to share at least part of the optical distribution networks. Potential advantages of tunable lasers over competing approaches (e.g., seeded reflective transmitters) include higher bit-rate × reach products and better tolerance to reflections in the fiber plant. Today, the main issue is still the lack of available low-cost tunables with sufficient tuning range and launch power. However, significant progress has been made in the last few years to bring such lasers closer to commercialization. In this paper, we will review low-cost tunable laser approaches and report on latest technical results. We will also give an overview on current standardization activities and give an outlook on next-generation optical access, backhaul and fronthaul networks which also support active-site consolidation.

Signal-signal beat interference cancellation in spectrally-efficient WDM direct-detection Nyquist-pulse-shaped 16-QAM subcarrier modulation

An experimental demonstration of direct-detection single-sideband Nyquist-pulse-shaped 16-QAM subcarrier modulated (Nyquist-SCM) transmission implementing a receiver-based signal-signal beat interference (SSBI) cancellation technique is described. The performance improvement with SSBI mitigation, which compensates for the nonlinear distortion caused by square-law detection, was quantified by simulations and experiments for a 7 × 25 Gb/s WDM Nyquist-SCM signal with a net optical information spectral density (ISD) of 2.0 (b/s)/Hz. A reduction of 3.6 dB in the back-to-back required OSNR at the HD-FEC threshold was achieved. The resulting reductions in BER in single channel and WDM transmission over distances of up to 800 km of uncompensated standard single-mode fiber (SSMF) achieved are presented.

Spectrally Efficient WDM Nyquist Pulse-Shaped 16-QAM Subcarrier Modulation Transmission With Direct Detection

The ability to transmit signals with high information spectral density (ISD) using low-complexity and cost-effective transceivers is essential for short- and medium-haul optical communication systems. Consequently, spectrally efficient direct detection transceiver-based solutions are attractive for such applications. In this paper, we experimentally demonstrate the wavelength-division multiplexed (WDM) transmission of 7×12 GHz-spaced dispersion pre-compensated Nyquist pulse-shaped 16-QAM subcarrier modulated channels operating at a net bit rate of 24 Gb/s per channel, and achieving a net optical ISD of 2.0 b/s/Hz. The direct detection receiver used in our experiment consisted of a single-ended photodiode and a single analog-to-digital converter. The carrier-to-signal power ratio at different values of optical signal-to-noise ratio was optimized to maximize the receiver sensitivity performance. The transmission experiments were carried out using a recirculating fiber loop with uncompensated standard single-mode fiber and EDFA-only amplification. The maximum achieved transmission distances for single channel and WDM signals were 727 and 323 km below the bit-error ratio of 3.8 × 10-3, respectively. To the best of our knowledge, this is the highest achieved ISD for WDM transmission in direct detection links over such distances.

PHOTOSS: the simulation tool for optical transmission systems

A general modeling and simulation strategy suitable for the fast and accurate analysis of a fiber-optical WDM system is presented, that may also include multi-span systems. Noise and fiber dispersion are considered as well as nonlinear effects like four wave mixing, self-phase modulation and cross-phase modulation. Furthermore, amplified spontaneous emission noise of the optical amplifiers and polarization-dependencies (e.g. PMD) are taken into account. Performance evaluation by means of eye patterns, spectral power densities, optical signal-to-noise ratio, the Q-Factor and the bit error rate are addressed. An analysis of the degradation effects against the position within the fiber is shown to get a better overview of the fibers behavior. An improved Split-Step algorithm is outlined as a fast alternative to supplement the FFT calculation within the fiber. A parameter variation, which can also be influenced during the simulation by the user, is presented in order to get an overview of the parameter space. Different modulation formats are taken into account, e.g. return-to-zero, non-return-to-zero and differential phase-shift keying. Both the separated channels and the total field approach are demonstrated. In the separated channels approach the different nonlinear effects can be switched on and off independently for detailed studies of inter-channel effects. Based on this work, a complete design environment (PHOTOSS, The Photonic System Simulator) has been developed. This simulation tool has been tested extensively by several industry partners. Simulation examples are presented here e.g. for PMD simulations.

Nyquist-shaped dispersion-precompensated subcarrier modulation with direct detection for spectrally-efficient WDM transmission

We report on the first experimental demonstration of 14 Gb/s direct detection single-sideband subcarrier modulated Nyquist QPSK transmission. Using electronic pre-compensation, transmission over 800 km of dispersion-uncompensated standard single-mode fiber was achieved.

Online physical-layer impairment-aware routing with quality of transmission constraints in translucent optical networks

We propose a novel online physical-layer impairment-aware routing algorithm taking into account a minimum quality of transmission (QoT) constraint, which must be satisfied in all cases, even if the network load is changing, and new channels are activated. Our online constraint-based routing (CBR) algorithm considers the actual network load to get a more exact prediction of the signal quality degradation due to (multi-channel) nonlinear fiber impairments. We present results showing that the proposed online CBR algorithm is superior to shortest path routing with maximum transparent distance constraints as well as offline CBR algorithms, which are based on worst-case Q-factor penalties, in terms of blocking probability.

First demonstration of a full C-Band tunable WDM-PON system with novel high-temperature DS-DBR lasers

We demonstrate automatic operation of a cooler-less tunable-laser based WDM-PON system. Using a pilot-tone based overhead channel and centralized wavelength locking scheme, 1 Gb/s and 10 Gb/s data transmission is demonstrated in a multi-user set-up.