C.-A. Bunge

Analysis of nonlinear phase noise in single-channel return-to-zero differential phase-shift keying transmission systems

Self-phase modulation and intrachannel cross-phase-modulation- (IXPM) induced nonlinear phase noise is investigated by the variational method. IXPM can cause a considerable increase of phase noise. We show, however, that IXPM leads to a partial correlation between the phase noises of adjacent pulses, which tends to reduce the influence of nonlinear phase noise in return-to-zero differential phase-shift keying transmission. In highly dispersive transmission systems, intrachannel four-wave mixing-induced differential phase fluctuations are typically larger than differential nonlinear phase noise. The analysis is validated by Monte Carlo simulation.

Electronic precompensation of intrachannel nonlinearities at 40 gb/s

Digital electronic precompensation of intrachannel nonlinearities is studied in a transmission system which consists of 100% dispersion-compensated spans. Different Mach-Zehnder-based transmitter structures are compared. Simulation results demonstrate that using a triple Mach-Zehnder modulator achieves effective compensation of intrachannel nonlinear effects at large launch powers

Fiber Nonlinearities in Systems Using Electronic Predistortion of Dispersion at 10 and 40 Gbit/s

Electronic predistortion (EPD) to compensate for chromatic dispersion is an attractive option to replace inline optical dispersion compensation (ODC). In this paper, we present a study on the impact of intra- and interchannel nonlinearities in EPD systems compared to optimized ODC systems at 10 and 40 Gbit/s for NRZ-OOK modulation. First, the theoretically achievable nonlinear tolerance of EPD and ODC systems is studied by neglecting the EPD transmitters hardware limitations and the dispersion compensating fibers loss and nonlinearity. At 10 Gbit/s, EPD shows stronger degradations due to intra- and interchannel nonlinearities than optimized ODC. We extend existing studies for 10 Gbit/s EPD by analyzing the relevant launch power levels before interchannel nonlinearities limit the performance. The limit is 8 dB larger for ODC than EPD at 10 Gbit/s. In contrast, operating at a bit rate of 40 Gbit/s significantly reduces this difference in the nonlinearity tolerance between EPD and ODC both for single channel and WDM transmission. The maximum power per channel of 40 Gbit/s EPD is only 1 dB smaller compared to ODC. We then conduct a more realistic comparison at 40 Gbit/s by including the effects of 60 GSa/s digital-to-analog conversion with 4-bit quantization in the EPD transmitter and by considering the loss and nonlinearity of the dispersion compensating fiber. Analyzing the optical signal-to-noise ratio margins confirms that the performance of the realistic EPD system is similar to optimized ODC making EPD more attractive for electronic dispersion compensation at bit rates of 40 Gbit/s and above.

Electronic Dispersion Precompensation With a 10-Gb/s Directly Modulated Laser

We present 10-Gb/s transmission with a directly modulated laser (DML) avoiding inline dispersion compensating by electronic precompensation. To apply this technique of electronic dispersion precompensation to DMLs, a new approach based on artificial neural networks will be introduced. We realized a transmission of 190-km standard single-mode fiber in a laboratory experiment. Simulations show that compensation of up to 350 km can be achieved.

Impact of Pump-Phase Modulation on FWM-Based Wavelength Conversion of D(Q)PSK Signals

We investigate both theoretically and experimentally the impact of pump-phase modulation on differential phase shift keying (DPSK) and differential quadrature phase shift keying (DQPSK) signals in fiber-based parametric wavelength converters. It will be shown that the pump-phase modulation used to suppress stimulated Brillouin scattering introduces critical signal degradations and optical SNR penalties on DPSK signals, and more severe on DQPSK signals. Different modulation schemes will be theoretically investigated and the quantitative results are compared to system experiments. Finally, the theoretical results for a single conversion will be extended to multiple conversions to study the cascadability of the wavelength converter.

Applicability of DMD-measurements to new 10-Gigabit-Ethernet fibres

It is shown by simulations that all kinds of offset single-mode launch applied in differential mode delay measurements (DMD) can excite but only a small fraction of all guided modes, mainly modes of low azimuthal order. Furthermore it is demonstrated that vertical cavity surface emitting laser (VCSEL) launches featuring angular tilts, spatial offsets, or air gaps between connector and fibre end face also excite only a small group of modes. Finally it is shown that the mode groups excited by VCSEL launch are always a subset of the modes being examined by DMD measurements, and thus DMD measurements are applicable to the assessment of 10-Gigabit-Ethernet fibres.

Reduced complexity precoding based peak-to-average power ratio reduction applied to optical direct-detection OFDM

DCT based precoding is proposed for PAPR reduction to improve the performance of optical OFDM at limited precoding complexity. Effective PAPR reduction and the resultant OSNR performance are shown.

Reliability of power distribution condition for 10-Gigabit-Ethernet transmission

With the simulation of optical transmission over multimode fibre the restricted modal launch (RML) is analysed as a tool for fibre bandwidth characterisation. The analysis shows the influence of a fibre dip on most of the LP/sub 0.n/ modes. It is demonstrated that such central dip can affect the link bandwidth even if the proposed criteria of encircled flux are fulfilled. Thus, for certain types of fibres the RML measurement seems not sufficient for the quality assessment of 10-Gigabit-Ethernet transmission. For this reason the DMD criteria, which are proposed for fibre characterisation in the 10-Gigabit-Ethernet standardisation, is more powerful to ensure high bandwidth-length products for a variety of possible launches.

Cross-phase modulation suppression method in multispan dispersion-managed WDM transmission systems

The accumulation of signal distortion caused by cross-phase modulation in multiple spans is investigated. A new method for its suppression in 10-Gb/s, NRZ-ASK modulated WDM transmission systems is both experimentally and numerically demonstrated.

Perspectives of principal mode transmission in a multi-mode fiber

The concept of mode-division-multiplexing (MDM) using principal modes as carriers is investigated. MDM transmission is studied for an exemplary MMF with three modes. A transmission rate of 3×40Gbit/s appears feasible using a 50km MMF with a bandwidth-length-product of 3 GHz·km.