We propose and investigate a novel electronic dispersion compensation technique, in which signal precompensation is achieved using a dual-drive Mach-Zehnder modulator, driven by adaptive nonlinear digital filters. The results demonstrate effective compensation of over 13600 ps/nm, equivalent to 800 km of standard single-mode fiber, at 10 Gb/s.

Electronic dispersion compensation by signal predistortion using digital Processing and a dual-drive Mach-Zehnder Modulator

We present a simple, silica waveguide optical equalizer that significantly mitigates intersymbol interference (ISI) impairments for many wavelength-division multiplexed (WDM) channels simultaneously. We study the mitigation of ISI arising from band-limited transmitters, narrow-band optical filtering, chromatic dispersion, and polarization-mode dispersion (PMD). We demonstrate significant improvements, both single- and multichannel, at 40 Gb/s with a single, potentially set-and-forget device.

Simple multichannel optical equalizer mitigating intersymbol interference for 40-Gb/s nonreturn-to-zero signals

We have reviewed experimental and numerical results on electrical signal processing for the reduction of penalty induced in the optical domain. Since a few years integrated electronic equalizer circuits are available for 10 Gb/s operation. Penalty reduction of signal distorted by chromatic dispersion, PMD, and self-phase modulation has experimentally been demonstrated. First studies on equalization of DWDM typical crosstalk have already been conducted. Nevertheless, as compared to the decade long experience with dynamic equalization of thermal noise limited signal, for amplified optical signal limited by the optical signal-to-noise-ratio (OSNR) the residual penalty after equalization roughly doubles and the fast responding LMS adaptation leads to a sub-optimum setting of the equalizer failing the optimum by up to 0.8 dB which can be avoided by the slower steepest-descend scheme which optimising Q-factor related criteria at equalizer output.

Electronic equalization of transmission impairments

We present simulations of novel electronic signal processing techniques that may be used to greatly improve the dispersion tolerance of DBPSK and DQPSK modulation formats by at least a factor of two.

Electronic signal processing for differential phase modulation formats

Duobinary signaling is combined with a proposed electrical pre-equalization scheme to extend the reach of 10-Gb/s signals that are transmitted over standard single-mode fiber. The proposed scheme is based on predistorting the duobinary signal using two T/2-spaced finite-impulse response (FIR) filters. The outputs of the FIR filters then modulate two optical carriers that are in phase quadrature. Simulation results show that distances in excess of 400 km at bit-error rates less than 10/sup -15/ are possible. Incorporating a forward-error correction scheme can extend the reach to distances in excess of 800 km. The reach limitation arises not from chromatic dispersion but from fiber nonlinearity, relative intensity noise due to phase-modulation-to-amplitude-modulation noise conversion, and optical amplifier noise accumulation. To demonstrate the feasibility of implementing the proposed scheme, a test chip is implemented in a 0.5-/spl mu/m SiGe BiCMOS technology. The chip incorporates two 10-tap T/2-spaced FIR filters, which are sufficient to equalize a 10-Gb/s duobinary signal that is transmitted over distances in excess of 400 km. The pre-equalization capabilities of the chip are tested by postprocessing the measured chip output to mimic the effects of the optical channel.

An electrically pre-equalized 10-Gb/s duobinary transmission system

At 10 Gbit/s a 3.3 dB reduction of the power penalty induced by the chromatic dispersion of an 127 km standard single-mode fiber (G.652) has been achieved (BER=10/sup -9/, PRBS 2/sup 23/-1) by processing the detected signal in the receiver with a nonlinear equaliser realized as SiGe integrated circuit.

T. Wehreu

Papers

Reduction of the chromatic dispersion penalty at 10 Gbit/s by integrated electronic equalisers