Henning Bülow

Fast adaptive control for electronic equalization of PMD

We propose an adaptive control scheme, based on the least mean squares algorithm, for electronic equalization of polarization mode dispersion. Fast adaptation is demonstrated by numerical simulations and experiments at 10 Gb/s.

Polarization QAM modulation (POL-QAM) for coherent detection schemes

A new polarization constellation diagram leads to polarization QAM modulation formats. At 28 Gband (112 Gb/s) POL-QAM 6-4 with six QPSK modulated states-of-polarization enables 1.7-dB higher sensitivity than PDM-QPSK by applying coded-modulation with an inner RS(511,455) FEC.

Experimental Demonstration of Optical Signal Detection Using Nonlinear Fourier Transform

The Ablowitz-Ladik-a mathematical tool for calculating the nonlinear Fourier transform (NFT) of a time-domain signal-is applied to coherently detected short 16-GBd BPSK sequences after transmission over a few spans of standard SMF fiber in lab. Decision schemes are investigated, which compare the nonlinear spectrum of received signal blocks consisting of a sequence of four BPSK symbols with a set of calculated reference spectra. Decision on the continuous part of the NFT spectrum was successfully demonstrated. At higher signal power performance, degradation was linked to peaks in the continuous amplitude spectrum. They are emerging at large signal noise and change depending on the noise seed and lead to an increased variance of the minimum distance criterion which was applied for decision. Decision based on the discrete part of the nonlinear spectrum worked successfully at high signal power. In particular, the position of one or more eigenvalues in the complex plane, referred to as eigenvalue pattern, exhibited a low variance for signal with noise and enable low error rate. However, the measurements also show that with increasing signal power, link length, and noise, the reliability of the proposed detection is limited, and further refinement of decision criteria seems necessary.

Performance of turbo equalizers for optical PMD channels

This paper investigates the performance of iterative (turbo) equalization to mitigate the effects of a polarization-mode dispersion (PMD) in nonreturn-to-zero (NRZ) intensity-modulated optical-fiber transmission systems. A PMD can lead to severe distortions in the received electrical signal and is a key limiter for the development of high-bit-rate transmission over currently used fibers. In order to reduce the distortions due to a PMD, the performance of symbol-by-symbol maximum a posteriori (sbs-MAP) soft-in/soft-out (SISO) decoders is studied. The SISO algorithms are adapted to the noise statistics of the optical channel where the photo detector leads to a non-Gaussian signal-dependent noise at the receiver side. The modified SISO algorithms are successfully employed for turbo equalization and results show that iterative (turbo) equalization and decoding for the compensation of a PMD can lead to a tremendous reduction in the bit error ratio (BER). Moreover, it is shown that, due to the robustness of mutual information, the extrinsic information transfer (EXIT) chart can be applied for the design of iterative receivers in optical transmission systems even with a non-Gaussian noise

Experimental Evaluation of Principal Mode Groups as High-Speed Transmission Channels in Spatial Multiplex Systems

The application of principal mode groups for the transmission of high bit rate data over OM4 graded-index multimode fiber (MMF) has been experimentally investigated. Eight principal mode groups have been identified as being suitable for spatially separated transmission channels at a wavelength of 1550 nm for the OM4 fiber. It has been shown that each of the eight mode groups can be used for the transmission of 10-Gb/s data over a 5-km-long graded-index MMF.

Experimental demonstration of nonlinear frequency division multiplexed transmission

We experimentally demonstrate an NFDM optical system with modulation over nonlinear discrete spectrum. Particularly, each symbol carries 4-bits from multiplexing two eigenvalues modulated by QPSK constellation. We show a low error performance using NFT detection with 4Gbps rate over 640km.

Stable coherent MIMO transport over few mode fiber enabled by an adiabatic mode splitter

Simulations confirm stable MIMO transport of three channels over a two mode fiber — even in the presence of fiber bending induced mode coupling — enabled by a new adiabatic mode splitter output coupler.

Electronic equalisation of PMD and chromatic dispersion induced distortion after 100 km standard fibre at 10 Gbit/s

Polarisation mode dispersion distortion equalisation with more then 11 dB power penalty reduction is demonstrated for the first time at 10 Gbit/s after 100 km standard fibre using electronic filtering in the receiver. We report on the combination of chromatic dispersion management using the dispersion supported transmission (DST) method and the compensation of the polarisation mode dispersion (PMD) distortion by an electronic equalisation filter realised in an optical receiver.

Transmission of 4-D modulation formats at 28-Gbaud

Transmission of a 4-D optimized format with the same spectral efficiency as PM-QPSK was experimentally investigated. Decision directed equalizer adaptation and phase estimation enabled detection of this format and PM-QPSK and coded POLQAM as well.

Experimental assessment of nonlinear fourier transformation based detection under fiber nonlinearity

16-GBd BPSK bursts transported over 3×80-km SMF with up to 12-dBm power were successfully detected by a maximum likelihood-nonlinear spectrum detection scheme using continuous or discrete part of the spectrum obtained by nonlinear Fourier transformation based processing in the receiver.