Sean Kilmurray

Comparison of the nonlinear transmission performance of quasi-Nyquist WDM and reduced guard interval OFDM

The nonlinear transmission performance of quasi-Nyquist wavelength-division multiplexing (qN-WDM) and reduced guard interval orthogonal frequency-division multiplexing (RGI-OFDM) using polarization-division multiplexing quadrature phase-shift-keying (PDM-QPSK) and quadrature amplitude modulation (PDM-QAM-8 and PDM-QAM-16) with high information spectral densities have been compared for the first time, both by simulations and analytically. The results show that both systems are able to reach similar maximum transmission distances of approximately 6700km, 2600km and 1100km over standard single-mode fibre for the spectral efficiencies of 3.43 bits/s/Hz, 5.25 bits/s/Hz and 7 bits/s/Hz respectively.

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.

Efficient photonic coding: a considered revision

In this paper we reconsider the energy consumption of traditional DC-balanced physical line coding schemes applied to optical communication. We demonstrate that not only does an implementation of the popular 8B10B coding scheme have higher power consumption than the optical power requirement, but actually has higher power consumption when transmitting idle sequences than for real data packets. Furthermore, we show that simple codes retain the DC balance performance of 8B10B and hence do not increase the optical power requirement. We propose the use of a coding scheme that permits a default-off transmission system through the addition of a preamble. By analysis of trace data taken from a network covering a 24 hour period, we show that the power saving is up to 93%. The proposed approach not only enables energy proportional links but is fully compatible with future low power optical switched networks.

Linear and nonlinear impairment mitigation in a Nyquist spaced DP-16QAM WDM transmission system with full-field DBP

A RRC filter with a 0.1% roll-off factor reduces the impact of linear crosstalk-induced penalty in a Nyquist spaced 10GBd DP-16QAM transmission system with a net ISD of 7.47(b/s)/Hz and the maximum reach is extended to 1940km using full-field DBP.

Experimental characterisation of digital Nyquist pulse-shaped dual-polarisation 16QAM WDM transmission and comparison with the Gaussian noise model of nonlinear propagation

We describe an experimental investigation of the performance of a DP-16QAM Nyquist WDM transmission system operating at 10 Gbaud with 10.01 GHz channel spacing, with an information spectral density (ISD) of 6.66 b/s/Hz (gross ISD of 8 b/s/Hz, with 20% FEC overhead). With seven WDM channels, the maximum transmission distance with BER <; 1.5×10-2 over uncompensated standard single mode fibre with EDFA amplification was found to be 1940 km, similar to the value predicted by analytical calculation using the perturbative Gaussian noise model of nonlinear propagation.

Experimental demonstration of 30 Gb/s direct-detection optical OFDM transmission with blind symbol synchronisation using virtual subcarriers

The paper investigates the performance of a blind symbol synchronisation technique for optical OFDM systems based on virtual subcarriers. The test-bed includes a real-time 16-QAM OFDM transmitter operating at a net data rate of 30.65 Gb/s using a single OFDM band with a single FPGA-DAC subsystem and demonstrates transmission over 23.3 km SSMF with direct detection at a BER of 10(-3). By comparing the performance of the proposed synchronisation scheme with that of the Schmidl and Cox algorithm, it was found that the two approaches achieve similar performance for large numbers of averaging symbols, but the performance of the proposed scheme degrades as the number of averaging symbols is reduced. The proposed technique has lower complexity and bandwidth overhead as it does not rely on training sequences. Consequently, it is suitable for implementation in high speed optical OFDM transceivers.

Nyquist-WDM-based system performance evaluation

We describe an experimental evaluation of a Nyquist-WDM-based transmission system. Nine 10.7 GHz-spaced WDM channels were generated, carrying polarisation-division-multiplexed QPSK with digital Nyquist pulse shaping at 10 Gbaud. Back-to-back characterisation and long-haul transmission tests using a recirculating fibre loop are described, and a comparison of experimental performance with that predicted by theory, based on the Gaussian-noise model of nonlinear propagation, is carried out.

Nonlinear transmission performance of digital Nyquist WDM and optical OFDM

A key question for tomorrows transmission systems is which modulation format should be used for optimal transmission performance? Much recent work has focused on the comparison of Nyquist-WDM and orthogonal frequency division multiplexing techniques to maximise spectral efficiency. In this paper, we compare digital quasi-Nyquist WDM and reduced-guard-interval optical OFDM signal formats, in terms of their tolerance to fibre nonlinearity in long-haul spectrally-efficient transmission. Using computer simulations and closed-form analytical expressions for four-wave-mixing induced noise, the maximum transmission distances achievable with QPSK, QAM-8 and QAM-16 formats were calculated for links employing standard single mode fibre (SSMF) and ultra large area fibre (ULAF). Interestingly, these studies predict similar performance, in terms of achievable transmission performance, with digital quasi-Nyquist WDM and RGI-OFDM.

Nyquist-WDM PDM-QPSK transmission over SMF-28 fibre using URFL amplification

Nyquist-WDM PDM-QPSK transmission over standard SMF-28 fibre with novel distributed URFL amplification is reported for the first time. Transmission over 6157 km in a recirculating loop, and 320 km in an unrepeatered link without a ROPA were demonstrated.