Comparison of Performance of SSB-AMI-RZ Formats in Long-Haul 40 Gbit/s/channel UDWDM Transmission Systems

Abstract

The transmission performance of single-sideband alternate mark inversion return-to-zero (SSB-AMI-RZ) formats, with duty-cycles of 15%, 30% and 50%, in long-haul 40 Gbit/s/channel ultra dense WDM systems with 50 GHz of channel spacing is assessed through systematic numerical simulation. After optimizing the bandwidths and detuning of optical multiplexer and demultiplexer, the dispersion maps are optimized for each duty-cycle. From these, the tolerances to the in-line residual dispersion (IRD) and total residual dispersion (TRD), and the nonlinear thresholds (NLT) are assessed. It is shown that the different SSB-AMI-RZ formats have high tolerance to linear crosstalk, due to a -20 dB bandwidth much smaller than the channel spacing, and similar tolerance to IRD. Numerical results indicate that the format with duty-cycle of 15% outperform the others because of its better tolerance to TRD and higher NLT. Keywords: alternate mark inversion (AMI), dispersion map, fiber nonlinearity, nonlinear threshold, residual dispersion, single-sideband (SSB), ultra-dense wavelength division multiplexing (UDWDM). INTRODUCTIONThe trend in the next generation of wavelength division multiplexing (WDM) transmission systems is to achieve very high spectral efficiency (increasingly close to 1 bit/s/Hz). Such systems are called ultra dense WDM (UDWDM). To achieve that goal, it is mandatory to carefully investigate the spectral efficiency of the used modulation format, optimize the optical multiplexer (MUX) and demultiplexer (DMUX) and electrical filters, and the dispersion map [1]. Single-sideband (SSB) filtering has been proposed to attain high spectral efficiency. In particular, SSB filtering of alternate mark inversion return-to-zero (AMI-RZ) format -which presents low spectral content around the carrier frequency -was proposed to generate a signal with features suitable for UDWDM systems [2]. In [2], it was shown that the SSB-AMI-RZ format with a full-width-at-half maximum (FWHM) of 33% of the bit time, i.e. a duty-cycle of 33%, has better long-haul UDWDM transmission performance than the bandwidth-limited duobinary format considered in [3]. In addition, the UDWDM transmission performance of the SSB-AMI-RZ format may still be improved by choosing adequately the pulse shape and the duty-cycle of the AMI-RZ signal.The purpose of this work is to compare, through extensive numerical simulation, the performance and resilience to dispersion map and fiber nonlinearity of the SSB-AMI-RZ formats with three different duty-cycles in long-haul UDWDM transmission systems. The analysis considers a link with 10 spans of standard singlemode fiber (SSMF), a transmission bit rate of R b = 40 Gbit/s per channel, and a channel spacing of 50 GHz.