Abstract
An experimental demonstration of direct-detection single-sideband Nyquist-pulse-shaped 16-QAM subcarrier modulated (Nyquist-SCM) transmission implementing a receiver-based signal-signal beat interference (SSBI) cancellation technique is described. The performance improvement with SSBI mitigation, which compensates for the nonlinear distortion caused by square-law detection, was quantified by simulations and experiments for a 7 × 25 Gb/s WDM Nyquist-SCM signal with a net optical information spectral density (ISD) of 2.0 (b/s)/Hz. A reduction of 3.6 dB in the back-to-back required OSNR at the HD-FEC threshold was achieved. The resulting reductions in BER in single channel and WDM transmission over distances of up to 800 km of uncompensated standard single-mode fiber (SSMF) achieved are presented.
Highlights
There is a continuously increasing demand for high bandwidth transmission due to data intensive services such as IP video, scientific and cloud computing, requiring low-cost and spectrally-efficient optical transmission systems in access, metropolitan and regional optical links [1, 2]
It was important to optimize the carrier-to-signal power ratio (CSPR) for each optical signal-to-noise ratio (OSNR) value, individually for the cases with and without signal-signal beat interference (SSBI) mitigation
It can be seen that the required OSNR at the 7% overhead hard-decision forward-errorcorrection (HD-FEC) threshold is found to be 20.7 dB without SSBI compensation, with an improvement by 4.2 dB to 16.5 dB for the case with SSBI compensation
Summary
There is a continuously increasing demand for high bandwidth transmission due to data intensive services such as IP video, scientific and cloud computing, requiring low-cost and spectrally-efficient optical transmission systems in access, metropolitan and regional optical links [1, 2]. Nyquist-pulse-shaped subcarrier modulation was proposed in [9, 10]. It has been shown that single-sideband (SSB) Nyquist-SCM with direct detection is a promising and practical spectrally-efficient modulation technique for metro and access networks [11]. A QAM signal is filtered using Nyquist pulse shaping, and modulated onto a single subcarrier. The generated pass-band (up-converted) signal is transmitted together with an optical carrier and is detected by a single-ended photodiode. If the SCM technique is performed, both the amplitude and phase information of the subcarrier can be recovered after direct detection from the beating between optical carrier and subcarrier signal. In order to maximize the spectral efficiency, high-order QAM encoding, Nyquist pulse shaping, a subcarrier frequency lower than the symbol rate and digital sideband filtering to generate a SSB signal are all implemented. NyquistSCM requires a lower optical signal-to-noise ratio (OSNR) and has improved transmission performance [12]
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