(a) (b)
Fig.3. Measured 16-QAM eye-diagrams at the transmitter when using: (a) the RRC filter, and (b) the optimized filter.
(a)
(b)
(c)
Figure 4. BER vs OSNR (noise bandwidth = 0.1 nm) for back-to-back (a), 800 km (b) and 1200 km (c).
For systems using multi-bit DACs operating at the Nyquist rate, the main advantage of the optimized pulse approach is that it is implemented at no extra hardware or computational cost, since the optimized pulse shaping function replaces the existing shaping filters. Yet another option would be to synthesise the optimized pulse transfer function by analog filters, thus enabling the use of simpler 2-bit DAC structures clocked at the baud rate.
4. Conclusion
The characteristics of an optimized pulse shape specifically designed to increase the nonlinear tolerance of long-haul optical transport systems were described. The specialized pulse was used in a 10 Gbaud DP-16-QAM transmission experiment and was demonstrated to significantly reduce the impact of intra-channel nonlinearities.
The authors would like to acknowledge the NSERC/Bell Canada Industrial Research Chair Program.
5. References
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