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Performance of 3 Â 10 Gbps duty-cycle division multiplexing (DCDM) is analyzed. The channel demultiplexing is performed electronically at single user bit rate (10 Gbps). At 30 Gbps, null-to-null spectral width of 80 GHz is measured for DCDM technique which is 33.3% less compared to 30 Gbps conventional return-to-zero (RZ). In this system, the worst channel required a receiver sensitivity of around À25:6 dBm at bit error rate (BER) 10 À9 . The chromatic dispersion tolerances of the system are 210.5 and 236 ps/nm for the worst and the best channel respectively.

An improved estimation of bit-error-rate (BER) for electrically multiplexed duty-cycle division multiplexing (E-DCDM), which is based on the probability of error, is presented. Performance of 3 × 10 Gbit/s E-DCDM is investigated in terms of optical signal-to-noise ratio (OSNR) and dispersion tolerance. This technique requires 29.4 dB OSNR and can tolerate ±96 ps/nm chromatic dispersion for the worst user.

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The effect of self-phase modulation (SPM) on 40 Gb/s absolute polar duty cycle division multiplexing (AP-DCDM) is investigated and reported. The study includes the influence of launched power, number of channels and dispersion compensation method. Dispersion postcompensation and combination of dispersion pre-and post-compensation are used to manage the transmission links. At high powers, SPM degrades the pulse recompression process and provides an upper bound on the AP-DCDM transmitted pulse energy. It is demonstrated that the 40 Gb/s AP-DCDM system shows a 4.1 dB improvement and less than 1 dB penalty in terms of SPM tolerance in comparison to 40 Gb/s 4-ary and on off-keying (OOK) systems, respectively. The SPM effect is stronger in the 100 post-compensated link than that in the combination of pre-and post-compensated links. Dispersion pre-compensation of 18 22 is found as the optimum range of pre-compensation ratio for AP-DCDM system, which makes optimisation of the launched power possible.

The performance assessment of a novel multilevel modulation format based on partial-response signalling called absolute added correlative coding (AACC) by numerical simulations is delineated, targeting short-range and interconnect high-speed optical networks. The spectral efficiency, chromatic dispersion tolerance and receiver sensitivity of 4-instensity level AACC are discussed and compared against other well-known existing modulation formats, namely, non-return-to-zero on-off keying and 4-ary pulse-amplitude modulation (4-PAM). The robustness of the higher order of AACC over 8-PAM and 16-PAM is also discussed.Introduction: The development of multilevel modulation formats and detection techniques is essential in enabling efficient high-speed and high-bit rate optical fibre links, such as the 40 G synchronous optical networking/synchronous digital hierarchy and 100 G Ethernet [1]. The goal of utilising higher-order modulation formats with coherent detection and digital signal processing is to set up a high-capacity optical communications system that combines high spectral efficiency and long transmission distance capability [1]. In contrast, intensitymodulated direct-detection (IM/DD) is more suitable for short-range applications, e.g. optical interconnects, storage area networks and data centres. Recently, on-off keying (OOK) and 4-pulse-mplitude modulation (PAM) are receiving mounting attention in short-range optical interconnects because of their outstanding performances and low cost [2]. However, M-PAM has an inherent back-to-back receiver sensitivity penalty in comparison with OOK.Partial-response signalling is an effective candidate in achieving narrow spectral width and high resilience to fibre dispersion; it was fruitfully demonstrated as binary signals, namely duobinary or phase-shaped binary transmission, and has received much attention recently for the long-haul 40 Gbit/s system [3]. However, the concept of the partialresponse format has never been applied in multilevel-intensity signalling.We therefore suggest in this Letter a novel approach of generating a 4-intensity level signal based on partial-response signalling, called absolute added correlative coding (AACC) in a 20 GBaud (40 Gbit/s) lightwave system.

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