RESUMEN
The impacts of limited bandwidth on the nonlinear transmission performance are investigated by employing a truncated probabilistic shaped 64-ary quadrature amplitude modulation (TPS-64QAM) and a uniformly distributed 16-ary quadrature amplitude modulation (UD-16QAM) over a bandwidth-limited 75-GHz spaced 25-Tb/s (60 × 416.7â Gb/s) 6300-km transmission system. In terms of nonlinear performance measured by optimal launch power, theoretical analyses show that a 0.4-dB improvement could be introduced by UD-16QAM with respect to TPS-64QAM over a 6300-km transmission without limited bandwidth. However, contrary results would be observed that TPS-64QAM would outperform UD-16QAM by about 0.8â dB in terms of optimal launch power when the impacts of limited bandwidth are considered. Besides, numerical simulations and experimental results could both validate that about 1.0-dB optimal launch power improvement could be obtained by TPS-64QAM under bandwidth-limited cases, which is roughly similar to the results of theoretical analyses. Additionally, WDM experimental results show that all 60 tested channels could agree with the BER requirements by employing TPS-64QAM, further validating the superiority of TPS-64QAM compared to UD-16QAM under bandwidth-limited cases.
RESUMEN
In this paper, for the first time, a probability-aided maximum-likelihood sequence detector (PMLSD) is experimentally investigated through a 64-GBaud probabilistic shaped 16-ary quadrature amplitude modulation (PS-16QAM) transmission experiment. In order to relax the impacts of PS technology on the decision module, a PMLSD decision scheme is investigated by modifying the decision criterion of maximum-likelihood sequence detector (MLSD) correctly. Meanwhile, a symbol-wise probability-aided maximum a posteriori probability (PMAP) scheme is also demonstrated for comparison. The results show that the PMLSD scheme outperforms the direct decision scheme about 1.0-dB optical signal to noise ratio (OSNR) sensitivity. Compared with symbol-wise PMAP scheme, PMLSD scheme can effectively relax the impacts of PS technology on the decision module and a more than 0.8-dB improvement in terms of OSNR sensitivity in back-to-back (B2B) case is obtained. Finally, we successfully transmit the PS-16QAM signals over a 2400-km fiber link with a bit error ratio (BER) lower than 1.00×10-3 by adopting the PMLSD scheme.
RESUMEN
In this paper, a polar coded probabilistic shaping (PS) 8-ary pulse amplitude modulation (PAM8) based on many-to-one (MTO) mapping is investigated for short-reach optical interconnection. By ingeniously assigning parity bits to ambiguities positions, no extra PS redundancy and no complex distribution matcher are required in the scheme comparing to traditional probabilistic amplitude shaping (PAS). The noise distributions after different transmission distances are studied and an optimal clock recovery method for PS signal is proposed to degrade the impact of severe eye skew effect on BER performance. The experimental results show that up to 1.2 dB and 0.8 dB shaping gains are respectively achieved over back-to-back (BTB) and 2-km standard single mode fiber (SSMF) transmission. With the help of the proposed optimal clock recovery method in the PS scheme, the shaping gain is improved from 0.15 dB to 0.4 dB after 10-km transmission. Moreover, compared to low-density parity-check (LDPC) code, the polar coded PS-PAM8 can provide an additional coding gain of 2.2 dB with code length of 256, which proves the performance superiority of polar code in short code length. Therefore, the proposed polar coded PS-PAM8 with low complexity and satisfactory BER performance is believed to be an alternative solution for the cost-sensitive short-reach optical interconnection.