No abstract

In this paper, we have designed a low-overhead lowcomplexity carrier phase tracking scheme for OFDM-based superchannel transmission system enabled by optical frequency combs. In this scheme, taking advantage of the broadband phase coherence provided by optical frequency combs among the OFDMbands, the carrier phase retrieved from pilot-subcarriers of the OFDM-band on the central wavelength channel is reused for the OFDM-bands on the other wavelength channels. In this case, the overall pilot-subcarrier overhead and DSP complexity is significantly reduced since the pilot-subcarriers occupy a small fraction of the overall OFDM bandwidth. The feasibility of this joint-carrier phase tracking scheme has been verified successfully via comprehensive simulation, where results show that the BER threshold for soft-decision FEC could be achieved for 50GHzspaced 5-band 4-QAM, 8-QAM, 16-QAM and 32-QAM OFDMbased superchannel signals with zero guard-band and both laser and nonlinear phase noise effects after 7000km, 4000km, 3000km and 2000km SSMF transmission respectively. The simulation results show that there exist chromatic dispersion-induced differential phase offset among the OFDM-bands whose impact on joint-carrier phase tracking depends on the modulation format, channel count and fiber length. Finally, we demonstrate experimentally the feasibility performance of the designed masterslave carrier phase tracking technique for comb-based OFDMbased superchannels.

Residue number system (RNS) is a promising technology for high speed, power efficient and fault tolerant hardware design. The reason is that in RNS, arithmetic operations are performed in parallel, thus reducing delays due to carry operations. Additionally, RNS computations are faster than binary computations because of the reduced wordlength due to modulo operations. Despite the advantages of RNS, its performance depends on the moduli set and the reverse conversion algorithm used to convert the residue numbers back to binary form. There is therefore the need to select the moduli set and the reverse conversion algorithm carefully so that the performance of the RNS hardware is not overshadowed by reverse conversion overheads. This paper proposes an 8n bit moduli set 2 4 , 2 2 + 1, 2 + 1, 2 − 1 and a reverse conversion hardware architecture based on the new Chinese remainder theorem I(new CRT I). Compared to existing hardware architecture, the proposed architecture shows good balance between the hardware cost efficiency and speed efficiency. Secondly, the proposed architecture outperforms existing systems in terms of cost-delay square (Δ 2).