Comparison of kramers–kronig and coherent receivers for few-mode long-haul optical transmission

The nonlinear effects in single-mode fiber and the constraints in device technology, time division multiplexing and wavelength division multiplexing cannot increase the capacity of optical fiber communication system unlimitedly. The development of space division multiplexing technology has increased the capacity of existing optical fiber communication systems by at least an order of magnitude. With the continuous improvement of transmission rate and system bandwidth in the long-haul communication, low cost and small size are also regarded as important factors in the future. In this work, the transmission performance of the low-cost self-coherent receiver and the mature coherent receiver in the long-haul mode division multiplexing system is compared. In the 32-Gbaud 6-mode dual-polarization QPSK transmission system with a fiber length of 80 km as the single span, two receiver schemes are compared considering the same configurations of the transmitter and the optical fiber link components. Compared the use of eight photodetectors integrated in the coherent receiver, the Kramers–Kronig (KK) receiver only requires two photodetectors to demodulate the dual-polarization transmission, while the phase recovery algorithm based on Hilbert transform in the KK receiver will increase the complexity of digital signal processing. Numerical results indicate that the KK receiver scheme has the advantages of lower cost and more compact size and shows the similar performance as the coherent receiver for the transmission of less than 2500 km, despite the requirement of larger transmitted power and algorithm complexity. It can also be concluded that, self-coherent receiver based on the KK algorithm can be a complementary detection solution to the coherent receiver for next-generation long-haul transmission networks with low-cost transceivers

A de novo evolved gene contributes to rice grain shape difference between indica and japonica

Abstract The role of de novo evolved genes from non-coding sequences in regulating morphological differentiation between species/subspecies remains largely unknown. Here, we show that a rice de novo gene GSE9 contributes to grain shape difference between indica/xian and japonica/geng varieties. GSE9 evolves from a previous non-coding region of wild rice Oryza rufipogon through the acquisition of start codon. This gene is inherited by most japonica varieties, while the original sequence (absence of start codon, gse9) is present in majority of indica varieties. Knockout of GSE9 in japonica varieties leads to slender grains, whereas introgression to indica background results in round grains. Population evolutionary analyses reveal that gse9 and GSE9 are derived from wild rice Or-I and Or-III groups, respectively. Our findings uncover that the de novo GSE9 gene contributes to the genetic and morphological divergence between indica and japonica subspecies, and provide a target for precise manipulation of rice grain shape