RESUMO
We propose a low-complexity frequency domain frame synchronization method for short-reach intensity modulation and direct detection (IM/DD) systems. A four-level pulse amplitude modulation-training sequence (PAM4-TS) is specially designed for the proposed method, which has an obvious peak in the amplitude spectrum that is higher than the normal signal. The proposed method comprises a coarse synchronization stage and a fine synchronization stage. Firstly, the coarse synchronization stage takes advantage of the feature of PAM4-TS to obtain the approximate position of the frame head by identifying the peak value in amplitude spectrum of the segmented received signal. Then, the fine synchronization stage calculates the correlation between the coarse synchronization result and PAM4-TS by multiplying the two in the frequency domain. Compared with the traditional sliding window correlation method realized in the time domain, both simulation and experimental results of C-band 50 Gbit/s PAM4 transmission demonstrate that the proposed method reduces the multiplication complexity by up to about 96.01% without any additional performance penalty.
RESUMO
We systematically studied several of the most traditional hollow-core anti-resonant fiber (HC-ARF) structures, with the aim of achieving low confinement loss, single-mode performance, and high insensitivity to bending in the 2 µm band. Moreover, the propagation loss of fundamental mode (FM), higher-order mode (HOMs), and the higher-order mode extinction ratio (HOMER) under different geometric parameters were studied. Analysis showed that the confinement loss of the six-tube nodeless hollow-core anti-resonant fiber at 2 µm was 0.042 dB/km, and its higher-order mode extinction ratio was higher than 9000. At the same time, a confinement loss of 0.040 dB/km at 2 µm was achieved in the five-tube nodeless hollow-core anti-resonant fiber, and its higher-order mode extinction ratio was higher than 2700.