Delivering 5G NR data by multiplexing OAM modes over an OAM fiber

Abstract

In order to enhance channel capacity (CC) and propagation distance, a new radio (NR) in sub-THz band (STB) is employed and propagated over an orbital angular momentum (OAM) fiber for delivering user data by OAM-based space-division multiplexing (SDM). For propagating the STB wave, A weakly-coupled optical fiber (WCOF) with four layers is designed and manufactured in our Lab for propagation OAM beams, where 6 OAM groups (OAMGs) can be supported with a larger difference of effective refraction index among different OAMGs. A propagation loss of less than 3.2 dBm/km for 6 OAMGs at 1550 nm is achieved in the proposed WOCF. A probative platform is also built for denoting the feasibility of the proposed scheme. Besides OAMG 0 without OAM, the OAM mode with an integral topological charge (TC) of −1/-2/-3/-4/-5 is utilized as the representative of OAMG 1/2/3/4/5 in the experiments, respectively. The captured intensities and interference patterns depict that the propagated five OAM beams can be successfully detected at receiving side, which shows that the proposed method is feasible. Bit error rates (BERs) and constellation plots (CPs) are also adopted for analyzing the performances of the proposed concept, respectively. When the SDM is employed or not, the measured BERs for five OAM channels with TC = −1, −2, −3, −4 and −5 degrade by 0.61/2.8, 0.83/3.21, 1.27/3.64, 1.63/4.05 and 1.98/4.39 dB compared with “BTB”, respectively, where a less than 2/5 dB degradation without/with SDM can be achieved. A less than 3 dB degradation for five OAM modes between “W/O SDM” and “W/SDM” can be observed, which can be contributed to the crosstalk induced by SDM. In addition, the measured CPs of 16-quadrature amplitude modulation (QAM) in five OAM channels are consistent with the measured BER distributions at an optical signal to noise ratio of 15.2 dB. Moreover, the influences of data speed and fiber length on the BER distributions are also explored, where the BER of the monitored channel of TC = −5 decreases as the data speed or fiber length increases. Compared to the data rate, the fiber length is more sensitive to fiber length. Although, the propagation loss can be degraded by reducing contrast of refraction index against the cladding (CRIC) between core layer and cladding for achieving a long-haul propagation, the number of OAM modes is also decreased. Consequently, the propagation distance and the supported number of OAM modes should be overall considered for balance in practical applications.