A two-way 224-Gbit/s PAM4-based fibre-FSO converged system

Hai-Han Lu,Yu-Ting Chen,Chung-Yi Li,Ting Ko,Wen-Shing Tsai,Poh-Suan Chang,Chen-Xuan Liu,Yan-Yu Lin

doi:10.1038/s41598-021-04315-3

Abstract

A two-way 224-Gbit/s four-level pulse amplitude modulation (PAM4)-based fibre-free-space optical (FSO) converged system through a 25-km single-mode fibre (SMF) transport with 500-m free-space transmission is successfully constructed, which adopts injection-locked vertical-cavity surface-emitting lasers with polarisation-multiplexing mechanism for a demonstration. Compared with one-way transmission, two-way transmission is an attractive architecture for fibre-FSO converged system. Two-way transmission over SMF transport with free-space transmission not only reduces the required number of fibres and the setups of free-space transmission, but also provides the advantage of capacity doubling. Incorporating dual-wavelength four-level pulse amplitude modulation (PAM4) modulation with polarisation-multiplexing mechanism, the transmission capacity of fibre-FSO converged system is significantly enhanced to 224 Gbit/s (56 Gbit/s PAM4/wavelength × 2-wavelength × 2-polarisation) for downlink/uplink transmission. Bit error rate and PAM4 eye diagrams (downstream/upstream) perform well over 25-km SMF transport with 500-m free-space transmission. This proposed two-way fibre-FSO converged system is a prominent one not only because of its development in the integration of fibre backbone with optical wireless extension, but also because of its advantage in two-way transmission for affording high downlink/uplink data rate with good transmission performance.

Highlights

A two-way 224-Gbit/s four-level pulse amplitude modulation (PAM4)-based fibre-free-space optical (FSO) converged system through a 25-km single-mode fibre (SMF) transport with 500-m free-space transmission is successfully constructed, which adopts injection-locked vertical-cavity surface-emitting lasers with polarisation-multiplexing mechanism for a demonstration
To the best of our knowledge, this system is the first to practically construct a two-way PAM4based fibre-FSO converged system with a high downlink/uplink transmission rate of 224 Gbit/s. Since that both downlink and uplink PAM4 data signals are transmitted by the same SMF, the Rayleigh backscattering (RB) noise is considered in this two-way PAM4-based fibre-FSO converged s ystem[19,20,21]
Injection locking behavior happens as a slave laser (VCSEL1) with a wavelength that is a slightly shorter than that of the master laser [distributed feedback (DFB) laser diode[1] (LD1)]

Summary

Introduction

A two-way 224-Gbit/s four-level pulse amplitude modulation (PAM4)-based fibre-free-space optical (FSO) converged system through a 25-km single-mode fibre (SMF) transport with 500-m free-space transmission is successfully constructed, which adopts injection-locked vertical-cavity surface-emitting lasers with polarisation-multiplexing mechanism for a demonstration. To meet the targets of long-haul transmission and high transmission capacity, a two-way 224-Gbit/s four-level pulse amplitude modulation (PAM4) fibre-FSO converged system through 25-km SMF transport with 500-m free-space transmission is thereby established, adopting injection-locked vertical-cavity surface-emitting lasers (VCSELs) with polarisation-multiplexing mechanism. A two-way 224-Gbit/s PAM4-based fibre-FSO converged system over 25-km SMF transport with 500-m free-space transmission is constructed, which adopts directly modulated VCSELs with polarisation-multiplexing mechanism and injection-locked technique as a presentation. Results show that such proposed two-way 224-Gbit/s PAM4-based fibre-FSO converged system is advantageous for developing a two-way long-haul fibre communication with free-space transmission It can be used in actual commercial systems to provide communication links in specific areas where RF communications are prohibited, such as in hospitals, in cabins or in oil refineries. A two-way fibre-FSO converged system with ultra-longhaul transmission and ultra-high transmission capacity is expected to be built by adopting PAM4 modulation and multi-stage injection-locked V CSELs24 with polarisation-multiplexing mechanism

Methods

Results

Conclusion