High capacity short-reach optical transmission system based on fiber-eigenmode multiplexing

Abstract

The fast development of bandwidth-hungry services is catalyzing the explosion of data in the current information and artificial intelligence (AI) era. Accordingly, the meteoric-growth capacity requirement has brought out the need to continuously accelerate the transmission rate to keep pace with the rapid-increasing traffic flow. Modedivision multiplexing (MDM), as an implementation of space-division multiplexing (SDM) technologies, is regarded as a promising solution to cope with the capacity crisis in fiber-based communication systems. Potentially, MDM can significantly increase the capacity of optical systems by multiplying the capacity of a single-mode fiber by the number of co-transmitted modes. Vector modes (VMs) are the full-vectorial eigenmodes supported by circular-core fibers. As true fiber-eigenmodes, VM-based MDM fiber transmission has captured much research interest recently. This thesis focuses on the studies of VM-based MDM short-reach optical transmission. The primary characteristic of fiber eigenmode is first investigated based on the high-order Poincaré sphere model. Then, the propagation characteristic of VM through free space and few-mode fiber (FMF) is studied. For free-space optical (FSO) transmission, the travel behavior of four VMs multiplexing-based link is evaluated under three atmospheric turbulence conditions. For FMF transmission, VM characteristic along the FMF transmission is simulated and presented. Based on VMs, two types of MDM short-reach fiber links, including uni-directional and bi-directional transmissions are demonstrated. For uni-directional transmission, two MDM links over 5 km FMF, including two VMs of the same order multiplexing transmission with 360 Gbit/s total capacity and two VMs of different orders multiplexing transmission with 400 Gbit/s total capacity are demonstrated based on Kramers-Kronig (KK) receiver, respectively. For bi-directional transmission, two MDM full-duplex bi-directional architectures including symmetrical and asymmetrical transmissions based on dual-VMs multiplexing over 3 km FMF are respectively implemented based on coherent detection and 2 × 2 MIMO. Firstly, four VMs, each carrying 14 GBaud quadrature phase-shift keying (QPSK) signal, is simultaneously employed on two terminals and a 224 Gbit/s homo-modal bi-directional transmission is demonstrated. To strengthen the immunity against backscattering crosstalk, hetero-modal bidirectional transmission is proposed, in which two VMs of l = 0 and two VMs of l = +2 are respectively utilized in the uplink and downlink and a 448 Gbit/s bi-directional transmission with 28 GBaud 16-ary quadrature amplitude modulation (QAM) modulation is realized. Furthermore, by combining with WDM technology, a 1.792 Tbit/s VM-based WDM-MDM full-duplex bi-directional transmission is also achieved. Next, a versatile scheme of MG filter for mode-group division multiplexing (MGDM) IM/DD transmission is proposed and experimentally demonstrated over 5 km FMF in a 152 Gbit/s MIMO-free IM/DD MGDM dual-channel simultaneous transmission and detection system. The bit error ratios (BERs) of each channel are below 7% hard-decision forward error correction (HD-FEC) threshold under both static and dynamic tests. Finally, unlike most MIMO-based SDM/MDM demonstrations without consideration of singular problems, non-Singular MIMO DSP based on multi-user constant modulus algorithm (MU-CMA) is implemented on the four-VMs-multiplexed KK reception system with an aggregate rate of 448 Gbit/s. None of the singular phenomena is observed under both static and dynamic performance evaluation.