Multi-user, low-loss, and cost-efficient characteristics are highly desired for widely deployed passive optical networks (PON), which are constrained by the upstream power combining loss induced by optical splitters in optical distribution networks (ODNs). We propose a multi-user low-upstream-loss PON utilizing graded-index multi-mode fiber (GI-MMF) and a compact ODN constructed by a multi-mode transformer (MMT) for the first time. Enabled by the MMT, the ODN achieves multi-mode multiplexing for low-loss combining in upstream and power splitting in downstream, simultaneously. An implementation approach for MMT using a single MPLC is also proposed, and a 44-mode MPLC-based MMT is designed for verification. Simulation results show that the device achieves a combining loss of lower than 1.13 dB and a modal crosstalk of lower than −19.5 dB in upstream and an excess splitting loss of less than 1 dB in downstream for all modes. The bandwidth characteristics and tolerance are also investigated through simulation.
The evolution of data centers' architecture and networks has been driven by cloud computing, 4/5G core networks virtualization, 5G services and artificial intelligence. Future data centers are evolving from centralized data centers to “data center clusters”. Therefore, interworking of “data center clusters” becomes more important than ever. The requirements of quality, bandwidth, latency and reliability of Data Center Interconnection (DCI) networks need to be met. Taking into account the characteristics of the data center architecture and traffic, several directions in next-generation DCI network have been pointed out, including SRv6-based efficient IP connection, hard network slicing supporting multi-services, ultra-low latency, software defined network-based strong control and high reliability. Neither traditional Ethernet switches/routers nor optical interconnection networks can easily meet these requirements simultaneously. Therefore, a completely new technology - Metro Transport Network (MTN) has been proposed. It brings the TDM characteristics based on the Ethernet systems and is capable of hard network slicing, ultra-low latency and ultra-high time synchronization accuracy. In this article, the MTN concept, ITU-T standardization work and its advantages for DCI are introduced. A field trial of an interconnection of three data centers via a commercial MTN network was presented as well. Virtual machine migration, dual-active storage backup and file delivery services were successfully implemented during the field trial. The results have verified that MTN interconnections can achieve hard slicing and a significant reduction of latency, jitter and switching time, which well match the requirements of next-generation DCI networks.
Weakly-coupled mode-division multiplexing (MDM) transmission technique over widely-deployed multimode fiber (MMF) is considered a promising approach to enhance the capacity of optical fiber communication systems. In order to be compatible with cost-efficient intensity-modulation/direct-detection (IM/DD) systems, effective mode-group demultiplexing approaches to simultaneously receive each mode group of MMF are highly desired. In this paper, we propose a scalable low-modal-crosstalk mode-group demultiplexer over MMF using multi-plane light conversion (MPLC), in which input Hermite-Gaussian (HG) modes of MMF are first converted to bridging modes that composed of HG00 modes distributed as a right-angled triangle in Cartesian coordinates, and then each HG00 mode belonging to the same mode group are respectively converted to different HGn0 modes at the same output for simultaneous detection. With the help of bridging modes, the MPLC-based mode-group demultiplexer can scale to demultiplex more mode groups with relatively few phase masks. A 5 mode-group demultiplexer is also design for demonstration, and simulation results show that the modal-crosstalk are lower than -22.26 dB for all mode groups.
With rapid economic, technological, and industrial development, the transport network is under increasing load pressure. Making the best use of existing road network resources and traffic management resources, improving traffic and travel management, and increasing the efficiency of road use are essential issues we need to face. In this paper, the traditional BPR model is modified to take into account complications such as intersections, traffic accidents, road maintenance under congestion, and delay time due to queueing under congestion. The queueing time of a congested traffic flow is estimated using a trajectory tracking method using the cell phone signal of the driver and the base station data in the traffic network. The traditional BPR model was creatively modified to develop a modified BPR functional model for estimating traffic delay, which can be applied in transportation network planning. The final experimental model simulates the effect of traffic delay during vehicle movement, reflecting road flow, and providing effect support for road network planning.
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