Future-proofing current fibre networks with quantum key distribution (QKD) is an attractive approach to combat the ever growing breaches of data theft. To succeed, this approach must offer broadband transport of quantum keys, efficient quantum key delivery and seamless user interaction, all within the existing fibre network. However, quantum networks to date either require dark fibres and/or offer bit rates inadequate for serving a large number of users. Here we report a city wide high-speed metropolitan QKD network-the Cambridge quantum network-operating on fibres already populated with high-bandwidth data traffic. We implement a robust key delivery layer to demonstrate essential network operation, as well as enabling encryption of 100 Gigabit per second (Gbps) simultaneous data traffic with rapidly refreshed quantum keys. Network resilience against link disruption is supported by high-QKD link rates and network link redundancy. We reveal that such a metropolitan network can support tens of thousands of users with key rates in excess of 1 kilobit per second (kbps) per user. Our result hence demonstrates a clear path for implementing quantum security in metropolitan fibre networks.npj Quantum Information (2019) 5:101 ; https://doi.

We fabricate a nanotube-polyvinyl alcohol saturable absorber with a broad absorption at 1.6 m. We demonstrate a pulsed fiber laser working in the telecommunication L band by using this composite as a mode locker. This gives ϳ498Ϯ 16 fs pulses at 1601 nm with a 26.7 MHz repetition rate.

avelength-division multiplexing (WDM) is currently being deployed in telecommunications networks in order to satisfy the increased demand for capacity brought about by both narrowband services and new broadband services such as high-speed Internet. While it is thought that WDM will ultimately evolve to interconnected rings or perhaps a mesh network, the objective of the Wavelength Switched Packet Network (WASPNET) project is to gain a more long-term understanding of how optical networks will develop. WASPNET is a WDM transport network that uses optical packet switching, resulting in greater flexibility, functionality, and granularity than possible with the current generation of WDM networks. These optical packets may be used to carry asynchronous transfer mode (ATM) or IP, for example, and the network is also designed to support synchronous digital hierarchy/synchronous optical network (SDH/SONET) traffic, thus permitting a smooth upgrade path. Optical packet switches [1-3] have attracted considerable research interest internationally due to their potential for overcoming projected difficulties with very large electronic switching cores, such as connection, pinout, and electromagnetic interference (EMI) problems. A key problem when designing packet switches of any kind is contention resolution, since multiple packets may arrive asynchronously at the same time to go to the same output. Buffering is often employed to solve this problem, but since optical random access memory (RAM) does not exist, delay lines (usually made of optical fiber) must be used to store optical packets and implement buffering. Various solutions to optical packet switching have been proposed, dictated by the buffering strategy [1]. Implement Medium to Large Buffers-The switches implemented by this technique may be cascaded to implement very large buffers, suitable for bursty traffic. Use No Buffers in the Switch Nodes, but Employ Deflection Routing-When multiple packets arrive destined for a given output, all but one are "deflected" to other outputs, to find their way to the destination by another route through the network. This not only provides fast and flexible routing, but also allows nodes to have no buffering. However, each packet transmitted from a node may be routed across a different path to the same destination. Some packets may wander within the network and waste bandwidth. Consequently, each packet will experience different propagation delays, and the traffic may not arrive at the destination node in sequence. Compromise by Using a Small Amount of Buffering with Deflection Routing-There are various such 2 x 2 buffered switches consisting of a chain of 2 x 2 switch devices and delay lines.

We report a simple way to fabricate a high optical quality single wall carbon nanotubes (SWNTs) polyvinyl alcohol (PVA) composite. The composites demonstrate strong saturable absorption at ~1.5 µm, the spectral range for optical communications. These are used as mode-lockers in a fiber laser. We achieve ~713 fs pulse generation and up to 8 mW output power.

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