The maximum data throughput in a single mode optical fibre is a function of both the signal bandwidth and the wavelength-dependent signal-to-noise ratio (SNR). In this paper, we investigate the use of hybrid discrete Raman & rare-earth doped fibre amplifiers to enable wide-band signal gain, without spectral gaps between amplification bands. We describe the widest continuous coherent transmission bandwidth experimentally demonstrated to date of 16.83 THz, achieved by simultaneously using the S-, C-and L-bands. The variation of fibre parameters over this bandwidth, together with the hybrid amplification method result in a significant SNR wavelengthdependence. To cope with this, the signal was optimised for each SNR, wavelength and transmission band. By using a system-tailored set of geometrically shaped constellations, we demonstrate the transmission of 660⇥25 GBd channels over 40 km, resulting in a record single mode fibre net throughput of 178.08 Tbit/s. Index Terms-Broadband transmission system, high order modulation format, geometric shaping.

The rapid growth of data transferred within data centres, combined with the slowdown in Moore's Law, creates challenges for the future scalability of electronically-switched data-centre networks. Optical switches could offer a future-proof alternative and photonic integration platforms have been recently demonstrated with nanosecond-scale optical switching times. End-to-end switching time, however, is currently limited by the clock and data recovery time, which typically takes microseconds, removing the benefits of nanosecond optical switching. Here we show a clock phase caching technique that can provide clock and data recovery times of under 625 ps (16 symbols at 25.6 Gb/s). Our approach uses the measurement and storage of clock phase values in a synchronised network to simplify clock and data recovery versus conventional asynchronous approaches. We demonstrate our technique using a real-time prototype with commercial transceivers and validate its resilience against temperature variation and clock jitter, based on measurements from a production cloud data centre. Main T he rate of data transmitted between servers within data centres has rapidly increased over the last few years [1], driven by cloud adoption and data-intensive cloud workloads such as data analytics and machine learning. Cloud providers have been able to accommodate this fast growth by relying on Moore's Law for networking: every two years the electronic switch integrated circuits (ICs) double their bandwidth at same cost and power. The long-term sustainability of this trend, however, is being questioned by two upcoming challenges: Firstly, similar to processor ICs, scaling transistor density on electronic switch ICs is fundamentally limited by power dissipation as few-nm transistor sizes are approached [2]. Secondly, electronic high-speed serial transceiver data rates are predicted to be hard to scale beyond 112 Gb/s due to the steep increase in dielectric loss when operating at high frequencies [3, 4]. Consequently, increasing the aggregate switch capacity will require a proportional increase in the number of serial transceivers surrounding the chip, resulting in greater power density and packaging complexity. Although continued bandwidth scaling in the near future could be supported by architectural optimisations such as co-packaged optics [5], preserving cost neutrality in the medium-to-long term appears very challenging. This uncertainty has motivated research in optical switches as a viable alternative to electronic switches [6]. Optical switches simply redirect the incoming signals onto output ports without any optical/electronic conversion or digital processing and, hence, they do not suffer from the limitations of transistor or transceiver technology. They could, therefore, provide a future-proof solution for bandwidth scaling within the data centre [7].

We demonstrate a clock and data recovery technique that achieves <625ps locking time for 25.6Gb/s-OOK and show its robustness under worst-case data centre temperature variation. The locking time was improved by 12×, making nanosecond optical switching viable in data centres.

We report a study of light-activated resistance switching in silicon oxide (SiOx) resistive random access memory (RRAM) devices. Our devices had an indium tin oxide/SiOx/p-Si Metal/Oxide/Semiconductor structure, with resistance switching taking place in a 35 nm thick SiOx layer. The optical activity of the devices was investigated by characterising them in a range of voltage and light conditions. Devices respond to illumination at wavelengths in the range of 410–650 nm but are unresponsive at 1152 nm, suggesting that photons are absorbed by the bottom p-type silicon electrode and that generation of free carriers underpins optical activity. Applied light causes charging of devices in the high resistance state (HRS), photocurrent in the low resistance state (LRS), and lowering of the set voltage (required to go from the HRS to LRS) and can be used in conjunction with a voltage bias to trigger switching from the HRS to the LRS. We demonstrate negative correlation between set voltage and applied laser power using a 632.8 nm laser source. We propose that, under illumination, increased electron injection and hence a higher rate of creation of Frenkel pairs in the oxide—precursors for the formation of conductive oxygen vacancy filaments—reduce switching voltages. Our results open up the possibility of light-triggered RRAM devices.

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