Spatially encoded telecoms and quantum technologies using spin-enabled all-optical switching - Spin Space

Lead Research Organisation: University of Essex
Department Name: Computer Sci and Electronic Engineering

Abstract

Our planet is criss-crossed with optical fibres that influence almost every aspect our lives in the 21st century. However, despite the great advances in optical fibre communications technologies that have occurred in the past 20 years, we have already almost run out of data capacity. With more of the world online, and the "Internet of Things" predicted to connect up to a trillion devices in the next 20 years, we need to find better ways of overcoming fundamental limits in how much data we can send. Also looming on the horizon are new technologies that may use optical fibre telecommunication networks, such as quantum optics technologies, sending, for example, completely secure data using single photons. However, sending many of these photons but keeping each one separate is a major challenge.

In answer to these new technologies, it has been suggested that sending information via a microstructured fibre may offer solutions to the challenges above. Microtructured fibres are rather like a stick of Brighton rock with a pattern running through. The simplest of these may be several cores running in parallel but optically isolated, whilst more complex designs involve controlled light leakage between the cores, or indeed a honeycomb structure with light travelling in the air. Recent ideas propose sending a pattern of light (either a light intensity pattern or a pattern of polarization) through the microstructured fibre with complex changes in the pattern containing encoded information.

While much work is presently being carried out on signal propagation in microstructured fibres, it is clear that to create the signal, a means of producing a spatial laser pattern is required that can switch pattern over GHz timescales. More importantly, to perform functions such as rerouting signals from one area of the array or changing the pattern one requires a device with an optical input and output to be fed into the later fibre network. Switching an array using electrical contacts is tricky - one needs to individually access many micron-sized areas at fast speeds. We propose that if small (few micrometer) lasers are fabricated into a small forest of pillars that emit individual points of light vertically, we can generate complex patterns easily. We use a semiconductor laser, where the spin, the electron's intrinsic magnet, interacts differently depending on the light polarization - in some cases the photon is absorbed, in other cases the spin is in the wrong direction and the light passes through. We will thus control light pulses to flip the spins and perform optical logic in spatial arrays of these devices. This will allow incoming signals to be switched and re-routed.

When the laser power is turned down, and very specific frequencies are used, we find that the light becomes intrinsically "grainy" - and turns into individual photons. We also know that the semiconductor can be prepared so that it behaves like a collection of atoms - at very specific wavelengths, the photon only "sees" one electron. Rather like an atom, the photon may be absorbed and an electron gains energy - however in our case it also interacts with the electron's spin. When the electron drops from its excited state and emits a photon, the photon has changed polarization. We can then filter out the outgoing photons from the incoming ones and use the scattered photons as a "single photon source" - where exactly one photon is produced per optical pulse. This source allows completely secure information to be sent, and is the starting point for photon quantum computing, where many of these individual photons are made to interact and encode information for a quantum computer.

Publications

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Description We have found that for certain waveguide designs, we can design for different types of dynamics in a coupled pair of VCSELs. We have also found that these can be locked together at particular frequencies using external optical injection into one of the devices. This may provide a means of laterally distributing signal in an array.

We have demonstrated experimentally a simple TAMM plasmon photodetector structures (in collaboration with our project partner University of Bristol) showing wavelength and polarisation selectivity.

We have demonstrated experimentally high spin-amplification in a spin VCSEL biased close to threshold.
Exploitation Route We hope that the finding might lead to methods for spatially distributing signals in an array of VCSELs, which might be useful for communications.

Tamm plasmon photodetectors have potential for use in arrays providing spatial wavelength/polarisation selectivity for use in communications or sensing

Spin-amplification has promise for spin-signal processing and spin logic.
Sectors Digital/Communication/Information Technologies (including Software),Environment,Healthcare

 
Description coupled nanowire lasers 
Organisation University of Strathclyde
Department Institute of Photonics
Country United Kingdom 
Sector Academic/University 
PI Contribution Our published work on the dynamics mutually coupled VCSELs done under our spin SPINSPACE project led to discussions about whether the same tools and techniques could be applied to the case of optically coupled nanowire lasers which is being studied at Strathclyde. We worked together to model the dynamics of example nanowire laser cases, and that has led to a publication (under review) and to a grant application which is in preparation.
Collaborator Contribution Strathclyde modelling the optical properties of mutually coupled nano wire lasers. Essex application of tools as techniques to study the dynamics of coupled devices
Impact Publication which is under review. Grant application which is in preparation.
Start Year 2018