High Dimensional Free-space Building-to-Building Link for Last-Mile Communications

Lead Research Organisation: University of Glasgow
Department Name: School of Engineering


I propose a new approach to supplying technologies for the last-mile global communication networks.

High-speed data links are central to an ever-more integrated digital economy where, every day, more and more data is shared on our already over-stretched communications networks. A key challenge is the development of new high-bandwidth, secure communication networks, particularly through the internet. The online multimedia services we use on a daily basis are huge users of network bandwidth. With the number of multimedia users in the UK increasing on a monthly basis, the result is a huge drain on the available network bandwidth. Even in standard definition, watching our favourite TV show uses around 1GB of data per hour (and 3GB per hour for high definition). Beyond multimedia, as cloud-based storage and computing becoming the norm establishing high-bandwidth communication networks will be vital. Core backbone communication networks are regularly upgraded to deal with these demands, however the last-mile network, which takes our Internet services to homes and offices, is difficult and expensive to upgrade. This difficulty arises from the distributed nature of this portion of the network and solutions for cost effective, and sustainable, upgrades are required to be commercially deployed over the next 5-10 years.

This project the aims to develop solutions to implementation of high-speed free-space last-mile networks. Using light beams carrying Orbital Angular Momentum, a single point-to-point link will increase the number of data carrying channels. Using orbital angular momentum in this way is an example of spatial multiplexing. These multiplexing techniques have the potential to offer multiplicative increases in data rates whilst simultaneously increasing the security of the link. A key deliverable will be the development of a last-mile building to building link within our new campus, for the development and testing of prototype novel multiplexing and de-multiplexing technology. Working with Industrial partners Intel and Corning, solutions will be developed in line with their market requirement, allowing near-term commercial uptake.

These industry inspired challenges raise some questions about the fundamental nature of long distance propagation of spatial modes. Hence, along with overcoming the technical hurdles this project aims to investigate the effect of turbulence within the free-space propagation of spatially multiplexed beams. In the early stages of this project, studies into the optical aberrations, and modal cross coupling will be carried out in different environmental settings. This vital data will provide a base to design and develop passive, and active approaches to overcoming the limitations imposed by atmospheric turbulence. Further to these challenges, techniques to allow integration into current installed fibre networks will be developed. The proof-of-principle link will allow real life user testing, where standard internet services will be demonstrated over the link, aiming to providing a commercially viable last-mile link design as a key deliverable of the project.

Planned Impact

In the short term (1-5 years), this research will have impact by developing a understanding of the physical challenges, along with the development of commercially viable solutions, through demonstration of a proof-of-principle of a high-dimensional free-space last-mile link. The link characteristic study in it's self will provide a useful set of data for the community on the effects atmospheric turbulence place on different form of optical spatial modes. Beyond this physical study, new bespoke optical tools will be developed that will have use beyond their implementation within communications, with various possible applications in optical metrology. The development of this proof-of-principle link will provide a potentially commercially viable solution for building-to-building last mile communications systems. Working with Intel and Corning, commercialization possibilities will be assessed throughout the development the system, where their input will shape the system to suit the current and future market requirements.

In the medium term (5-10 years), communications providers will have begun their 5G deployment to their installed customer base. This extensive technological role out will have begun to place strain on the large distributed communications networks, where customers are costuming ever more data; spurred on by the increase networks speeds. The desire for fast, secure reliable last-mile networks will become an imminent concern, as end users bandwidth usage will place increased strain on the last-mile portion of the network. The technical outcome from this project will have provided technology that could be installed as part of the 5G role for use with in last-mile network upgrades. High dimensional spatial multiplexed links will be vital in the medium term to relieve the stress on point-to-point communications links.

In the long term (10-50 years), it is likely the network architecture will have drastically changed from that of the current installed systems. Traditional backbone, to local nodes, which are connected to the distributed last-mile network will potentially no-longer be the most efficient network architecture. With the internet of things changing the landscape of what devices are network enabled and integrated, our network will also have taken on a different more natural form. Smart, Adaptive networks will be the norm, where physical network will themself adapt to network usage and failure. Such a rich digital ecosystem will limit the appropriateness of tethered devices, and limit the feasibility of optical fiber for last-mile networking solutions. The last-mile, distributed network could become the main workhorse of the movement of data traffic, managing the best way to route data the network removing the requirement for incredibility high-backbone network links. Developments made now in the technology requirements for high speed spatially multiplexed free-space links will prove formative in the technology utilized in these possible future network architectures.


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Song R (2020) Multi-Channel Signal-Generator ASIC for Acoustic Holograms. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

Description 1) We investigated the propagation of a set of orthogonal spatial modes across a free-space channel between two buildings separated by 1.6 km. Given the circular geometry of a common optical lens, the orthogonal mode set we choose to implement is that described by the Laguerre-Gaussian (LG) field equations. We present experimental data for the modal degradation in a real urban environment and draw a comparison to recognized theoretical predictions of the link. Our findings indicated that adaptations to channel models are required to faithfully simulate the effects of atmospheric turbulence placed on high-dimensional structured modes that propagate over a long distance.

2) We developed a verifiable physical model of the propagation of these optical fields in a turbulent environment is important for developing effective mitigation techniques for the modal degradation that occurs in a free-space link. Our new model simulates this modal degradation that agrees with recently reported experimental findings. A 1.5 km free-space link is emulated by decomposing the optical turbulence that accumulates over a long distance link, into many, weakly perturbing steps of 10 m. This simulation shows that the high-order vortex at the centre of the helical phase profiles in modes that carry orbital angular momentum are unstable and fracture into many vortices when they propagate over the link. This splitting presents issues for the application of turbulence mitigation techniques.

3) Free-space optical (FSO) systems offer the ability to distribute high speed digital links into remote and rural communities where terrain, installation cost or infrastructure security pose critical hurdles to deployment. We developed of a low-cost FSO system prototype that could allow for out of the box self aligning optical systems that requires no specialist engineer for installation. Our prototype system is based on commercial telescope mount, which is controlled by Raspberry Pi 3 (RPi) compact computer and incorporates 4 spatially multiplexed channels, each with an integrated 1-Gbps small form factor pluggable (SFP) transceiver. Using the global positioning system (GPS), the location of the transceiver is determined and communicated to near by transceivers through low-speed radio link operating at 446-Mhz. The low-speed radio link supports the communication of automated alignment instructions between the remote transceivers. To perform the alignment, we adopt a spiral path alignment method widely for used for inter-satellite and ground-to-space optical communication systems. To facilitate this alignment method both the Transmitter and Receiver systems are equipped with a laser beacon, which is detected by CCD camera located on the external casing of each transceiver. The system automatically completes three stages of alignment to fully align a duplex spatially multiplexed FSO link. In our experimental test of the system over both 15m and 200m, we measured the total link loss to be 10dB and 15dB respectively and demonstrate error free-transmission at 1 Gbps per channel.

URLS for publications on each of the key findings. Please see associated publications for full list of link work linked to the findings of the project.
1) https://advances.sciencemag.org/content/3/10/e1700552.full
2) https://iopscience.iop.org/article/10.1088/1367-2630/aaae9e
3) https://www.nature.com/articles/s41598-019-55670-1
Exploitation Route 1) With these new developments, I am confident that we can now re-think our approaches to channel modelling and the requirement places on adaptive optics systems. We are getting ever closer to developing OAM communications that can be deployed in a real urban setting. This key finding will start a conversation about the issues that need to be addressed in real world deployment of spatial mode multiplexing and how we are going to move towards the resolution. These findings will allow researchers to address challenges - not previously observed - and spur the developing adaptive optics for quantum and classical information transfer. These finding could move towards a new age of free space optics that will eventually replace fibre optics as a functional mode of communication in urban environments and remote sensing systems.

2) These finding will be taken forward to develop effective correction schemes for complex fields propagating in a turbulent environment.

3) These technical advances have already become a central feature of two projects with British Telecom, looking to utilise this low cost technology within its telecommunication network as back up system in the event of fibre network breaks.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Security and Diplomacy

URL http://advances.sciencemag.org/content/3/10/e1700552.full
Description The research carried out within my EPSRC First Grant, greatly support the development of commercial prototype for underwater communication system that is due to on the market late in 2019 or early 2020. The ground work put in place by the First Grant supported the development of funded project from OGIC and Censis, that supported the successful prototype development. This project has further supported the development and successful funding of two further projects one from the EPSRC called High Dimensional Wireless Passive Optical Networking for Access Deployment (PON-HD), with British Telecom as a core partner and a project called Terabit free-space Orbital Angular Momentum communication technologies that will enable future 6G networks entirely funded by Huawei. Technologies developed in this project have been highly applicable to Industry lead challenges and could results in future commercial prototypes, evidenced by the large investment from these major industry leaders in the communication sector.
Sector Digital/Communication/Information Technologies (including Software),Electronics
Impact Types Economic

Description (Super-Pixels) - Super-Pixels: Redefining the way we sense the world.
Amount € 2,479,003 (EUR)
Funding ID 829116 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 03/2019 
End 08/2022
Description Development of Underwater Communication Systems for Oil and Gas Industry (CENSIS)
Amount £30,457 (GBP)
Funding ID CAF 290 
Organisation Innovation Centre for Sensor and Imaging Systems CENSIS 
Sector Charity/Non Profit
Country United Kingdom
Start 02/2017 
End 08/2017
Description Development of Underwater Communication Systems for Oil and Gas Industry (OGIC)
Amount £30,018 (GBP)
Funding ID 16OP_43 underCom 
Organisation Oil & Gas Innovation Centre 
Sector Private
Country United Kingdom
Start 02/2018 
End 08/2018
Description EPSRC-IAA: Development of Commercially Viable Free-Space Optical Communications Technologies (FreeCOMM)
Amount £35,188 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 11/2017 
End 09/2018
Description High Dimensional Wireless Passive Optical Networking for Access Deployment (PON-HD)
Amount £730,354 (GBP)
Funding ID EP/T009012/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 09/2019 
End 09/2022
Description Terabit free-space Orbital Angular Momentum communications technologies that will enable future 6G networks
Amount £461,295 (GBP)
Funding ID YBN2019125105/309832 
Organisation Huawei Technologies Sweden AB 
Sector Private
Country Sweden
Start 03/2020 
End 02/2023
Description Collaboration with British Telecom on FSO systems 
Organisation BT Group
Country United Kingdom 
Sector Private 
PI Contribution My research group developed a demonstrator of a self aligning free-space optical transceiver that could be deployed within the BT Network for less than £500 per resident and conducted testing with a bandwidth greater than 1 Gb/s.
Collaborator Contribution BT will provided vital information about their network, carried out cost to benefit analysis of the proposed technologies, and develop deployment scenarios for the inclusion for including of FSO technologies within their optical network. They hosted, Dr Mansour Abadi and myself at Adastral Park Research Labs to test the early prototype will be tested with their carrier grade GPON/XPON point-to-point equipment that is currently used within the BT network.
Impact We conducted field tests at Adastral Park in August 2018, and has lead to further developments of the prototype development. This has become a central component of a funded project called High Dimensional Wireless Passive Optical Networking for the Access Deployment (PON-HD) ( EP/T009047/1).
Start Year 2017
Description Free-space propagation of high-dimensional structured optical fields in an urban environment 
Organisation Max Planck Society
Department Max Planck Institute for the Science of Light
Country Germany 
Sector Academic/University 
PI Contribution I led this project, which focused on studying the propagation of optical modes over long distances similar to that required in urban environments. This study revealed an unexpected phenomena that is potentially a critical concern the deployment of free-space optical systems that operate in turbulence optical paths over 500m in length. I developed the experiment, provided the equipment for the measurements of Orbital Angular Momentum (OAM) spectra and constructed the experiment on site. Data was collected with assistance from researchers from the Max Planck. I was responsible for processing the data and conducting the analysis to confirm the phenomena reported.
Collaborator Contribution The team at the Max Planck Institute for the Science of Light provided access for me conduct OAM propagation experiments over their 1.6 km long range free space optics link test bed. They provided equipment, expertise and offed in kind support by providing local accommodation for two visits to Erlangen. Our experimental successes resulted in a Science Advances Journal Article that received considerable coverage after publication.
Impact 1 Publication: Lavery et al., Science Advances 3 (10), e1700552 2017 and 2 Invited Talks: Cleo Pacific Rim 2017 and Asia Photonics and Communication Conference 2017. This work received over 10 news articles in internationally recognised media outlets. This work was a collaboration between Engineering and Physics
Start Year 2016
Description Beyond the Selfie: Introduction to the Digital World. 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact In partnership with the Digital Learning Foundation, a charity specialising in interactive STEM outreach events, the we developed a workshop for schools on the importance and the technical foundations of digital communications. Students and the general public, are generally unaware of the technology that connects our digital society. This public engagement will promote awareness of current and future technologies. Such familiarity will be beneficial to the field of communications as new technology developments could be more readily accepted by the general public and it will raise the profile of the research field.
We have developed an interactive lesson for 10-14 year olds that covers the technologies required for a what many consider trivial act of taking a selfie. It covered the digital sensor, the encoding of information and how it transferred around the world. The work comprised both presented components and interactive practical sessions.
The workshop was develop in 2017, and a early stage shows trails were conducted in late 2017. 101 primary school students at Kelburn Primary School in Largs participated in the events. The student were highly engaged through out the event where 70% gave the event an Excellent Rating and further 25% gave it Good. On assessing specific learning outcomes an increased student knowledge base was measured on the topics discussed. As this was the first test of the show, this is very encouraging and the show is currently been further developed in response to the feedback over the next year.
Year(s) Of Engagement Activity 2017