Exploiting the bandwidth potential of multimode optical fibres

Lead Research Organisation: University of Southampton
Department Name: Optoelectronics Research Centre

Abstract

Historically the optical fibre was perceived to provide "unlimited" bandwidth, however, the capacity of current communications systems based on single mode optical fibre technology is very close to the limits (within a factor of 2) imposed by the physical transmission properties of single mode fibres. The major challenge facing optical communication systems is to increase the transmission capacity in order to meet the growing demand (40% increase year-on-year) whilst reducing the cost and energy consumption per bit transmitted. If new technologies are not developed to overcome the capacity limitations inherent in single mode fibres and unlock the fibre bandwidth then the growth in the digital services, applications and the economy that these drive is likely to be curtailed. The need for increased capacity in the core and metro areas of the network and within computing data centres is likely to become even more acute as optical access technologies, providing far greater bandwidths directly to the users, take hold and services such as ubiquitous cloud computing are adopted.
Multimode optical fibres (MMF) offer the potential to increase the capacity beyond that of current technologies by exploiting the spatial modes of the MMF as additional transmission paths. To fully exploit this available capacity it is necessary to use coherent optical (CO) reception and multiple-input multiple-output (MIMO) digital signal processing techniques analogous to those already used in wireless communication systems such as WiFi. This project aims to develop the technologies and sub-systems required to implement a CO-MIMO system over MMF that exceeds the capacity of current single mode fibre systems and reduces the cost and energy consumption per bit transmitted. To achieve this goal the project addresses the following key engineering challenges necessary to realise a complete system demonstrator.
Engineer the channel: The multimode optical fibre MIMO channel, unlike its wireless counterpart, presents the opportunity to engineer the optical channel to optimise its performance for MIMO operation by designing and fabricating new optical fibres, using proven solid core technology, to maximise the MIMO capacity of the fibre.
Dynamically control the channel: The transmission characteristic of the multimode optical fibre channel varies with time. We will exploit both the flexible and fast adaptive nature of digital signal processing, and the less energy intensive and slower adaptation of liquid crystal spatial light modulator based optical signal processing to compensate for the channel variation and recover the spatially multiplexed data channels.
Employ energy efficient optical amplification: In order to reduce both the energy consumption and cost per bit and to extend the propagation distance into the hundreds of kilometres region it is essential to develop optical fibre amplification technologies that provide amplification to multiple spatial and wavelength channels and thus share the cost.
Coherently detect the optical signal to exploit the wavelength and spatial domains: The developed system will combine spatial multiplexing with existing dense wavelength division multiplexing, polarisation multiplexing and multilevel modulation techniques to maximise the capacity. The key to achieving this is the use of coherent optical detection and digital signal processing, which is essential not only to fully exploit the spatial capacity of the MMF channel, but also facilitates the use of existing multiplexing techniques that are difficult to realise in conventional multimode transmission systems.
The technologies and systems developed within this project will find applications, ranging from capacity upgrades of existing MMF data networks in data and computer processing centres, through to the installation of new high capacity metro and long haul fibre transmission systems using the MIMO optimised fibres and technologies developed in this project.
 
Description We have investigated and understood the use of fibres with an annular core (as opposed to on-axis doped central core) for mode-division multiplexed data transmission and gained strong insight as to how many separate information channels can be simultaneously transmitted over the fibre. Moreover, we have demonstrated the benefits the ring core approach confers to the design of few-mode optical amplifiers in terms of equalizing the gain per mode. We have advanced the state of the art in terms of ring core technology producing >20km fibre lengths with record low loss (<0.3 dB/km) and demonstrated transmission experiments using these fibres and associated ring core amplifiers. Fibres and amplifiers were provided to our project partners which were successfully used in a variety of experiments.We also learned how better to exploit the gain in multimode on-axis doped core fibres for high power fibre applications as a result of this research.
Exploitation Route We have worked with a Chinese fibre manufacturing company Yangtze Optical Fibre Company (YOFC) who may be interested to further develop this technology should telecommunication companies such as Huawei, Nokia or Coriant decide that it presents the best means of scaling the data carrying capacity of future optical networks. The technology may also have merits in the area of high-power fibre lasers and optical fibre sensors and we are currently exploring the potential of this through a number of collaborations with Chinese and UK universities as detailed in the collaboration section of this report. We are particularly intrigued by the possibility of generating exotically shaped laser beams in time and space and their application in materials processing and biomedical imaging and have won funding where we will be able to explore such possibilities further based on the understanding and results generated in this project (again as detailed in the funding section of this report).
Sectors Digital/Communication/Information Technologies (including Software),Healthcare,Manufacturing, including Industrial Biotechology

 
Description The results from this project have helped inform the debate within the telecommunications industry as to the best way to build future optical networks - in particular how to deal with the fact that the current single-mode fibre technology used to build networks is beginning to saturate in terms of how much data per fibre strand it can carry. Moving to fibres that support more than 1 mode per fibre (such as the ring core fibres explored in this project) offers the potential to reduce the cost-per-bit relative to the more conservative approach of simply adding multiple single mode systems due to the possibility to share expensive components (such as optical amplifiers) across multiple spatial data channels, thereby reducing the total system component count and hence cost. An agreed pathway within the industrial community is still not firmly established but it is now generally accepted that some form of "Space Division Multiplexing" will be needed and that increased device integration/sharing will be critical. Results from this project also helped demonstrate to the high power laser community that accurate control of the spatial modes in active fibre devices, such as amplifiers and lasers is possible and generated increased interest in investigating the use of different spatial modes, including ring modes, in industrial materials processing applications and also in medical imaging. Follow-on projects in both of these areas were secured based in part on the results from this project (as detailed in the funding section of this report). The University of Southampton spin out company, SPI Lasers Ltd (now owned by Trumpf Ltd and a partner on one of these follow-on projects) has recently launched a beam-shaped fibre laser system capable of generating ring shaped modes on demand. Energy efficiency savings of 25% have been achieved using ring-mode operation (relative to the conventional Gaussian mode approach) along with improved cutting quality.
First Year Of Impact 2019
Sector Digital/Communication/Information Technologies (including Software),Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description Compact fibre collimator and associated optical components for space division multiplexed (SDM) transmission (Impact Acceleration Award - PI Y: Jung)
Amount £17,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 10/2016 
End 03/2017
 
Description Collaboration on SDM fibre design 
Organisation University of Oxford
Country United Kingdom 
Sector Academic/University 
PI Contribution Fibre fabrication.
Collaborator Contribution Fibre design.
Impact Results submitted for publication.
Start Year 2012
 
Description Collaboration on SDM fibre transmission. 
Organisation University College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Supply of fibre samples/know how.
Collaborator Contribution Characterisation of fibre transmission properties
Impact Results submitted for publication.
Start Year 2012
 
Description Collaboration on SDM fibres 
Organisation University of Cambridge
Country United Kingdom 
Sector Academic/University 
PI Contribution Development and supply of novel fibres for Space Division Multiplexing.
Collaborator Contribution Fibre characterisation
Impact Research results submitted for publication.
Start Year 2012
 
Description Collaboration with Boston University (OAM amplifiers) 
Organisation Boston University
Country United States 
Sector Academic/University 
PI Contribution Development and testing of an optical amplifier for signals carrying orbital angular momentum
Collaborator Contribution Fibre design and early fibre characterisation
Impact Several papers as outlined in individual grant publication lists.
Start Year 2014
 
Description Collaboration with Nanyang Technical University (Singapore) on fibre fabrication 
Organisation Nanyang Technological University
Country Singapore 
Sector Academic/University 
PI Contribution Laser and amplifier development work - in particular thulium doped fibre amplifier and laser studies, testing of large mode area ytterbium doped fibres and associated laser development, hollow core fibre studies.
Collaborator Contribution Fabrication of various bespoke fibres including thulium doped fibres of varying designs and compositions, large mode area high concentration ytterbium doped fibres and various hollow core fibres. Provision of two visiting PhD students ( two x 2 years stay at Southampton).
Impact Various high profile papers as listed in the individual supporting grants
Start Year 2014
 
Description Collaboration with Shanghai University (visiting PhD student) 
Organisation Shanghai University
Country China 
Sector Academic/University 
PI Contribution Research on components for space division multiplexing - access to novel fibres and fibre characterisation laboratories
Collaborator Contribution 1 year visit of CSC funded PhD student (Yaping Liu)
Impact Several high profile technical papers anticipated.
Start Year 2019
 
Description Collaboration with Sun Yat-sen University (visiting PhD student) 
Organisation Sun Yat-Sen University
Country China 
Sector Academic/University 
PI Contribution Development of newv theoretical fibre concepts/designs for SDM data communications.
Collaborator Contribution 1 year CSC funded visiting PhD student (Guoxuan Zhu)
Impact EPSRC grant application submitted based on the SDM fibre concepts developed during this visit. Unfortunately not funded. Has also strengthened an ongoing collaboration with Bristol University.
Start Year 2018
 
Description Collaboration with Tianjin University (visiting PhD student) 
Organisation Tianjin University
Country China 
Sector Academic/University 
PI Contribution Support of research on spatial mode shaped fibre lasers..
Collaborator Contribution CSC funded visiting studentship for 1 year (Teng Wang)
Impact Technical papers anticipated.
Start Year 2019
 
Description Collaboration with University of Bristol, Herriot Watt and Glasgow towards developing fibres, amplifiers and components for high capacity mode multiplexed data transmission. 
Organisation Heriot-Watt University
Country United Kingdom 
Sector Academic/University 
PI Contribution Contribution of ideas towards the development of a significant ~ £2M research proposal on mode-division multiplexed data transmission to EPSRC. University of Southampton contributed to the definition of novel fibre amplifiers and transmission fibres capable of ultrahigh capacity data transmission. Unfortunately we have just heard that the application has not been selected for funding. We still hope to undertake some aspects of research - likely principally further numerical modelling.
Collaborator Contribution Bristol - ideas for MDM data transmission experiments. Heriot Watt University - development of concepts of new ideas for chip based mode multiplexing. Glasgow - development of new concepts for integrated components for mode division multiplexed transmission systems.
Impact No outputs other than a grant application as of yet.
Start Year 2018
 
Description Collaboration with University of Bristol, Herriot Watt and Glasgow towards developing fibres, amplifiers and components for high capacity mode multiplexed data transmission. 
Organisation University of Bristol
Country United Kingdom 
Sector Academic/University 
PI Contribution Contribution of ideas towards the development of a significant ~ £2M research proposal on mode-division multiplexed data transmission to EPSRC. University of Southampton contributed to the definition of novel fibre amplifiers and transmission fibres capable of ultrahigh capacity data transmission. Unfortunately we have just heard that the application has not been selected for funding. We still hope to undertake some aspects of research - likely principally further numerical modelling.
Collaborator Contribution Bristol - ideas for MDM data transmission experiments. Heriot Watt University - development of concepts of new ideas for chip based mode multiplexing. Glasgow - development of new concepts for integrated components for mode division multiplexed transmission systems.
Impact No outputs other than a grant application as of yet.
Start Year 2018
 
Description Collaboration with University of Bristol, Herriot Watt and Glasgow towards developing fibres, amplifiers and components for high capacity mode multiplexed data transmission. 
Organisation University of Glasgow
Country United Kingdom 
Sector Academic/University 
PI Contribution Contribution of ideas towards the development of a significant ~ £2M research proposal on mode-division multiplexed data transmission to EPSRC. University of Southampton contributed to the definition of novel fibre amplifiers and transmission fibres capable of ultrahigh capacity data transmission. Unfortunately we have just heard that the application has not been selected for funding. We still hope to undertake some aspects of research - likely principally further numerical modelling.
Collaborator Contribution Bristol - ideas for MDM data transmission experiments. Heriot Watt University - development of concepts of new ideas for chip based mode multiplexing. Glasgow - development of new concepts for integrated components for mode division multiplexed transmission systems.
Impact No outputs other than a grant application as of yet.
Start Year 2018
 
Description Collaboration with Yangtzee Optical Fiber Company (YOFC) 
Organisation Yangtze Optical Fibre & Cable (Shanghai) Company Ltd.
Country China 
Sector Private 
PI Contribution Optical fibre design and characterisation. Advice on the characterisation of few mode fibres.
Collaborator Contribution Fibre fabrication.
Impact Joint experiments underway and publications planned.
Start Year 2015