Exploiting the bandwidth potential of multimode optical fibres

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


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 dope central core) for mode-division multiplexed data transmission and understood 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.
Exploitation Route We have worked with a Chinese 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.
Sectors Digital/Communication/Information Technologies (including Software),Manufacturing, including Industrial Biotechology

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 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