Super Receivers for Visible Light Communications

Lead Research Organisation: University of Oxford
Department Name: Engineering Science

Abstract

In the near future, light emitting diodes (LEDs) will replace all other sources of light - from the lamps that light homes and offices to the headlights of cars. As well as providing illumination, these LEDs can be used to transmit data, and so offer an opportunity to create a new wireless infrastructure for data transmission. The demand for wireless communications to smartphones, watches, tablets and other devices is growing at a rate of 50% per year, and new technologies are needed to augment the capacity of conventional WiFi. Using LEDs in visible light communications offers a huge potential capacity to support this growth and to provide new services that use localised wireless communications.

While LEDs can transmit the information, an optical receiver is needed to collect the transmitted light, convert it to an electrical signal and extract the transmitted data. The maximum amount of light that can be transmitted is limited by the illumination brightness and concerns for the eye safety and comfort of users. The sensitivity of the receiver therefore ultimately determines the range over which optical data can be transmitted and/or the maximum possible data rate. The sensitivity of existing receivers for visible light communications is limited by a combination of the methods used to collect light and the devices used to convert this light to an electrical signal.

In this project we aim to create new super receivers that are significantly more sensitive than existing optical receivers; that overcome conventional limits for combining speed, sensitivity and easy alignment; that are thin and flexible enough to be easily integrated onto any device. A dramatic change in performance will be achieved by combining two technologies- fluorescent concentrators and arrays of single-photon avalanche photodiodes- in a receiver for the first time. The first will use fluorescent materials to absorb the transmitted light signal and re-emit it at a different wavelength onto the detector. Using this method we will collect light over large areas using a thin, flexible layer which guides and concentrates the emitted light to its edges.

The second technology is a light detector capable of detecting individual photons. We will develop methods to count photons from the transmitter in the presence of ambient light. We will explore how to optimise the fluorescent materials and light collecting layer to efficiently concentrate light onto one or more light detectors, and develop methods to maximise the amount of data transmitted by optimising how the data is represented. These super receivers will be tested in free-space visible light communications links to quantify their performance. Our estimates suggest that this approach could lead to a 100 times improvement in performance over current receivers, enabling faster data transmission, longer transmission ranges and the ability to operate in difficult environments, such as in the presence of bright ambient light.

Planned Impact

This proposal aims to develop a new type of optical receiver that will achieve much higher sensitivity and thereby faster and more reliable visible light wireless communications. Optical wireless networks- known as LiFi- are expected to be a $75.5 Billion market by 2023, and the UK has recognized leaders in this emerging market (e.g. our project partner PureLiFi). Creating planar, efficient receiver structures that can be incorporated in almost any surface, with several orders of magnitude higher performance than currently available receivers has the potential to significantly increase the range of uses for LiFi. We therefore anticipate that this new kind of receiver could have a significant societal and economic impact in the UK in three main ways: through wider/faster adoption of LiFi in future wireless communications; new market applications of SPAD detectors; new internet services for the public:

Wider/faster adoption of LiFi in future wireless communications

A key part of the success of any communications technology is the data rate that can be achieved, and the ability to operate under a wide range of conditions. The orders of magnitude increase in receiver sensitivity that a successful project will achieve could be used to increase the data rate and/or reliability of LiFi communications systems. In addition the radical change in form-factor, from bulky 3D optics to a thin conformal layer, which will occur when these new receivers are employed, will mean that almost any surface could be used as a receiver. This will be an advantage in any LiFi system however this change in form factor will significantly increase the chances that LiFi will play a substantial role in the Internet of things, manufacturing 4.0, and future 'smart' environments. Overall the benefits of super receivers will significantly increase the chances that LiFi will become a widely adopted, every-day technology with an even bigger market than current predictions.

New market applications of SPAD detectors

The use of SPADs and fluorescent concentrators together is unknown, and therefore potential new applications and markets will be generated by the work. Our research will have an impact in the design of new SPAD detectors optimized for communications, or for other applications for which large area, sensitive optical detectors are required such as for sensing.

New internet services for the public

Communications and instant access to information are now a fourth utility, which is expected to be even more readily available than water, gas and electricity. Consequently, society increasingly relies on wireless access to information for entertainment and to function efficiently. Smart-cities and other information-centred organization structures are increasingly used to create efficient sustainable communities. LiFi is 'human centred' in that the light used to communicate can be seen by the user and sometimes controlled by them. This offers the potential to build trust in communications and interactions with infrastructure, with impact in areas such as smart-cities.
A successful outcome of this project would directly impact the users of wireless communications systems by allowing high-speed wireless access in new practical configurations with increased range and security. In turn, by providing improved underlying infrastructure, this will enable the continued growth of the digital economy. Areas in which there could be significant impact from improved wireless communications include healthcare, the armed forces and police, car-to-car communications on motorways, the airline industry and in sports stadia. In addition to existing uses the ability to provide site-specific information at different locations in a building creates new possibilities. For example, it will be possible to give museum visitors information about nearby exhibits or shoppers' information about nearby products.