Highly Sensitive Photon Counting Receivers for Li-Fi Systems
Published on July 3, 2015
A New Solution to Long Distance Communication
The concept of Li-Fi, first introduced to the general public by Professor Harald Haas, Chair of Mobile Communications at theUniversity of Edinburgh, in a TED Talk in 2011, is currently attracting a great deal of interest and many researches have stepped into the field by proposing new devices as potential transmitters and receivers for Li-Fi systems.
There has been significant progress towards the realisation of optical receivers fully integrated with the standard digital CMOS technology. Recent trends towards integrated CMOS high-speed optical receivers have specially employed avalanche photodiodes (APDs). However, the maximum achievable gain of an APD is limited due to low sensitivity and the gain-dependent excess noise. This necessitates the use of intricate high gain transimpedance amplifiers (TIAs), limiting amplifiers and adaptive equalisation.
These challenges can be tackled by operating the APD in Geiger-mode as a single photon avalanche diode (SPAD). Due to the high electric field, avalanche multiplication leads to a large internal gain, creating a density modulated pulse train and the additional noise source can then be avoided .
The high sensitivity and time resolution of SPADs have highlighted the potential of employing SPADs as photon counting receivers for Li-Fi systems. They can be used with the long term aim of power efficient, high sensitivity receivers and are particularly attractive because they are able to closely approach quantum-limited sensitivity in the detection of weak optical signals in long distance communications, such as in the gas extraction industry, or in downhole monitoring communication systems .
Despite advances, the maximum achieved data rate by a SPAD receiver is still limited to a few MHz . Currently at the Li-Fi Centre at the University of Edinburgh, we are conducting research on these state of the art receivers and trying to provide solutions to possible challenges by investigating alternative approaches.
Li-Fi Postgraduate Research Student
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