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Emerald Group Publishing Limited
Copyright © 2011, Emerald Group Publishing Limited
Fibre optic sensors: has the effort been worthwhile?
Article Type: Viewpoint From: Sensor Review, Volume 31, Issue 4
Keywords Fibre optics, Sensors
The development of single-mode optical fibres, solid-state light sources, beam splitters, optical couplers and other components by the telecoms industry in the 1970s led to a global endeavour to develop fibre-based sensors. Almost overnight, phenomena such as Raman and Brillouin scattering, Bragg’s law and the Sagnac, Pockles and Kerr effects, to name but a few, emerged from being little more than scientific curiosities, languishing in relative obscurity, to become critical to the development of fibre optic sensors (FOSs). Interest peaked during the 1980s and anyone working on sensor technology at that time could be forgiven for thinking that the industry was poised on the brink of a technological revolution. Indeed, many analysts predicted such a revolution, whereby FOSs would replace conventional sensors across large sectors of industry. The argument was that they offer a range of key benefits, such as small size, flexibility, immunity to electromagnetic radiation and RF interference, intrinsic safety, distributed and multi-point sensing, high sensitivity, rugged construction and low costs. However, the highly application-specific nature of the sensor industry meant that these “benefits” were only truly beneficial in particular instances and some were questionable at best: the sensor might be small, rugged and inexpensive but the spectrometer used to interrogate it was none of these things. Nevertheless, it was clear that FOSs offered real prospects and in recognition of this, many schemes were set up to explore their potential. In the UK, the Optical Sensors Collaborative Association (OSCA) was founded in 1982 to disseminate information and explore the potential of FOSs and at about the same time, the UK Government established the Advanced Sensors Technology Transfer Programme which placed a strong emphasis on FOS research and applications. These and other schemes were a great success in elevating awareness and were, of course, in the pre-internet era when information on research was limited to those with access to the learned journals or who attended academic conferences. The 1980s saw an explosion of university research and groups from around the world started to investigate all manner of optical phenomena and technologies and develop prototype devices. Several established world-class reputations and many remain active today. The 1980s also saw the first attempt to commercialise FOSs and several companies, large and small, took the plunge early, many collaborating with academic groups. As with all efforts to exploit new technologies, some ventures ended in failure but the technology gradually matured, the true benefits, and limitations, were understood and the commercialisation process commenced, albeit rather more slowly than many had originally anticipated.
So, after more than three decades of research, where are we today and has the effort been worthwhile? Some of the answers to the first part of this question can be found elsewhere in this issue and as far as the second is concerned, the answer must be a resounding “yes”. With global markets now running at over half a billion dollars per year, FOSs have established themselves in a multitude of largely niche applications in many of the major sensor-using industries. Physical sensors dominate today’s market, largely reflecting that certain inherent features of the technology offer real user-benefits, such as distributed, multi-point sensing, immunity to EMI, rugged construction and small size. Perhaps, the biggest disappointment, however, has been the failure of FO technology to exert a significant impact on the chemical sensing market. The apparent potential was such that OSCA set up a dedicated Chemical Sensing Group in 1986; two years earlier the OSRU (Optical Sensors Research Unit) had been founded at the University of Manchester Institute of Science and Technology to foster pre-competitive FO chemical sensor research and in the early 1990s Frost & Sullivan predicted that chemical sensors would account for 24 per cent of the total FOS market by 1999. However, for reasons that are both technological (difficulty in achieving selectivity, etc.; performance governed by the sensing chemistry rather than the optical technology) and operational (heavy user-reliance on laboratory analysis, particularly for regulatory measurements), there has yet been only modest commercial progress.
What, then, of the future? Market forecasts are more conservative than formerly and predict gradual rather than spectacular growth, notably in the oil and gas, civil engineering, security and perhaps medical sectors – in many respects “more of the same”. This seems the most likely future scenario and although new applications will certainly emerge, much market development will arise from many of today’s applications growing in importance, for example structural monitoring, boundary security and oil and gas exploration and production. Perhaps, though, reducing the size of a fibre to nanometre dimensions will open up a whole new field of research with the discovery of novel effects and phenomena and stimulate the development of a second wave of “optical nanofibre” sensors. In any event, FOSs have come of age and although there has not been the technological revolution some predicted, they now play a crucial role in many industries vital to maintaining the wealth and security of the world’s industrialised nations.
Robert BogueAssociate Editor of Sensor Review