Experts: Luc Thévenaz (EPFL)
Due to their small diameters, fibre-optic sensors can be embedded in a very wide variety of materials, and are able to measure changes in structure and temperature even under adverse conditions, which predestines them for use in medicine. In addition, they provide measurements that cover long distances seamlessly, a property used primarily in the monitoring of energy infrastructure and buildings. Here, being "Swiss-made" can bring a decisive competitive advantage. As innovative solutions mainly come from start-ups, shaping the business environment accordingly is likely to pay off.
Image: Solen Feyissa, Unsplash
Fibre-optic sensors are fibres that are used as measuring devices. They transmit measurements not as electrical signals, but as optical ones – using light. The majority of the sensors are made of silicon dioxide, also known as quartz sand, the main component of glass. This material is electrically insulating and chemically non-reactive. These properties, combined with small diameters similar to that of a human hair, mean that the sensors can be embedded in a very wide variety of materials and objects.
In messaging and communications technology, data is transmitted as optical signals in fibre-optic cables. However, signal transmission in the cables reacts to geometric changes, such as pressure or tension. This is where fibre-optic sensors come in: Signal disturbance caused by deformation is desired in their context and used as a measured variable. Thus, thanks to their material properties, the optical fibres measure structural or temperature changes in the material in which they are embedded – even under harsh conditions, such as electromagnetic interference or radioactivity, or in toxic substances. Moreover, these sensors can be multiplexed: As a single fibre can conduct signals of different wavelengths, it enables communication with up to 100 individual sensors. Conventional electrical sensors need separate connections for this, resulting in a cable bundle. Multiplexing is particularly attractive for aerospace and for monitoring the condition of infrastructure, as these applications require the activation of countless measuring points.
One decisive and unique advantage of fibre-optic sensing is the possibility of enabling each point along the fibre to provide an independent measurement of the respective variable: The fibre acts as a continuous linear sensor, providing a complete map of the measured variable in relation to distance. In this way, fibre-optic sensors detect leaks along extensive oil and gas pipelines, hot spots in power cables, and deformations in wind turbines’ blades. They thus help to optimise load in energy systems.
In the future, medical applications will gain in importance: Fibre-optic sensors are cheap and small enough to be easily inserted into catheters, creating ideal conditions for monitoring patients – in fact, for MRI or CT examinations, they are the only option. Alternatively, the sensors can be incorporated into clothing worn during an examination. Possible applications in the construction industry include burglary protection and early warning of earthquakes, as well as systematic monitoring of public infrastructure, water pipes and roads.
This advanced technology facilitates the development of instruments with high added value and benefits from a highly skilled workforce. It is very suitable for Swiss industry, which has a tradition of precision manufacturing. Being "Swiss made" can make a decisive difference here, as the safety and control of critical infrastructure are involved. Fibre-optic sensors constitute a product range in which Switzerland can demonstrate its excellence and which is also aimed at a global market. Furthermore, the technology can position Switzerland as a leader of a global societal endeavour to ensure that the use of infrastructure is energy-efficient and safe.
The challenges on the technical side lie in the high cost of the interrogation units (10,000–100,000 Swiss francs). In particular, this severely limits applications in the construction industry, as a large number of measuring points are required to monitor structures. Photonic integrated circuits offer one possible solution. However, most of the construction industry is conservative and slow to adopt new technologies.
On a societal level, large-scale data collection can be perceived as a threat to privacy; the legal framework should be adapted at an early stage to counteract potential misuse of data.
To date, research into optical fibres has not been supported by any large national research programme, but by telecommunication firms. Innovation will take place within young firms, not large companies, and it may be worthwhile to direct (cantonal) funding for economic development accordingly. Swiss firms are still leading in niche markets, but competition from Europe and China is developing rapidly and is likely to close the gap.
