Biomed. Opt. Express 3, 3325–3331 (2012)

A photonic-crystal fibre interferometer that can function as an optical breath sensor and is safe to use inside a magnetic resonance imaging scanner could prove to be a useful alternative to electronic sensors in hospitals. The face-mask device works by optically sensing the change in air humidity when the patient exhales. A 1-mm-long photonic crystal fibre inside the mask is filled with agarose, whose refractive index is highly sensitive to humidity. This sensitivity causes changes in the optical path length inside a fibre interferometer and thus a rise or fall in the output signal, thereby providing a real-time indicator of the patient's breathing pattern. The researchers behind the invention, from the Dublin Institute of Technology in Ireland, say that before clinical trials can take place the device must be modified so that the patient's eyes are protected from the laser light. Furthermore, the sensor will need to be protected from contamination in case the patient coughs or sneezes.