Sensing applications of a low-coherence fibre-optic interferometer measuring the refractive index of air

A remote fiberised low-coherence interferometric sensor has been used to measure the refractive index of air. The relative humidity, temperature, pressure or carbon dioxide content may be determined from the measurement of the refractive index of air if the values of the other parameters are known. The sensor works linearly, for example, over the full range of humidity and does not suffer from aging or hysteresis. This maintenance-free sensor has a relative accuracy of 1.6% with a fast response time. The relative sensitivity of the sensor to changes in the values of the other parameters influencing the refractive index of air has also been deduced. The sensor is designed primarily for industrial applications where conventional electronic sensors cannot be used in environments where materials degradation prevents the use of conventional gas and humidity sensors.