Temperature and strain discriminating sensor based on the monitoring of cladding modes of a single femtosecond inscribed grating

In this paper we demonstrate a simple temperature and strain discriminating sensor based on a single fibre Bragg grating inscribed by a femtosecond laser via the point-by-point technique. These gratings exhibit strong and extensive cladding mode structures and by simultaneously monitoring both the Bragg wavelength and a cladding mode spaced by ~ 40 nm from the Bragg peak, as a function of both temperature and strain, it is possible to distinguish between the two effects and potentially obtain and increased sensitivity over prior reports for similar systems. In preliminary experiments the two parameters were determined with an accuracy of 1°C and 40 με respectively. Due to the close spectral separation of the two peaks that were monitored, quick and simultaneously measurements of the two parameters was possible, allowing for real time measurements of the temperature and strain and making the device practical for use in various applications.