The use of erbium fiber laser relaxation frequency for sensing refractive index and solute concentration of aqueous solutions

We report a novel‐principle fiber‐laser intra‐cavity sensor for measuring refractive index and solute concentration of aqueous solutions. The sensor operation is based on a variation of the laser oscillation relaxation frequency (the measured parameter), sensitive to the intra‐cavity loss change. The sensor capacity is demonstrated on the example of measurements of sugar concentration in water. A modeling of the sensor operation is presented, allowing its performance optimization. (© 2008 by Astro Ltd., Published exclusively by WILEY‐VCH Verlag GmbH & Co. KGaA)