Highly sensitive chemical sensor based on the measurement of the separation of dual resonant peaks in a 100-μm-period fiber grating

A novel chemical or surrounding refractive index sensing scheme based on the measurement of the separation of the dual resonant peaks in a long-period fiber grating with a period of 100 mu m is demonstrated. Because the dual resonant peaks shift in opposite directions with the variation of surrounding refractive index, extremely high sensitivity can be achieved with the scheme. As an example, the minimum concentration change as small as 0.01% for aqueous solutions of cane sugar can be detected. The separation varied 229.2 nm and an average resolution of 4.8 x 10(-5) for the refractive index is achieved in the 1.33-1.44 index range. (C) 1999 Published by Elsevier Science B.V. All rights reserved.