A novel ultrasensitive fiber-optic refractive index (RI) sensor is proposed and experimentally demonstrated for solute concentration measurement. To realize higher RI sensitivity, we insert a fiber-optic multimode interference sensor into a fiber-loop configuration to produce a steeper spectrum. The interaction with multimode interference is repeated and enhanced by the fiber loop, resulting in an output spectrum steeper than that obtained without a fiber loop. An ultrahigh RI resolution of 3.06 ' 10%7 refractive index unit (RIU) is obtained in the steepest RI range, and it is higher by approximately 53.6 times. We apply this sensor to the measurement of the concentration of a sodium chloride solution and obtain a resolution of 1.87 ' 10%4 wt %. This result agrees well with the RI measurement result. The results show that this ultrasensitive RI sensor has the potential for detection applications in the chemical and biomedical fields.
ASJC Scopus subject areas
- Physics and Astronomy(all)