Structural Modulated Ultralong Period Microfiber Grating for the Simultaneous Measurement of the Refractive Index and Temperature in a Low-Refractive-Index Range

An optical fiber sensor based on a structural modulated ultralong period microfiber grating (SULPMG) for the simultaneous measurement of the refractive index and temperature within a low-refractive-index (RI) range is experimentally demonstrated. By using the arc discharge method followed by hydrogen-oxygen flame drawing technology, an SULPMG with a small waist diameter provides a strong evanescent field. The results show that a sensitivity as high as 2418.6 nm/RIU and -561.4 dB/RIU can be achieved in the low-RI range from 1.3359 to 1.3402. An experimental temperature sensitivity of approximately -0.145 nm/°C can be achieved over an ambient temperature range of 30-80 °C. The theoretical analysis and experimental results are consistent. The proposed sensor with an outstanding response to a low RI can be applied to research in the chemical analysis and biomedical fields.