Fig. 1. Diagram of sensor structure and fiber photo. (a) Schematic of the designed sensor structure; (b) cross sectional view of PCF; (c) microscope image of waist-enlarged taper

Fig. 2. Reflection spectra of the designed sensor with different PCF lengths

Fig. 3. Spatial frequency spectra of the designed sensor with different PCF lengths

Fig. 4. Setup of humidity sensing experiment

Fig. 5. Humidity response of the sensor. (a) Reflection spectra of the designed sensor under different relative humidities; (b) intensity and wavelength varying with relative humidity; (c) relative humidity sensitivity of the designed sensor with different PCF lengths

Fig. 6. Sensor's temperature response. (a) Reflection spectra of the designed sensor under different temperatures; (b) intensity and wavelength varying with temperature

Fig. 7. Stability of the designed sensor, inset is reflection spectra at RH of 20%, temperature of 27 ℃

Fig. 8. Response time of the designed sensor