Microstructured Fiber Sealed-Void Interferometric Humidity Sensor

This paper reports a simple sealed-void photonic crystal fiber (PCF) interferometric humidity sensor that operates in reflection mode and is presented here for the first time. The sensor was fabricated by collapsing the holes of the PCF at both ends to form an interferometer, which excites the core and cladding modes. As a result, the reflection spectrum of the sensor exhibits a sinusoidal interference peak that shifts when the adsorption and desorption of H₂O molecules happen along the surface of the PCF. This 1.3 cm long PCF interferometer sensor exhibits a sensitivity of 20.3 and 61.6 pm/%RH in the range of 60%RH-80%RH and 80%RH-95%RH, respectively. The sealed-void configuration sensor has a fast response time of ~ 750 ms and also protects the holes of the PCF from contamination. In addition, the all-silica nature of the sensing element has made the sensor insensitive to temperature. The proposed sensor has potential in medical applications for monitoring breathing conditions.