Simple and Temperature-Insensitive Pressure Sensing Based on a Hollow-Core Photonic Crystal Fiber

Abstract

The sensitivity to pressure of lossy air-guided modes in a commercial hollow-core photonic crystal fiber was experimentally exploited to develop a novel pressure sensor. The transmission of these modes was directly modulated by the measurand, which makes the interrogation system very simple. Using a supercontinuum source, these specific modes were identified within the visible spectral range and correspond to narrow transmission windows well away from the fiber’s main bandgap, centered around 1550 nm. The origin of these windows is being investigated but is likely to be related to cladding bandgaps. One of these windows, around 633 nm, was used for the analysis presented in this paper. An attenuation increase was observed when pressure was applied to a ~3-cm long cell, which was traversed by the fiber. The attenuation reached 5 dB with 300 kgf/cm2 gauge pressure. The transmission was found to be insensitive to temperature up to 100%, which is a highly attractive feature for sensing applications. It was also found that much higher sensitivities (a few dB attenuation with ~0.5 kgf/cm2 gauge pressure) could be obtained when pressure was internally applied to the fiber microstructure. This fact allows for the construction of sensors with a wide range of sensitivities, which can, thus, suit different applications. Transmission within the infrared bandgap was insensitive to pressure and can serve as a reference.