Liquid Modified Anti-Resonant Reflecting Guidance in Silica Capillary for Sensing Applications

In this work, the transmission characteristic of a single mode fiber-silica capillary-single mode fiber (SMF-Capillary-SMF) structure is modified by introducing liquids inside and outside the silica capillary. The anti-resonant reflecting guidance mechanism in the silica capillary is influenced by the presence of the liquids. By immersing a section of liquid-filled SMF-Capillary-SMF structure into liquids, both the resonant wavelength and transmission intensity are altered due to a liquid-modified resonant condition. Temperature change will lead to the refractive index (RI) variation of liquids, causing the resonant wavelength to shift. Experimental results indicate that the temperature sensitivity is dependent on the RI value of the liquids, and the liquid temperature sensitivity of 2.99 nm/°C is experimentally achieved in the temperature range of 25 °C-60 °C when the liquid RI is 1.39. On the other hand, the transmission intensity at resonant wavelength, which is determined by the reflectivity at the inner and outer surfaces of the ring cladding, can be affected when the RI of the ambient liquid changes. The intensity at resonant wavelength increases as the ambient RI rises, and the RI sensitivity varies from 240 dB/RIU to 60 dB/RIU in the RI range of 1.31 to 1.39. Such a device is simple and easy to fabricate, which can find wide applications in liquid environments like biochemical and pharmacy industries.