Whispering-gallery mode sensor based on coupling of tapered two-mode fiber and glass capillary

A novel whispering-gallery mode (WGM) sensor is fabricated by coupling a tapered two-mode fiber and a glass capillary. By utilizing the relatively large orifice of glass capillaries, polydimethylsiloxane (PDMS) and magnetic fluid are directly injected into two WGM structured glass capillaries, respectively, allowing these materials to substantially interact with the light field of the WGM, thereby achieving temperature, pressure, and magnetic field measurements. λ1 and λ2 are the two resonant peak wavelengths of the WGM after injecting PDMS into a glass capillary. λ3 is the resonant peak wavelength of the WGM after injecting the magnetic fluid into the glass capillary. The experiments found that λ1 and λ2 exhibit high sensitivity to temperature and air pressure, and λ3 is sensitive to magnetic field. The temperature and air pressure sensitivities of λ1 are −624 pm/°C and −7.04 nm/MPa, respectively. The temperature and air pressure sensitivities of λ2 are −964 pm/°C and −15.08 nm/MPa, respectively. The magnetic field sensitivity of λ3 is 107 pm/mT in the range of 9.45–62.91 mT. The proposed sensors have the advantages of low cost, simple fabrication, and high sensitivity, and they can be applied to temperature, gas pressure, and magnetic field measurements.