Micro-bottle resonator for sodium hypochlorite sensor

Optical micro-bottle resonator (MBR) structure fabricated based on arc fusion approach is widely deployed to fabricate compact, cheap and versatile sensors. In this work, MBR sensor is proposed and demonstrated for measuring sodium hypochlorite concentration. The MBR has a bottle diameter, bottle length and stem diameter of 180 µm, 183 µm and 125 µm respectively. It is fabricated through a ‘soften-and-compress’ method using a fusion splicer. A tapered microfiber with a 2 µm diameter is used to launch light into the structure. The wavelength gallery mode resonances are observed with a Q-factor of approximately 7.95 × 105. It seems that the power of the transmitted light through the MBR reduces with the increase of sodium hypochlorite concentration from 1% to 6%. The sensitivity of the sensor is about 3.7319 dB/%ppm, which is higher than that of the bare microfiber-based sensor. The whispering gallery mode's resonance wavelength also shifts from 1552.203 nm to 1552.213 nm with a sensitivity of 0.002 nm/%ppm and linearity of 97.64%, as the hypochlorite concentration increases from 1% to 6%. These results indicate that the MBR structure has a great potential to be used as a sodium hypochlorite sensor.