Whispering gallery modes in a single silica microparticle attached to an optical microfiber and their application for highly sensitive displacement sensing.

A compact and relatively stable structure is experimentally demonstrated to excite whispering gallery modes (WGMs) in a single chemically fabricated silica microparticles with a diameter of around 10.6 μm attached to an optical microfiber. The resonance dip with an extinction ratio of 14 dB and Q factor of around 300 has been achieved. Based on the WGMs in this structure, an in-line fiber-optic displacement sensor is presented with a high sensitivity of 33 dB/mm and a measurement range of over 400 μm. The measurement resolution of this displacement sensor can reach to ~10 μm. The good reversibility and repeatability are also verified. This work offers a scheme to observe the WGMs in a single silica microparticles and demonstrates their application for in-line highly-sensitive displacement sensing.