Packaging and ultra-sensitive sensing of micro optical resonators with flow paths

Whispering-gallery-mode micro optical resonators have a very high Q-value, so they are sensitive to small changes in the environment around the resonator. Even a slight change in the complex permittivity allows light to interact for a long time, so that absorption (Q-value) or refractive index changes (resonance wavelength) can be captured. Using this property, ultra-sensitive optical sensors at the molecular level have been demonstrated.

However, previous studies have been conducted under strict laboratory conditions. In order to use the device as a sensor, it is necessary to take the device out of the laboratory, which requires the development of packaging techniques with optical fibers and flow paths. However, the whispering-gallery-mode micro optical resonator requires a nanofiber with a tapered diameter to input and output light via evanescent light, and precise positioning has been indispensable. We packaged nanotapered fibers and micro optical resonators by using a curing agent with a small volume change. We also integrated them with flow paths. This is an example of optofluidics, a research field in which the integration of optical circuits and channels provides novel functions.