Direct Laser Writing Polymer Micro-Resonators for Refractive Index Sensors

A sensitive refractometric polymer micro-resonator sensor is fabricated using direct laser writing. The design consists of two tapered waveguides that can be directly coupled by single mode fibers, two Y splitting waveguides that are combined in a Mach-Zehnder interferometer (MZI) configuration and a micro-cylinder that evanescently couples with the arms of the MZI. The resonant wavelength shifts in response to the refractive index change in the surrounding medium of the micro-cylinder. The strong interaction between the medium and the whispering gallery mode results in a sensitivity of 154.84 nm/RIU (refractive index units), which demonstrates that such micro-resonators can be used for measurements of refractive index of liquids.