PMMA Solid bottle optical microresonator for measure relative humidity.

Abstract

In this work we studied experimentally the performance of an solid bottle optical resonator made of PMMA (polymethylmethacrylate) for measure the relative humidity of the medium. In the developed device, the WGMs modes within the microcavity are excited by the proximity of an optical fiber taper with an outer diameter of the order of 3-5 microns made from stretching a standard optical fiber of Silica by the flame brushing technique. In the resonant device, the field produced by a laser system tunable TLS is guided through the fiber taper and is coupled into the microcavity by the approach of the fiber taper to the equatorial zone of the microbottle, causing the excitation of the WGMs resonant modes inside the same. When the device is subjected to changes in relative humidity of the medium, the wavelengths of resonance of WGMs modes that have been coupled in the microresonator are shifted spectrally depending on the external humidity, showing an experimental sensitivity in the resonator due to changes in the relative humidity of the medium.In the experiment, it was possible to produce different samples of optical resonators with a profile shaped bottle with different maximum diameters achieving a maximum sensitivity of 0.032 nm/% RH for a resonator with equatorial diameter of 1250 μm.