Mode family analysis for PMMA WGM micro resonators using spot intensity changes

The whispering gallery modes (WGM) micro resonators are based on elliptical objects, which can be made from optically transparent materials, The geometry of the object enables optical wave circulating inside the ellipse using total internal reflection. If there is a monochromatic light source with constant intensity to the ellipse, constructive interference may be observed. Poly methyl methacrylate acrylic (PMMA) WGM micro resonators are commercially available with typical optical quality factor of 103-104. These could limit problems with WGM micro resonator expensive manufacturing. Thanks to advances in high resolution image processing, read-outs using spectroscopy (single photo detector) could be replaced with image processing. Image processing (4.5μm/px) allows to split elliptical WGM micro resonator in regions and analyze separate sectors of the ellipse, which can used as a representation of surface irregularity interaction with higher order special mode groups. In the present work new type of image processing for micro-resonators were developed, to analyze intensity distribution in separate regions for the PMMA WGM micro-resonators (40-70 μm). Resonators were coupled using a tapered fiber and fixed wavelength VCSEL laser (760nm). Temperature was change from 20-80 0C which affected the PMMA refractive index (α), for 760nm dn/dT = -1.32 10-4 (0C-1) and thermal expansion (β) dR/dT = 2.60 10-4(0C-1). Combining the following physical changes, total changes (α+ β), WGM PMMA micro-resonator mode mapping was obtained. The following work offers new type of intensity processing methods for measuring applications using PMMA WGM micro resonators.