Development of measuring system of whispering gallery mode resonances for evaluating a diameter of microsphere

Abstract

A sphere is a frequently used shape as a reference of calibration for 3-dimensional measurement instruments because of its isotropic shape. It is demanded to measure the diameter of the reference sphere with high accuracy. For micro-scale 3-dimentional metrology, size of the reference sphere is from several millimeters to a few tens of micrometers. These spheres have to be measured with accuracy of better than 10 nm. Therefore, we have proposed the new measurement method of a microsphere based on whispering gallery mode resonances. One of the key points to the proposed method is to measure the whispering gallery mode resonant wavelength accurately and precisely. In this paper, the measurement system for WGM was developed. Using this system, the measurement repeatability of WGM resonant wavelength better than 0.2 pm was achieved.