A passive integrated optical waveguide refractometer based on bendloss changes in a spiral-shaped channel waveguide is proposed and fabricated inSi3N4/SiO2technology. The experimentally determined performance and the theoretical predictions, based on a simple model for so-called “whispering gallery modes,” agree very well. The minimum detectable refractive index change was measured to be&Dgr;n=1.3×10−5.©1997 American Institute of Physics.