An optical sensing system and method of using it includes a light source and a first bus waveguide having an input port that is in optical communication with the light source. The system further includes a microresonator configured so that the light source excites at least first and second resonant guided optical modes of the microresonator. The microresonator includes a first location on a surface of a core of the microresonator where a field intensity of the first mode is greater than a field intensity of the second mode. The microresonator core has a first cladding at the first location. The microresonator also has a second location on a surface of the core of the microresonator where a field intensity of the first mode is less than or equal to a field intensity of the second mode, the microresonator core having a second cladding at the second location. The first cladding is different than the second cladding.