A general relation for group delay and the relevance of group delay for refractometric sensing

The relevance of our definition for sensitivity in refractometric sensing, being the relative change of the transmittance of a certain output channel of an optical device over the change of the refractive index of the probed material, is discussed. It is compared to one based on spectral shift per refractive index unit change. Further, it is discussed how group delay and sensitivity are interrelated, can be converted into each other and which physical quantities are relevant for high sensitivity. As a byproduct of the presented theory a general expression relating group delay and the ratio of the time-averaged optical energy and the input power is presented.