A self-referencing composite Fabry-Pérot cavity sensor, including methods of use and manufacture. The cavity sensor comprises a substrate defining a first cavity portion juxtaposed to a second cavity portion. The first and second cavity portions are provided having a predetermined depth offset. A polymer or other dielectric material is disposed within the first and second cavity portions. An interference spectrum resulting from a light source of a known wavelength is reflected through the sensor and produces a first refractive index from the first cavity portion offset by a second refractive index from the second cavity portion. The difference in refractive indices can be used to determine various physical parameters. An optical sensor according to the present technology may be used with vapor sensing, pressure sensing, protein detection, photo-acoustic imaging, and the like.