In a device for measuring physical parameters, such as temperature, light from a light source is coupled through one or more optical wavelengths into and out of a microparticle forming an "optical resonator". To optically and mechanically couple the resonator to the optical waveguide in the most favorable manner, the resonator is disposed within a recess in the optical waveguide, is retained there in a mechanical manner, and is optically coupled to the optical waveguide. The optical waveguide can be configured as a hollow guide. Alternatively, a cuneiform measuring tip is provided, comprising two converging webs, between which the resonator is arranged. The webs are made of light-conducting material while being coupled to at least one light-conducting fiber connected to the light source.