A spectroscopic prism coupler for measuring the refractive indices and thicknesses of dielectric films
A spectroscopic prism coupler is created for measuring refractive indices nf and thicknesses Hf of dielectric films. The operating principle of the device is based on the simultaneous resonance excitation of several waveguide modes in a film by a focused TE or TM polarized light beam in the geometry of frustrated total internal reflection. Calculations of nf and Hf are performed using measured angular positions θm of dark m-lines in the cross section of the specularly reflected beam. Using obtained angles θm, we can calculate effective refractive indices βm of modes. By solving a set of nonlinear dispersion equations for the modes of a planar waveguide, we can calculate refractive index nf and thickness Hf of a film. The proposed prism coupler has no moving parts and allows us to measure the optical parameters of films 0.5–10 μm thick in the 400–1100 nm range of wavelengths. The device can also be used as a spectroscopic refractometer for measuring the refractive indices of bulk media. The device is used to measure refractive index and thickness of a SiO film and the refractive index of TF4 glass.