Měření optických materiálů a struktur interferenčními metodami

Abstract

The thesis deals with the use of a technique of white-light spectral interferometry for measuring the group dispersion of optical materials and optical fibres, the effective thickness of optical elements and the thickness of a SiO2 thin film on silicon substrate, respectively. The thesis presents the theoretical analysis and the measurement results obtained by using new experimental setups. Using a Michelson or a Mach-Zehnder interferometer and their combination, respectively, that is a tandem configuration, the group dispersion of optical samples was measured. The recorded spectral interferograms for measuring the equalization wavelength and the knowledge of the thickness of optical element as well are utilized. The measurement was applied to a glass plate and a birefringent quartz crystal. Using a Mach-Zehnder interferometer, the group dispersion of optical fibres was measured. The recorded spectral interferograms for measuring the equalization wavelength and the knowledge of the length of optical fibre, which is placed in one of the arms of the interferometer, are utilized. In the first step, the differential group refractive index of the outer cladding and modes guided by the optical fibre is measured. In the second step, the fibre is replaced by the reference sample of the known thickness and group dispersion to determine the absolute group index of the fibre. The measurement was applied to two different optical fibres made of two different optical glasses - pure silica glass and SK222 glass. Next, two methods of spectral interferometry are presented for measuring the effective thickness of optical elements of known dispersion. The methods utilize a Michelson or a Mach-Zehnder interferometer. The first method is suitable for thinner samples and from the recorded spectral interferograms the phase function is retrieved by using a windowed Fourier transform. From the phase function, the effective thickness of optical element is determined under the knowledge of phase dispersion. The second method is suitable for thicker samples and we measure the equalization wavelength as a function of the mirror displacement from which the thickness of optical sample is determined under the knowledge of group dispersion. The measurement was applied to a glass plate and a birefringent quartz crystal. In this thesis we also present the use of spectral interferometry with a Michelson 3 interferometer for measuring the thickness of a SiO2 thin film on silicon substrate. We utilize two different approaches. First, we compare the recorded spectral interferogram with the theoretical one evaluated by using the known optical parameters and dispersion relations. Second, we compare the measured spectral functions (the optical path difference and the nonlinear phase function) with theoretical ones under the knowledge of optical parameters of the thin film and the substrate. 4