High-accuracy characterization of optical components: Detectors, coatings and fibers: Dissertation

The work described in this thesis is concentrating on the high-accuracy characterization of optical components.

Two trap detectors utilizing germanium and GaAsP photodiodes are constructed and characterized. The results for germanium detectors show that trap detector is well-suitable for applications where harmful inter-reflections need to be avoided. Furthermore, the spatial uniformities of the germanium photodiodes have improved significantly during the recent years. However, germanium detectors have relatively low shunt resistance, which needs to be taken into account when high-accuracy measurements are carried out. Unlike silicon detectors, the GaAsP detectors offer smooth spectral responsivity in the ultraviolet wavelength region and solar blindness. In addition the trap configuration approximately doubles, otherwise relatively low, spectral responsivity of the GaAsP photodiodes. The responsivity of both studied trap detectors is traceable to the cryogenic radiometer making them suitable for absolute power calibrations.

The reliability of the optical characterization methods relies strongly on the accuracy and properties of the applied detectors. High precision spectrophotometric measurements performed at various oblique angles of incidence can improve the determination of optical parameters of thin films. However, this requires systematic error factors such as misalignment in polarization plane and incidence angle and quality of beam collimation to be taken into account. The spectral reflectance and transmittance measurements are carried out for incidence angles varying between normal and Brewster's angle and the results are compared. For the first time, the reached consistency of ∼ 0.2 % between the results confirms the accuracy of the spectrophotometric characterization technique.

The determination of nonlinearity of optical fibers has become more important as the transmission lengths and used optical power has increased in optical long-haul networks. In the thesis, two major improvements for the continuous-wave self-phase modulation method for the determination of nonlinear coefficient of optical fibers have been demonstrated. The first one is a technique to take the effects of dispersion into account by using mathematical modeling based on the Nonlinear Schrödinger Equation. Another one is a measurement scheme of high fiber optic power based on the integrating sphere detector. Together these improvements reduce the uncertainty in the determination of nonlinear coefficient to the level of 2.0 % (k = 2).