Antti Lamminpää

Characterization of thin films based on reflectance and transmittance measurements at oblique angles of incidence

The optical parameters of a SiO2 thin-film coating determined from the spectral reflectance and transmittance measurements at various incidence angles, including the normal incidence and the Brewsters angle, are compared in this paper. The high-accuracy measurements were carried out through visible-near-infrared spectral regions by using our purpose-built instruments. The optical parameters obtained from the reflectance and the transmittance data are consistent over the angles of incidence and agree within 0.2%. The effect of important systematic factors in the oblique-incidence spectrophotometric measurements is also discussed.

Characterization of germanium photodiodes and trap detector

We have developed and characterized new detectors based on germanium (Ge) photodiodes to be used in the wavelength region between 900 and 1650 nm. The effects of spatial uniformity, temperature and low shunt resistance on the spectral responsivity measurements are studied. Our results for the spatial uniformities show improvements as compared with earlier studies. The spectral reflectances of a Ge photodiode and trap detector are also studied, and the trap reflectance is found to be less than 10−4 at wavelengths longer than 900 nm. The results of this study show that with careful use, the large area Ge photodiodes can offer a cost-effective alternative as compared with InGaAs photodiodes of similar diameters.

Reliable Determination of Optical Fiber Nonlinearity Using Dispersion Simulations and Improved Power Measurements

We have improved the accuracy of the continuous-wave self-phase modulation method for measuring the nonlinearity of optical fibers. Evaluation of the measurement uncertainty shows that the most significant source of uncertainty is the measurement of fiber-optic power. However, chromatic dispersion can also have a significant effect on the apparent results if it is not taken properly into account. We demonstrate means to achieve an expanded uncertainty of 2% (coverage factor k=2) for the measurement of the nonlinear coefficient n2 /Aeff. Also, the metrological aspects related to the determination of the nonlinear coefficient and the measurement uncertainty are discussed

Characterization of GaAsP trap detector for radiometric measurements in ultraviolet wavelength region

A trap detector was constructed of three Schottky-type 10×10mm2 GaAsP photodiodes. The spectral reflectance of the trap detector was calculated from the measured spectral reflectances of a single GaAsP photodiode in the wavelength range between 240 and 600nm, and compared to the measured spectral reflectance of the trap detector at three laser wavelengths. The absolute spectral responsivity of the trap detector was measured. The internal quantum efficiencies (IQE) of the trap detector and a single photodiode were calculated in the wavelength region between 250 and 400nm from the spectral reflectances and responsivities. The comparison revealed reduction of the apparent IQE of the trap detector as compared to the single photodiode at the level of 10%. The spatial uniformity of the responsivity of the trap detector was measured, and the corresponding uncertainty component at 325nm was calculated to be 4×10−4. The effect of moderate ultraviolet exposure at the level of 50mJ∕cm2 on the stability of the respon...