Real-time in situ ellipsometric control of antireflection coatings for semiconductor laser amplifiers using SiOx

Abstract

We demonstrate an innovative technique based on real-time in situ ellipsometry to achieve precise monitoring and control of the refractive index of antireflection coatings for semiconductor laser amplifier facets. The refractive index and the layer thickness are extracted every 0.5 s using two thin-film models: the conventional four-medium model which provides an averaged refractive index over the total deposited film, and an adaptive multilayer model which keeps tract of all the previous thin layers that have been deposited and provides a sensitive and instantaneous response to any new refractive index change. A simple procedure to account for polarization effects due to strain in the windows of the evaporator is also described. Using the weighted average of the refractive indices obtained with these two techniques as a feedback parameter, control of the averaged refractive index of SiOx deposited films within ±0.01 and facet reflectivities of order 10−4 or better are reproducibly obtained.