Sensitive and simple methods to examine the quality of waveguide layers, such as in-plane scattering method and laser beam scattering method, are newly introduced. We apply this methods to evaluate the silica-based CVD and FHD waveguides layers and compare these methods with others such as the stylus scan measurement of the surface, the interferometric test of waveguide layer, and the measurement of propagation loss. The Fl-ID waveguide generally shows higher loss with more surface waviness than the CVD waveguide, which comes from the different nature of the FHD process. The quality of the best optimized FHD wafer aproaches that of the CVD wafer, but depends highly on the process condition.
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