Characterization of thermo-optic coefficient and material loss of high refractive index silica sol-gel films in the visible and near-IR

Over the past several decades, silica sol-gel materials have attracted significant interest from the optics community because of their extremely versatile synthesis method. Because silica sol gels are fabricated using liquid precursors, dopants can be directly and uniformly incorporated into the silica matrix. Additionally, judicious selection of the dopant material and sol-gel catalyst allows the refractive index of the final silica film to be tuned over a wide range. Tuning the refractive index of silica materials enables the direct integration of silica devices on a silicon substrate, benefiting applications in telecommunications and integrated optics. While previous materials characterizations studies have focused primarily on the near-IR, given the rapidly emerging field of biophotonics, it is equally important to understand how these materials behave at visible wavelengths. In the present work, thin silica sol-gel films are formed from either tetraethyl orthosilicate (TEOS) or methyltriethoxysilane (MTES) with titanium butoxide (Ti(OBu)(4)). We characterized the basic material properties using Fourier Transform Infrared Spectroscopy (FTIR) and ellipsometry. In addition, by spin-coating the sol gel films onto optical resonant cavities, we determined the thermo-optic coefficient and the transmission loss of the material at both visible and near-IR wavelengths. The addition of titanium allows the films' refractive index, material loss, and thermo-optic coefficient to be tuned, making these films useful for integrated optics and sensing applications. (C)2012 Optical Society of America