Amorphous Silicon-Doped Titania Films for on-Chip Photonics

High quality optical thin film materials form a basis for on-chip photonic micro- and nanodevices, where several photonic elements form an optical circuit. Their realization generally requires the thin film to have a higher refractive index than the substrate material. Here, we demonstrate a method of depositing amorphous TiO2 films doped with 25% Si on various substrates, a way of shaping these films into photonic elements, such as optical waveguides and resonators, and finally, the performance of these elements. The quality of the film is estimated by measuring thin film cavity Q-factors in excess of 105 at a wavelength of 790 nm, corresponding to low propagation losses of 5.1 db/cm. With a refractive index of n > 2, the film supports waveguiding on different substrates, such as quartz, YAG, and sapphire, and shows evanescent coupling to chromium ions embedded in YAG, presenting film substrate interaction. Additional functionalization of the films by doping with optically active rare-earth ions such as erbium is also demonstrated. Thus, Si:TiO2, films allow for creation of high quality photonic elements, both passive and active, and also provide access to a broad range of substrates and emitters embedded therein.