Intensive researches are currently conducted on the miniaturization of photonic devices and on the combination of photonics and electronics to decrease the power consumption and to create novel functionalities for a myriad of applications including datacom, telecom, sensing and quantum optics, to name few. In this context, functional oxides have emerged as promising materials to expand the functionalities of current photonic circuit thanks to their wide range of properties including multiferroicity, piezoelectricity and optical nonlinearities. Among these materials, Yttria-Stabilized Zirconia (YSZ) is well known as a buffer layer for oxide-based thin films heterostructures, extensively used for LiNbO3, PbTiO3, Pb(Zr,Ti)O3 and YBa2Cu3O7 integration on silicon. YSZ is also well known for its extraordinary thermal and chemical stability, as well as its hardness and mechanical durability. An increasing quantity of applications uses this material for the combination of its excellent mechanical and optical properties, such as its high refractive index, large optical band gap and transparency from the ultraviolet (UV) to the mid-infrared (mIR). However, no work has been performed for its use in integrated optics, yet.
This work has been mainly focus on the integration of YSZ functional oxide on sapphire substrates. Due to the refractive index contrast between sapphire (1.75) and YSZ (2.12) at a wavelength of 1300 nm, optical YSZ waveguides can be designed with good mode confinement. The study and optimization of growth parameters using Pulsed-Laser Deposition (PLD) technique allowed achieving high quality YSZ films on sapphire (0001) with remarkably sharp X-Ray diffraction rocking curve peaks in 10-3 degrees range for two different out-of-plane orientations. We have demonstrated that a thermal annealing of the sapphire substrate before the growth, played an important role in thin film orientation. Passive photonic structures including grating couplers, single-mode waveguides and resonators have been then designed and fabricated using electronic lithography and Ion-Beam Etching (IBE) techniques. Preliminary optical characterization results of integrated structures will be presented such as propagation losses in YSZ waveguides as low as 2 dB/cm, ring and disk resonators with Q factors up to 12000, narrow-band Bragg filters with 16.2 dB extinction ratio for 1.5 nm bandwidth. Finally, large third-order nonlinear susceptibility has been estimated to be three times larger than in silicon with the absence of two photon absorption at telecom wavelengths. Our results demonstrated the fabrication of passive devices and basic building blocks, which combined with the outstanding nonlinear properties, provide a promising robust platform for functional oxides-based nonlinear on-chip applications. Furthermore, the first integration of YSZ on silicon photonics platform will also be reported.