Towards optical amplification in complex functional oxides: exploring optical gain in erbium-doped yttria-stabilized zirconia waveguides

Functional oxides are a very interesting class of materials due to their singular properties. Material engineering is commonly employed to tune and manipulate such properties at will, thus being functional oxides often used to build active reconfigurable elements in complex systems. In this regard, Yttria-Stabilized Zirconia (YSZ) stands as an interesting material since it has stable thermal and chemical properties and offers a wide transparency range from the visible to the mid-IR wavelength range. Moreover, it has a moderate refractive index of 2.1 which provides a good potential for the development of low-loss waveguides when grown over a low contrast substrate. While these optical properties are very interesting for various applications, including on-chip optical communications and sensing, YSZ has remained almost unexplored in photonics. In this regard, we recently demonstrated YSZ waveguides with propagation losses as low as 2 dB/cm at a wavelength of 1380 nm³. Based on the encouraging preliminary results, we have recently explored the possibility to introduce active rare-earth dopants into YSZ waveguides to demonstrate on-chip optical amplifiers based on YSZ. This work explores the introduction of Er³⁺ ions using a multilayer approach deposited by pulsed laser deposition (PLD) technique, providing outstanding luminescence around λ = 1.55 μm, in correspondence with C-band of telecommunications. Such active layers have been grown onto different platforms, including SiN_x and sapphire. The optical properties of Er-doped YSZ waveguides under resonant pumping and its propagation losses will be discussed in this paper. These results pave the way towards the implementation of new rare-earth-doped functional oxides into hybrid photonic platforms in a customized and versatile manner, adding novel light amplification functionalities.