The discovery of ferroelectricity in Hafnia (HfO2) and Zirconia (ZrO2) in 2011 raises the question of using these materials in photonic applications due to their compatibility with silicon. In this study, we used first-principles calculations to investigate and report on the electro-optic properties of the ferroelectric orthorhombic Pbc21 and rhombohedral R3m phases of ZrO2 and HfO2. We considered three main contributions to the Pockels effect: electronic, ionic, and piezoelectric. The highest Pockels coefficient of approximately 12 pm/V was found in pure ZrO2. We discuss the potential ways to increase the electro-optic response of ZrO2/HfO2-based materials and the experimental challenges of stabilizing the ferroelectric phase in these materials.
Silicon photonics has been largely developed as a platform to address the future challenges in several applications including datacom, sensing or optical communications, among others. However, the properties of silicon itself is not enough to overcome all limitations in terms of speed, power consumption and scalability. New strategies have then been encouraged based on the hybrid integration of new materials in the silicon photonics platform. In this paper, we will introduce the recent advances in the hybrid integration of doped crystalline-oxides on silicon and silicon nitride waveguides. Especially, Yttria-stabilized zirconia (YSZ) with a lattice parameter compatible with the silicon lattice has been considered because it exhibits promising linear and nonlinear optical properties: low propagation loss, no two photon absorption (TPA) due to its large bandgap energy, a large transparency window from the ultraviolet to the mid-infrared and a good Kerr effect. Furthermore, YSZ can be doped with many dopants to develop active photonic devices with strong second- and third-order nonlinearities and light emission. We have recently demonstrated propagation loss in YSZ waveguides as low as 2dB/cm at a wavelength of 1380 nm, a nonlinear refractive index (Kerr effect) comparable with the SiN coefficient and light amplification in Er3+ doped YSZ on SiN waveguides. The recent results are very promising to pave the way for the development of low cost and low power consumption devices.
New optical materials for hybrid photonic integration on silicon platform have become a hot research topic aiming at providing additional functionalities. In this regard, 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. Transparent oxides with moderate refractive indexes are targeted for hybrid integration due to the rewarding benefits envisioned. Yttria-Stabilized Zirconia (YSZ) is a chemically stable oxide1 with a transparency range that spans from the visible to the mid-IR2, with a refractive index around 2.1, which makes this functional oxide interesting 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 up to now. Nevertheless, this complex functional oxide shows interesting optical properties such as low-moderate propagation losses of 2 dB/cm at telecom wavelengths3.
In our work, we explore the deposition of erbium doped YSZ by pulsed layer deposition (PLD) on a multilayer approach providing outstanding luminescence in correspondence with C-band of telecommunication window (λ=1530 nm) and in the visible range by means of up-conversion processes. The optical properties of active layers of Er-doped YSZ grown on waveguides in different platforms and under resonant pumping will be discussed in this paper, as well as their propagation losses. Based on the preliminary study of these active hybrid systems, we envision light amplification functionalities based on rare-earth doped functional oxides.
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 SiNx 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.
The purpose of this work is to explore an alternative approach for high speed and low power consumption optical
modulation based on the use of the Pockels effect in silicon. Unfortunately, silicon is a centro-symmetric crystal leading
to a vanishing of the second order nonlinear coefficient, i.e. no Pockels effect. To overcome this limitation, on possibility
would be to break the crystal symmetry by straining the silicon lattice with the epitaxial growth of crystalline functional
oxides. Indeed, the induced strain due to lattice parameter mismatch and the difference in the thermal expansion
coefficients between oxides and silicon are strong and may induce strong strain into silicon. Furthermore, functional
oxides can exhibit very interesting multiferroicity and piezoelectricity properties that pave the way to a new route to
implement silicon photonic circuits with unprecedented functionalities.
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