We introduce a novel method to geometrically tune the tension in prestrained resonators by making Si3N4 strings with a designed predisplacement. This enables us, for example, to study their dissipation mechanisms, which are strongly dependent on the stress. After release of the resonators from the substrate, their static displacement is extracted using scanning electron microscopy. The results match finite-element simulations, which allows a quantitative determination of the resulting stress. The in- and out-of-plane eigenmodes are sensed using on-chip Mach-Zehnder interferometers, and the resonance frequencies and quality factors are extracted. The geometrically controlled stress enables tuning not only of the frequencies but also of the damping rate. We develop a model that quantitatively captures the stress dependence of the dissipation in the same SiN film. We show that the predisplacement shape provides additional flexibility, including control over the frequency ratio and the quality factor for a targeted frequency.

Aluminum nitride (AlN) is an emerging material for integrated quantum photonics due to its large chi((2)) nonlinearity. Here we demonstrate the hybrid integration of AlN on silicon nitride (SiN) photonic chips. Composite microrings are fabricated by reactive DC sputtering of caxis oriented AlN on top of pre-patterned SiN. This new approach does not require any patterning of AlN and depends only on reliable SiN nanofabrication. This simplifies the nanofabrication process drastically. Optical characteristics, such as the quality factor, propagation losses and group index, are obtained. Our hybrid resonators can have a one order of magnitude increase in quality factor after the AlN integration, with propagation losses down to 0.7 dB/cm. Using finite-clement simulations, phase matching in these waveguides is explored. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Reciprocal space engineering allows tailoring the scattering response of media with a low refractive-index contrast. Here it is shown that a quasiperiodic leveled-wave structure with well-defined reciprocal space and random real space distribution can be engineered to open a complete photonic bandgap (CPBG) for any refractive-index contrast. For these structures, an analytical estimation is derived, which predicts that there is an optimal number of Bragg peaks for any refractive-index contrast. A finite 2D or 3D CPBG is expected at this optimal number even for an arbitrarily small refractive-index contrast. Results of numerical simulations of dipole emission in 2D and 3D structures support the estimations. In 3D simulations, an emission suppression of almost 10 dB is demonstrated with a refractive index down to 1.38. The 3D structures are realized by additive manufacturing on millimeter scale for a material with a refractive index of n approximate to 1.59. Measurements confirm a strong suppression of microwave transmission in the expected frequency range.

Visualizing eigenmodes is crucial in understanding the behavior of state-of-the-art micromechanical devices. We demonstrate a method to optically map multiple modes of mechanical structures simultaneously. The fast and robust method, based on a modified phase-lock loop, is demonstrated on a silicon nitride membrane and shown to outperform three alternative approaches. Line traces and two-dimensional maps of different modes are acquired. The high quality data enables us to determine the weights of individual contributions in superpositions of degenerate modes.

Aluminum nitride (AlN) is an emerging material for integrated quantum photonics with its excellent linear and nonlinear optical properties. In particular, its second-order nonlinear susceptibility χ(2) allows single-photon generation. We have grown AlN thin films on silicon nitride (Si3N4) via reactive DC magnetron sputtering. The thin films have been characterized using x-ray diffraction (XRD), optical reflectometry, atomic force microscopy (AFM), and scanning electron microscopy. The crystalline properties of the thin films have been improved by optimizing the nitrogen to argon ratio and the magnetron DC power of the deposition process. XRD measurements confirm the fabrication of high-quality c-axis oriented AlN films with a full width at half maximum of the rocking curves of 3.9° for 300 nm-thick films. AFM measurements reveal a root mean square surface roughness below 1 nm. The AlN deposition on SiN allows us to fabricate hybrid photonic circuits with a new approach that avoids the challenging patterning of AlN.

We demonstrate sputtering of high-quality aluminum nitride films onto prefabricated silicon nitride photonic circuits, simplifying their nanofabrication. Hybrid microring devices show reduced bending loss and low propagation losses, enabling future on-chip quantum optics experiments.

Recent developments in quantum computing and the growing interest in optomechanics and quantum optics need platforms that enable rapid prototyping and scalability. This can be fulfilled by on-chip integration, as we present here. The different nanofabrication steps are explained, and our automated measurement setup is discussed. We present an opto-electromechanical device, the H-resonator, which enables optomechanical experiments such as electrostatic springs and nonlinearities and thermomechanical squeezing. Moreover, it also functions as an optomechanical phase shifter, an essential element for our integrated quantum optics efforts. Besides this, the equivalent of a beam splitter in photonics-the directional coupler-is shown. Its coupling ratio can be reliably controlled, as we show with experimental data. Several directional couplers combined can realize the CNOT operation with almost ideal fidelity.