Monolithic 3D integration of tantalum pentoxide nonlinear photonics

The photonics landscape encompasses a wide scope of material platforms, each optimized for specific functionalities, yet no platform meets the demands of all current and evolving photonic applications. Although combining integrated-photonics materials enhances overall capability, such as unifying nonlinear optics, low-loss passive devices and electro-optics, material and process compatibility remains a major challenge. Here we introduce full-wafer, monolithic 3D integration of tantalum pentoxide (Ta₂O₅, hereafter tantala¹) photonics directly onto a patterned substrate, demonstrated here with thin-film lithium niobate². Tantala's unique properties, importantly room-temperature deposition, moderate-temperature annealing and low residual stress in thick films optimized for phase matching, make it well suited for monolithic 3D integration without compromising substrate performance or compatibility. We demonstrate low-loss, high-quality-factor microresonators and nanophotonics in tantala, robust quasi-phase-matching in poled lithium niobate waveguides³, and efficient 3D interlayer routing. These capabilities enable us to demonstrate a rich palette of nonlinear frequency conversion processes, including χ⁽³⁾ four-wave mixing for supercontinuum generation, optical parametric oscillation and dark-pulse microcomb generation in tantala microresonators and photonic crystal resonators, χ⁽²⁾ second-harmonic generation in periodically poled lithium niobate, and combinations thereof.