Abstract
Development of low-loss photonic components in the ultraviolet (UV) band will open new prospects for classical and quantum optics. Compared with other integrated platforms, aluminum nitride (AlN) is particularly attractive as it features an enormous bandgap of ~6.2 eV and intrinsic chi(2) and chi(3) susceptibilities. In this work, we demonstrate a record quality factor of 2.1 x 105 (optical loss ~ 8 dB/cm) at 390 nm based on single-crystalline AlN microrings. The low-loss AlN UV waveguide represents a significant milestone toward UV photonic integrated circuits as it features full compatibility for future incorporation of AlGaN-based UV emitters and receivers. On-chip UV spectroscopy, nonlinear optics and quantum information processing can also be envisioned.
Highlights
Integrated photonic components have gained remarkable progress at the telecom band thanks to the maturity of silicon photonics [1]
Since the relatively narrow bandgap (∼1.1 eV) of silicon limits its utility at short wavelengths, the development of a wide bandgap photonic platform, such as aluminum nitride (AlN), is desirable
This wideband transparency allows AlN photonic components to interact with ions at UV and visible regions, such as ytterbium (171Yb+) at 369.5 nm, nitrogen vacancy (NV) centers in diamond at 637 nm, and rubidium (85Rb) at 778.1 nm, as required for on-chip quantum computing [6] and precision optical clocks [7]
Summary
Crystalline AlN is grown on c-plane sapphire by metalorganic chemical vapor deposition (MOCVD). Since the AlN-on-sapphire wafer is highly insulating, we spin 300 nm poly(4-styrenesulfonic acid) (PSSA) on top of the FOx-16 resist and sputter 10 nm gold to mitigate charging effects. The wafer is embedded in SiO2 by plasma-enhanced chemical vapor deposition (PECVD) and is cleaved to expose waveguide facets. When optimizing the alignment at 390 nm, we observe a large transmission background variation of ∼20 dB for the wavelength from 389.5 to 390.5 nm (Supplementary 1). To address this issue, we divide the 1-nm scanning range into several sections, and optimize the alignment separately to suppress the power fluctuation into the fiber
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