Low-loss, low-background aluminum oxide waveguide platform for broad-spectrum on-chip microscopy

A versatile wide-spectrum photonic integrated circuit (PIC) platform, spanning from ultraviolet (UV) to infrared (IR) wavelengths, is essential for advancing on-chip optical microscopy and spectroscopy applications. The key desirable requirements for PICs are low-loss, low-autofluorescence background signals, and high-refractive index contrast (HIC) to enable compact designs. Here, we present a low-loss, low-autofluorescence aluminum oxide (Al₂O₃) waveguide platform developed using atomic layer deposition (ALD). At 405 nm, the Al₂O₃ strip waveguide exhibits an autofluorescence background approximately 200 times lower than silicon nitride (Si₃N₄) and a propagation loss of less than 0.5 dB/cm. We demonstrate the suitability of the Al₂O₃ platform for multicolor on-chip total internal reflection fluorescence (TIRF) and super-resolution optical microscopy. The proposed Al₂O₃ platform offers a promising solution for highly sensitive on-chip bioimaging and spectroscopy applications.