Aluminum Oxide 50/50 Splitter Based on Multimode Interferometer for the Blue/Near-UV Spectral Range

Research on integrated blue and near-ultraviolet photonics has been increasingly investigated in recent years. To enable the development of photonic integrated circuits in this wavelength range, one of the challenges is to identify a transparent platform that can provide a variety of integrated components. Aluminum oxide (Al₂O₃) was demonstrated to exhibit low propagation losses for wavelengths below 450 nm, making it a very promising platform to operate at short wavelengths. MMIs are very convenient integrated components for splitting or combining signals and can be used for many applications such as on-chip spectrometry or microscopy. The development of a 50/50 coupler at 405 nm is reported based on symmetrical multimode interferometer (MMI) presenting a splitting ratio of $3.20~\pm ~0.34$ dB/MMI. Characterizations at 375, 420, and 454 nm are also presented.