Sapphire Integrated Photonics Written by Femtosecond Laser

There is a growing interest in the study of sapphire as an integrated photonics platform, especially because of its excellent resilience to extreme environments and its superior optical and mechanical properties. While other types of femtosecond laser-written waveguides have been identified in crystals, the depressed cladding waveguide (DCW) is preferred due to its thermal stability and polarization-independent performance [1]. However, one drawback of a DCW is propagation loss, which is primarily dominated by radiation loss due to its limited cladding size [2]. In this work, we demonstrate multi-layered DCWs and their potential for fabricating evanescently coupled devices.