Improving the reliability of optical phase change materials-based devices

Abstract

Optical components are part of our daily lives, including vision and camera systems, data transmission in telecommunication, sensing applications, manufacturing and medicine, and more. Compact on-chip integrated optics such as photonic integrated circuits and optical metasurfaces can provide us with the desired functionality, but there is a continuous need for active non-volatile tuning capabilities of these devices. Chalcogenide optical phase change materials (PCM) (e.g. Ge₂Sb₂Te₅) have gathered sustained interest in the past several years in the photonics community exactly due to their potential for non-volatile control of optical signals. Prior work had showcased the integration of PCMs via free-space metal heaters for metasurfaces, demonstrating switching for several tens of cycles. To understand the limiting mechanisms preventing extended cycling of such devices, we have developed a near IR transparent platform on doped silicon-on-insulator for testing both material behavior and device performance, along with the auxiliary code and design needed for such testing. Using this platform, a Ge₂Sb₂Se₄Te-based transmissive metasurface filter was demonstrated with a cycling performance of 1250 cycles. Following, the mechanisms limiting the performance of such devices were explored, providing guidelines to improve their reliability and endurance both at the phase change material scale as well as the accompanying device level. Furthermore, we showcase future potential devices that can be leveraged for PCM photonics, including a theoretical design that avoids free carrier absorption losses from the doped silicon heater by placing the dopants at the node of a resonant mode, limiting their overlap with the regions of high field amplitude, and a matrix array of heaters for higher device functionality. Finally, we point towards areas to focus in order to scale these concepts to commercial applications.