Optical phase shifters are key building blocks for integrated photonics. Phase modulation is a pivotal operation to enable a diverse range of applications such as optical routing, sensing, light ranging and detection, quantum information processing, or neural networks, to name a few. Phase shifters relying on thermo-optic effects have become mainstream due to their minimal optical losses and straightforward implementation by leveraging microelectronics fabrication. Yet, thermo-optic phase shifters (TOPS) are usually power-hungry and slow. Although intense research has been undertaken over the last decade to improve their performance, optimized structures have been mostly aimed at operating in the visible and near-infrared, thus hindering access to the mid-infrared (MIR) spectral region. Optimized structures are needed for MIR photonics, which is a very appealing field to a broad number of applications such as spectroscopy, chemical and biological sensing, or materials processing due to the strong characteristic absorption of many vital molecules in the MIR range. Here, X. Chang and coauthors propose a power-efficient and fast TOPS with a Figure of Merit of only 7 mW·µs on a Ge-based integrated photonics platform for MIR applications. Such a value is achieved by providing high thermal insulation with air trenches and Si-Ge multilayers, while few-layer graphene is used to speed up heat transfer.

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