Hexagonal boron nitride is a layered material with some very interesting optical properties: when the edge of a thin flake of boron nitride is illuminated with infrared light, part of the light becomes trapped inside the flake and can only propagate across the two-dimensional surface of the flake as a surface wave – known as a phonon polariton. In recent work, we show a simple way to control the propagation of these waves of light by placing flakes of boron nitride on the surface of the phase change material GeSbTe (GST). Using laser pulses, GST can be reversibly switched between its amorphous and crystalline states, which possess very different optical densities. This property is commonly used in rewritable optical discs such as Blu-rays where it allows for the recording, erasing and rewriting of information bits. Using the same principle, we created lenses, prisms and waveguides by directly writing them into the phase change material layer. Additionally, we demonstrated for the first time that it is possible to erase and rewrite the optical components we created. This work has important implications for the future of optical circuits: Unlike electronic integrated circuits, integrated optics are difficult to miniaturize beyond the diffraction limit with commonly-used materials. However, using polaritons, light can be tightly confined to the nanoscale, and potentially, even to the thickness of just one atom. This study was published in Nature Communications and can be found here. A press release from Harvard SEAS describing this work can be found here.