Optically tunable topological photonic crystal

Topological photonic insulators can enable the development of efficient integrated photonic devices with minimized scattering losses. The optical properties of the majority of topological structures proposed to date are fixed by designs such that no changes to their performance can be made once the device has been fabricated. However, tunability is important for many applications, including modulators, switches, and optical buffers. We therefore propose a straightforward way to dynamically control transmission in a silicon-based topological photonic crystal using all-optical free-carrier excitation that allows for fast refractive index modulation. The changes in both the real and imaginary parts of the refractive index cause a blue shift of the transmission spectrum by up to 20 nm and a reduction in transmission by approximately 85% . With the control mechanism used here, we can achieve switching times of the order of nanoseconds. The structures proposed here are compatible with the standard semiconductor industry fabrication process and operate at telecommunication wavelengths.