Topological photonic crystal nanocavities for confinement of light at telecom wavelengths

Bringing topological physics from condensed matter to the optical domain offers unprecedented prospects in the control of light. Recently, the photonic analogue of the quantum spin Hall effect (QSHE) was proposed in 2D photonic crystal (PhC) structures featuring an interface between two topological distinct domains. Photonic spin-orbit coupling, mediated by the specific lattice symmetries, results in the emergence of helical edge states, guided along the interface in a protected manner. We fabricate and study topological PhC cavities emulating the QSHE that are coupled to the radiation continuum and perform imaging and Fourier spectroscopy in the far field to characterize their properties. We examine the robustness of cavity spectra and intrinsic loss against varying cavity size and shape, and demonstrate pseudo-spin conserved coupling between topological waveguides and cavities. The reliance on only passive media render such components promising building blocks for on-chip devices.