Broadband time-asymmetry of light through a topological loop around an exceptional point

Abstract: Exceptional-point singularities and their experimental consequences are of strong interest for a variety of wave-mechanical systems in electromagnetics, acoustics, solid-state physics, and optics. Among various associated phenomena, encircling an exceptional point (EP) is presently a subject of intense experimental study as it reveals the essence of unique non-Hermitian dynamics supported by a self-intersecting energy-spectral topology and consequent time asymmetry. Here, we experimentally demonstrate a robust silicon-photonic structure where such effects manifest while dynamically encircling an EP in the optical domain. Remarkably, the proposed structure enables the time-asymmetric light transmission over an extremely broad spectral band exceeding 100 nm in the telecommunications window (~1550 nm). Thus, we establish a first experimental step towards broadband on-chip optical devices based on unique non-Hermitian topological dynamics. Our results further suggest the technological relevance of non-Hermitian wave interactions in various other branches of physics.