Coherent control of chaotic optical microcavity with reflectionless scattering modes

Non-Hermitian wave engineering has attracted a surge of interest in photonics in recent years. Prominent non-Hermitian phenomena include coherent perfect absorption and its generalization, reflectionless scattering modes, in which electromagnetic scattering at the input ports is suppressed due to critical coupling with the power leaked to output ports, and interference phenomena. These concepts are ideally suited to enable real-time dynamic control over absorption, scattering and radiation. Nonetheless, reflectionless scattering modes have not been observed in complex photonic platforms involving open systems and multiple inputs. Here we demonstrate the emergence of reflectionless scattering modes in a chaotic photonic microcavity involving over a thousand optical modes. We model the optical fields in a silicon stadium microcavity within a quasi-normal mode expansion, which is able to capture a dense family of reflection zeros at the input ports, associated with reflectionless scattering modes. We observe non-Hermitian degeneracies of reflectionless scattering modes in the telecommunication wavelength band, enabling efficient dynamic control over light radiation from the cavity. Non-Hermitian physics enables dynamic control of optical behaviour in real time, such as reflectionless scattering modes, which have now been demonstrated in a chaotic photonic microcavity.