Enhanced sensing and broadened absorption with higher-order scattering zeros

Non-Hermitian systems offer a compelling platform for enhancing sensitivity in measurement applications. Here, we propose a multimode non-Hermitian optical configuration comprising three coupled whispering-gallery-mode microcavities and a waveguide. The transmission spectrum of the configuration reveals valleys influenced by zeros and poles of polynomial ratios and can exhibit higher-order scattering zeros. We then propose a sensing protocol based on higher-order scattering zeros, which shows enhanced sensitivity but operates without the eigenbasis collapse, exhibiting a cubic root response to small perturbations. Furthermore, we show that the transmission spectrum can feature a sextic lineshape at purely real zeros and thus holds promise for the development of high-performance optical absorbers.