Nonlinear guided exciton-polaritons in a van der Waals layered waveguide

Abstract

Layered van der Waals materials offer promising opportunities for on-chip waveguiding and the development of integrated photonic circuits. In the strong light–matter coupling regime, their nonlinear response can be significantly enhanced, which is crucial for developing active photonic devices. However, probing the nonlinearity of waveguide modes in subwavelength-thick structures is challenging as they are not directly accessible from far-field. Here, we apply a nonlinear spectroscopic technique based on evanescent-wave coupling through a GaP solid immersion lens and femtosecond laser excitation to study nonlinearity of guided modes in monolayer WS2 encapsulated in hBN under the strong light–matter coupling regime. We reveal the formation of exciton-polaritons with a ∼50 meV Rabi splitting and demonstrate sensitive optical control of the light–matter coupling strength. Our results show that exciton resonance saturation and broadening lead to an efficient nonlinear response of guided polaritons, which can be employed for developing compact van der Waals photonic switches and modulators.