Design and Polarization Control of the Modal Splitting in Hybrid Anisotropic Nanocavities

Abstract

MDM architectures can be easily fabricated through physical vapor deposition processes, which makes them attractive for light confinement and waveguiding applications. [1] Depending on the thicknesses of the individual layers, MDMs can be used as color filters, [2] super absorbers, [3] negative index materials, [4] and for highresolution color generation. [5] By carefully choosing the materials and thicknesses of the metal and insulator layers, the cavity resonance frequency can be tuned over a broad spectral range. [1] The properties of such ultrathin cavities enable several interesting applications in nonlinear optics and nano-optical circuits, [6] including Purcell effect enhancement. [7] The straightforward fabrication process of MDM structures makes it possible to design multilayered configurations, in which two or more MDM cavities are stacked on top of each other. This results in strong coupling of the resonant modes, provided that the connecting metallic layers are sufficiently thin and possess an adequate refractive index. Such strongly interacting optical cavities are highly interesting systems from both a fundamental and an applied point of view. [8,9] The strong coupling dynamics between optical cavities have been recently described in the framework of a quantum mechanics-classic electromagnetism analogy, [10] highlighting their use as an experimental demonstration to observe the The strong coupling of optical resonators results in a mode splitting proportional to the coupling strength, which can be achieved with metal-dielectricmetal (MDM) cavities that have similar thickness and refractive index. However, an active control of the mode coupling is challenging. Here, an alternative configuration of an MDM cavity coupled with a Guided-Mode-Resonator (GMR) is explored. The GMR grating is fabricated on top of the MDM cavity, such that the coupling can be tuned by the thickness of the central metal. The typical modal anti-crossing (with a splitting of ≈50-65 meV) detected in the angular dispersion of the GMR-MDM is observed. Excellent agreement of the experimental reflectance with simulations allows to report the angular dispersion from −50° to 50°. The anisotropy of the GMR modes enables to switch in and out of the strong coupling by changing the polarization of the incident light. Moreover, the asymmetry of the GMR-MDM architecture induces a side-dependent response. The MDM cavity is only transparent at its resonances, which leads to a suppression of all modes outside the resonance bands when impinging from the MDM side. These features are highly interesting for optoelectronic applications such as optical switches and multi-level optical multiplexing.