Experimental demonstration of coupled nano-Fabry-Perot groove resonators

Fabry-Perot (FP) resonances are ubiquitous in plasmonic resonators; however, their quality factor is mostly driven by the losses of the material and has a typical value of 10 for noble metals. The coupling of two FP nanocavities (cFP) was theoretically shown by Opt. Lett.42, 5062 (2017)10.1364/OL.42.005062 to enable the control of the quality factor, thanks to a geometrical parameter. Here, we experimentally demonstrate in the infrared range the cFP resonance with a quality factor of 30 in a structure made of metallic grooves with a trapezoidal-shaped profile that is simultaneously easier to fabricate and more complex to model. An analytical one-mode model is derived that undoubtedly attributes the resonance to the coupling of interferences between the two nanocavities. Finally, we also experimentally demonstrate the combination of two cFP either in orthogonal polarizations or for distinct wavelengths.