Deep subwavelength Fabry-Perot-like resonances in a sandwiched reflection grating

A Fabry-Perot (FP) resonance cavity can be made to be subwavelength by manipulating the reflection phase at the boundaries. Here, we employ the open-ended slit cavities within a simple sandwiched reflection grating and show that a deep subwavelength FP-like resonance in the slits can be realized. An FP cavity with the length and width of tens of nanometers, which is two orders of magnitude smaller than the resonance wavelength, has been suggested. The effect is very robust and can operate from infrared to microwave frequencies.