Farfield-field transmission pattern of a asymetic double sub-wavelength apertures milled on a gold film

We investigate both experimentally and theoretically the far-field diffraction of a set of asymmetric double subwavelength apertures milled on a thin gold film. Asymmetries can arise from a differrence in diameter or a difference in the refractive index between the two apertures. In both cases, the light emerges from the apertures with a relative phase difference, and therefore we anticipate a deflection in the far-field signal. We present a combined experimental and computational study of this system. In particular, we explore the impact of device geometry, presence of refractive index contrast, polarization, and the impact of surface plasmon polariton. We demonstrate that the device is a near-field optical interferometer that provides a far-field monitor for a near-field detection mechanism.