360 degrees Star Coupler for Detecting Subwavelength Features

We propose a novel 360 degrees star coupler. We show theoretically how this coupler can detect perfectly conducting cylinders with radii significantly smaller than a wavelength, in the far field. We experimentally demonstrate detection of a metal probe using the 360 degrees star coupler in a silica planar lightwave circuit. With improvements, this coupler may be able to perform subwavelength 2-D imaging.