Three-dimensional N x N passive optical star coupler based on the exact eigenmode coupling and diffraction theory.

Abstract

A technique for a 3-Dimensional passive N x N optical star coupler is described. 3-Dimensional antiresonant reflecting optical waveguides (ARROW) are analyzed and utilised as the input and output waveguides of the N x N coupler. The effective Index Method will be employed to replace the 3-Dimensional ARROW waveguide by an equivalent slab waveguide with its refractive index profile determined by the geometrical shape of the ARROW Waveguide. In the slab waveguide analysis, the input waveguides are coupled to their neighbours. The interaction of the waveguides is described in terms of the normal modes. The resultant field distribution is then diffracted into the free space region which separates the input and output sections. The radiation illuminates the receiving aperture from which the receiving waveguide branches into N different individual output elements, each output element obtaining equal power levels. Different types of loss such as bending loss, spill-over loss, mismatch loss, reflection loss were analyzed and estimated for N = 5. A 5 x 5 star coupler with a transmission efficiency of 56% at a wavelength of 1.3 $\mu$m is achievable.