Multimode Waveguides Coupled to Single Mode Ring Resonators

A planar integrated optical device based on the interaction of two spatial eigenmodes with a single eigenmode ring resonator is presented. Solutions for the output mode amplitudes are determined theoretically and are shown to be strong functions of the relative phases of the two input modes. A device was fabricated in a polymer-silicon material system by a photolithographic process. The modal response as a function of wavelength is measured by the twin-fiber interferometer technique through fringe visibility. It is found that sharp visibility lineshapes may be achieved through the adjustment of input mode phase and twin-fiber spacing on the radiated output beam. These sharp lineshapes are also possible in the presence of high loss in the resonator. The on-chip test device incorporates a single mode to two-mode converter and a far-field wavefront sampler. The measured fringe visibility slope with respect to wavelength reaches a maximum value of 74 nm^{- 1} which is 56 nm^-1 larger than a single mode waveguide coupled to a single mode microring with the same ring loss and 15 dB extinction ratio. Such sharp lineshapes in visibility may be exploited for optical applications in sensing, communications, and computing.