Engineering the spectral properties of non-uniform coupled micro-ring resonator optical filters using numerical optimization

We discuss a new approach for tailoring the spectral properties of coupled micro-ring resonator optical filters using numerical optimization methods. By allowing the micro-rings to have different radii, we obtain considerably lesser crosstalk in a wide frequency region, unlike the uniform ring case commonly found in literature, where the stop-band is limited by the periodic nature of the transfer function. We apply the coupled-mode approach for efficiently calculating the transfer function at each optimization step, scalable to an arbitrary number of rings. Using standard minimization methods we obtain transfer functions with relatively flat pass-band and small cross-talk depending on the number of rings considered in the design. Our technique may open up new paths for designing and implementing compact optical filters with tailored spectral properties.