Wavelength Tunable Matched-Pair Vernier Multi-Ring Filters using Derivative-Free Optimization Algorithms

We demonstrate matched pairs of multi-ring Vernier filters that mutually suppress the out-of-band resonances resulting from the Vernier effect to increase the free-spectral range (FSR) while achieving high out-of-band extinction ratio. These filters can be aligned to any center wavelength within the Vernier FSR. Both the design methodology and alignment procedure rely on derivative-free optimization methods. We report on an O-band silicon microring optical filter achieving out-of-band extinction of −52 dB over an FSR $>$ 100 nm.