A Highly Compact Third-Order Silicon Elliptical Micro-Ring Add-Drop Filter with a Large Free Spectral Range

We demonstrate a highly compact third-order elliptical micro-ring add-drop filter based on a silicon-on-insulator wafer. The elliptical micro-ring resonator has a major radius of 6 μm (minor radius of 4.112 μm) and a large free spectral range of 18 nm. Experimental results show a box-like channel dropping response, which has a 3 dB bandwidth of \sim2.7 nm, high out-of-band signal rejection of around 40 dB and a very low drop loss ( < 0.5 dB). Simulation agrees well with the experiments. The footprint of the whole chip is only 0.0003 mm^2.