Compact microring notch filters

Microresonator filters reported so far have been ah-pole-type filters. We report two experimental realizations of zero-type (notch) filters using GaAs-AlGaAs microring resonators. The first is a ring coupled to one side of a Mach-Zehnder interferometer, the Y-branch of which has an effective splitting angle of 50 degrees with 0.5-dB loss, The second is a ring whose toss exactly matches the coupling to the input/output waveguide with an extinction greater than 20 dB.