Compact microring notch filters

Microresonator filters reported so far have been all-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/spl deg/ with 0.5-dB loss. The second is a ring whose loss exactly matches the coupling to the input/output waveguide with an extinction greater than 20 dB.