  We demonstrate an add-drop filter based on a dual photonic crystal nanobeam
cavity system that emulates the operation of a traveling-wave resonator and
drops light on resonance to a single output port. Realized on an advanced SOI
CMOS (IBM 45nm SOI) chip without any foundry process modifications, the device
shows 16dB extinction in through port and 1dB loss in drop port with a 3dB
bandwidth of 64GHz. To the best of our knowledge, this is the first
implementation of a four-port add-drop filter based on photonic crystal
nanobeam cavities.
