We have developed a compact all-optical gate switch with a footprint less than 1 mm², in which an optical nonlinear waveguide using all-optical phase-modulation associated with intersubband transition in InGaAs/AlGaAs/AlAsSb coupled double quantum wells and a Michelson interferometer (MI) are monolithically integrated on an InP chip. The MI configuration allows a transverse magnetic pump light direct access to an MI arm for phase modulation while passive photonic integrated circuits serve a transverse electric signal light. We also demonstrate all-optical demultiplexing of a 160-Gb/s signal to a 40-Gb/s signal. The device is expected to be used in ultra-high-speed optical transceivers able to simultaneously send and receive ultra high-definition images.