Hitless wavelength-selective switch based on quantum well second-order series-coupled microring resonators

A hitless wavelength-selective switch (WSS) based on InGaAs/InAlAs multiple quantum well (MQW) second-order series-coupled microring resonators is proposed and fabricated. In the core layer, a five-layer asymmetric coupled quantum well (FACQW) structure is employed. The WSS is driven by the electrorefractive index change in the FACQW core layer caused by the quantum-confined Stark effect (QCSE). The wafer for the WSS is grown by molecular beam epitaxy and waveguide structures are formed by dry etching. Boxlike spectrum responses and hitless switching characteristics of the WSS are successfully demonstrated for the first time. The change in coupling efficiency at a coupler between a ring and a busline and between rings and its effect on the switching characteristics are also discussed.