Control of quality factor and critical coupling in microring resonators through integration of a semiconductor optical amplifier

We demonstrate the integration of ring resonators with semiconductor optical amplifiers (SOAs) using a vertically stacked asymmetric twin waveguide structure. The ring resonator and the bus waveguides are fabricated on a dilute waveguide structure while the active material for the optical amplifier is comprised of compressively strained In_0.8Ga_0.2As_0.75P_0.25 multiple quantum wells. The racetrack-shaped ring resonators with optical amplifiers integrated at the input showed ∼10-dB contrast, a quality factor of 2.2×10⁴, and a free spectral range of 0.25 nm. The main aspect in the present work is the control of the quality factor and critical coupling in microring resonators by altering the internal loss in the ring by means of an integrated SOA.