Semiconductor racetrack resonator coupled to an S‐bent waveguide: Influence of the coupling coefficients on the unidirectional operation

Abstract

Abstract Semiconductor ring lasers have attracted remarkable interest as laser sources in photonic integrated circuits. They result in bidirectional laser owing to the rotation symmetry between the two counter‐propagating modes of the ring cavity. This symmetry can be broken embedding an S‐bend waveguide in the racetrack resonator, which generates an unbalanced loss mechanism and a non‐reciprocal gain between clockwise and counter‐clockwise direction beams. The propagating field along the resonator in the undesirable direction is evanescently coupled to the S element in correspondence of two coupling regions and converted into the preferred one. The authors examined how the field coupling coefficients of the couplers impact the resonator unidirectionality. In numerical simulations, the authors changed the coupler gap distance and the coupler length of the directional couplers to scan the full range of variability of the coefficients. The simulated performances of the resonator are discussed in terms of the extinction ratio between the clockwise and the counter‐clockwise modes as well as the power truly circulated in the two directions of the resonator net of all losses. The finite‐difference time‐domain method within Synopsys RSoft© suite was used to simulate the evolution of the counter‐propagating field along the racetrack.

Keywords

• finite difference time-domain analysis
• laser cavity resonators
• semiconductor lasers
• ring lasers
• integrated optics
• optical waveguide theory