Selection of lasing direction in single mode semiconductor square ring cavities

Abstract

We propose and demonstrate a selection scheme of lasing direction by imposing a loss imbalance structure into the single mode square ring cavity. The control of the traveling direction is realized by introducing a taper-step section in one of the straight waveguides of the square ring cavity. It was shown by semi-analytic calculation that the taper-step section in the cavity provides effective loss imbalance between two travelling directions as the round trip repeats. Various kinds of square cavities were fabricated using InGaAsP/InGaAs multiple quantum well semiconductor materials in order to test the direction selectivity while maintaining the single mode. We also measured the pump power dependent lasing spectra to investigate the maintenance property of the lasing direction. The experimental results demonstrated that the proposed scheme is an efficient means for a unidirectional lasing in a single mode laser.

Unidirectional lasing in nonlinear Taiji microring resonators

“…Here we demonstrate how the values of the Hermitian and non-Hermitian coefficients describing backscattering (21)(22) control the lasing chirality in a ring resonator. This fact can be employed to construct unidirectional lasers by properly engineering the resonator's microscopic backscattering, for example by means of one or more nanotips coupled with the evanescent field of the resonator, similarly to the experiment of [22].…”

“…This is easily understood by exploring Eqs. (21)(22): either n = 0 or h = 0 imply in fact an equal coupling strength in the two directions, i.e.…”

“…The TJR has found further application in paritytime (PT ) symmetric micro-ring lasers [19] and non-Hermitian active structures [20]. The idea of controlling the chirality of the laser emission via P-symmetry breaking has also been exploited by establishing a loss imbalance [21] and a coupling asymmetry between the two counterpropagating modes using two non-Hermitian nanoscatterers [22]. Very recently, a passive nonlinear TJR has been shown to break Lorentz reciprocity [23] and display direction-dependent transmission.…”

Optical Characteristics of Unidirectional Single-mode Lasing Square Ring Cavities

“…비교적 간단하게 구현 가능한 테이퍼-스텝 구조를 사각 링 공진기의 한 변의 도파로에 적용하여, 두 개의 반대방향 사 이에서 결과적으로 이득을 다르게 부과하여 단 방향 발진이 가능한 사각 링 공진기를 구현하였으며 [15] , 나아가 본 연구에 서는 단 방향 발진을 가능하게 만드는 테이퍼-스텝 구조에 서, 테이퍼의 입력으로부터 출력으로 이어지는 테이퍼 길이 변화를 통하여 소자의 손실을 최적화하였다. 이러한 다양한 종류의 소자는 InP를 기반으로 성장된 InGaAsP/InGaAs 다 중 양자 우물구조의 반도체 기판을 사용하여 제작하였다.…”

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

“…Liang et al [17] forced the unidirectionality of a triangular ring laser cavity by employing a tapered section in one of the straight waveguides, providing loss of imbalance between the two opposite lasing directions, and a similar approach was recently used by Lee et al [18] in a square ring cavity.…”