To reduce the threshold and achieve unidirectional lasing emission in a whispering gallery mode microcavity, we propose and demonstrate a GaN-based eccentric microring with an inner hole located off the center. Compared to microdisk with the same outer diameter, the eccentric microring structure exhibits a remarkable reduction of lasing threshold by up to 53%. The introduction of the hole disturbs and eventually suppresses the field distribution of the higher order modes. Laser emission with high unidirectionality with a far-field divergence angle of about 40° has been achieved, meanwhile the Q factor of the whispering gallery modesis remains high as 6388. Finite-difference time-domain numerical simulation is carried out to prove that the far-field profile of the eccentric microring structure can be controlled by the position and the size of the hole. The properties of the whispering gallery mode microcavities are improved greatly through a simple structure and process, which has an important guiding significance to the research and development of the microcavity lasers.

中文翻译：

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低阈值的GaN基偏心微环激光器的单向发射

为了降低阈值并在回音壁模式微腔中实现单向激光发射，我们提出并演示了一种GaN基偏心微环，其内孔位于中心。与具有相同外径的微盘相比，偏心微环结构的激射阈值显着降低了53％。空穴的引入干扰并最终抑制了高阶模的场分布。已经实现了具有高单向性且远场发散角约为40°的激光发射，与此同时，回音壁模式的Q因子仍然高达6388。进行了时域有限差分数值模拟，以证明偏心微环结构的远场轮廓可以通过孔的位置和大小来控制。通过简单的结构和工艺大大改善了耳语画廊模式微腔的性能，这对微腔激光器的研究和开发具有重要的指导意义。