Global modes and coupled modes for integrated twin circular-side octagon microlasers

Whispering-gallery mode (WGM) microlasers are potential light sources for photonic integrated circuits and optical information processing. In this paper, an integrated twin circular-side octagon microlaser (TCOM) composed of two identical circular-side octagon microcavities (COMs) is proposed and demonstrated for realizing lasing mode control. In a TCOM, we found a global mode with the mode field of an “8” pattern (labeled “8” mode) in addition to weak coupling modes of traditional four-bounce modes. The “8” mode belongs to the whole coupled cavity and is insensitive to the refractive index offset of coupled COMs, but the weak coupling modes are strongly sensitive to the refractive index offset. Lasing mode transformation from multiple coupled modes to a single “8” mode is demonstrated by adjusting the refractive index offset through injection currents. Weak coupling modes for directly connected TCOMs and lasing mode control make the COM a potential unit for large-scale photonic integration and optical information processing.