Dual‐Wavelength Resonant Modes with Different Emission Directions in a Non‐Circular Inner and Circular Outer Cavity

Abstract Symmetry breaking is commonly employed to optimize the functionalities of cavities, such as the single‐wavelength resonance, directional output, or high quality‐factor ( Q ). Due to the mutual influence and restriction of these performance metrics, it is a great challenge to realize high‐ Q multiple‐wavelength resonances with each wavelength's emission being directional and distinguished. Here, a non‐circular inner and circular outer (NICO) cavity is proposed, and dual‐wavelength resonant modes with different in‐plane emission directions for the two wavelengths are realized. More importantly, the Q of the two modes in the NICO cavity remains unchanged (100%) compared to the fully circular cavity. To gradually change the inner ellipse shape to the outer‐circle shape, only the coordinates (not the refractive index) are transformed. This transformation makes the cavity easy to fabricate in the experiment. Both the band‐gap confinement effect of the outer circle layers and the gradual change from the inner ellipse shape to the outer‐circle shape significantly halt the Q ‐spoiling phenomena. Solutions of increasing refractive index differences and further breaking symmetry are provided to improve the Q factors (as high as 10 13 ) and narrow the emission divergence angles (by approximately twice), as well as increase the splitting wavelengths (by ≈6 times).