GaN Ultraviolet Laser based on Bound States in the Continuum (BIC)

Abstract Optical bound states in the continuum (BICs), realizing substantial suppression of out‐of‐plane radiative losses, have been utilized to realize strong light confinement and optical modes with high quality‐factor ( Q ). Lasing actions with narrow linewidths based on optical BIC modes have been demonstrated in the near‐infrared and the visible ranges, but BIC‐based lasers in the ultraviolet (UV) region have not been reported. As light sources possessing wavelengths at the UV scale are essential in various fields, the strategy to design compact UV lasers based on high‐ Q modes and directional emissions is highly desirable. Here, the first BIC‐based laser in the UV region is demonstrated by designing a 1D periodic resist structure on top of a GaN film. Using the symmetric‐protected BIC mode, the fabricated laser is having a directional single‐mode lasing emission with a small full‐width at half‐maximum of 0.10 nm and beam divergence of 1.5°. The lasing action is observed with a periodic structure area corresponding to a structure side length as small as 8 µm. Moreover, the wavelength control of the UV lasing is achieved by varying the period and temperature. This work provides strategies to design UV lasers having a small footprint together with narrow‐linewidth and out‐of‐plane emissions.