ABSTRACT
The ability to confine light has great significance in both fundamental science and practical applications. Optical black hole (OBH) cavities show intriguing zero radiation loss and strong field confinement. In this work, we systematically explore the whispering gallery mode (WGM) in a group of generalized OBH cavities, featuring bound states and strong field confinement. The field confinement in generalized OBH cavities is revealed to be enhanced with the increase of index-modulation factors, resulting from the increase of a potential barrier. Furthermore, we reveal the anomalous external resonant modes, exhibiting fascinating field enhancement in the low-index region far beyond the cavity boundary. These anomalous WGMs are attributed to the potential bending effect and above-barrier resonance. Our work may shed light on tailoring WGM fields in gradient-index cavities and find potential applications in light coupling and optical sensing.