Abstract
By introducing the symmetry-breaking in geometry, we reveal the existence of thresholdless crescent waves in an elliptical ring. An effective nonlinear Schrödinger equation along the azimuthal direction is derived by taking the transformation in the curvilinear coordinate of elliptical symmetry, which illustrates the formation of trapping potentials (barriers) along the semi-major (minor) axis. Our results demonstrate an alternative but efficient approach to access optical modes with a variety of inhomogeneous potentials. © OSA 2013.