A vortex optical fiber for use in an illumination subsystem of an optical imaging system (e.g., a stimulated emission depletion (STED) microscopy system) includes an elongated optically transmissive medium having a set of regions including a core region, a trench region surrounding the core region, a ring region surrounding the trench region, and a cladding region, the set of regions having a doping profile providing a Δ；neff for vector modes in an LP11 mode group of greater than 1×10−；4 in the visible spectral range so as to simultaneously guide stable Gaussian and orbital angular momentum (OAM) carrying modes at corresponding visible wavelengths.
