Abstract We investigate a dispersion relation of a spin wave of an effectively one-dimensional chiral helimagnet CrNb₃S₆, which is under stationary radiation of a resonant optical vortex beam coaxial to that spiral magnetic order axis. We derive a classical magnetic structure by solving Landau–Lifshitz–Gilbert equation and calculate the collective excitation on it. We show that the optical vortex radiation makes the energy gap at k ∼ 0, and the exceptional points appear in the dispersion relation. Because such a dispersion relation implies the dynamical properties with instability, our result implies a possibility to control spin wave transport.