Abstract: A Brillouin ring laser has a laser source, a resonator ring, a fiber optical coupler arrangement for coupling light waves from the laser source with opposite directions of propagation into the resonator ring. The coupled-in light waves have an intensity to cause acoustic waves in the resonator ring. Thereby Brillouin light waves propagating in opposite directions in the resonator ring are generated by Brillouin scattering of the coupled-in light waves at the acoustic waves. The ring laser has detectors and a coupler arrangement for the coupling-out of such Brillouin light waves propagating in opposite directions in the resonator ring and for superimposing the coupled-out Brillouin light waves at the detectors. The fiber optic coupler arrangement has a first leg and a second leg, the legs being coupled through a coupler with the resonator ring, and a six-port coupler, which couples the first and second legs with a pump fiber exposed to a laser light beam from the laser source.