In this paper we investigate theoretically the behaviour of a quantum optical oscillator, consisting of two-level atoms strongly coupled to a cavity mode, in the optical domain. In contrast with the usual laser theory, we include explicitly the effects of atomic spontaneous emission and of cavity decay in the interaction of the atoms with the cavity field, using a quantum mechanical master equation approach. It is shown that such an oscillator produces sub-Poissonian light with a large degree of noise reduction even for the case when the atom–field coupling constant is only marginally larger than the spontaneous decay rate.