We show that when a coherent light beam is sent through a passive bistable device, the output beam may exhibit a substantial reduction of photon noise below the shot-noise level, within some frequency range of the noise spectrum. This effect is not limited to the case of a high-finesse cavity and is observable as soon as a bistability turning point is approached. Linear losses have the unexpected consequence of improving the noise-reduction factor at low frequencies.

• Received 21 March 1989

DOI:https://doi.org/10.1103/PhysRevA.40.1440