Regenerative amplification of a weak cw optical signal in an active frequency shifted feedback cavity

Abstract

A system is demonstrated whereby weak optical cw signals can be amplified with high frequency resolution to a macroscopically detectable level by regenerative amplification in a frequency shifted feedback cavity. The output of this amplifier has a logarithmic dependence on the intensity of the injected signal providing a dynamic range of five orders of magnitude. It is possible to detect injected signals as low as the spontaneous noise level in the amplifier with amplification factors of more than 10 4 being observed. This behaviour is related to the introduction of a new experimentally controllable parameter, the frequency shift, which limits the growth time in the cavity. This system when more strongly pumped, but with only the spontaneous noise as a seed, produces laserlike emission. The output versus pump power characteristics, output spectrum and buildup dynamics differ from a conventional laser oscillator. A rate equation model provides good qualitative agreement with the observed results and insight into the dynamics of such systems.