We demonstrate an optical fiber recirculating loop for test of optical communications systems and devices. The proposed configuration employ sections of dispersion shifted fibers, standard fiber, and a set of inline devices, such as tuning filters, optical amplifiers, polarization controllers, etc. The main results presented here are related to the observation of the effects due to the slow dynamics of optical amplifiers and also to the possibility to simulate extra lengths of fiber with an attenuator.2 447452