A periodic add/drop system in a fiber ring network was investigated using a reconfigurable optical add/drop multiplexer (ROADM) in a re-circulating fiber loop. After seven cascaded add/drop nodes at every 150km along the transmission, at bit error ratio (BER) equals to 10 −9 and data rate of 10Gbps, we observed a 2.5dB power penalty for the passing through channels with 1050km transmission distance, and 0.3dB sensitivity penalty variation for the periodic add/drop channels at every 150km, respectively.