Recirculating Loop System

To simulate and test long distance fiber optic communication lines, Brimrose has developed a fiber-coupled AO modulation system. The recirculating loop system consists of two fiber-coupled AO modulators/switches and a corresponding RF driver. One of the AO modulators/switches is placed outside the loop to define the loading time and the second AOM is placed inside the loop to define the recirculating time or distance of the pulse transmission, which corresponds directly to the length of the long distance fiber optic line. Since conventional Acousto-Optic devices will frequency shift the transmitted light by the acoustic carrier frequency, the Brimrose recirculating loop system utilizes a no-shift AO device inside the loop that will keep the frequency of light at a constant value even after multiple passes. The no-shift AO device does not complicate testing nor degrade system performance.