Fiber link loss monitoring scheme in bidirectional WDM transmission using ASE-injected FP-LD

We propose and demonstrate a novel fiber link loss monitoring method for a wavelength-division-multiplexed (WDM) passive optical network. This method is based on the optical signal comparison between a reference amplified spontaneous emission signal and its reflection from an optical reflector. Therefore, we can calculate the link loss exactly and also measure the characteristics of upstream optical signals without suspending the in-service channels. Since this scheme does not use narrow-band wavelength-dependent components such as fiber Bragg gratings, it is cost-effective in implementation and maintenance within a real optical network. We experimentally demonstrate that the link quality of upstream signals as well as fiber link faults on all WDM channels can be monitored in real time.