We propose an N-channel power-compensated reconfigurable optical add/drop multiplexer (ROADM) based on using fiber Bragg gratings (FBGs). Both tunable FBGs and wavelength-fixed FBGs are used in this ROADM. By using the dual-pass amplification scheme with two pieces of erbium doped fibers, an 8.0 dB optical net gain has been achieved with a gain variation less than 0.5 dB for each add/drop/pass-through channel. System performance was studied for a four-WDM-channel 10 Gb/s100-km lightwave transmission trial network and bit error rate of 10-9 is observed for the 50 km added signal, 100 km pass-through signal and 50 km dropped signal at -18.3, -19.4 and -18.9 dBm received power, respectively. Only 1.1 dB of power penalty was observed compared to the back-to-back transmission.

In a bidirectional wavelength-reused system, polarization control is used to reduce power penalty induced by coherent mixing of the signal with Rayleigh backscattering. The reduction of the effect of Rayleigh backscattering is theoretical study and experimental demonstration. For a 50km, 10Gb/s bidirectional transmission system, an error floor of about 510-10 under the worst polarization state is occurred. Nevertheless, the power penalty is reduced from 3.5dB to only 0.3dB when the signals are under optimum polarization control. The results indicate that the proposed technique may find vast applications in bidirectional ring networks with add/drop as well as cross-connect nodes using wavelength-reused technology.

High-capacity multiwavelength ring networks with bidirectional WDM add/drop multiplexer (WADM) having built-in EDFAs is analyzed and demonstrated. All WDM channels can be added/dropped independently in each direction. The capacity of a bidirectional ring is found to be approximately twice that of an unidirectional ring. An eight-wavelength WADM is demonstrated for a data rate of 10 Gb/s per channel, providing an overall capacity of 80 Gb/s. The performance of the add/drop multiplexer is not degraded by backward backscattering light. The same WADM is also demonstrated to be able to serve as a bidirectional in-line optical amplifier.