Bidirectional add/drop could help rings heal
Paula Noaker Powell
Jang-Won Park and Chang-Hee Lee of the Korea Advanced Institute of Science and Technology (Taejon, Korea) have demonstrated a bidirectional add/drop amplifier (BADA) that can be implemented with only one N × N arrayed waveguide grating multiplexer. Equally important, no optical bandpass filter is required to suppress relative intensity noise. When two BADA modules were used in bidirectional transmission and add/drop muliplexing of WDM signals over 120 km of conventional single-mode fiber, there was less than 0.6 dB in power penalty in the receiver sensitivity.
For demonstration purposes, the researchers implemented the BADA module using a 16 × 16 arrayed waveguide grating multiplexer, which had 100-GHz channel spacing, 5-dB insertion loss, and 30-dB crosstalk. Upstream and downstream WDM channels were interlaid-channels 1, 3, 5, and 7 for downstream and channels 2, 4, 6, and 8 for upstream-with 200-GHz channel spacing, although the device can accommodate up to seven channels in each direction with 100-GHz spacing.
Signals were demultiplexed at the eleventh port of the waveguide grating and then dropped or passed through the amplifier module. The added or passed signals were multiplexed at the fifth port on the other side of the grating. Signal routing was with an optical circulator (with insertion loss of approximately 1.5 dB) on each side of the amplifier.
The signal gain from the BADA module was roughly 11 dB without any appreciable power penalty caused by relative intensity noise or crosstalk. The researchers believe that this relatively simple device could help realize cost-effective bidirectional self-healing WDM ring networks.