We realize a multicore erbium-doped fiber amplifier (MC-EDFA) with 2dB optical gain improvement (average) by recycling the residual 0.98μm pump light from the MC-EDF output. Eight-channel per core wavelength division multiplexed (WDM) Nyquist PM-16QAM optical signal amplification is demonstrated over a 40-minute period. Furthermore, we demonstrate the proposed MC-EDFA's stability by using it to amplify a Nyquist PM-16QAM signal and evaluating the resulting Q-factor variation. We found that our scheme contributes to reducing the total power consumption of MC-EDFAs in spatial division multiplexing (SDM)/WDM networks by up to 33.5%.

Research and development of a multi-degree colorless, directionless and contentionless reconfigurable optical add-drop multiplexer (CDC-ROADM) has recently been attracting a lot of attention. A large-scale transponder aggregator (TPA) is indispensable for providing high-capacity flexible connections to optical networks. In this paper, we report our study of the requirements for the TPA, which is a key technology for achieving flexible optical networks. To meet the requirements, we have developed an 848 TPA prototype based on Si photonics technology. This prototype was made with a few 88 Si optical switches and designed to be used with a commercial ROADM system. The 88 Si optical switches are made by integrating 152 Mach Zehnder (MZ) Thermo Optoelectronic (TO) 22 optical switch elements. A double gate structure is introduced to achieve the high extinction ratio (ER) required for optical communication. To the best of our knowledge, this is the world's first Si-TPA that can be used with a commercial ROADM system. By evaluating the basic optical characteristics utilizing real-time 100 Gbps digital coherent detection as one of today's practical technologies and a 4.4 THz spectral bandwidth 20 Tbps super-channel with digital coherent detection, as a promising future technology, we have confirmed that our prototype Si-TPA has the potential for practical use and future extensibility.

We propose a cyclic sleep control technique for backup resources in reconfigurable optical add/drop multiplexer (ROADM) systems to simultaneously achieve power savings and high-speed recovery from failures. Processes to check the reliability of backup resources, backup transponders and paths, are also provided in the control technique. The proposed technique uses sleep mode where backup transponders are powered down to minimize power for power savings. At least one of the backup transponders is always activated after self-checking using the loopback fiber connection in the ROADM and it becomes a shared backup for working transponders to enable high-speed recovery from failures. This activated backup transponder is powered down again after the next transponder is activated. These state transitions are cyclically applied to each backup transponder. This “cyclic” aspect of operation enables network operators to continuously monitor the reliability for all backup resources with the sleep mode. The activated backup transponders at both ends of the path are used in checking the reliability of backup paths. Therefore, all backup resources, both transponders and paths, can be regularly checked with the sleep mode to ensure data are stably forwarded. We estimated the power consumption with this technique under various conditions and found a trade-off between power reduction and the recovery capabilities from failures. We achieved more than 34% power saving of backup transponders maintaining the failure recovery time within 50ms in experiments. Furthermore, we confirmed the reliability of backup paths in experiments using backup transponders with the cyclic sleep control technique. These results indicated that the proposed control technique is promising in dramatically and reliably reducing the power consumption of backup resources.