Lightpath tracing in photonic networks

Summary form only given. Deployment of photonic networks, in which wavelengths are routed optically, is now underway. As network operators reap significant cost savings by removing O-E-O conversion from many nodes, they will lose the management functions, such as performance monitoring and path trace, that the electronic equipment provides. We discuss one possible option for implementing such a path trace function in photonic networks, a new technology that we call LightLabel. LightLabel is an in-band auxiliary channel, which enables the use of ubiquitous, low-cost path trace receivers throughout the network. It is all-digital, based on a novel encoding process at the lightpath source. To assure low system cost, the path trace receivers are required (1) to operate from a low-power optical tap coupler; (2) to use only low-speed photodiodes and circuits, and (3) to operate without a wavelength filter. For example, a photonic network has multiple lightpaths that can be carried on a single wavelength. If a reconfigurable optical add/drop module (ROADM) or photonic crossconnect (PXC) is set incorrectly or malfunctions, data streams may be sent to the wrong terminals. Lightpath tracing allows identification and localization of the fault, expediting repair. LightLabel encoding is carried out by binary electronics at the lightpath source, in a manner similar to forward error correction (FEC) coding. The encoding algorithm includes a layer of block coding with complementary constant-weight codes (CCWC), which creates weight variations detectable by a low-speed receiver. A second layer of coding, based on CDMA (code-division multiple access) techniques, is used to distinguish the LightLabel signals from multiple wavelengths without requiring a tunable wavelength selection filter at the path trace receiver. System operation was emulated in the laboratory, using a preprogrammed data pattern at 10.24 Gb/s, a LightLabel chip rate of 10.0 Mchip/s, and an auxiliary channel rate of 50.0 Kb/s. This talk shows the experimentally observed error rate of a single LightLabel channel operating in the presence of ASE noise. Error rates for chip-by-chip detection and for the 10 Gb/s payload channel are also shown for comparison. The excellent noise rejection of the LightLabel - signal is in close agreement with theoretical calculations. Even with the penalty expected from multiple user interference, the LightLabel error rate will remain lower than the payload error rate at all OSNR values, so LightLabel encoding will not require changes in line amplifiers or span engineering rules.