Interoperable pilot tone technology applied in 100Gb/s multichannel IM-DD optical modules

In order to implement the network management and fault location towards cross domain optical networks, pilot tone technology is introduced to the optical modules which are located at both ends of the cross domain network so as to manage and control the remote optical modules. For the hardware based pilot tone circuit design applied on the widely used 100GBASE-LR4 optical modules, we propose to use one specified lane of the four lanes to implement the transmission of pilot tone signal. After unifying the modulation type, coding format and transmission protocols for pilot tone, the optical module can realize the interoperability for both high-speed service and low-frequency pilot tone signals. The experiment results show that the 100GBASE-LR4 optical modules can support 10km transmission with 5dB margin reserved when pilot tone function is enabled and 5% modulation depth is used. Since different modulation depth may lead to receiving sensitivity degradation in terms of Ethernet application, the balancing point of modulation depth and sensitivity need to be concerned at the stage of optical module design aiming to reducing the pilot tone penalty. In addition, as the increasing lane rate of high-speed optical modules that use PAM4 modulation instead of NRZ, how to solve the problem of poor anti-noise performance of PAM4 signal would become an important precondition for the continuous development of next generation of pilot tone technology.