Self-tuning architecture enabling bidirectional transceiver normalization and low differential latency

Due to having only one working wavelength, single wavelength bidirectional transmission combines the advantages of fiber saving and transceiver normalization. This is beneficial for reducing the CAPEX and OPEX of networks, and can also improve the time synchronization accuracy of mobile CRAN networks. However, the performance of single wavelength bidirectional transmission is invariably sensitive to backward reflected emission light. Frequency shifting and digital signal processing are typical approaches to eliminate this penalty, but it leads to higher cost and power consumption. In this paper, we first apply a self-tuning architecture and physical layer negotiation in bidirectional transceiver, to allow the transceiver to support two modes. Then a single-fiber bidirectional transmission can be setup by this normalized transceiver as single working wavelength but without performance penalty. Except wavelength, other performances of manufactured 25 G Baud PAM4 self-tuning bidirectional transceiver are compliant with IEEE 802.3cp 40 km ER specification. When the two working mode wavelength interval is 0.4 nm, the latency difference over 40 km is 250 ps, which is on the same order of magnitude as the delay difference in single wavelength bidirectional transmission.