Clock and Data Recovery-Free Data Communications Enabled by Multi-Core Fiber With Low Thermal Sensitivity of Skew

Optical switching has the potential to scale the capacity of data center networks (DCN) with a simultaneously reduction in latency and power consumption. One of the main challenges of optically-switched DCNs is the need for fast clock and data recovery (CDR). Because the DCN traffic is dominated by small packets, the CDR locking time is required to be less than one nanosecond for achieving high network throughput. This need for sub-nanosecond CDR locking time has motivated research on optical clock synchronization techniques, which deliver synchronized clock signals through optical fibers such that the CDR modules in each transceiver only need to track the slow change of clock phase, due to change of the time of flight as temperature varies. It is desired to remove the need for clock phase tracking (and thereby the CDR modules) if the temperature-induced clock phase drift can be significantly reduced, which would reduce the power consumption and the cost of transceivers. Previous studies have shown that the temperature-induced skew change between multi-core fiber (MCF) cores can be forty times lower than that of standard single mode fibers. Thus, clock-synchronized transmission maybe possible by using two different MCF cores for clock and data transmission, respectively, enabling the sharing of an optical clock with stable clock phase. To investigate the potential of MCF for CDR-free short-reach communications, we first improve the measurement method of the temperature dependent inter-core skew change by using a modified delay interferometer, achieving a resolution of 3.8 femtoseconds for accurate inter-core skew measurements. Building on the MCF measurement results, we carried out an MCF-based clock-synchronized transmission experiment, demonstrating the feasibility of CDR-free data communications over a temperature range of 43 °C that meets DCN requirements.