'Institute of Electrical and Electronics Engineers (IEEE)'
Abstract
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 temperatureinduced 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