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 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
$^{\circ }$
C that meets DCN requirements.
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