Abstract
A pilot-carrier coherent low-earth-orbit (LEO) satellite to ground (LEO-to-Ground)
downlink system using an optical injection phase lock loop (OIPLL) technique
is proposed and its feasibility under Doppler frequency shift conditions is
demonstrated. A fiber-optic based experimental system is configured and it
is demonstrated that a 10 Gbps BPSK transmission system based on the proposed
configuration can successfully maintain stable frequency and phase locking
status under simulated Doppler frequency shift conditions. It is demonstrated
that the stable locking status is maintained over a 10.3 GHz (54$~$ppm) frequency offset with a maximum
rate-of-change of up to 32.4 GHz/s (168 ppm/s), which is ample to meet the
requirement for a coherent LEO-to-Ground downlink system. The locking capability
of the experimental system for more rapidly changing Doppler frequency shift
is investigated. It is shown that the OIPLL receiver remains locked for maximum
rates of change of 2.6 THz/s (13$\thinspace$500$~$ppm/s)
or more for peak-to-peak frequency offsets up to 2 GHz (10.7 ppm). The phase
noise performance of the system is also investigated and phase noise power
of less than ${-}100$ dBc/Hz at greater than 1 MHz offset frequency is achieved even
if the received laser signal suffers from a simulated Doppler frequency shift
with peak-to-peak frequency offset of 2.4 GHz (12.5 ppm) and maximum rate
of change of 750 GHz/s (3 900 ppm/s).
© 2012 IEEE
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