Abstract
The growth in demand for high bandwidth services has stimulated the
deployment of Passive Optical Networks (PONs), directly to the home or to
the kerb. In many cases, particularly extended reach PONs which may cover
distances of 100 km or more ,
there is the need for low cost reach extension technologies. Semiconductor
Optical Amplifiers (SOAs) have a key role in this context, particularly because
upstream traffic is commonly carried at 1.3 μm. Upstream traffic in a PON (from
the Optical Network Unit, ONU to the Optical Line Terminal, OLT) is normally
Time Division Multiplexed (TDM) with a wide variation in path loss arising
from differences in transmission distances and splitting losses. The bursty
nature of this traffic combined with a wide dynamic range of signal strength
(-15 dBm
to -28 dBm—the
difference between a very close ONU with a small split ratio and a distant
ONU with a high split ratio), places severe demands on the burst mode receiver
at the OLT. Conventional fibre amplifiers cannot adjust their gain with packet
to packet variations due to their response time. Similarly, conventional SOAs
suffer loss of linearity if their bias current and hence gain is rapidly reduced.
The paper reports on an adjustable gain-clamped semiconductor optical amplifier
(AGC-SOA) designed to maximize the output saturated power while adjusting
gain to regulate power differences between packets without loss of linearity.
Theoretical modeling predicts that this device is able to modulate gain at
nanosecond rates. The analysis is validated experimentally.
© 2011 IEEE
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