Abstract
We numerically and analytically calculate sensitivity and link power budget of an optically amplified
electronically compensated dual polarization quadrature phase-shift keying (DP-QPSK) coherent homodyne optical system,
taking into account the main parameters of both the optical amplifier and the coherent receiver. After deriving an
expression for the signal-to-noise ratio (SNR) of the amplified coherent receiver, we calculate an analytical
expression for the optimum local oscillator (LO) optical power which maximizes the SNR, and an approximated
closed-form solution for the receiver sensitivity, valid in most of practical cases. This analytical calculation
allows to derive, when the impairments of the fiber are compensated, the position of the amplifier into the link that
maximizes the optical link power budget. The approximated closed-form solutions are compared with results obtained
with a numerical approach. From our investigation it emerges that, in a single-channel fully compensated DP-QPSK
coherent system, the performances of both booster and in-line configurations can be even better than that ones of the
preamplifier, but they are strongly dependent on the unamplified receiver features, and can require a proper
adjustment of the LO optical power, to make the sensitivity compliant with the requirements. Diversely, the
performances of a preamplified coherent receiver can be worse, but the amplifier position makes the coherent receiver
practically independent on its intrinsic noise sources.
© 2013 IEEE
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