Regular Perturbation and Achievable Rates of Space-Division Multiplexed Optical Channels

Regular perturbation is applied to space-division multiplexing (SDM) on optical fibers and motivates a correlated rotation-and-additive noise (CRAN) model. For
$S$
spatial modes, or 2
$S$
complex-alphabet channels, the model has 4
$S$
(
$S$
+ 1) hidden independent real Gauss-Markov processes, of which 2
$S$
model phase noise, 2
$S$
(2
$S$
- 1) model spatial mode rotation, and 4
$S$
model additive noise. Achievable information rates of multicarrier communication are computed by using particle filters. For S = 2 spatial modes with strong coupling and a 1000 km link, joint processing of the spatial modes gains 0.5 bits/s/Hz/channel in rate and 1.4 dB in power with respect to separate processing of 2
$S$
complex-alphabet channels without considering CRAN.