Impact of the band upgrade sequence on the capacity and capital expenditure of multi-band optical networks

Multi-band transmission over existing fibers would be a key strategy for ongoing capacity expansion even though upgrading from the conventional C band to multi-band, such as the
${\rm C} + {\rm L}$
-band transmission being deployed by operators, would be a slow and complex process. After the
${\rm C} + {\rm L}$
band, which band should be upgraded first in the next stage is an open question. We try to answer this by proposing three different band upgrade strategies, including near-to-far, far-to-near, and performance-prediction strategies, and comparing the potential capacity increase and the investment cost to upgrade different bands. We introduce an optical signal-to-noise ratio (OSNR) estimation model comprehensively covering various impairments to evaluate the quality of transmission of an optical channel and develop what we believe to be a novel method to find optimal launch powers for optical channels. Along with routing and spectrum assignment, an OSNR-aware traffic grooming algorithm is also developed to evaluate the capacity that can be achieved after upgrading different bands in an optical network. Our study shows that the performance-prediction strategy always outperforms the other two strategies. When capacity is considered a key performance metric, the E band should be the first to be upgraded next since it both expands the transmission capacity significantly using only a few additional amplifiers and the band upgrade sequence should be E, O, S, and U. For the performance-prediction strategy, we also evaluate the impact of the upgraded band on the performance of other bands. It is found that the upgraded band always has a significant impact on adjacent bands, with the upgrade of high-frequency bands improving the performance of existing low-frequency bands and the upgrade of low-frequency bands degrading the performance of existing high-frequency bands. In addition, the “
${\rm C} + {\rm L} + {\rm E} + {\rm O} + {\rm S} + {\rm U}$
” scenario can achieve 3 times the capacity of the “
${\rm C} + {\rm L}$
” scenario when all the bands are upgraded.