Which Band Should be Upgraded First after C+L Bands: A Comprehensive Case Study.

Multi-band transmission over existing fibers would be a key strategy for ongoing capacity expansion even though upgrading from conventional C-band to multi-band, such as the C+L-band transmission being deployed by operators, would be a slow and complex process. After the C+L band, which band should be upgraded first in the next stage is an open question. In this paper, we try to answer this by comparing the potential capacity increase and the investment cost to upgrade different bands. We propose an OSNR estimation model comprehensively covering various impairments to evaluate the quality of transmission of an optical channel. Along with routing and spectrum assignment, a traffic grooming algorithm is also developed to evaluate the capacity that can be achieved after upgrading different bands in an optical network. Our studies show that 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 also improves the quality of transmission of the C+L band.