WHITE PAPER A Model for Business Case Analysis of C/L-band Network Architectures in Fiber Optic Networks based on Leased/IRU Dark Fiber Background for C-band components. L-band components, on the other Telecommunications networks generally have hand, are currently produced in light volumes, which results in higher prices and a 15 to 20 percent premium for L-band been deployed in the C-band optical spectrum optoelectronics and photonics. But even given these facts, (1530nm-1565nm) in Figure 1, where fiber the OPEX cost savings in dark fiber leases/IRUs that L-band attenuation is lowest (see below). However, as deployment enables is so large, it is easily one of the most network traffic continues to grow rapidly, driven attractive options for network operators to increase network largely by video traffic, network operators are capacity cost-effectively. quickly running out of C-band spectrum to increase Advances in technology such as coherent optical detection network capacity. Expanding network deployment have enabled system vendors to continue to increase network to the L-band is a cost-effective approach to capacity out of the available C-band spectrum of ~ 30nm enable operators to reduce OPEX for dark fiber (Figure 2). However, the Shannon Limit represents the practical leases/Indefeasible Rights of Use (IRU). limit beyond which squeezing more capacity out of the C-band spectrum becomes impossible, resulting in C-band spectrum However, deploying networks in the L-band comes at a premium exhaust. This means network operators are faced with a for two reasons: (i) fiber attenuation is higher in the L-band, choice to either continue with C-band-only deployment—via resulting in higher optical power budget and cost, and (ii) new dark fiber lease/IRU—or expand network deployment to C-band photonics and optoelectronics are produced in very the L-band. That choice is going to be determined by network high volumes, resulting in economies of scale that lower prices economics. Which is more cost-efficient: investing in a one- time CAPEX (including a premium for L-band opto-electronics Optical Transmission Frequency/Wavelength Bands and photonics) to upgrade the network to C+L-band, or Fiber Optics Wavelength Spectrum leasing a new pair of dark fibers and paying OPEX for dark fiber Description Optical Spectrum Range (nm) (THz) lease/IRU in perpetuity? This white paper seeks to answer to O band Original 1260 - 1360 this important business question for network operators. E band Extended 1360 - 1460 S band Short 1460 - 1530 Spectrum: 11.4Thz pectrum 30 65 (nm) Conventional C band 1530 - 1565 4.3674 (Erbium Window) O E S C L U Wavelength L band Long 1565 - 1625 7.0705 1260 1360 1460 1530 1565 1625 1675 Range (nm) U band Ultralong 1625 - 1675 Figure 2. Optical Transmission Frequency Bands Figure 1. Optical transmission frequency/wavelength bands.