358 CHAPTER 12 Optical amplifier for maintenance friendly fiber networks In this MFFN proof-of-concept trial, 19 lit DWDM 10 Gb/s channels, three SONET OC-48 tributaries fed into two DWDM channels, two hybrid switches, and seven field fibers were involved. The total traffic can be freely switched among the fiber spans between two line amplifiers without causing an interruption severe enough to trigger automatic traffic protection. The results show MFFN is a feasible concept. 12.7 SUMMARY Future generation meshed-based networks will have very high capacity links that support multiple service types, each with its own protection/restoration schemes. Consequently, moving traffic off a particular link in an orderly fashion to do physical layer maintenance will be very time consuming and expensive because it increases the amount of spare capacity needed in the network. The concept of an MFFN using fast optical switches provides a means to localize the inevitable fiber moves such that no spare capacity is used, no coordination is required, and no extra latency is added to the circuit path. This is particularly important given the sophisticated nature of multiple nested protection and restoration layers. In addition, the added latency can impact customer circuits when traffic is rerouted to accommodate maintenance events that affect fiber cables every day in every global network. In this chapter we have discussed the concept of MFFN, in which optical amplifiers are modified to integrate fiber switches. Two designs are presented: one with the large fiber switch only, which requires the DWDM system to tolerate a 10 ms or longer optical interruption; and one that uses a small fast switch with a large fiber switch, significantly reducing the optical interruption. A preliminary proof-of-concept trial is presented as well, demonstrating that the concept of MFFN is feasible and can be included in the next generation of optical amplifier designs. ACRONYMS ADC ADM APR APS BER BLSR CD DCC DGD DSP DP-QPSK Analog-to-digital conversion Automatic power reduction Automatic protection switch Bit error ratio Bidirectional line switched ring Chromatic dispersion Data communication channel Differential group delay Digital signal processing Dual polarization quadrature phase shift keying