l to an electronic signal and back to an optical signal (O-E-O conversion). Hence, in a typical DWDM network, each optical wavelength traveling through a fiber has to be routed through an expensive SONET regenerator that performs 3R functions. Although performance varies by manufacturer, wavelengths traveling at higher signal rates (for example, OC-192) could need up to eight full bays of SONET equipment to regenerate just eight wavelength signals. Optics Primer Figure 2-46 Typical EDFA 2,000 GHz amplifier profile. On 2,000 GHz window: 51s when spaced 400 GHz 10Xs when spaced 200 GHz 201s when spaced 100 GHz 40Xs when spaced 50 GHz 801s when spaced 25 GHz f @ 1530 nm = 1.960 X 1014 f @ 1540 nm = 1.948 X 1014 f @ 1550 nm = 1.935 X 1014 f @ 1560 nm = 1.923 X 1014 Gain-Flattening Filter (GFF) Advantages Figure 2-47 Gain-flattening filter advantages. On 4,000 GHz window: 4,000 GHz 10Xs when spaced 400 GHz Expanded range 201s when spaced 200 GHz of operation 401s when spaced 100 GHz 801s when spaced 50 GHz 160Xs when spaced 25 GHz Raman amplification, a new technology for next-generation DWDM sys- items, mitigates the costly regeneration process. It operates by enabling wavelengths to travel further along the fiber between amplification points. Whereas EDFA amplification takes place in the 50 m of fiber coiled inside the box, Raman amplification takes place outside the box, along the regular fiber in the trench, for about 10 km or SO. This improves the performance of amplification and reduces the number of regenerators the network needs. Chapter 2 Without Figure 2-48 Optical Amplifiers Reduction of regeneration when using optical ~ 40 km ~ 40 km ~ 40 km ~ 40 km ~ 40 km amplifiers. B1, JO B1, JO B1, JO B1, JO B1, JO processing processing processing processing processing Optical Amplifiers ~ 65 - 100 km ~ 65 - 100 km ~ 65 - 100 km B1, J0 processing TE: Terminal Equipment (SONET) B1, JO: SONET Bytes 3R/RRR: Reshaping, Retiming, Regeneration 2.9.5 Optical Add/Drop Modules (OADMs) Multiplexers called optical add/drop modul