"Introduction". In: Fiber-Optic Communication Systems

242 CHAPTER 6. OPTICAL AMPLIFIERS cascaded SOAs [21]. SOAs have also been employed to overcome distribution losses in the local- ...

6.3. RAMAN AMPLIFIERS 243 Figure 6.10: Schematic of a fiber-based Raman amplifier in the forward-pumping configuration. It is cl ...

244 CHAPTER 6. OPTICAL AMPLIFIERS Figure 6.11: Raman-gain spectra (ratiogR/ap) for standard (SMF), dispersion-shifted (DSF) and ...

6.3. RAMAN AMPLIFIERS 245 Consider first the case of small-signal amplification for which pump depletion can be neglected [the l ...

246 CHAPTER 6. OPTICAL AMPLIFIERS Figure 6.12: Variation of amplifier gainG 0 with pump powerP 0 in a 1.3-km-long Raman am- plif ...

6.3. RAMAN AMPLIFIERS 247 Figure 6.13: Gain–saturation characteristics of Raman amplifiers for several values of the un- saturat ...

248 CHAPTER 6. OPTICAL AMPLIFIERS laser then pumps the Raman amplifier and amplifies a 1.3-μm signal. The same idea of cascaded ...

6.3. RAMAN AMPLIFIERS 249 orthogonally polarized. The polarization problem can be solved by pumping a Raman amplifier with two o ...

250 CHAPTER 6. OPTICAL AMPLIFIERS Figure 6.14: Measured gain profile of a Raman amplifier with nearly flat gain over an 80-nm ba ...

6.4. ERBIUM-DOPED FIBER AMPLIFIERS 251 Figure 6.15: (a) Energy-level diagram of erbium ions in silica fibers; (b) absorption and ...

252 CHAPTER 6. OPTICAL AMPLIFIERS power. Pumping at 1480 nm requires longer fibers and higher powers because it uses the tail of ...

6.4. ERBIUM-DOPED FIBER AMPLIFIERS 253 length because of pump power variations. The total gain is obtained by integrating over t ...

254 CHAPTER 6. OPTICAL AMPLIFIERS Figure 6.16: Small-signal gain as a function of (a) pump power and (b) amplifier length for an ...

6.4. ERBIUM-DOPED FIBER AMPLIFIERS 255 Since the optimum value ofLdepends on the pump powerPp, it is necessary to choose bothLan ...

256 CHAPTER 6. OPTICAL AMPLIFIERS Figure 6.17: (a) noise figure and (b) amplifier gain as a function of the length for several p ...

6.4. ERBIUM-DOPED FIBER AMPLIFIERS 257 Relatively low noise levels of EDFAs make them an ideal choice for WDM light- wave system ...

258 CHAPTER 6. OPTICAL AMPLIFIERS Figure 6.18: Schematic of an EDFA designed to provide uniform gain over the 1530–1570- nm band ...

6.4. ERBIUM-DOPED FIBER AMPLIFIERS 259 Figure 6.19: Schematic of an L-band EDFA providing uniform gain over the 1570–1610-nm ban ...

260 CHAPTER 6. OPTICAL AMPLIFIERS 6.4.6 Distributed-Gain Amplifiers Most EDFAs provide 20–25 dB amplification over a length∼10 m ...

6.5. SYSTEM APPLICATIONS 261 6.5 System Applications Fiber amplifiers have become an integral part of almost all fiber-optic com ...