Raman amplification is a nonlinear optical effect that provides distributed gain along the length of a transmission fiber. This is achieved by transferring energy from a high-power pump laser to the signal. This process does not alter the fundamental linear properties of the fiber itself. Chromatic dispersion is a linear property determined by the fiber's material composition and waveguide structure, which dictates how different wavelengths travel at different speeds. Raman amplification provides gain but does not change this intrinsic fiber characteristic. Therefore, the statement that chromatic dispersion is increased is false.

A. Raman amplification is, by definition, a distributed amplification scheme where the transmission fiber itself acts as the gain medium along its length.

C. The Raman gain spectrum is determined by the pump wavelength(s). Using multiple pumps allows for the creation of a broad, flat gain profile in any desired band (C, L, S, etc.).

D. By amplifying the signal throughout the span, Raman amplification prevents the signal power from dropping to very low levels, resulting in a superior Optical Signal-to-Noise Ratio (OSNR) compared to discrete EDFAs.

1. Nokia Application Note: "Unleashing the full potential of optical networks with Raman amplification" (2018).

Reference for A, C, D: Page 3, Figure 1, illustrates the principle of distributed amplification along the fiber (supports A). Page 4, "The main benefit of distributed Raman amplification is OSNR improvement," directly supports D. Page 5, Figure 3, shows how multiple pumps are used to achieve a flat gain profile, supporting C. The document makes no mention of Raman amplification affecting chromatic dispersion.

2. Agrawal, G. P. (2010). Fiber-Optic Communication Systems (4th ed.). Wiley.

Reference for B: Chapter 2, Section 2.3, "Chromatic Dispersion," describes dispersion as a fundamental, linear property of the fiber. Chapter 6, Section 6.4, "Raman Amplifiers," describes the gain mechanism. The text treats these as separate, independent physical phenomena. The process of stimulated Raman scattering does not alter the fiber's group-velocity dispersion parameter. (ISBN: 978-0-470-50511-3).

3. Nokia Data Sheet: "1830 Photonic Service Switch (PSS) portfolio."

Reference for A, D: Product descriptions for Raman amplifier cards (e.g., RA2P) consistently highlight their use for "distributed Raman amplification" (supporting A) in long-haul and unrepeatered systems to improve OSNR and extend reach (supporting D).