光电子材料导论 色散补偿.ppt

信息传输材料与技术－－－传输色散补偿 Once upon a time, the world assumed that fiber possessed infinite bandwidth and would meet mankind’s communication needs into the foreseeable future. In 1550 nm region, with a loss of only 0.2 dB/km, seemed like the answer. Millions of kilometers of fiber were installed around the world creating a high-speed communication network. as the data rates increased and fiber lengths increased, limitations due to dispersion in the fiber became impossible to avoid. Dispersion was initially a problem when the first optical fibers, multimode step-index fiber, were introduced. Multimode graded-index fiber improved the situation a bit, but it was single-mode fiber that eliminated severe multimode fiber related dispersion and left only chromatic dispersion and polarization mode dispersion to be dealt with by engineers. Chromatic Dispersion Chromatic dispersion represents the fact that different colors or wavelengths travel at different speeds, even within the same mode. Chromatic dispersion is the result of material dispersion, waveguide dispersion, or profile dispersion. Figure 1 below shows chromatic dispersion along with key component waveguide dispersion and material dispersion. The example shows chromatic dispersion going to zero at the wavelength near 1550 nm. This is characteristic of bandwidth dispersion-shifted fiber. Standard fiber, single-mode, and multimode has zero dispersion at a wavelength of 1310 nm. Refractive Index of Fused Silica MLM Laser Spectral Output Dispersion with a Normal DFB Laser Dispersion with a Narrow DFB Laser Dispersion with an FP Laser Dispersion of SM Fiber Types Non-DSF: Nondispersion-shifted fiber zero dispersion near 1310 nm. DSF: Dispersion-shifted fiber works well in single channel 1550 nm systems, but in DWDM systems, fiber nonlinearities near to the zero-dispersion wavelength cause problems. (+D) NZ-DSF: Similar to DSF, except that the zero-dispersion wavelength is intentionally pla