Study On The Gain Equalized Few-mode Erbium Doped Fiber Amplifiers And Fiber Raman Amplifiers

As the capacity of the optical fiber telecommunication in single-mode fiber approaches the nonlinear Shannon limit,mode division multiplexing based on few-mode fiber becomes active research area in recent years.The few-mode optical amplifiers are the key building blocks for long-haul mode division multiplexing transmission system.Based on the theories of the few-mode erbium doped fiber amplifier(FM-EDFA)and few-mode fiber Raman amplifier(FM-FRA),different kinds of gain equalized optical fiber amplifiers for mode division multiplexing transmission are proposed and studied.The innovation and content of the thesis are listed as follows:1.To simplify the pump configuration and avoid the angular dependence of degenerate pump mode,a gain equalized six spatial modes inline erbium doped fiber amplifier with only 980 nm fundamental mode core pumped is proposed and demonstrated.By using the few mode erbium doped fiber with a simple two-layer erbium doped structure,the average modal gain at 1550 nm is about 15 d B and the differential modal gain is lower than 2.5 d B.At the same time,the gain ripple is about3.5 d B at the wavelength range of 1540?1565 nm.2.To realize the modal gain equalization of much more modes,the cladding pumped 21 spatial modes gain equalized FM-EDFA are proposed and demonstrated.The differential modal gain is dramatically reduced by using the double cladding erbium-doped fiber with a refractive index trench structure,which helps to tightly confine all 21 spatial modes in the core.Our experimental results show that the differential modal gain is about 3 d B when the average signal modal gain for all mode groups is up to 15 d B across the C-band.The gain ripple is about 4 d B at the wavelength range of 1540?1565 nm.3.The dependence of polarization and spatial modes of spontaneous Raman scattering in common few-mode fiber,panda few-mode fiber and elliptical core few-mode fiber are investigated.The vector mode coupling induces the dependence of polarization and spatial modes.The relative ratios of the effective overlap between different mode groups are measured based on the spontaneous Raman scattering when the polarization and spatial mode of the pump are completely random coupling.4.To realize the modal and wavelength gain equalization for mode and wavelength division multiplexing transmission system,the multi-wavelength(1440nm,1455 nm and 1480 nm)and multi-mode pumped FM-FRA is demonstrated.The average on-off modal gain and differential modal gain are about 10 d B and 0.5 d B,respectively.And the gain ripple is about 3 d B at the wavelength range of 1530?1590nm.The second order pumped FM-FRA and the influence to its equivalent noise figure at each mode are investigated in simulation.Moreover,to realize the broadband amplification,a few-mode remote optically pumped amplifier by combining FM-EDFA and FM-FRA with the 1480 nm LP₁₁ mode pump is proposed.