Design And Optimization Of Few Mode Optical Parametric Amplifiers

The spontaneous emission noise of traditional optical amplifiers and the nonlinear damage of fibers make the transmission capacity of single-mode fibers approaching the Shannon limit.Spatial division multiplexing technology is an effective way to break through the transmission capacity of single-mode fiber.This technology has aroused the interest of researchers.Among them,few-mode optical parametric amplification technology is one of the research hotspots.Few-mode optical parametric amplifiers have the advantages of large bandwidth and low noise,and are of great significance in long-distance,large-capacity communication systems.However,there are still great challenges to realize high-performance few-mode optical parametric amplifiers.The main problem is how to design suitable few-mode high nonlinear fibers to achieve low differential mode gain and low inter-mode nonlinear crosstalk.Aiming at this problem,starting from the basic theory of parametric amplification of few-mode fiber,based on the coupled mode equation of the parametric amplifier of few-mode fiber,the theoretical basis for designing few-mode fiber is given,and the non-linear relationship between any two modes is deduced.On these basis,a new structure of few-mode fiber is designed,which realizes the zero-dispersion wavelength point modulation of different modes of the fiber,and breaks the coupling of degenerate modes,and then study the gain characteristics and nonlinear crosstalk characteristics of the few-mode fiber parametric amplifier and the few-mode fiber phase-sensitive optical amplifier.Finally,the feasibility of the designed few-mode fiber is verified from the simulation point of view.The main contents of this paper are:(1)The semi-analytical expression of the inter-mode nonlinear crosstalk of the few-mode fiber parametric amplifier is deduced.The results of the semi-analytical expression are in good agreement with the results of the numerical solution,and the physical process of crosstalk generation is well explained,which is of great significance for guiding the design of few-mode fibers.(2)An elliptical-core graded-index few-mode fiber is designed,which can realize parametric amplification of five modes in the C-band with a gain bandwidth of 20 nm.By adjusting the pump power of each mode reasonably,a differential mode gain of no higher than 0.7 d B can be achieved under phase-insensitive parametric amplification,and the gain of each mode can reach more than 5.06 d B;The differential mode gain of no higher than 1.12 d B can be achieved under the phase-sensitive parametric amplification,and the gain of each mode can reach more than 10.2 d B.