Research On Mode Purification Technology Of Multi-mode Pump Source Based On Photonic Lantern

With the development and wide application of optical fiber communication technology,the demand for high-quality information and large-capacity transmission has increased dramatically.In recent years,effective technologies to further increase capacity have been explored using the spatial dimension.In this paper,a mode mismatching photonic lantern(MMPL)is proposed based on the source supply of space-division erbium-doped fiber amplifier,which is applied to the mode purification technology of multi-mode pump source in erbium-doped fiber amplifiers.The mode mismatching photonic lantern can not only realize the low-loss coupling of multi-mode pump source to multi-channel single-mode pump sources,but also realize the coupling of multi-mode to fundamental modes,that is,mode purification.In this paper,starting from the mode purification technology of multimode pump source and the basic theory of optical fiber,the mode existing in multi-mode fiber is simulated and modeled.At the same time,the basic theory of the photonic lantern was analyzed through the research of the principle,mode matching theory and mode coupling theory.The three-mode,six-mode and seven-mode mode mismatching photonic lanterns have been designed.Meanwhile,three-mode and seven-mode mode mismatching photonic lanterns were experimentally fabricated and tested to achieve low-loss coupling from a multi-mode pump source to multi-channel single-mode pump sources.The main work contents are as follows.1.The photonic lantern applied to multi-mode pump source mode purification technology is proposed.The mode distribution of the 980nm multi-mode pump source at different output powers was analyzed and tested.Meanwhile,the mode purification efficiency of the photonic lantern was tested using 980nm multi-mode pump source.2.Based on the basic theory of optical fiber,the number of modes existing in multi-mode fiber is analyzed,and multiple groups of uniformly distributed multi-mode are generated by randomly superimposing all modes existing in the fiber.Taking the multi-mode distribution as the simulated pump source,the numerical simulation of the photonic lantern is completed through the simulation excitation.3.According to the basic theory of photonic lantern,a mode mismatching photonic lantern is proposed for mode purification technology of multi-mode pump source.The three-mode,six-mode and seven-mode mode mismatching photonic lanterns are designed respectively,and the mode purification coupling efficiency of the three-mode,six-mode and seven-mode mode mismatching photonic lanterns is studied based on the finite element method and the beam propagation method.From the simulation,the coupling of hundreds of modes in multimode fibers to three,six,and seven single-mode fibers is realized.The efficiencies of mode purification obtained through simulation are 2.94%,5.33%,and 5.52%,respectively.The simulated coupling efficiency is higher than that obtained from the mode matching theoretical calculation,which provides numerical guidance for the experimental preparation of mode mismatching photonic lanterns.4.The multi-mode pump source mode purification technology based on 980nm photonic lantern is experimentally studied.The specific experimental preparation methods of the three-mode and seven-mode mode mismatching photonic lanterns are introduced in detail,and the insertion loss of the photonic lantern device and the coupling efficiency of the pump mode purification are tested respectively.The purification efficiencies of three-mode and seven-mode mode mismatching photonic lantern from multi-mode to fundamental modes are 7.41%and 11.96%,respectively.