Research On Pumping Optimization Technology Of All-fiber Few-mode Erbium-doped Fiber Amplifier

Few-mode erbium doped fiber amplifier(FM-EDFA)is an important component of long-distance mode division multiplexing transmission system.Compared with the space optical structure,all-fiber FM-EDFAs have more application advantages in the actual optical fiber communication system,and can effectively promote the practical process of FM-EDFAs.Therefore,fiberization has become one of the future development directions of FM-EDFAs.In this thesis,experimental research is carried out on the pump optimization technology of all-fiber FM-EDFA.A mode detection method based on pure-mode calculation is proposed,a mode power detection unit is developed,an all-fiber FM-EDFA experimental platform based on mode-selective photonic lanterns is built,and the low differential mode gain amplification of six spatial modes is realized by pump optimization.The main contents and innovations of the thesis are as follows:1.In order to avoid the influence of crosstalk from the photonic lanterns on the measurement of the mode gain,a wavelength mapping method based on a pure-mode calculation method is proposed.The measurement errors between the mixed-mode and pure-mode power calculation methods are analyzed and compared.The experiments show that the pure-mode calculation method is not sensitive to the polarization disturbance in the few-mode fiber,and the polarization dependence of the mode transmittance is less than 0.025.2.A mode power detection unit is developed,which is mainly composed of a photonic lantern and a wavelength division multiplexer.The mode gain is respectively measured by the mode power detection unit and the optical spectrum analyzer(OSA),and the difference between the two measurement results is not more than 0.5 d B.Compared with the OSA measurement method,the mode power detection unit has the advantages of low measurement cost and higher optical power;it can also directly be used to filter out the pump light and the few-mode signals.3.An all-fiber FM-EDFA experimental platform was built with a fiber-optic photonic lantern mode multiplexer and a self-developed mode power detection unit.Based on a commercial three-mode erbium-doped fiber,and two pump modes of LP_11aand LP_11bwith the wavelength of 1480 nm,an all-fiber FM-EDFA was designed and developed to achieve LP₀₁,LP_11a and LP_11b modes signal simultaneous amplification.The gain of each mode is greater than 25d B,and the differential mode gain is less than2d B.4.In order to verify whether the six-mode erbium-doped fiber self-developed by the project team can meet the mode gain requirements,the all-fiber FM-EDFA experimental platform built above was used to simultaneously amplify six spatial modes of LP₀₁,LP_11a,LP_11b,LP_21a,LP_21b,LP₀₂.In the experiment,by optimizing the pump combination,that is,when the pump powers of LP₀₁,LP_11a,LP_11b and LP_21a are23.01d Bm,25.8d Bm,23d Bm and 23.6d Bm,respectively,their mode gain is greater than22d B,and the differential mode gain is less than 2d B,which has reached the project index requirements.