Research,fabrication And Test On Photonic Lanterns

With the development of information technologies such as 5G and AI,the requirements of human society for data transmission are constantly increasing.As the further increase of information transmission rate and capacity has been restricted by the non-linear effects of the single-mode optical fibers for a long time,the mode division multiplexing has been widely expected by exploiting potentialities in the spatial dimension.The mode multi-/demultiplexer is one of the most critical devices in the MDM optical fiber communication system.As a fiber-based mode control device with good performance,photonic lantern has become the most favored mode multi-/demultiplexer due to its low-loss,ultra-wideband,scalability and compatibility.The application of the photonic lantern is vital to the increase of the transmission rate and capacity of the MDM optical fiber communication system.We start from the basic theory of the mode analysis in fibers,mode coupling and super-mode theory,adiabatic taper theory and so on.We research the basic principles and simulation design methods of the photonic lantern.We fabricate fiber-based three-mode and six-mode photon lanterns.And we propose a new method for the design of orbital angular momentum mode-selective photon lanterns.The main attributions and innovations of this paper are as the following three aspects:1.We analyze the basic principles of the eigenmodes and the OAM modes in few-mode fibers and the photonic lanterns.We research the common methods of numerical calculation design,experimental fabrication and test of the photonic lanterns.Based on the beam propagation method and the finite element method simulation,we show an optimized simulation design of the three-mode selective photonic lantern,with the total loss less than 0.07dB and the mode selectivity higher than 18dB.And we show an optimized simulation design of the six-mode selective photonic lantern,with the total loss less than 0.07dB and the mode selectivity higher than 22dB.We systematically show the effect of the initial single-mode-end core normalized frequency value of the mode-selective photonic lanterns for the first time,which provides a novel and direct supplementary idea for the traditional design method of mode-selective photonic lanterns.2.In current experiment condition,we fabricate and test the three-mode and six-mode selective photonic lanterns inland for the first time.We show the fabrication,packaging procedure and test performance of the first finished domestic three-mode photonic lantern,with the total packaged loss less than 5.0dB,mode dependent loss less than 3.0dB,and bandwidth wider than 70nm.We show the fabrication and test performance of the domestic six-mode photonic lantern,with the mode loss of LP01,LP11a,LP11b,LP21a,LP21b and LP02 less than 2.1dB,3.1dB,3.2dB,3.4dB,3.4dB and 3.7dB respectively.3.Aiming to create a simple and feasible fiber-based OAM mode multiplexing method,we innovatively analyze the mode evolution in mode-selective photonic lanterns with respect to taper lengths,affected by possible mode phase differences varying along the taper.As a result,we firstly design the OAM mode-selective photonic lantern by optimizing the taper length,which employs only one single mode fiber port to selectively generate one OAM mode.The simulation results show that the mode crosstalk of the first-order OAM-MSPL is below-24dB.The first-order OAM-MSPL works stably in the whole C-band and L-band,with insertion loss below 0.03dB and taper length error tolerance longer than 1 mm.The mode crosstalk of the second-order OAM-MSPL is below-24dB,with insertion loss below 0.04dB.In this paper,for the first time,there is a one-to-one correspondence between the fundamental mode in the single-mode-end and the target OAM mode excited correspondingly in the few-mode-end,when injecting light selectively.Consequently,we propose a simple and feasible method for fiber-based OAM multiplexing.