Research On Polymer Few-mode Optical Waveguide Amplifier

With the development of data centers and high-performance computers,their internal data rate and throughput are increasing rapidly.The traditional electrical interconnection method is limited by Moore’s law,which cannot meet the needs of high rate and high-capacity data transmission.As an emerging interconnection technology,Photonic Integrated Circuits（PICs）have the advantages of high speed,high bandwidth and low energy consumption,which are more suitable for the dense layout inside modern data centers,and become a potential solution to solve the bottleneck of data transmission.In order to further improve the bandwidth density and channel capacity required for on-chip communication,the introduction of Mode Division Multiplexing（MDM）technology in PIC systems can significantly improve the data transmission capacity and integration level without increasing the physical size.However,the use of core mode devices such as mode multiplexers/demultiplexers and mode converters introduces large losses,which restricts the practical application of mode division multiplexing technology in on-chip optical interconnect systems.Therefore,there is an urgent need for an on-chip few-mode waveguide amplifier to effectively compensate the losses of various functional mode devices.Organic polymer materials have the advantages of low cost,simple fabrication process and easy integration,which make them a good choice for fabrication of on-chip optical waveguide amplifiers.Therefore,in this paper,combining the unique advantages of polymer Waveguide,a high-gain,multi-mode,equalized on-chip Few Mode-Erbium Doped Waveguide Amplifier（FM-EDWA）is studied to achieve effective amplification of multiple modes.The transmission loss of the mode division multiplexing on-chip optical interconnect system was compensated to further improve the amount of data transmission and integration scale of the system.The main innovative work carried out is as follows:1.An Improved Grey Wolf Optimization（IGWO）algorithm is proposed to design the few-mode waveguide amplifier structure.By using the IGWO algorithm,the optical waveguide amplifiers with single,double and three-layer doping structures are optimized.The signal Differential Modal Gain（DMG）is determined by the overlap degree of signal mode,pump mode and erbium ion distribution.Therefore,the algorithm is used to optimize the pump structure and erbium-doped distribution to reduce the overlap integration factor difference between different modes,so as to realize the gain equalization of different modes in few-mode optical waveguide amplifier.The simulation optimization results show that the single-layer erbium-doped structure waveguide amplifier can achieve three-signal mode equalization amplification by using dual-mode multiplexing pump,and the optimal pump structure is LP₀₁+LP_21b,and the minimum difference of overlap integration factor before and after optimization by IGWO algorithm is reduced from 0.1256 to 0.0047.The double-layer and three-layer erbium-doped structure waveguide amplifiers are pumped by single mode,and the differences of overlap integration factors of three signal modes are as low as 0.0092 and 0.0019,respectively.Compared with the existing methods for the design of few-mode erbium-doped optical waveguide amplifiers,the application of IGWO can improve the convergence speed and convergence accuracy.The design lays the foundation for the realization of few-mode waveguide amplifier.2.A single-layer erbium-doped polymer three-mode waveguide amplifier is proposed,and the mode gain equalization is realized by combining the pump control scheme.Na YF₄:Er³⁺,Yb³⁺nanoparticles were prepared by high temperature thermal decomposition method,and the absorption spectrum and fluorescence spectrum characteristics were characterized.Combined with Judd-Ofelt theory,the parameters required for the gain characteristics simulation are calculated.The gain characteristics of the three-signal mode in the waveguide amplifier are simulated and analyzed,and the key parameters such as the length of the waveguide,the doping concentration of rare earth ions and the input power of the signal light and the pump light are optimized.The device was fabricated by semiconductor technology,and a dual-pump mode end-face coupling test system was built based on the mode-selective photonic lantern,and the transmission loss,gain characteristics and noise characteristics of each mode of the device were tested.In the process of magnification,the mode is maintained well,and the light spot has no large distortion.When the pump power of LP₀₁+LP_21b is 320 m W+120 m W,the average gain of LP₀₁,LP_11a and LP_11b in the 1.3-cm device is 10.4 d B at 1555 nm,and the lowest differential mode gain is 0.4 d B.The average mode gain in C-band is more than 7.4 d B,DMG is less than 2.3 d B,and noise figure is less than 5 d B.This is the first polymer few-mode optical waveguide amplifier to achieve three-mode equalization amplification in the world.3.A double-layer erbium-doped polymer few-mode optical waveguide amplifier is proposed,and the erbium ion regulation scheme is used to achieve gain equalization.The structure amplifier can realize the balanced amplification of three signal modes in a single mode pump,simplify the pump structure complexity,and effectively reduce the system integration.The double-layer waveguide structure was fabricated by high-precision alignment and secondary etching technology,and the loss,crosstalk and near-field spot characteristics of the device were measured and characterized.The spot is not distorted before and after amplification,and the crosstalk between the three signal modes is lower than-12.47 d B.The maximum gain at 1529 nm for LP₀₁,LP_11aand LP_11b signal modes is 14.91 d B,14.35 d B and 14.05 d B,respectively,when the pump power is 200 m W with LP₀₁ pumping.The average gain is 11.5 d B and DMG is less than 1.3 d B in the wavelength range of 1525 to 1565 nm.