Effect Of Erbium-doped Nanocrystalline Size On Relative Gain Of Polymer-based Optical Waveguide Amplifiers

Er³⁺ion doped optical amplifier is an indispensable component in C band optical communication system.Compared with the optical fiber amplifier（EDFA）,the optical waveguide amplifier（EDWA）has the characteristics of small device size,easy to realize the integration of other miniaturized devices on the silicon substrate,and has become a key component in the rapid development of integrated optical communication system.As far as optical waveguide amplifiers are concerned,they can be divided into two main categories by the core gain dielectric materials in the waveguide devices:inorganic optical waveguide amplifiers and organic optical waveguide amplifiers.Organic optical waveguide amplifiers have become a research focus in the field of optical waveguide devices because of their advantages such as simple fabrication process,low processing cost,easy adjustment of gain medium refractive index and high electro-optical coupling coefficient.Erbium-doped rare earth nanocrystals have excellent optical properties in the C band of optical communication and become attractive dopants for the preparation of polymer optical waveguide amplifiers.At present,the development of polymer-based optical waveguide amplifiers using rare earth nanocrystals as dopants and their optical amplifying properties have attracted wide attention.There are many reports about improving the gain performance of optical waveguide amplifiers by optimizing the fabrication process of erbium-doped nanocrystals,but there is no systematic study on the effect of the size change of erbium-doped nanocrystals on the gain performance of polymer-based optical waveguide amplifiers.In our study,it is found that the size of nanocrystals has a great influence on the gain performance of polymer-based optical waveguide amplifiers.The larger nanocrystals have better luminescence properties in the C band,but the larger nanocrystals also bring larger scattering loss in the device.In this paper,we prepared erbium-doped rare earth nanocrystals with a series of size changes,modified oil-soluble groups with double bonds on the surface,doped erbium-doped rare earth nanocrystals into polymers by copolymerization,and prepared a series of optical waveguide amplifiers that polymerized rare earth nanocrystals with different sizes.The effects of the size of nanocrystals on the gain performance of polymer-based optical waveguide amplifiers were systematically studied.In this paper,two series of erbium-doped rare earth nanocrystals with different sizes were prepared and polymerized as gain medium in methyl methacrylate polymer to investigate the effect of the size of erbium-doped rare earth nanocrystals on the gain performance of polymer-based optical waveguide amplifiers.Specific research work is as follows:（1）Firstly,a series of NaYF₄:18%Yb³⁺,2%Er³⁺@（X-shell,X=2-6 nm）NaLuF₄nanocrystals with sizes ranging from 19 to 23 nm were synthesized by coating one to multiple layers of inert shells to change the size of the nanocrystals.A series of polymer based optical waveguide amplifiers polymerized with 19-23 nm NaYF₄:Yb³⁺,Er³⁺@NaLuF₄ nanocrystals were prepared,and the effect of erbium-doped rare earth nanocrystals with different sizes on the gain performance of polymer based optical waveguide amplifiers in C band was studied.The experimental results show that as the size of the nanocrystals increases,the gain of the waveguide amplifier also increases.In polymer based optical waveguide devices doped with 23 nm NaYF₄:Yb³⁺,Er³⁺@NaLuF₄ nanocrystals,the maximum relative gain measured at 1550 nm is 12.3 d B/cm.Due to the design and synthesis of NaYF₄:Yb³⁺,Er³⁺@NaLuF₄ nanocrystals,the size only increased within a small range,and the gain change of the optical waveguide device was not significant.However,it was observed that the relative gain of the optical waveguide amplifier showed a trend of increasing with the increase of nanocrystal size.（2）In order to further investigate the influence of nanocrystal size on the gain of polymer based optical waveguide amplifiers,rare earth nanocrystals with good luminescent properties and a wider range of size changes were designed and synthesized using high-temperature pyrolysis method.By adjusting the concentrations of Lu³⁺and Y³⁺,NaLuYF₄:Yb³⁺,Er³⁺nanocrystal sizes were adjusted from 20 nm,30nm,40 nm,50 nm,and 60 nm.A series of polymer based optical waveguide amplifiers polymerized with 20-60 nm NaLuYF₄:Yb³⁺,Er³⁺nanocrystals were prepared,and the effect of different sizes of erbium-doped rare earth nanocrystals on the gain performance of polymer based optical waveguide amplifiers in C band was studied.The experimental results show that as the size of the nanocrystals increases,the gain of the waveguide amplifier also increases.In polymer based optical waveguide devices doped with 60 nm NaLuYF₄:Yb³⁺,Er³⁺nanocrystals,the maximum relative gain measured at a signal wavelength of 1550 nm is 20 d B/cm.The relative gain of polymer-based optical waveguide amplifiers increases with the increase of NaYF₄:18%Yb,2%Er@NaLuF₄ nanocrystals and Na Lu_80-xY_xF₄:18%Yb,2%Er nanocrystals.Large size nanocrystals are expected to achieve a net gain in waveguide devices.It is of great significance to use large size nanocrystalline polymer optical waveguide amplifiers to achieve high gain of small devices in a new generation of integrated optical communication systems on chip.