Down Conversion Luminescence Of Er³⁺ And Yb³⁺ Doped NaYF₄ Nanocrystals And Its Application In EDWA

With the continuous development and progress of the times,the pace of communication technology permeating into people's daily life is gradually accelerating,and the traditional electric communication mode is increasingly unable to meet people's demand for high-speed and stable communication.The emergence of this demand promotes the development of optical communication technology,but the loss of light in the long distance transmission process cannot be avoided,so the optical amplifier which can compensate the signal loss has become the core of optical network system.Erbium-doped fiber amplifier(EDFA)has been widely used because of its advantages of low loss,wide frequency band and high gain.However,the optical fiber length in communication is at least in the order of meters,which makes it difficult to apply in short-range communication and plane photon integration.Erbium-doped waveguide amplifier(EDWA)has gradually become the focus of research.The matrix of EDWA is mainly divided into inorganic and organic polymers.Compared with inorganic substrates,organic polymer substrates have low cost,simple preparation process and easy integration.Therefore,many scholars gradually focus their research on organic polymer optical waveguide amplifiers.In the organic polymer EDWA,the electron transition from the⁴I_13/2energy level of erbium ion to the ground ⁴I_15/2energy level emits a photon with a wavelength of 1530 nm,which corresponds to the low loss communication window of optical communication network at 1530?1565 nm.When Yb³⁺was added into the matrix as sensitizer,the concentration quenching caused by the high Er³⁺concentration could be alleviated,and the pump threshold power of the device could be effectively reduced,so that the device could produce higher gain performance at a smaller pump power.Based on these theoretical models,a series of NaYF₄:Er³⁺,Yb³⁺nanocrystals with different Er³⁺and Yb³⁺doping concentrations were synthesized.The effects of Er³⁺and Yb³⁺doping concentrations on the down conversion luminescence properties of nanocrystals were systematically studied,and the optimized nanocrystals were used in optical waveguide amplifiers.In this paper,nine kinds of NaYF₄:Er³⁺,Yb³⁺nanocrystals with different concentrations of Er³⁺and Yb³⁺were synthesized by high temperature thermal decomposition method,and the morphology of nanocrystals was characterized.It can be seen that the size of nanocrystals was uniform and the morphology was clear without agglomeration.The absorption spectra and emission spectra were tested.According to the analysis,when the doping concentration of Yb³⁺was the same,the absorption intensity and emission intensity increased first and then decreased gradually with the increase of Er³⁺concentration.When the doping concentration of Er³⁺and Yb³⁺was 2%and 18%,NaYF₄:Er³⁺,Yb³⁺nanocrystals obtained the strongest absorption and emission intensity and the maximum full width at half maximum of emission spectrum,which was 62.5 nm.The optimized NaYF₄:2%Er³⁺,18%Yb³⁺nanocrystals were uniformly dispersed in the SU-8 polymer,then were spin coated on the silicon wafer,and the refractive index of the core material was measured by ellipsometer;the rectangular waveguide structure was designed and fabricated,the lower cladding was Si O₂substrate,the core material was SU-8 photoresist doped with NaYF₄:2%Er³⁺,18%Yb³⁺nanocrystals,and the upper cladding was PMMA polymer.The optical field distribution of waveguide cross section was simulated by COMSOL software,and the effects of erbium ion doping concentration,overlap integral factor and signal optical power on the gain performance of the device were simulated by Matlab software.Polymer optical waveguide amplifiers were fabricated by spin coating,photolithography,wet etching and other semiconductor processes.The gain performance of the device was tested.When the signal wavelength was 1525 nm,the power was 0.1 m W,and the 980 nm pump power was 400 m W,the maximum relative gain of the 7 mm long device was2.44 d B,and the unit maximum relative gain was 3.49 d B/cm.