Rare Earth Doped Up-conversion Optical Waveguide Transmission And Directional Emission Research

Micro-nano optical waveguides are capable of directing the transmission of light at sub-wavelength scales.The use of semiconductors,polymers,and luminescent waveguides that locally absorb ultraviolet excitation light to achieve fluorescence transmission and directional emission has been widely reported.Compared with ultraviolet excitation,near-infrared excitation light has the advantages of strong bio-penetration and small destructiveness.Rare-earth doped upconversion luminescent materials have the advantages of narrow emission line width,rich spectral range,long fluorescence lifetime and low biotoxicity.They have important applications in cell imaging,display,laser,fluorescent bioprobe and anti-counterfeiting coding labels.An luminescent waveguide based on a rare earth doped upconversion luminescent material can be excited by near-infrared light and produce fluorescence transmission and directional emission.The efficient excitation of the luminescent waveguide and the regulation of the far-field spatial emission angle play an important role in its application in the biological field and in the field of optical communication.In this thesis,a one-dimensional rare-earth beveled microtube is designed as an up-conversion illuminating waveguide.The special chamfering structure can achieve high-efficiency coupling of excitation light,greatly improving the excitation efficiency of excitation light and the intensity of far-field emission.The main research contents of this thesis include:A beveled NaYF4:Yb3+/Er3+(20/2%)microtube was prepared by sodium citrate assisted hydrothermal method.The length of the NaYF4:Yb3+/Er3+ microtube can be adjusted by changing the order of addition of sodium citrate and rare earth nitrate.The directional transmission characteristics of single microtubes under different excitation modes were studied.Research results show that microtubes can limit the transmission of fluorescence inside.In the end-excitation mode,simultaneous coupling of laser and fluorescence can be achieved,and there is strong fluorescence emission at the end of the microtube.In the same excitation mode,the fluorescent green emission band is more easily coupled into the waveguide for transmission than the red emission band.In the end-excitation mode,changing the bevel direction of the microtube top can control the degree of coupling of the laser in the microtube,which is consistent with our geometrical optical simulation results.Using the self-built Fourier imaging system,the effects of different excitation modes and the shape of the emitter on the spatial emission angle of far-field fluorescence were studied.By near-infrared excitation,the microtubes are capable of directing fluorescence with a wider spectral range,a narrower emission band,at the end,and the emitted fluorescence is directional.The results show that the spatial emission angular intensity distribution is mainly affected by the morphology of the micron tube emission end.The research will have potential applications in the field of multichannel optical communications.