An Experimental Study Of Influence Of Doping On Electro-optic Property Of Lithium Niobate Crystal

Lithium niobate crystal?LiNbO₃?is widely used in various electro-optical devices such as electro-optic modulator,electro-optic deflector and electro-optical switch due to its excellent electro-optical properties.Based on rare earth doped and titanium diffused lithium niobate?Er:Ti:LiNbO₃?,optical waveguide amplifiers and other active optical waveguide devices can be fabricated.Mg-doped lithium niobate crystal can effectively improve its photorefractive ability.Rare earth ions and photorefractive ions co-doped LiNbO₃ crystal combine the advantages of both,expanding its scope of application.In this experiment,the electro-optical properties of LiNbO₃ crystals with different compositions and doping concentration were studied.The electro-optic coefficients?₃₃and?₁₃of Ti⁴⁺ion and Er³⁺ion doped,erbium magnesium(Er³⁺/Mg²⁺)and erbium indium(Er³⁺/In³⁺)co-doped lithium niobate crystals and LiNbO₃ with different compositions were measured by Mach-Zehnder interferometer.In this study,two kinds of applied electric field were adopted respectively to study the variation of electro-optic coefficient with different compositions and doping concentration,and the theoretical model was proposed from the point of doping ions occupied in crystal to explain the compositions effect and doping effect on the properties of lithium niobate crystal reasonably.The main work of the experiment include:?1?We built a Mach-Zehnder?M-Z?interferometer system.Then used the M-Z system to measure the electro-optic coefficients?₃₃and?₁₃of the congruent lithium niobate crystal with two kinds of electric field to verify the accuracy and reliability of this interferometer.?2?The compositions effect on the electro-optical properties of Li NbO₃ crystal was studied.A series of LiNbO₃ crystals with different compositions and a series of Li-poor LiNbO₃ crystals doped with 5mol%MgO were prepared by vapor phase transport equilibrium?VTE?technique by controlling the diffusion temperature and diffusion time,and the electro-optic coefficients were measured.It was found that the electro-optic coefficients?₃₃and?₁₃decreased with the increase of crystal compositions.?3?Then the doping effect of rare-earth erbium ion and transition metal titanium ion on the electro-optical properties of Li NbO₃ were investigated.We carried out the experimental research of change rules of the electro-optic coefficients with the doping concentration of different erbium ion doping concentration?0-2 mol%?and different titanium ion doping concentration?0-16 mol%?.It was found that,within the error range,erbium ion doping effect of Er:LiNbO₃ crystal had little effect on the electro-optical properties,and titanium ion doping effect made the electro-optic coefficients?₃₃and?₁₃of Ti:LiNbO₃ crystal reduced.?4?Finally,we also studied the magnesium and erbium(Er³⁺/Mg²⁺),indium and erbium(Er³⁺/In³⁺)co-doping effect on the electro-optical properties of lithium niobate crystal was studied.the Er³⁺/Mg²⁺and Er³⁺/In³⁺co-doping effect on the electro-optic properties of LiNbO₃ crystal.The experiment measured the variation of the electro-optic coefficient with magnesium doping concentration?0-7 mol%?and indium doping concentration?0-3 mol%?.The results showed that there was a threshold effect on the doping of magnesium ions,and the electro-optic coefficients?₃₃and?₁₃showed a nonlinear variation with the increase of magnesium doping concentration.However,there was no obvious trend in the variation range of indium doping concentration,although it was not monotonic.