Fabrication Of Rare-earth-doped LinbO₃Crystal For Integrated Optics

Rare-earth-doped LiNbO₃（LN） crystal is a promising substrate material foractive optical waveguide devices because it combines excellent electro-optic,acousto-optic and nonlinear optical properties of LN with laser properties ofrare-earth ion, together with the possibility of using the well-developed techniques tofabricate low loss channel waveguides in Integrated Optics.Diffusion properties of Tm³⁺in congruent LiNbO₃crystal have been investigated,together with other two related issues, i. e. Tm³⁺-doping contribution to refractiveindex of LiNbO₃substrate and Li out-diffusion. Several X-cut and Z-cut congruentLiNbO₃substrates locally coated with15-31nm thick Tm-metal films were annealedin surrounding air under different temperatures of1030-1130℃for differentdurations of20-70h. After the anneal, refractive index at Tm³⁺-doped and Tm³⁺-freeparts of crystal surface was measured at the wavelengths of1311and1553nm andsurface Li₂O contents were evaluated from the measured refractive index. The resultsshow that Tm³⁺-doping has a weak effect on substrate index and a small contributionto index increment in waveguide layer in comparison with Ti4+-doping. The Li₂Ocontent at the Tm³⁺-doped surface equals that at the Tm³⁺-free surface. The Liout-diffusion depends mainly on the diffusion temperature. Below1100℃, the Liout-diffusion is not measurable. At1130℃, a30h diffusion procedure may cause0.2-0.3mol%Li₂O content loss. Secondary ion mass spectrometry was used to studythe Tm³⁺diffusion properties. The results show that the diffused Tm³⁺ions in allsamples follow a complementary error function profile. From the measured Tm³⁺profiles, characteristic diffusion parameters such as diffusivity, diffusion constant,activation energy, solubility, solubility constant and heat of solution were obtained.Meanwhile，Characteristics of Er³⁺and Tm³⁺co-diffusion in congruent LiNbO₃crystal have been investigated, together with other two related issues, i. e.Tm³⁺-doping contribution to refractive index of LiNbO₃substrate and Liout-diffusion.Like what has been mentioned above, several X-cut and Z-cut congruentLiNbO₃substrates were locally coated with20-40nm thick Tm and Er metal filmswere annealed in surrounding air under different temperatures of1030-1130℃fordifferent durations of20-70h. The results show that doping has a weak effect onsubstrate index and a small contribution to index increment in waveguide layer in comparison with Ti4+-doping. The Li out-diffusion depends mainly on the diffusiontemperature. Secondary ion mass spectrometry was used to study the Er³⁺and Tm³⁺diffusion properties. Characteristic diffusion parameters such as diffusivity, diffusionconstant, activation energy, solubility, solubility constant and heat of solution wereobtained.Based on the experiment data, we could offer more reference for fabricatingactive optical waveguide devices...