| Locally Er-doped Ti:LiNbO3waveguide devices have wide application prospects. However, the solubility of Er ions in these devices is limited, which restricts the further increment of gain and hence the performance in the devices. The main work of this dissertation is to increase the Er3+concentration in LiNbO3substrate by the method of vapor transport equilibration(VTE) treatment, and to fabricate locally high-solubility Er-doped Ti:LiNbO3waveguides.The main work can be summarized as below:1. Aiming at the difficulty of mode refractive index measurement in Ti:LiNbO3strip waveguides, a prism coupling method based on waveguide array was proposed. Moreover, a special waveguide structure with strip waveguide array embedded in a planar waveguide was proposed for the fabrication of long-period waveguide grating.2. The influence of factors on VTE treatment was investigated, which is as follows: Li-poor VTE temperature and time dependence of surface composition of LiNbO3crystal is in accordance with Arrhenius law and square root equation, respectively; the molar ratio of raw materials has less effect for Li-rich VTE case, but larger hollow space volume and older crucible tend to degrade the VTE growth efficiency; Li-poor VTE is less affected by the molar ratio of raw materials, the hollow space volume and the period of use.3. The Li2O-content depth profile of Li-poor VTE treated LiNbO3, which follows the profile of integral of errorfunction complement, was obtained by alternatively doing the optical polish to one crystal surface and the Li2O-content characterization. The Boltzmann–Matano mathematical analysis was applied to obtain the Li2O-content dependence of Li+diffusivity. The results show that the diffusivity decreases with the decreased Li2O-content. The diffusion shows slight anisotropy and is faster along the optical axis direction of crystal. In combination with previously reported result in the near-stoichiometric regime, the diffusivity in47-50mol%regimes is presented.4. Er3+diffusivity and solubility increases in off-congruent, Li-deficient LiNbO3crystal was studied. As the Li2O content at the X-cut crystal surface decreases from48.0to47.0mol%, the Er3+diffusivity is nearly doubled that increases from (3.3±0.2) ×10-2to (5.7±0.3)×10-2μm2/h. The Er3+solubility increases with the decrease of the crystal composition. As the Li2O content decreases only from48.0to47.7mol%, the solubility similarly increases0.6mol%. In locally Er-diffused, noncongruent, Li-deficient Ti:Er:LN strip waveguide fabricated on an X-cut initially congruent undoped substrate, the Er diffusivity is similar to (12.8±0.3) μm2/h, which is considerably larger than that of the diffusion in the congruent material(<7×10-2μm2/h).5. A Z-cut Y-propagating and a X-cut Z-propagating locally high-solubility Er-doped Ti:LiNbO3waveguides were fabricated. Their surface Er concentration results are1.33×1020cm-3and1.26×1020cm-3, which respectively increased by20%and13%than the Ti:Er:LiNbO3waveguides based on congruent LiNbO3crystal. By experiment and calculation, the mode sizes, emission and absorption cross sections and transmission loss were obtained.The1547nm small signal enhancement in waveguides was observed under980nm or1480nm LD pumping. The maximum of signal enhancement with a980nm coupled pump power of100mW in Z-cut waveguide is0.9dB/cm(TE) or0.7dB/cm(TM). Because of the impact of photorefrective effect, the signal enhancement was degrade when the coupled pump power continued to increase. The signal enhancement in X-cut waveguide, which has a stronger anti-photorefractive ability than Z-cut one, did not show a downward trend even though the980nm coupled pump power was as high as200mW. At this pump power level, the signal enhancement is1.0dB/cm(TE) or1.4dB/cm(TM).The1480nm LD can lead to less photorefrective effect than980nm LD. Therefore, the signal enhancements in both Z-cut and X-cut waveguides increase along with the increment of1480nm coupled pump power. When the coupled pump power is18.5mW, the signal enhancement is: Z-cut1.1dB/cm(TE),1.4dB/cm(TM), X-cut1.8dB/cm(TE),2.2dB/cm(TM), respectively.Finally, the evolution of light in waveguide was simulated. The maximum gains under980nm and1480nm pump in Z-cut waveguide are2.4dB/cm and2.5dB/cm, respectively, which are at least1.0dB/cm and0.7dB/cm larger than that in the previously reported Z-cut Ti:Er:Mg:LN waveguide.The innovation of this work is as follows:(1) The influence of some factors on VTE treatment was first investigated in detail.(2) The Li2O-content dependence of Li+diffusivity in Li-poor LiNbO3crystal is roundly studied for the first time.(3) Taking the lead in fabrication and characterization of locally high-solubility Er-doped Ti:LiNbO3. |
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