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Two optimized methods for accurately measuring the 1.5 µm lifetime of Er[sup 3+] in LiNbO[sub 3] crystals and waveguides are proposed. The first method, suitable for measurement of bulk material, was suggested by forming an annealed proton exchanged sandwich structure and fluorescence was collected through an adjustable aperture. This excitation collection scheme was used to investigate bulk Er-doped LiNbO[sub 3] crystals with eight different Er[sup 3+] doping levels, three different crystal thicknesses, and three different cut orientations. The 1.5 µm lifetime was investigated in three configurations: with both a sandwich and an aperture, with a sandwich but without an aperture, and without not only a sandwich but also without an aperture. In addition, the effect of the aperture was also studied. The second method, suitable for a waveguide structure, was proposed on the basis of transversely gathering the fluorescence aided by an outcoupling fiber. It was optimized by comparing three different fluorescence collection schemes. Using this method, the lifetimes of some Ti: Er:LiNbO[sub 3] strip waveguides were measured. In addition, the effect of radiation trapping on the polarized fluorescence spectrum was also investigated. The experimental results are discussed and summarized. [ABSTRACT FROM AUTHOR]

(The origin of the formation of nanoprecipitates of ErNbO[SUB4] induced by vapor transport equilibration (VTE) in Er:LiNbO[SUB3] crystals was investigated by comparing x-ray powder diffraction patterns of VTE-treated, annealed and as-grown Er:LiNbO[SUB3] crystals. The results indicated that annealing an Er:LiNbO[SUB3] crystal in ambient atmosphere, whether the crystal is x or z cut, and whether it is highly or lower doped, does not influence its crystalline structure, and hence cannot cause the formation of the precipitate. The elevated temperature is not a sufficient requirement for the formation of this additional phase, but is only an essential prerequisite, together with the high-doping level of erbium. The incorporation of a certain amount of additional Li[SUP+] ions accompanying the VTE procedure is considered as the direct reason for the formation of the precipitate. The mechanism of the formation of the precipitates of ErNbO[SUB4] was tentatively suggested from both microscopic and macroscopic points of view. In addition, the origin of VTE-induced cracking, which occurs only in higher-doped x-cut crystals, was also considered based on the experimental results of annealed crystals. The incorporation of a certain amount of additional Li[SUP+] ions by the VTE procedure is again correlated with the cracking. [ABSTRACT FROM AUTHOR]

At room temperature, polarized visible and near infrared emission characteristics of 488 nm pumped vapor transport equilibration (VTE) treated Er:LiNbO[sub 3] crystals were investigated in comparison with the corresponding as-grown ones. The observed characteristics of the VTE crystal, whether it precipitates or not, include the retained polarization dependence, slight shift (less than 5 Å) of peak position, narrowing of some individual emission peaks, the appearance of additional emission peak near 1536.5 nm and the about 10% lengthening of 1.5 µm lifetime. In addition, in the case of lower Er doping level, the spectral shape are well reserved for the VTE crystals and no obvious changes in both visible and IR emission intensity. On the other hand, for those highly doped crystals, the VTE treatment not only results in a definite change of relative intensity between some emission peaks in IR region, but also causes the drop of both visible and IR emission intensity. Combining with the related absorption characteristic allow to conclude that the drop of the emission intensity results from the scattering of the nanocrystalline grains inside these crystals formed by VTE treatment. [ABSTRACT FROM AUTHOR]

The visible and infrared transmission spectra of vapor transport equilibration (VTE) treated Er:LiNbO[sub 3] crystals, which have different doping levels (0.2%, 0.4%, and 2.0% Er per cation site), different cut orientation (X and Z cut) and different VTE duration (80, 120, 150, and 180 h), were recorded at room temperature in the wavelength range of 250-3700 nm. All of 2.0 mol % doped VTE crystals have precipitated whether X cut or Z cut, while the others have not. Their absorption characteristics were summarized and discussed in contrast to those of corresponding as-grown crystals. The OH[sup -] absorption feature of VTE treated Er:LiNbO[sub 3] is found to be different from that of pure VTE LiNbO[sub 3] crystal. The significant reduction of OH[sup -] absorption band implies that the hydrogen content in the VTE crystals has been reduced substantially whether the crystal precipitates or not. The electron transition absorption characteristics of the lower-doped, not precipitated crystals mainly include the higher transmittance, slight shift of peak or band position, slight absorption intensity change, the appearance of some additional peaks or bands, the narrowing of the peak width (full width at half maximum), and the definite blueshift of the optical absorption edge. The spectral changes are associated with the redistribution of Er[sup 3+] spectroscopic sites induced by the VTE procedure. In comparison with those lower-doped VTE crystals, the highly doped VTE crystals display more significant absorption characteristics: the significant enhancement of 1480 nm pumping band and the obvious weakening of 1531 nm peak, the appearance of many additional peaks in the infrared region, and the interesting evolution of the transmittance with the wavelength. These substantial spectral changes are unambiguously conducted with the formation of a precipitate ErNbO[sub 4] induced by the VTE treatment in these crystals. The mechanism for the formation of the precipitate has... [ABSTRACT FROM AUTHOR]