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A highly sensitive and flexible, multichannel thermometer prepared by exploiting the emission behaviors of Er3+ in Y7O6F9:Er/Yb crystal-embedded polyacrylonitrile fibers is reported. This sensor could be operated at 303–433 K, and the maximum relative sensitivity based thermal-coupling level was 1.285% K−1 at 303 K. More interesting is that the self-calibration could be achieved from the single Er3+ emission avoiding the intervention of other calibration tools. Repeatability experiments also confirmed the accuracy and durability of this fabricated material. Further details have been provided to reveal the multi-channel sensing mechanism, in which the green–green emission and red–red emission based thermal-coupling level, and the blue-green emission based non-thermal coupling level are discussed. All the above results showed that the Y7O6F9:Er/Yb crystal-embedded polyacrylonitrile fibers have extraordinary potential in intelligent wearable devices, industrial safety protection, and anti-counterfeiting mark fields. [ABSTRACT FROM AUTHOR]

Sr2(La1−xErx)F7/polyacrylonitrile composite fibers with special pliability and excellent crystal dispersibility have been fabricated, which provide smaller size and appropriate temperature sensitivity. Up-conversion emission shows quadratic dependence of the photoluminescence intensity on pump power, confirming the participation of two photons during the excitation processes. The composite fibers, combining main and auxiliary sensing derived from green and red emissions, give fibers the ability to obtain accurate results and better reproducibility. Among them, assigning the green emission as the main indicator of non-contact temperature sensing, the absolute and relative sensitivities are 0.514% K−1 and 0.654% K−1 at 373 K, respectively. Furthermore, the ratio of green and red emission serves as an auxiliary monitoring parameter to calibrate the deviation, where the absolute and relative sensitivities reach 7.208% K−1 and 0.901% K−1 at 373 K. In general, composite fibers with excellent dual-ratiometric temperature sensing are expected to be applied in biological probes, miniature devices and accurate temperature sensors. [ABSTRACT FROM AUTHOR]

Multichannel transition visible and near-infrared (NIR) fluorescences have been captured in Dy3+-doped fiber-adaptive Na2O-ZnO-PbO-GeO2-TeO2 glasses. The maximum stimulated emission cross-sections σem-max were derived to be 0.33 × 10-21, 3.66 × 10-21, and 0.67 × 10-21 cm2 for conventional visible emissions assigned to 4F9/2→6HJ (J = 15/2, 13/2, and 11/2) transitions, respectively. Infrequent multi-peak NIR emissions were recorded in the spectral range of 900-1500 nm, among which the values of σem-max were solved to be 1.05 × 10-22 and 1.56 × 10-22 cm2 for ∼1.02 and ∼1.18 μm emission bands. Internal quantum efficiency for the 4F9/2 level and external quantum yield for visible emissions of Dy3+ were determined to be 88.44% and 12.38%, severally. Effective multichannel radiative emissions reveal a potential in developing fiber-lighting sources, tunable lasers, and NIR optical amplifiers. [ABSTRACT FROM AUTHOR]

Conventional visible and novel infrared (IR) emissions of Sm3+ in heavy-metal-gallate glasses (Li2O–K2O–BaO–PbO–Bi2O3–Ga2O3, LKBPBG for short) with low phonon energy have been observed. Judd–Ofelt parameters Ω2 (3.00×10-20 cm2), Ω4 (5.19×10-20 cm2), and Ω6 (1.69×10-20 cm2) indicate a higher asymmetry and stronger covalent environment in the optical glasses. For the visible fluorescence bands peaked at 564, 601, 648, and 710 nm, the maximum stimulated emission cross-sections (σe) were derived to be 1.35×10-22, 9.21×10-22, 9.58×10-22, and 3.91×10-22 cm2, respectively, the values are larger than those in phosphate, oxyfluoroborate, tellurite, and calibo glasses obviously. The observed 1185 nm IR emission lies in the low-loss window of telecommunication system, and the maximum value of σe for this band was obtained to be 6.09×10-23 cm2. The characterization of multichannel radiative transitions of Sm3+ in LKBPBG glasses is beneficial in exposing its potential applications in visible and IR optoelectronic devices. [ABSTRACT FROM AUTHOR]

Diffusivity of Er3+ into LiNbO3 crystal has been studied as a function of Li2O content and crystal orientation. The Li2O content in single-crystal LiNbO3 plates was adjusted by Li-rich vapor transport equilibration (VTE) technique. Five X-cut and five Z-cut congruent substrates were VTE treated at first at 1100 °C for different durations ranging from 6 to 74 h, and then were subjected to a special post-VTE anneal procedure at the same temperature for 60 h to obtain homogeneous Li2O content. The Li2O content was determined from the measured fundamental optical absorption edge. Its homogeneity is verified by measuring the optical absorption edge as a function of the crystal thickness. After the composition characterization, the substrates were coated with 45 nm thick Er film and annealed at 1130 °C for 40 h in argon atmosphere. The Er3+ profile was analyzed by secondary ion mass spectrometry. The results show that the Er3+ diffusivity decreases monoexponentially with the increase in the Li2O content in both cases of X- and Z-cut. As the Li2O content is increased from the congruent point (48.4 mol %) to the near-stoichiometric composition (∼49.9 mol %), the diffusivity decreases from 0.107 (0.072) to 0.017 (0.018) μm2/h for the Z (X)-cut substrate. The diffusion shows considerable anisotropy for the lower Li2O content and the diffusivity in a Z-cut substrate is larger. The anisotropy weakens gradually with the increase in the Li2O content, and the diffusivities in the X- and Z-cut substrates ultimately tend to a same value (∼0.02 μm2/h) at the Li-rich phase boundary. After the Er diffusion procedure, endface coupling experiment was carried out to check if a planar waveguide layer was formed near the Er-diffused surface due to the Li outdiffusion. The results show that the Li outdiffusion did not accompany the Er diffusion procedure. [ABSTRACT FROM AUTHOR]

The thermal diffusion of Er3+ into X- and Z-cut congruent LiNbO3 crystal in Li-enriched atmosphere [i.e., vapor transport equilibration (VTE)], created by Li3NbO4–LiNbO3 two-phase powder at the temperature around 1130 °C, was attempted. Single-crystal x-ray diffraction, micro-Raman, photoluminescence spectroscopy, and secondary ion mass spectrometry (SIMS) were used to study the crystalline phase with respect to Er3+ ion and the Er3+ diffusivity. The results show that the thickness of the Er film coated should not be thicker than 10 nm for an X-cut plate and 15 nm for a Z-cut plate. In this case, the diffusion is complete if the duration is long enough (>150 h) and the Er3+ ions in the diffused layer still retain the LiNbO3 phase. On the other hand, if the initial thickness of the Er metal film is thicker than 10 nm for the X-cut plate and 15 nm for the Z-cut plate, the diffusion will be incomplete no matter how long the duration is. This is because the residual Er3+ ions form irremovable ErNbO4 grains on the surface of the crystal. SIMS analysis on an X-cut VTE (1130 °C/192 h) and a Z-cut VTE (1129 °C/158 h) crystal coated, respectively, with 10 and 15 nm thick Er film reveals that the Er diffusion shows obvious anisotropy with the mean diffusion coefficients of 0.0155 and 0.0957 μm2/h, respectively. The surface concentrations are 1.5×1020 and 1.0×1020 at./cm3, respectively. The diffused Er3+ ions follow the stretched-exponential decay profile with a stretching factor of 1.85 and 3.5, respectively. The Li/Nb ratio in the Er-diffused layer is similar to 99.4% for the X-cut sample coated with 10 nm thick Er film and 99.3% for the Z-cut crystal coated with 15 nm thick Er film. The rms roughness of the diffused surface is better than 6 and 4 nm for the X-cut and Z-cut samples, respectively. [ABSTRACT FROM AUTHOR]

Standard thermal diffusion of Er3+ into X-cut congruent LiNbO3 crystal with the MgO doping level close to the antiphotorefractive threshold concentration, 4.5 mol%, was attempted at the temperature close to Curie point of the crystal. Single-crystal x-ray diffraction, photoluminescence spectroscopy and secondary ion mass spectrometry (SIMS) were used to study the crystalline phase with respect to Er3+ ions and the depth profile of the diffused Er3+ ions. The results show that the thickness of the Er metal film coating should not be thicker than 4.6 nm. In this case, the diffusion is complete, the diffused surface is clean, and the Er3+ ions in the diffused layer still retain the LiNbO3 phase. On the other hand, the diffusion will be incomplete if the initial thickness of the Er metal film is thicker than 4.6 nm. The residual Er3+ ions form ErNbO4 grains on the surface of the crystal. SIMS analysis shows that the diffused Er3+ ions follow a monoexponential decay profile. The experimental results also show that the diffusivity of Er3+ in the X-cut congruent Mg(4.5 mol %):LiNbO3 is similar to 4.69×10-3 μm2/h at 1130 °C. Further vapor transport equilibration treatment following the standard diffusion procedure results in transformation of the diffused Er3+ ions from LiNbO3 into the ErNbO4 phase and, hence, substantial spectral change of the 1.5 μm emission. [ABSTRACT FROM AUTHOR]

Congruent LiNbO3 crystals doped with 5.5/1, 6/0.15, and 7/0.8 mol %/mol % of Zn/Er were thermally treated at 1120 °C over 101 h using vapor transport equilibration (VTE) technique. Unpolarized visible and infrared absorption spectra of the VTE-treated and corresponding as-grown crystals were recorded at room temperature. It is shown that VTE treatment has brought these crystals closer to stoichiometric composition. X-ray powder diffraction and optical absorption results show that the VTE treatment induces the crystalline phase transformation with respect to Er3+ from the original Er3+:LiNbO3 to the ErNbO4 in all crystals studied. The formation of the ErNbO4 phase results in substantial absorption changes that include the drop of the transparency in the visible region, the reduction of Er3+ absorption, and the Zn-doping-level-dependent changes in spectral shape and peaking position at 0.98 and 1.5 μm regions. Based upon the measured absorption spectra, the influences of Zn-doping level and VTE treatment on the Er3+ spectroscopic properties were studied by using the Judd-Ofelt (JO) theory. The results show that the VTE treatment has a little effect on the fluorescence branch ratio, while a large effect on the JO parameters, oscillator strength, and electron transition probability. The Zn doping level affects the JO parameters, oscillator strength, and transition probabilities of some individual manifolds. In addition, the VTE treatment leads to the increases of the theoretical radiative lifetimes of almost all manifolds considered. For the emission at 1.5 μm, the lifetime increase is as much as 30% and the theoretical results are in well agreement with the experimental data. The VTE-induced lifetime increase is qualitatively explained. [ABSTRACT FROM AUTHOR]

A model is proposed for describing two-dimensional diffusion of Ti into an initially congruent LiNbO3 crystal under a Li-enriched atmosphere created by a mixed two-phase (Li3NbO4 and LiNbO3) powder at elevated temperature [vapor transport equilibration (VTE)]. The influence of VTE treatment on Ti diffusivity is considered in the model. To solve the model, four key input parameters including Li-concentration-dependent Li and Ti diffusivities and two switching times t1 and t2 were determined. Prior to solve the Ti-diffusion model, a one-dimensional VTE model is solved at first to obtain the dynamic Li2O concentration depth profile. Both the Li-diffusion and Ti-diffusion models were solved by using finite difference method. Based on secondary-ion-mass spectrometry analysis, the validity of the VTE and Ti-diffusion models as well as the numerical method employed are confirmed. After that, diffusion at 1100 °C of an 8-μm-wide, 100-nm-thick Ti strip defined on the surface of a Z-cut or an X-cut substrate was simulated for the VTE duration up to 130 h. Based on the numerical results, the Ti-(Li-)diffusion characteristics are discussed in the aspects of (1) the relation of depth and width profile function of Ti concentration to the VTE duration, (2) the substrate cut effect on both the Ti and Li diffusions, (3) the relation of the 1/e Ti-concentration depth and half-width to the VTE duration, and (4) the VTE duration dependence of the mean [Li]/[Nb] ratio within the Ti-diffused layer. [ABSTRACT FROM AUTHOR]

Polarized visible, near-infrared, and 980-nm up-conversion emission characteristics in near-stoichiometric Z-cut Er(0.6 mol %)/Yb(0.3 mol %)-codoped LiNbO3 crystals, prepared by vapor-transport-equilibration (VTE) technique, were investigated and discussed in comparison with corresponding as-grown crystal, thermally calcined ErNbO4 powder, as well as Z-cut only Er(2.0 mol %)-doped LiNbO3 crystal that was subjected to the same VTE procedure as one of the Er/Yb-codoped crystals. The VTE-induced crystalline phase transformation is discussed in combination with optical absorption results reported previously. The percentage of Er3+ ions present in the crystals as the ErNbO4 phase is evaluated based upon the optical absorption and the emission data at 1.5 μm. An empirical expression for evaluating the Li composition in a near-stoichiometric Er(/Yb)-doped LiNbO3 crystal from the narrowing percentage of the σ- or α-polarized 1530 nm emission peak is established based upon the emission spectra of singly Er-doped VTE LiNbO3 crystals. From the measured absorption band areas and the Judd-Ofelt theory, the influence of the VTE treatment on the Er3+ spectroscopic property was studied. The experimentally observed VTE effect on the emission intensity is conducted with the theoretical results of the transition probability. Both the theoretical and experimental results reveal that the VTE treatment results in the lengthening of the 1.5 μm lifetime as much as 15%. A mechanism that the VTE treatment induces the crystalline phase transformation and the reduction of both OH- and intrinsic defect contents is proposed to explain the VTE effect on the lifetime. [ABSTRACT FROM AUTHOR]

Buried channel waveguide amplifiers in erbium/ybtterbium codoped phosphate glass were fabricated using proton-beam writing. Single-mode waveguides were fabricated with fluences ranging from 0.4 to 2.0×1015 particles/cm2. The end-of-range and surface profiles of the waveguides were investigated using atomic force microscopy. The waveguiding effect was investigated using the end-fire coupling technique. From the near-field mode profiles, the refractive index profiles of these waveguides were recovered using the propagation mode near-field method. From these results, it can be deduced that for phosphate glass waveguides fabricated with fluences <1.0×1015 particles/cm2, the ionization from the electronic stopping, rather than the nuclear damage processes, is the major contributing factor leading to an increase in the refractive index near the end of range. [ABSTRACT FROM AUTHOR]

Z-cut MgO heavily codoped (6 mol %) Er(0.4 mol %) :LiNbO3 crystals were thermally treated at 1110 and 1120 °C over 100, 120, and 220 h using vapor transport equilibration (VTE) technique. Visible and infrared-absorption and x-ray powder diffraction have been used to characterize their spectral, spectroscopic, and crystalline phase characteristics in comparison with the as-grown crystal. The experimental results show that VTE treatment results in the reduction of background absorption and 4-5-nm blueshift of the optical-absorption edge, qualitatively showing that these crystals have been brought closer to stoichiometric composition. The VTE procedure also results in remarkable Er3+ absorption changes. These spectroscopic changes imply that the VTE treatment may result in the formation of ErNbO4 precipitates in all VTE crystals. In addition, the VTE treatment also results in substantial spectral changes with respect to OH- absorption. These OH- spectral changes are explained from the viewpoint of VTE-induced site-occupancy alterations of intrinsic and extrinsic defects. Based upon the measured absorption spectra, the influences of VTE treatment on the Er3+ spectroscopic parameters were studied by using the Judd-Ofelt (JO) theory. The theoretical results show that VTE treatment has a little influence on the branch ratio, and a substantial influence on JO parameters and electron transition probability because of the phase transformation with respect to Er3+. The VTE treatment results in the increase of the JO parameters by more than 50% and theoretical radiative lifetime by 50%-120%. [ABSTRACT FROM AUTHOR]

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]

Two optimized methods for the accurate, measurement of 1.5micrometr lifetime of Er(super 3+) in LiNbO3 crystals and wave-guides are put forth. The first method is suitable for bulk material while the second method is suitable for a wave-guide structure.

Rare earth doped opaque aluminum tellurite ceramics exhibiting multicolor upconversion and color tunability have been synthesized and characterized. The multicolor fluorescence comprises of green, red, and blue upconversion emissions from Ho3+ and Tm3+ ions. By varying the intensity ratios between the upconversion emission bands, the fluorescence color can be tuned from multicolor to white color by changing the infrared wavelength pump power. The fluorescence color tunability in Ho3+/Tm3+/Yb3+ triply doped aluminum tellurite ceramics will lead to new applications in the field of multicolor fluorescence technology. [ABSTRACT FROM AUTHOR]

Rare-earth ion doped bismuthate (LZBB) glasses without traditional glass formers, lead and cadmium, have been attempted to prepare. In Er3+ doped LKBB glass system, Judd–Ofelt parameters Ω2, Ω4, and Ω6 have been derived to be 3.48×10-20, 9.47×10-21, and 1.01×10-20 cm2, respectively, which shows a medium symmetry of the ligand field in the site occupied by Er3+ and a less covalent environment of Er3+. Effective 1.53 μm fluorescence was recorded and the peak emission cross section is proved to be more than 9.0×10-21 cm2, which is much higher than those in phosphate, silicate, germanate, and tellurite glasses and beneficial to achieving powerful stimulated emission of Er3+ in LZBB glass system. Pr3+, Tm3+, and Ho3+ doped LZBB glasses with the maximum phonon energy of only ∼600 cm-1 are potential candidates for developing O-, S-, and U-band amplifiers and medical lasers. [ABSTRACT FROM AUTHOR]

Composition effect on electro-optic (EO) properties of a LiNbO3 (LN) single-crystal has been investigated in a Li2O-content range of 47.0-49.95 mol%. Some non-congruent LN crystals with different Li2O-contents were prepared by performing Li-deficient or Li-rich vapour transport equilibration treatments on as-grown congruent LN crystals. Unclamped EO coefficients γ13 and γ33 of these samples were measured by a Mach-Zehnder interferometric method. The measurements show that in the Li-deficient regime both γ13 and γ33 increase by ~8% as Li2O-content decreases from the congruent 48.6 mol% to the 47.0 mol% in the Li-deficient regime. The feature is desired for the EO application of the Li-deficient crystal. In the near-stoichiometric regime, both γ13 and γ33 reveal a non-monotonic dependence. As the Li2O-content increases from the 48.6 mol%, the EO coefficient decreases. Around Li2O-content 49.5 mol%, a minimum is reached. After that, the EO coefficient recovers slowly. At the stoichiometric composition, it recovers to a value close to that at the congruent point. Comparison shows that different crystal growth methods give rise to different defect structure features and hence different composition effects. [ABSTRACT FROM AUTHOR]

Discusses a study which characterized fabricated waveguides in iron doped KTiOPO[sub4] substrates. Background on the sample materials; Methodology; Findings.

Presents a study which demonstrated the fabrication and characterization of proton-exchanged optical waveguides in z-cut magnesium-oxide-doped lithium niobate crystal (MgO:LiNbO[sub3]) using adipic acid as a proton source. Background on the crystal; Description of the experimental setup; Findings.

Provides information on a study that reported on the crystal growth and the photorefractive properties of a manganese-doped (KNa)[sub0.1](Sr[sub0.6]Ba[sub0.4])[sub0.9]Nb[sub2]0[sub6]. Formula of tungsten-bronze potassium sodium strontium barium niobate crystals; Method used for growing the crystals; Equation of the two-wave coupling gain; Conclusion.

Multichannel transition emissions in Pr3+-doped fluorotellurite (4BaF2–4AlF3–16BaO–6La2O3–70TeO2, BABLT) glasses have been quantitatively characterized. Broadband ∼1.48 µm near-infrared (NIR) emission due to 1D2 → 1G4 transition covering a 1.28–1.68 µm wavelength region possesses a full-width at half-maximum of 120 nm, along with the spontaneous emission probability (Aij) and maximum stimulated emission cross-section (σem) are calculated to be 693 s−1 and 8.97 × 10−21 cm2, respectively. Intense visible fluorescence originating from 3P0 and 1D2 levels has been observed and the radiant flux for the visible fluorescence of Pr3+ is solved to be 299 µW under commercial blue LED excitation. Quantitative characterization reveals that Pr3+-doped BABLT glasses exhibit a quantum yield (QY) as high as 14.9%, which is 3.1% higher than that in Pr3+-doped heavy metal germanium tellurite glasses. High QY and broadband ∼1.48 µm emission illustrate great advantages of Pr3+-doped BABLT glasses as fibre luminescence sources in photodynamic therapy treatment and gain media for tunable lasers and NIR optical amplifiers. [ABSTRACT FROM AUTHOR]

Oleic acid-coated erbium–ytterbium co-doped NaYF4nanocrystals, NaY78%F4 : Yb20%Er2%, have been synthesized. The cubic nanocrystals were of an average size of 10 nm. The nanocrystals showed excellent redispersibility in common organic solvents and the KMBR® polymer matrix. An optical waveguide amplifier was fabricated by doping 0.1 wt% of the nanocrytals into the KMPR® polymeric host. At a small input signal power of 150 nW and a pump power of 150 mW, an optical gain of 4.81 dB cm−1at 1535 nm was achieved. [ABSTRACT FROM AUTHOR]

The variational method is proposed to analyze the influence of the fabrication parameters on the performance of buried K+–Na+ ion-exchanged Er3+–Yb3+ ions co-doped glass waveguide. The unknown parameters of the Hermite–Gaussian functions as the trial field distribution are determined based on the scalar variational principle. It is demonstrated that the results calculated in this paper agree with those measured in the experiment. The mode dimensions, the effective refractive index, and the overlap factor as the functions of the fabrication parameters are investigated. These results of the variational analysis are useful for the design and optimization of Er3+–Yb3+ ions co-doped waveguides. [ABSTRACT FROM AUTHOR]

Er3+(/Yb3+)-doped Li3NbO4 powder were prepared by thermally sintering mixtures of Er2O3 (0.5, 1.0 mol%), Yb2O3 (0, 0.5, 1.0 mol%), Li2CO3 (48–49 mol%) and Nb2O5 (50 mol%) at 1125, 1150 and 1450 °C over the durations of 8–22 h. The crystalline phases contained in these samples were determined by using X-ray diffraction and discussed in comparison with a vapor-transport-equilibration-treated (VTE-treated) Er(2.0 mol%):LiNbO3 single crystal and ErNbO4 powder previously reported. The results show that the X-ray patterns of the rare-earth-doped samples reveal little difference each other, but large differences with those of the VTE crystal and ErNbO4 powder. The doped rare-earth ions Er3+ (and Yb3+) present in the powder as the ErNbO4 (and YbNbO4) phase(s). The possibility that the highly Er-doped LiNbO3 crystal contains Li3NbO4 precipitates is small. Optical absorption and emission studies show that the only Er-doped Li3NbO4 powder shows similar absorption and emission characteristics with the pure ErNbO4. The codopant Yb3+ ion enhances the 980-nm-upconversion emissions of Er3+ ions, results in remarkable spectral alterations at 0.98 μm region, and causes the alterations of relative absorbance and relative emission intensity of individual peaks or bands at 1.5 μm region. On the other hand, the Yb-codoping hardly affects the Er3+ energy structure and the lifetime of Er3+ ion at 1.5 μm. The measured lifetimes at 1.5 μm of Er3+ ions in the singly Er3+- and doubly Er3+/Yb3+-doped mixtures have a nearly same value of ∼ 1.5 ms. For the pure ErNbO4 powder, the lifetime is prolonged to ∼2 ms perhaps due to radiation trapping effect. [ABSTRACT FROM AUTHOR]

Based on rate equations of semiconductor laser, a symbolically-defined model for optical transmission system performance evaluation and network characterization in both time- and frequency-domains is presented. The steady-state and small-signal characteristics, such as current–photon density curve, current–voltage curve, and input impedance, can be predicted from this model. Two important dynamic characteristics, second-order harmonic distortion and two-tone third-order intermodulation products, are evaluated under different driving conditions. Experiments show that the simulated results agree well with the published data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 539–542, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22180 [ABSTRACT FROM AUTHOR]

Secondary-ion-mass spectrometry was applied to study Ti-concentration profiles in the depth direction and on the surface of near-stoichiometric (NS) Ti:LiNbO3 strip waveguides fabricated using vapour transport equilibration (VTE) and co-diffusion of Ti-metal strips. Results show that the profile of Ti concentration along the width direction on the waveguide surface can be well fitted by a sum of two error functions, while, in the depth direction, the Ti concentration follows either a complementary error function or a generalized Gaussian function. Surface Ti concentration, 1/e width and depth, mean diffusivities along the width and depth directions of the guide are, respectively, 1.04 × 1021 cm–3, 8.5 µm, 6.3 µm, 0.18 and 0.1 µm2/h. Two-dimensional refractive index profile in the NS waveguides is indirectly constructed by assuming linearity between Ti-induced index change and Ti concentration. The surface refractive index increments at 1545 nm, Δno and Δne, are evaluated to be 3.132 × 10–3 and 1.186 × 10–2, respectively. All of the above-mentioned diffusion and optical parameters are compared with the corresponding data of the common congruent Ti:LiNbO3 waveguide or NS waveguide fabricated starting from a NS substrate. The rationality of the assumed linear relationship between the index change and the Ti concentration is discussed. The results show that the assumed linearity remains controversial, and all expressions and data with regard to the refractive index are the approximate results and need to be verified by direct measurement on refractive index. [ABSTRACT FROM AUTHOR]

The newly synthesized polymer, bisphenol A-aldehyde resin (BPA-resin) has many unique thermo-optical characteristics. The polymer has high transparency, relatively high refractive index, low birefringence, and large thermo-optics coefficient at the optical telecommunication wavelengths. Also, the single-mode channel waveguides have been fabricated using BPA-resin polymer. The experimental results show, that the polymer waveguide has a low propagation loss of 0.43 and 0.51 dB/cm at a wavelength of 1.31 and 1.55 µm, respectively, for both TE and TM polarizations. The low polarization dependence loss (PDL) of the waveguide was less than 0.1 dB/cm at above wavelengths, which can be applied in thermal-optical tuned devices. [ABSTRACT FROM AUTHOR]

Light-induced absorption (LIA) in thermally reduced congruent and near-stoichiometric Er:LiNbO3 crystals, which have different cuts of crystal (X- and Y-cut) and different doping levels of Er3+ (0.2, 0.4, 0.6 and 1.0 mol %), has been studied within continuous-wave light intensity by using polarized 632.8 nm beam as probe light and polarized 488 nm beam as pump light. Effects of thermal reduction condition, pump intensity, Li/Nb ratio and Er-doping level on the LIA are summarized and discussed. Studies on spectral characteristics of both linear absorption and light-induced absorption show that photo-ionization of bipolarons into small polarons plays a predominant role in the LIA process. The role of the Er3+ ion in the LIA is investigated by studying the doping level and the thermal reduction effects on the absorption and emission properties of Er3+. The results show the possibility that the Er3+ ion directly participates in the light-induced charge transport is small. It affects the LIA only via the bypassing part of pump intensity to excite near-infrared emissions of Er3+. The thermaleffect on the LIA is demonstrated. A two-center model with inclusion of the thermal contribution can qualitatively explain two major LIA characteristics that include the appearance of a slow stage in the LIA procedure and the unsaturation behavior of the LIA coefficient in high pump intensity regime. In addition, the pump depletion effect on the LIA characteristics is discussed. The possibility of pump beam fanning arising from light-induced scattering is ruled out experimentally. [ABSTRACT FROM AUTHOR]

A polarization-isotropic two-colour light-induced diffraction (LID) phenomenon from thermally reduced congruent and near-stoichiometric Er:LiNbO3 crystals was observed when these crystals were exposed to superposed 632.8&ThickSpace;nm probe and 488&ThickSpace;nm pump beams. The LID is characterized by expansion of the probe beam spot and the appearance of alternate bright and dark diffraction rings at higher pump light intensities. This phenomenon is absent not only in all other Er-doped crystals which either were as grown or had experienced other post-growth treatments such as vapour transport equilibration (VTE), oxidation and strong annealing but also in a pure VTE-treated crystal even though the crystal was subjected to the same reduction procedure. The LID characteristics of five reduced crystals, which have different Li-to-Nb ratios and different doping levels of Er 3+ , were studied in detail by changing the light intensity, polarization state and wave vector direction of both the pump and the probe beams. The origin of the LID was investigated from the viewpoints of the red fluorescence of Er 3+ excited by a 488&ThickSpace;nm pump beam, light-induced scattering and light-induced thermal nonlinearity. The results have shown that the thermal nonlinearity mechanism is preferred as it can reasonably explain almost all the observed experimental phenomena. [ABSTRACT FROM AUTHOR]

Raman spectra of as-grown and reduced (or annealed) Er:LiNbO3 crystals, which have different cut orientations, varied Li/Nb ratio, and different Er-doping levels of 0.2, 0.4, 0.6, 1.0, and 2.0 mol%, were recorded at room temperature over a wavenumber range of 50–1000 cm-1 by use of backward scattering geometries. The spectra are assigned on the basis of their Raman scattering features and previous relevant work. A weak but well-resolved peak around 633 cm-1 appears in the E(TO) spectra that were recorded under the configuration of X(ZY)X̄(for an X-cut sample) or Y(ZX)Ȳ(for a Y-cut sample) for all crystals studied. The appearance of this peak in the E(TO) spectrum provides further evidence for a previous attribution of this peak to E(TO9) mode. Some additional peaks distributed in the low wavenumber region ranging from 101–137 cm-1 are attributed to Er3+ fluorescence with a wavelength range of 490.41–491.3 nm. The reduction effects include a significant drop of the Raman scattering intensity and a slight narrowing instead of a broadening in the linewidth. The reduction procedure hardly affects the spectral shape and the wavenumber of most of the phonons. The anneal effect is similar to the reduction effect and both effects are not as obvious as the vapor transport equilibration (VTE) effect. In addition, the present Raman scattering result provides evidence for our earlier reported individual result on light-induced diffraction from strongly reduced Er:LiNbO3 crystals. [ABSTRACT FROM AUTHOR]

A new-type flat-field arrayed waveguide grating (AWG), with the focal signals of all wavelengths of operation focusing along a straight line, has been designed. The work bases on the aberration theory of AWG, in which the restraints imposed on the conventional Rowland-type AWG have been released. In the design of flat-field AWG, three stigmatic points restrain three dominant geometry parameters: geometry of star couplers, ports distribution of phased-array, and length increment between adjacent paths. An eight-channel 200-GHz spacing flat-field AWG has been designed and simulated. As stigmatic points introduced, the aberration of this device is much lower than that of the Rowland-type AWG. [ABSTRACT FROM AUTHOR]

Er 3+ doped Na2O–Nb2O5–TeO2 (NNT) glasses suitable for making optical waveguide devices has been fabricated and characterized. Intense 1.53 μm infrared fluorescence and green upconversion luminescence were observed under 975 nm diode laser and 798 nm laser excitation. The optical absorption, the Judd–Ofelt parameters and the spontaneous transition probabilities have been measured and calculated. The quantum efficiency of 1.53 μm emission band is proved to be ~100%. The maximum emission cross-section is 1.02×10-20 cm2 at 1.533 μm, and it is more than 30% higher than the values in silicate and phosphate glasses. Under 798 nm excitation, strong green and weak red upconversion luminescence was observed at room temperature. The 546 nm green band shows a broad full-width at half-maximum of 16 nm. Intense and broad green upconversion fluorescence in Er 3+ doped NNT glass can be used in colour display, undersea communication and infrared sensor. High concentration of Na2O is a benefit to developing waveguide device from the glass. [ABSTRACT FROM AUTHOR]