Search

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]

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]

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  nm probe and 488  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  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]

Annealing properties of proton-exchanged optical waveguides in z-cut LiNbO3 fabricuted using toluic acid are reported. Variations in the surface refractive index and waveguide depth with annealing time are found to follow a power-taw relationship, and a minimum propagation loss of 0.23 dB/cm is measured at 0.633-µm wavelength. [ABSTRACT FROM AUTHOR]

Annealing of proton-exchanged planar optical waveguides in z-cut LiNbO3 fabricated using stearic acid has been studied systematically. The effects of annealing on waveguide propagation loss, surface index change, and waveguide depth were measured as a function of annealing time, and were found to follow a power-law relationship. [ABSTRACT FROM AUTHOR]