A study of environmental effects on the attenuation of chalcogenide optical fibre

The attenuation of a number of chalcogenide glass optical fibres has been studied with regard to their exposure the environment. We demonstrate that gallium lanthanum sulfide (Ga:La:S) based glasses appear to be as resilient if not more so than arsenic sulfide (As₂S₃) glass to the attack of moisture when stored uncoated in ambient conditions for various periods exceeding 1 year. The increase in the characteristic OH⁻ attenuation peak was ∼3–4 dB/m for all fibres following storage. Given the significant improvements achieved in As₂S₃ glass technology over recent years we believe that Ga:La:S based fibres can also be improved to at least match these levels with the advantage of being non-toxic and having a significantly higher melting temperature. Studies of the time-dependant attenuation of the optical fibres during immersion in water have also been carried out. These results show that the deleterious effect of moisture on these glasses occurs over a short time, ∼24 h, thus having implications on the treatment and storage of fibre preforms prior to optical fibre drawing.     

Effect of the substitution of S for Se on the structure and non-linear optical properties of the glasses in the system Ge0.18Ga0.05Sb0.07S0.70−xSex

Glasses in the system Ge–Ga–Sb–S/Se have been elaborated with different S/Se ratios in order to increase the non-linear optical properties of these glasses. We report results of a systematic study examining the relationship of the physical properties to the structure of the glasses in the system Ge_0.18Ga_0.05Sb_0.07S_0.70−xSe_x with x = 0, 0.02, 0.05, 0.10, 0.20, 0.30 and 0.40 where the replacement of S by Se has been made. The non-linear refractive index has been measured using the Z-scan technique, with picosecond pulses emitted by a 10 Hz Q-switched mode-locked Nd-Yag laser at 1064 nm under conditions suitable to characterize ultrafast non-linearities. The decrease of the glass transition temperature, the increase of the non-linear refractive index and of the density with the progressive replacement of S by Se have been correlated along with the red shift of the absorption band gap, to associated structural reorganization. A corresponding progressive decrease of corner-sharing GeS_4/2 and the formation of mostly two edge-sharing Ge₂S₄S_2/2, S₃Ge–S–GeS₃ as well as mixed GeS_4−xSe_x units have been identified by Raman spectroscopy.     

Optical and structural properties of new chalcohalide glasses

New class of chalcohalide glasses has been prepared in the GeS₂–In₂S₃–CsI system with regard to their potential non-linear properties. The study of glass-forming region was undertaken to select glassy compositions, which present high non-linear (NL) optical properties with a low two-photon absorption. Thermal analyses, structural examination by Raman spectroscopy, non-linear optical measurements were investigated as a function of CsI contents. Introduction of CsI has shifted the band-gap edge towards the blue region of the absorption optical spectrum and therefore has limited the two-photon absorption. Their NL refractive index n₂ are 60 times higher than silica glasses without any NL absorption. Moreover, second harmonic signal was observed in thermally poled samples similar to silica glass. However, this second order non-linearity is not temporally stable.     

X-Ray Natural Circular Dichroism in Langasite Crystal at the Ga and La Edges

X-ray natural circular dichroism (XNCD) and its structural nature have been investigated in a langasite (La₃Ga₅SiO₁₄) crystal at an incident radiation energy close to the Ga K-absorption edge and the La L_2,3-absorption edges. An XNCD signal was observed mainly beyond the absorption edge, which confirmed the existence of delocalized mixed p–d electronic states in Ga and d–f and d–p electronic states in La. Calculations with application of the multiple scattering method have made it possible to separate the contributions from three crystallographically nonequivalent Ga sites to the absorption spectrum and the XNCD signal and explain adequately the largest contribution of the Ga atom occupying the 1a site to the XNCD signal.     

La3Ga5SiO14晶体电子结构及光学性质的第一性原理研究

采用基于密度泛函的第一性原理平面波赝势法对La3Ga5SiO14晶体基态的几何参量、能带结构、态密度和光学性质进行了系统的研究.优化了La3Ga5SiO14晶体中原子的内部坐标,利用精确计算的能带结构、态密度和电荷密度等值线分析了晶体的吸收谱、介电函数、折射率,计算结果与实验符合较好,为La3Ga5SiO14晶体材料的分子设计与应用提供了理论依据.     

Structural dependence of ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses

Ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses at the wavelength of 820 nm has been measured using femtosecond time-resolved optical Kerr (OKE) technique. The results show that Ge–Ga–Ag–S glasses have large third-order optical nonlinear susceptibility, χ⁽³⁾ and the response time is also subpicosecond, which are predominantly due to the ultrafast distortion of electron cloud surrounding the balanced positions of Ge, Ga, Ag and S atoms. What’s more, a strong dependence of χ⁽³⁾ on the composition and microstructure of these glasses was found which shows that [GeS₄] and [GaS₄] tetrahedra play an important role on the third-order optical nonlinearity. These Ge–Ga–Ag–S chalcogenide glasses would be expected as promising materials applied on all-optical switching devices.     

Synthesis and optical properties of MPTMS-capped CdS quantum dots embedded in TiO2 thin films for photonic applications

CdS nanoparticles have been prepared via a colloidal route using 3-mercatopropyltrimethoxysilane as a capping agent. The stability of the particles in solution and embedded in TiO₂ matrices has been followed by optical absorption. Both the size and the size distribution of the particles are well controlled, thus allowing a tunable emission. Raman and photoluminescence spectroscopies have been used to characterize colloidal CdS, TiO₂:CdS solutions and thin films deposited on soda-lime slides. The Z-scan technique has been used to measure the non-linear refractive indices of the solutions and the non-linear absorption coefficients of the thin films.     

The color of langatate crystals and its relationship with composition and optical properties

Langatate crystals grown by the Czochralski method in 〈0001〉 and 〈01 1〉 directions both without subsequent annealing (from colorless to orange crystals) and with vacuum (colorless and pale‐green crystals) and air (orange crystal) annealing have been investigated by neutron diffraction, X‐ray diffraction and optical spectroscopy. The main types of point defects were compared with absorption bands: oxygen vacancies ‐ V_O^•• (0.35‐0.36 µm), the vacancies in the lanthanum position ‐ V_La‴ (0.29‐0.30 µm); the absorption band at 0.48‐0.49 µm is typical for the colored samples. The relationship between the X color coordinate (red component) and the oxygen contents has been obtained. The green color of the sample annealed in vacuum is due to the presence of Ta⁺³ ions in the La(Ta³⁺,Ga)O₃ phase that has the structural and geometric agreement with langatate structure. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and characterization of chemically deposited (Cd0.7‐Zn0.3)S:CdCl2,Gd nanocrystalline films

Nanocrystalline films of (Cd_0.7‐Zn_0.3)S:CdCl₂,Gd are prepared by chemical deposition technique on microscopic glass substrates with varied concentrations of capping agents thiophenol and methanol. The deposition is based on the principle of precipitation followed by condensation. Results of XRD, SEM, optical absorption spectra and photoluminescence emission spectra are presented. The crystalline nature of (Cd_0.7‐Zn_0.3)S:CdCl₂,Gd was found by XRD studies in which different diffraction peaks of CdS and ZnS are observed. The SEM micrographs show long tubes and irregular distributions of particles in presence of capping agents. The blue shift observed from optical absorption spectra in the present case indicates a quantization effect. Band gaps are also found to increase due to particle size reduction. The photoluminescence emission spectra show shift of peaks in the lower wavelength side due to reduction in particle size. The particle sizes are determined from optical absorption and XRD studies. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the effects of Ga3+ and La3+ ions in MgCu ferrite: Humidity‐sensitive electrical conduction

Pure and gallium or lanthanum substituted MgCu ferrites, Mg_0.5Cu_0.5Fe_2‐xM_xO₄ (with x = 0 or 0.2 and M = La or Ga) have been prepared by solid state reaction. Sintering experiments were carried out at different temperatures between 900 and 1100°C. The phase composition and lattice parameters were determined by XRD, while the effect of Ga and La substitutions on the granular structure was studied by SEM. Experimental results revealed that the densification behaviour and some physical properties are in close relation with the structural changes of pure ferrite caused by the presence of La and Ga substitutions. The gallium containing compound, Mg_0.5Cu_0.5Fe_1.8Ga_0.2O₄, is monophasic and contains a great number of pores, whereas the lanthanum containing compound, Mg_0.5Cu_0.5Fe_1.8La_0.2O₄, is biphasic and exhibits a high density. The humidity characteristics show that the gallium ion enhances the humidity sensitivity of the MgCu ferrite sintered at 1000°C. This interesting effect is promising for the future of the Ga‐substituted MgCu ferrite to be used as sensitive material for fabrication of ceramic humidity sensors. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of Pr3+ in selenide glasses modified with CsI

Effects of CsI content on the optical properties of Ge₃₀Ga₅Sb₅Se₆₀ glasses were evaluated. Linear and non-linear absorption properties of the glasses without Pr³⁺ were examined in addition to 1.6 μm emission properties of the Pr-doped glasses. Blueshift of the UV-side absorption edge was accompanied with increasing CsI concentration, while non-linear absorption coefficients measured at 1.06 μm by the Z-scan method remained unaffected. Measured lifetimes of the 1.6 μm emission from modified glasses were comparable to those of the unmodified glass. These experimental observations are discussed in connection with a pronounced weak absorption tail appeared in selenide glasses with the addition of CsI.     

Aggregation effects in non-linear absorption of CuPc-SiO2 sono-xerogels

It is known that aggregation effects in metallophthalocyanine/SiO₂ composites play an important role in the optical properties of these materials. With the aim to avoid phthalocyanine dimer and oligomer formation induced in aqueous solution, alternative processing methods for trapping the organic in the matrices have been tested. The combination of ultrasonic energy used to promote the reactions and the methanol used as solvent, makes it possible to obtain monolithic xerogels under extremely acid conditions, preserving their homogeneity and transparency. Textural parameters and pore size distribution of the composites and the optical absorption features have been evaluated. Finally, the effects of molecular self-association degree on the non-linear absorption of the samples have been analyzed. All the samples studied exhibit reverse saturable absorption behavior but the figure of merit is strongly determined by the aggregation state of the active phase in the composite.     

S-La共掺杂ZnO性能的第一性原理研究

采用基于广义梯度近似的第一性原理方法,研究了纯ZnO、S单掺、La单掺和S-La共掺ZnO的能带结构、态密度和光学性质.S单掺ZnO后,价带和导带同时向低能量转移,导致带隙减小.La单掺ZnO后在导带底产生杂质能级使得带隙减小.S-La共掺ZnO导致La的局部化减弱,表明La形成的施主能级由于S的3 p态的影响变得更浅...     

Local Hydrogen Vibrational Modes in GaAs doped with Chalcogenides

Infrared absorption on GaAs doped with Chalcogenides under hydrogen plasma treatment has shown the presence of two new localised modes, namely stretching and wagging modes. We present a simple nine atom molecular model to compute these defect modes by assuming the hydrogen to be bound in the antibonding position of the nearest Ga atom, resulting in a defect complex of C_3V symmetry. Group theoretical methods are employed to obtain the frequencies of the normal modes enabling precise identification of localised modes.     

Effect of ZnO and Bi2O3 addition on linear and non-linear optical properties of tellurite glasses

Glasses in the system TeO₂-Bi₂O₃-ZnO were studied with respect to their linear refractive indices and optical absorption in the UV-vis range. The third order non-linear refractive indices were measured using degenerated four wave mixing (DFWM). The optical Kerr susceptibilities calculated hereof were in the range from 5.49 to 6.58 × 10⁻¹³ esu and hence 34-41 times larger than that of fused SiO₂. They are roughly proportional to values theoretically calculated by the theory of Lines.     

Neutron diffraction and X-ray diffraction investigations of langasite crystals

Crystals of langasite La₃Ga₄(GaSi)O₁₄ grown by the Czochralski method are studied using neutron diffraction for the first time. It is established that the compositions of the upper and lower parts of an orange crystal grown from the La₃Ga_5.14Si_0.86O₁₄ seed in an (Ar + O₂) atmosphere (the 〈 0001 〉 growth direction) can be written as(La_2.85(2)□_0.15)(Ga_0.95(2)□_0.05) Ga₃(Ga_1.15 Si_0.85(5))(O_13.72□_0.28(7)) and(La_2.89(1)□_0.11)·(Ga_0.98(1)□_0.02) Ga₃(Ga_1.06Si_0.94(4))(O_13.81□_0.19(9)), respectively. The La content in the upper and lower parts of this crystal is lower and higher than the Ga content, respectively, and the Ga content exceeds the Si content in the (GaSi) position. By contrast, in a colorless crystal of the composition(La _2.97(4)□_0.03) Ga(1)(Ga_2.94(9)□_0.06)(Ga_0.7(1) Si_1.3)(O_13.9□_0.1(1)), which is grown from the La₃ Ga₅SiO₁₄ seed in an argon atmosphere (the 〈 01\(\bar 1\)1 ?growth direction), the Ga content in the (GaSi) position is lower than the Si content. A relation between the Ga: Si ratio and the (Ga,Si)-3O interatomic distances is found.     

Local structure and its effect on the oscillator strengths and emission properties of Ho in chalcohalide glasses

The formation of structural units in Ge-Ga-S glass with CsBr addition and its effect on the optical band gap and several spectroscopic properties of Ho³⁺ were investigated. The optical band gap of the host glasses and the oscillator strengths of Ho³⁺ absorption decreased sharply when the ratio of CsBr/Ga became close to unity. These property changes were associated with the formation of structural units of [GaS_3/2Br]⁻ and they have a crucial effect on the changes of the local structure around Ho³⁺ ions. The local structure was not sensitive to the As or Br addition but was critically dependent on the concentration of CsBr.     

X-ray diffraction studies of the structure of LaA1Ga metallic glasses

The LaLa and LaA1 partial atomic distribution functions have been determined for glassy La_1?xA1_x from X-ray diffraction studies of isomorphous alloys of La_1?xA1_x, La_1?x(A1Ga), and La_{1 ?x}Ga_x for x = 0.20, 0.24 and 0.28. The atomic short range order of these La based metallic glasses is quite different from that of typical amorphous transition metal-metalloid alloys and from dense random packing models. A relatively short and well defined LaA1 nearest neighbor distance suggests some covalency in the bonds between unlike atoms and possible chemical ordering in the alloys.     

Determination of the non-resonant non-linear refractive index of germano-silicate glass fiber with an arbitrary GeO2 concentration profile

We propose a new method to measure the non-resonant third-order optical non-linearity of germano-silicate glass fiber having arbitrary GeO₂ concentration profile using wavelength dependence of mode field diameter. The measured non-linear refractive indices of Samsung’s single mode fiber and the Sumitomo’s highly non-linear optical fiber were found to be in good agreement with the published results within 3.2% and 3.1% error, respectively. The method is applicable only for the optical fibers whose dispersion is dominated by the material dispersion.     

Optical properties of Ga1–xInxAs LPE-layers and p-n structures

The multiple layer structure nGaAs(n Ga_1–xIn_xAs) p Ga_1–xIn_xAs (0 ≦ × ≦ 0.18) was realized by liquid phase epitaxy from In–Ga–As-melts on (111)-oriented GaAs substrates. The InAs-content of the mixed crystal layers was found to be dominating for crystal perfection and growth rate. The cathodoluminescence spectra of p-and n-type Ga_1–xIn_xAs and spectral distribution of the electroluminescence from pn-junctions were measured at T = 77 K and 300 K. The external quantum efficiency wa found to have a maximum for diodes with x ≈ ≈ 0.006. This is caused by the decrease of the optical absorption with increasing x and increasing dislocation density on the other hand.