Nonlinear Optical Glasses Research Articles

Highly Efficient and Stable Binary Cross-Linkable/ Self-Assembled Organic Nonlinear Optical Molecular Glasses.

The development of electro-optical materials with high chromophore loading levels that possess ultrahigh electro-optic coefficients and high long term alignment stability is a challenging topic. Anthracene-maleimide Diels-Alder (DA) reaction and π-π interaction of Anthracene-pentafluorobenzene and benzene-pentafluorobenzene are developed for making highly efficient binary cross-linkable/self-assembled dendritic chromophores FZL1-FZL4. A covalently or non-covalently cross-linked network is formed by DA reaction or π-π interaction after electric field poling orientation, which greatly improves the long-term alignment stability of the materials. An electro-optic coefficient up to 266pmV-1 and glass transition temperature as high as 178°C are achieved in cross-linked film FZL1/FZL2, and 272-308pmV-1 is achieved for self-assembled films FZL1/FZL4 and FZL3/FZL4 due to high chromophore density (3.09-4.02×1020 moleculescm-3 ). Long-term alignment stability tests show that after heating at 85°C for over 500h, 99.73% of the initial r33 value is maintained for poled crosslinked electro-optic films 1:1 FZL1/FZL2. The poled self-assembled electro-optic films 1:1 FZL1/FZL4 and 1:1 FZL3/FZL4 can still maintain more than 97.11% and 98.23%, respectively, of the original electro-optic coefficient after being placed at room temperature for 500h. The excellent electro-optic coefficient and stability of the material indicate the practical application prospects of organic electro-optic materials.

Bismuth-Germanate Glasses: Synthesis, Structure, Luminescence, and Crystallization

Bismuth-germanate glasses, which are well known as a promising active medium for broadband near-infrared spectral range fiber lasers and as an initial matrix for nonlinear optical glass ceramics, have been synthesized in a 5–50 mol% Bi2O3 wide concentration range. Their structural and physical characteristics were studied by Raman and FT-IR spectroscopy, differential scanning calorimetry, X-ray diffraction, optical, and luminescence methods. It has been found that the main structural units of glasses are [BiO6] and [GeO4]. The growth in bismuth oxide content resulted in an increase in density and refractive index. The spectral and luminescent properties of glasses strongly depended on the amount of bismuth active centers. The maximum intensity of IR luminescence has been achieved for the 5Bi2O3-95GeO2 sample. The heat treatment of glasses resulted in the formation of several crystalline phases, the structure and amount of which depended on the initial glass composition. The main phases were non-linear Bi2GeO5 and scintillating Bi4Ge3O12. Comparing with the previous papers dealing with bismuth and germanium oxide-based glasses, we enlarge the range of Bi2O3 concentration up to 50 mol% and decrease the synthesis temperature from 1300 to 1100 °C.

An energy-stable finite element method for nonlinear Maxwell's equations

In this paper, we consider the three-dimensional (3D) nonlinear Maxwell's equations in the optical media characterized by linear Lorentz dispersion, nonlinear Kerr effect and delayed Raman scattering. Using Crank-Nicolson time discretization and special treatment of the nonlinearity, we propose a second order accurate (in time) finite element method for the nonlinear problem. Fully discrete energy stability analysis is established to show that the scheme is unconditionally stable. The nonlinear system is solved by Newton-Krylov method. In order to efficiently solve the linearized algebraic system in each Newton sub-iteration, we further develop an effective preconditioner by using suitable approximations to the nonlinearity and the auxiliary space preconditioning technique. Numerical experiments are provided to examine the accuracy, the energy stability, the parallel scalability and the robustness in preconditioning of our proposed scheme. We then apply the scheme to simulate the spatial soliton propagation in 3D nonlinear glass. We also demonstrate the performance of the scheme in handling complex geometry through simulating the wave scattering by a spherical hole in the nonlinear optical glass.

Improving the optical, electrical, and dielectric characteristics of MgO doped borate glass for optoelectronic applications

Established on the appealing properties of borate glass, a new magnesium borate glass of definite composition (56 − x)B2O3–40Na2O–4MoO3–xMgO (x = 0, 2, 4, 8 mol. %) is prepared via the melt quenching technique. The present study clarified the consequence of dopant and co-dopant on the borate glass. Different physical properties are sustained to investigate and explain the optical and electrical properties of the obtained glass as a result of the replacement of B2O3 by MgO. FTIR confirmed the conversion of MgO6 into MgO4. The index of refraction increased is accompanied by a decrease in bandgap energy. At a frequency of 0.1 Hz, the ac-conductivity varies between 4 and 20 pS/cm at 25 °C and between 10 and 30 nS/cm at 150 °C without the systematic effect of MgO concentration, which indicates that heating plays the main role in improving conductivity. The metallization criterion is between 0.41 and 0.425. The computed two-photon absorption values ranged from 5.313 to 8.391 cm/GW; therefore, it is recommended that the prepared glasses are ideal for optical signal-processing equipment and are considered promising as a new member of the nonlinear optical glass.

Supramolecular self-assembled nonlinear optical molecular glasses with enhanced electro-optic activity and alignment stability

We have developed a series of self-assembled electro-optic dendrimers. Four dendrimers H1, H2, H3 and HLD 1 were synthesized by introducing aromatic dendron (HD), trifluorobenzyl dendron (TFD), pentafluorophenyl dendron (PFD) and anthracene ring (AH) into the donor and bridge parts of chromophores. In addition, three-arm trifluorobenzyl dendron containing multichromophore H4 was also synthesis and evaluated. These molecules were supramolecular self-assembled through the π-π interaction of HD-PFD/HD-AH/TFD-TFD to minimize the dipole-dipole interaction of chromophores and maximize the accentric order of chromophores under high load densities. High r33 (328, 317 and 279 p.m./V) have been achieved for neat films containing chromophores 1:1 H1: H3, 1:2 H3: HLD 1 and H4, respectively. Moreover, the long-term orientation stability of chromophores were also improved. After 1000 h at room temperature, the initial electro-optic coefficient of the electrode self-assembled film still remains above 95%.

Structure, stability and optical parameters of cobalt zinc borate glasses

In this study, the impact of cobalt oxide (CoO) on the structure, stability, linear and nonlinear optical parameters of B2O3–Na2O–ZnO glasses was scrutinized. A series of glass system (ZnCoNaB-glasses) was successfully prepared through the melt quenching approach. Optical absorbance, reflectance, transmittance and FTIR spectroscopy were performed for all ZnCoNaB-glasses. The FTIR results showed that the BO4 units are enhanced while nonbridging oxygens are decreased with further CoO addition. Furthermore, ZnO exists as four-coordinated [ZnO4] units and these units decreased with further doping of CoO. These structural variations produce a decreasing impact in Urbach energy and nonlinear refractive index, meanwhile enhance the glass stability. Further, the metallization criterion (M) values indicate that our glass samples can be used for a new generation of nonlinear optical glasses. The preceding results can predict that the investigated ZnCoNaB-glasses will be utilized in versatile applications; especially optical switching and computing.

Optical nonlinearity and supercontinuum generation of tellurite glass at 1.064 μm

Nonlinear optical glasses have aroused great interest due to its compatibility with existing optical fiber systems and excellent infrared transmission. Supercontinuum (SC) is an inherent feature of nonlinear optics, and accurate knowledge of the nonlinear characteristics of glass is important for understanding and optimizing their performance. Two kinds of tellurite glasses with refractive indices of 2.0394 and 2.0211 were synthesized by melt quenching method. The nonlinear absorption and third-order nonlinearity of tellurite glasses were investigated using Z-scan technique with 1.064 μm picosecond pulses in detail. The values of the respective nonlinear parameters were determined by fitting the experiment data. The nonlinear absorption coefficient, the nonlinear refractive index, and the figure of merit (FOM) are (4.2 ± 0.4) × 10−13 m/W, (5.2 ± 0.6) × 10−19 m2/W, and 11.5, respectively, for the high-refractive-index tellurite glass. A SC spectrum spanning from 0.34 up to 2.6 μm was obtained by pumping a 30 mm high-refractive-index tellurite glass rod with 170 kW, 1.064 μm picosecond pulse laser. The tellurite glasses show the great potential as the core and cladding materials of a fiber for generating a broadband mid-IR SC.

Enhancement the structural, optical and nonlinear optical properties of cadmium phosphate glasses by nickel ions

Cadmium phosphate glasses containing nickel oxide have successfully prepared through conventional melt quenching technique. The impact of nickel ions on the cadmium phosphate network has investigated by replacing the nickel oxide at the expense of the cadmium phosphate glass network. Structural investigation showed that CdO bands overlapped with P2O5 bands to form stable glasses while the NiO acts as a modifier. The density for the base glass is 3.743 g/cm3 increases to 4.094 g/cm3 for the glass containing the highest nickel oxide content. The optical absorption spectra illustrate that the nickel ions existed as divalent state. Optical band gap values decrease as the nickel oxide increases revealing that the nonbridging oxygen linkage formed as the nickel ions intercalated the cadmium phosphate network. The nonlinear refractive index investigated in terms of the linear refractive index and the nonlinear susceptibility. These glasses are exhibited to be lying in semiconductor and nonlinear optical glass category.

Broadband optical limiting and nonlinear optical graphene oxide co-polymerization Ormosil glasses

A class of graphene oxide (GO) Ormosil glasses with excellent nonlinear optical properties were made with sol-gel method. The as-prepared GO Ormosil glasses were highly transparent in visible and near-infrared region, due to the uniform dispersion of modified GO in the matrix. These Ormosil glasses have a broadband optical limiting effect from 532 to 1570 nm, with lower optical limiting onset energy density (FON). The nonlinear absorption coefficients of the Ormosil glass could reach 210.62, 647.96, and 43.10 cm GW−1 at 532, 1064, and 1570 nm. The optical limiting properties of the Ormosil glasses come from nonlinear absorption proved by Z-scan measurements. Therefore, the Ormosil glasses have potential applications in nonlinear optical areas.

Influence of Al2O3 incorporation on the third-order nonlinear optical properties of Ag2O–TeO2 glasses

TeO2-based glasses have been attractive because of their high refractive index and third-order nonlinear optical properties. In general, long melting time is required to obtain the homogeneous glass, but it also leads to enhanced interaction between the crucible and the glass melt. In this study, 20Ag2O–80TeO2 nonlinear optical glasses were fabricated by a melt-quenching method using an alumina or platinum crucible for various melting times. And their thermal characteristics, final glass-compositions, glass structures and linear/nonlinear optical properties were evaluated in order to investigate the influences of the incorporation of Al2O3 in 20Ag2O–80TeO2 glass on third-order nonlinear optical susceptibilities.

Nanoscale Phase Analysis of Molecular Cooperativity and Thermal Transitions in Dendritic Nonlinear Optical Glasses

A broad nanoscopic study of a wide-range of dendritic organic nonlinear optical (NLO) self-assembly molecular glasses reveals an intermediate thermal phase regime responsible for both enhanced electric field poling properties and strong phase stabilization after poling. In this paper, the focus is on dendritic NLO molecular glasses involving quadrupolar, liquid crystal, and hydrogen bonding self-assembly mechanisms that, along with chromophore dipole-dipole interactions, dictate phase stability. Specifically, dendritic face-to-face interactions involving arene-perfluoroarene are contrasted to coumarin-containing liquid crystal mesogen and cinnamic ester hydrogen interactions. Both the strength of dendritic interactions and the impact of dipole fields on the relaxation behavior have been analyzed by nanoscale energetic probing and local thermal transition analysis. The presence of dendritic groups was found to fundamentally alter transition temperatures and the molecular relaxation behavior. Thermal transition analysis revealed that molecules with dendritic groups possess an incipient transition (T(1)) preceding the glass transition temperature (T(2)) that provides increased stability and a well-defined electric field poling regime (T(1) < T < T(2)), in contrast to molecular groups lacking dendrons that exhibit only single transitions. On the basis of enthalpic and entropic energetic analyses, thermally active modes below T(1) were found to be intimately connected to the dendron structure. Their corresponding activation energies, which are related to thermal stability, increased moving from cinnamic ester groups to coumarin moieties to arene-perfluoroarene interacting groups. While dendritic NLO materials were found to possess only enthalpic stabilization energies at temperatures relevant for device operation (T < T(1)), the apparent molecular binding energies above T(1) contain a substantial amount (up to ~80%) of cooperative entropic energy. The multiple interactions (from dipole-dipole interactions to local noncovalent dendritic interactions) are discussed and summarized in a model that describes the thermal transitions and phases.

The superluminal propagation in an organic nonlinear optical glass at room temperature

We investigated the light propagation in an organic glass with phthalocyanine gallium (GaPc) dispersed in polymethyl methacrylate (PMMA) fabricated by injection molding. The GaPc/PMMA organic glass is a reverse saturation absorption medium. We observed the superluminal propagation in this organic glass by using the technique of coherent population oscillations at room temperature. The largest time advancement is 2.21 ms and the corresponding group velocity is −0.90 m/s at the wavelength of 532 nm and with the input power of 89 mW. The density matrix theory with four-level model was used to analyze the experimental data. The theoretical simulations showed that the time advancement not only depends on the modulation frequency but also on the lifetime of the first triplet-state of the GaPc. We compared the time advancements between the GaPc/PMMA organic glass and the C60/toluene solution. Although the value of the former is smaller, it is more suitable for practical applications such as optical information processing than the latter.

Local structure and disorder in crystalline Pb 9Al 8O 21

Crystalline Pb 9Al 8O 21 is a model compound for the structure of non-linear optical glasses containing lone-pair ions, and its structure has been investigated by neutron powder diffraction and total scattering, and 27Al magic angle spinning NMR. Rietveld analysis (space group Pa 3 ¯ (No. 205), a=13.25221(4) Å) shows that some of the Pb and O sites have partial occupancies, due to lead volatilisation during sample preparation, and the non-stoichiometric sample composition is Pb 9− δ Al 8O 21− δ with δ=0.54. The NMR measurements show evidence for a correlation between the chemical shift and the variance of the bond angles at the aluminium sites. The neutron total correlation function shows that the true average Al–O bond length is 0.8% longer than the apparent bond length determined by Rietveld refinement. The thermal variation in bond length is much smaller than the thermal variation in longer interatomic distances determined by Rietveld refinement. The total correlation function is consistent with an interpretation in which AlO 3 groups with an Al–O bond length of 1.651 Å occur as a result of the oxygen vacancies in the structure. The width of the tetrahedral Al–O peak in the correlation function for the crystal is very similar to that for lead aluminate glass, indicating that the extent of static disorder is very similar in the two phases.

Large and Ultrafast Third-Order Nonlinear Optical Propertiesof Ge-S Based Chalcogenide Glasses

We report ultrafast third-order nonlinear optical (NLO) properties ofseveral chalcogenide glasses GeSx (x = 1.8, 2.0, 2.5)measured by femtosecond time-resolved optical Kerr gate technique at820 nm. The third-order nonlinear susceptibility of GeS1.8 glassis determined to be as large as 1.41×10−12 esu, which is themaximum value of the third order nonlinear susceptibility χ(3)for the three compositions investigated. The symmetric Gauss profiles ofoptical Kerr signals reveal the nature of ultrafast nonlinear responseof these samples, which are originated from the ultrafast polarizationof the electron clouds. By detailed microstructural analysis of theseglasses based on the chain-crossing model (CCM) and therandom-covalent-network model (RCNM), it can be concluded thatχ(3) value of GeSx glasses can be enhanced greatly by S–Scovalent bonds or S3Ge–GeS3 ethane-like units.

Ti3+‐Free Multicomponent Titanophosphate Glasses as Ecologically Sustainable Optical Glasses

Ti3+‐free multicomponent titanophosphate glasses were developed as ecologically sustainable optical glasses. Especially, recent advances in the glasses as molding glass, athermal glass, nonlinear optical glass, and self‐cleaning glass were presented. The Ti3+‐free binary TiO2–P2O5 glasses containing TiO2 up to 74 mol% were prepared by melt quenching and long‐term post‐annealing around the glass transition temperature in the air, and possessed high transparency, high index, high dispersion, and low density. Li2O–ZnO–TiO2–P2O5 glasses have the lowest Tg (=560°C) among titanophosphate glasses, with high index (nd=1.8), and high dispersion (νd=22) being retained, while ZnO–TiO2–P2O5 glasses have the highest refractive index (nd=1.9) among glasses with Tg lower than 600°C. Thus, ZnO–TiO2–P2O5 and Li2O–ZnO–TiO2–P2O5 glasses can be expected as high‐index molding glasses. A very small temperature coefficient of refractive index, dn/dT, or very small temperature coefficient of optical path length, dS/dT, was obtained for K2O–TiO2–P2O5 glasses, meaning that they are considered as high‐index athermal glasses and athermal NLO glasses. Ag2O–TiO2–P2O5 glasses showed photocatalytic activity and photo‐induced hydrophilicity comparable with commercially available TiO2‐coated self‐cleaning glasses.

Transparent Non-Linear Optical Composites Based on Glass and Ferroelectric KNbSi2O7

Transparent glass composites containing nonlinear optical (NLO) and luminescent crystals are of significant interest for the optical materials science in spite of a lot of difficulties to synthesize high-quality NLO composites: refractive index and density matching of glass matrix and crystal, controlled chemical interaction between them, absence of crystal aggregation, cords, bubbles, etc. Low density and refractive index, high second harmonic generation (SHG) activity, rather a high melting point allow to refer KNbSi2O7 ferroelectric to a promising candidate for using in the NLO glass composite technology. Manifestation of NLO properties of crystals in glass composites is established to depend drastically on glass matrix composition. During re-melting lead containing glasses react chemically with KNbSi2O7 forming pyrochlore Pb2Nb2O7 which is dissolved gradually up to nano-scaled state exhibiting moderate SHG efficiency by analogy with nanostructured glasses because of space modulation of polarizability originated from nano-sized inhomogeneities enriched with Pb and Nb. Using of TeO2-based glasses permits to match refractive indexes of glass matrix and crystal, reduce glass melting temperature and fabricate transparent composites containing micron and sub-micron crystals with high second harmonic generation activity.

IR optical limiting in europium and thulium doped oxide glasses

IR-induced two-photon absorption in PbO–Ga 2O 3–Bi 2O 3–CdO (PGBC) glasses doped by Eu 3+ and Tm 3+ rare earth (RE 3+) ions is reported. A pulsed CO laser ( λ=5.5 μm, power density up to 3.8 GW/cm 2 per pulse) was applied as a photoinducing IR-light beam. An optical parametrical generator cut from a proustite crystal was used as a source of the fundamental TPA beam within the 3–7.5 μm spectral range. Absolute values of the TPA coefficients were more than 13% higher compared to corresponding value for other similar glasses: As 2Te 3–CaCl 2–PbCl 2 [J. Appl. Phys. 85 (1999) 425; Phys. Rev. B 60 (1999) 942; Opt. Lasers Technol. 33 (3) (2001) 157; Mater. Lett. 54 (2002)] or Sb 2Se 3–BaCl 2–PbCl 2 [J. Mater. Sci. 35 (1) (2000) 215; Mater. Lett. 49 (2001) 272; J. Non-Cryst. Solids 297 (2002) 285]. The PGBC system possesses a shorter time response (about 12 ps), compared with other IR non-linear optical glasses. We have also established that all non-linear optical susceptibilities are crucially dependent on the type of RE 3+ ion. A maximal value of the TPA is achieved for the PGBC glasses doped by Tm 3+. The TPA values increase significantly below 45 K. We have carried out molecular dynamics and quantum chemical simulations in order to evaluate contribution of electron–phonon anharmonic interactions to the TPA.

Nonlinear IR absorption in europium- and thulium-doped oxide glasses

Infrared (IR)-induced two-photon absorption (TPA) in synthesized PbO–Ga2O3–Bi2O3–CdO (PGBC) glasses doped by Eu3+ and Tm3+ rare earth (RE3+) ions was investigated. Temperature-dependent measurements of TPA were carried out in the mid-IR spectral range. A CO pulsed laser (λ = 5.5 μm, energy power density up to 3.8 GW/cm2 per pulse with picosecond pulse duration) was applied as the source of photoinducing IR radiation. An optical parametrical generator cut from a proustite crystal was used as the source of the fundamental TPA beam within the 3–7.5 μm spectral range. Absolute values of the TPA coefficients were more than 13% higher than corresponding values obtained for other similar glasses (As2Te3–CaCl2–PbCl2 [1] or Sb2Se3–BaCl2–PbCl2 [2]). The PGBC system investigated possessed a shorter time response (about 12 ps) compared with other IR nonlinear optical glasses. It was also established that all nonlinear optical susceptibilities were dependent on the type of RE3+ ion. A maximum value of the TPA was achieved for the glasses doped by Tm3+. The TPA values increased significantly below 45 K. Ab initio molecular dynamics and quantum chemical simulations were performed in order to evaluate the possible role of electron–phonon anharmonic interactions in the observed phenomena. The influence of the external CO photoinduced pump beam through the photoinduced electrostricted anharmonic electron–phonon interactions was simulated. A decrease of picosecond delaying time response compared with other glasses was achieved. To obtain independent confirmation of the observed dependencies, measurements were carried out of χxxxx(E) during the external IR pumping. The measured and theoretically calculated dependencies of the third-order susceptibilities were also compared. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesized rare-earth doped oxide glasses for nonlinear optics

Photostimulated nonlinear optical effects in synthesized PbO–Ga2O3–Bi2O3–CdO (PGBC) glasses doped by Yb3+, Er3+, and Dy3+ rare-earth (RE3+) ions were discovered. Temperature-dependent measurements of optical photoinduced second-harmonic generation (PISHG) and two-photon absorption were performed in the infrared (IR) range. CO pulse laser (λ=5.5 μm, energy power density up to 3.8 GW/cm2 per pulse) was applied as a source of IR-photoinducing and probing (fundamental) light. Absolute values of the PISHG were more than 22% higher than corresponding values obtained for other glasses: As2Te3–CaCl2–PbCl2 [1] or Sb2Se3–BaCl2–PbCl2 [2] type. The investigated PGBC system possesses a shorter time response (about 18 ps), compared with other IR nonlinear optical glasses. We have also established that all nonlinear optical susceptibilities are dependent on the type of RE3+ ion. A maximal value of the PISHG is achieved for the glasses doped by Yb3+. The PISHG values increase significantly below 25 K. We have carried out ab initio molecular dynamics and quantum chemical simulations in order to evaluate the possible contribution of electron–phonon anharmonic interactions in the observed phenomena. We have modeled the influence of the external CO photoinduced beam through the photoinduced anharmonic electron-phonon interactions. A decrease of the delaying time response is achieved. To obtain independent confirmation of the observed dependencies, we have carried out measurements of the ε2(E) during the external IR pumping. We have also compared the measured and theoretically calculated dependencies of the IR-induced effects.

Planar waveguides formed by Ag^+–Na^+ ion exchange in nonlinear optical glasses: diffusion and optical properties

All-optical communication systems are the subject of intense research related to the integration of nonlinear optical materials. In sodiocalcic borophosphate glasses that contain niobium oxide and exhibit high nonlinear optical indices, planar waveguides have been formed by a Ag(+)-Na(+) ion-exchange technique. WKB analysis has been used to characterize the diffusion profiles of silver ions exchanged in glass substrate samples chemically by an electron microprobe technique and optically by an M-line technique. These methods permit the Ag(+) penetration depth and diffusion profile shape and index profiles to be determined. The results are analyzed and discussed in relation to Ca(2+) concentration and exchange conditions in glasses. The Ag(+) diffusion in these glasses can be almost entirely controlled for index-profile engineering.