Infrared GRIN GeS2–Sb2S3–CsCl chalcogenide glass–ceramics

Chalcogenide glasses show a unique potential for creating gradient refractive index (GRIN) lenses, which would reduce the size and weight of infrared thermal imaging system and remain/improve its performance. Here, we propose a new method that forms a GRIN chalcogenide glass–ceramics (GCs) by creating low refractive index (n) CsCl nanocrystals within a high n GeS₂–Sb₂S₃ glass matrix. After specific gradient thermal treatment, the GRIN structure of Δn ∼ 0.04 was formed through the gradient precipitation of CsCl. This work would pave a new path to design the GRIN chalcogenide GCs through a selective crystallization of halide crystals with low n.     

Chalcogenide glasses with embedded ZnS nanocrystals: Potential mid‐infrared laser host for divalent transition metal ions

Chalcogenide glasses (ChGs) containing II‐VI chalcogenide (ChG) nanocrystals such as ZnS/Se have recently been intensively studied as promising mid‐infrared nonlinear optics and laser materials, yet preparation of pure‐phase II‐VI nanocrystals embedded in ChGs via controlled crystallization is still very challenging. In this study, a new system of ChGs and glass ceramics (GCs), viz., (100?x)As₂S₃–xZnSe (x = 0 ~ 30 mol%), is synthesized, and its physical and optical properties including density, molar volume, microhardness, glass transition temperature, glass network structure, transmission, and refractive index are comprehensively characterized. Significantly, it is initially demonstrated that pure ZnS nanocrystals can be precipitated in GCs simply by a thermal treatment process. The composition and thermal treatment temperature dependencies of crystallization are studied using X‐ray diffraction spectroscopy, and the morphology of the nanocrystals by high‐resolution transmission electron microscope. The ChG GCs with embedded ZnS nanocrystals retaining good transparency can be a potential host laser material for divalent transition metals (e.g., Cr²⁺/Fe²⁺, etc.), and thus used for ultrabroadband tunable continuous or ultra‐short‐pulsed mid‐infrared fiber lasers.     

Preparation and refractive index characterization of chalcogenide glasses with gradient refractive index

Infrared gradient refractive index (GRIN) lenses have great application value and potential in multispectral imaging systems. This study reports various chalcogenide axial GRIN glasses prepared using the hot-pressing diffusion method. It is worth noting that the S4–S60 GRIN sample has a difference in refractive index (RI) Δn of greater than 0.3 and a diffusion depth of about 5 mm, which is the deepest diffusion depth reported in chalcogenide glass to date. In addition, the linear portion in the profile of the GRIN sample has a RI difference of 0.15 and a thickness of 1.2 mm. The effects of the temperature, concentration difference, and diffusion time on the sample diffusion process are discussed. The dispersion properties of the GRIN samples were further calculated, providing a new option for correcting chromatic aberrations in optical systems. In addition, a method for the indirect nondestructive characterization of sample RI using the Raman intensity ratio is proposed, and the reliability of the method is verified by practical experiments, which is convenient for the subsequent measurement of the GRIN profile.     

Mapping the glass forming region and making their phosphor-in-glass for application in W-LEDs packaging

The application of phosphor-in-glass (PiG) packaging material in white-light emitting diodes (W-LEDs) can improve the thermal stability and luminous efficacy of LED devices. In this work, a low melting point glass of TeO₂–ZnO–Na₂O–B₂O₃ (TZNB) was selected as glass matrix, and mixed with YAG: Ce³⁺ phosphor powders to obtain phosphor-in-tellurite glass (PiTG). In a significant advance, we mapped the glass forming region of TZNB for the first time. This high refractive index glass matrix with low melting temperature was achieved by optimizing the glass composition. The refractive index increased regularly from 1.61 to 2.03, when the dosage of TeO₂ increased from 15 to 75 mol%. Through Monte Carlo simulations and numerical calculations, the optimal structure of gradient refractive index (GRIN) was designed, which is consisted of TZNB-1 (n = 2.03), TZNB-4 (n = 1.79), TZNB-6 (n = 1.66), and glass substrate (n = 1.52). The PiTG with GRIN coating was fabricated by screen printing and low-temperature sintering, and the optimized sintering temperature is 575°C. Compared with the single refractive index (SRIN) coating, the luminous efficacy of PiTG with GRIN coating was enhanced from 9.51% to 23.12%. Therefore, this work provides a significant application in high-power W-LEDs.     

Effect of halogen on imprinting gradient refractive index microstructure in GeS2–Ga2S3–NaX (X=F,Cl, Br,I) glasses for broadband infrared diffraction gratings

Chalcohalide glasses with a gradient refractive index (GRIN) microstructure were imprinted by microthermal poling for realizing diffractive optical elements covering the visible to middle-infrared wavelength range. The effect of halogen ions on the saturation poling voltage (U), surface profile, diffraction pattern, optical transmittance, GRIN microstructure, and structural rearrangement of poled glass is investigated. An effective imprinting formation region for a GRIN microstructure based on the U and glass composition is observed under fixed poling time and temperature. The onset U (60 V–150 V) and activation energy of mobile cations (0.449 eV–0.533 eV) decreases with the atomic number of the halogen from F to I, but the saturation diffractive order (8th to 11th levels) and phase difference (~0.08λ to 0.18λ) increases accordingly. The onset U and activation energy decrease with the deformability of the glass network and radius of the halogen ions. The phase difference and saturation diffractive orders decrease with the proportion and electronegativity of interval halogen atoms in the glass network. Thus, chalcohalide glasses with GRIN microstructures can be tailored by adjusting the type of halogen ions for realizing various diffraction optical elements.     

Evaluation of high temperature polymers in nanolayered films and gradient refractive index (GRIN) lenses

A new polymer nanolayer gradient refractive index (GRIN) system with more robust thermal stability because of incorporation of a high glass transition temperature polyester, OKP4HT, was demonstrated. A combination of extruded nanolayered GRIN film systems, comprised of five unique polymer materials, were combined to produce laminate optics comprised of a large internal refractive index gradient distribution, n = 1.445 – 1.630, without degradation of optical transmissive properties. The optical performance of a series of varied magnitude GRIN lenses, ranging from Δn = 0 to 0.185, was evaluated. Increasing the lens refractive index range resulted in decreased optic sphericalaberrations that followed analytical predictions. An analytical approach was reported to correlate the polymer material upper service temperature (UST) to the onset of polymer material loss modulus as measured by DMTA. Thermo‐optical interferometry measurements of irreversible lens deformation confirmed the lenses UST at 125°C for the OKP4HT/PC system as compared to 75°C for a PMM/SAN17 system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42741.     

Polymer‐polymer miscibility study for plastic gradient index optical fiber

Gradient index (GRIN) materials have many applications in optical fiber communication, imaging and optical instruments. Almost all GRIN optical fiber or lenses are made of glass, which has limitations due to poor flexibility, difficulty in processing and high price. Therefore, polymers are being investigated to produce a GRIN material that solves the problems of GRIN glass. In this study, the optical transmittance and refractive indices of three kinds of miscible copolymers of Methyl Methacrylate/Benzyl Methacrylate, Methyl Methacrylate/Trifluoro‐ethyl Methacrylate and Benzyl Methacrylate/Trifluoro‐ethyl Methacrylate were examined.     

Optical properties,thermal stability,and forming region of high refractive index La2O3–TiO2–Nb2O5 glasses

The high refractive index La₂O₃–TiO₂–Nb₂O₅ glasses were prepared by containerless processing, and the glass‐forming region was determined. The refractive index showed the range from 2.20 to 2.32, and the values were much higher than those of most optical glasses. The completely miscible 30LaO_3/2–(70?x)TiO₂–xNbO_5/2 (0 ≤ x ≤70) system was fabricated to study the compositional dependence of refractive index and optical transmittance. The crucial determinants of the refractive index of oxide glasses, oxygen molar volume, and electronic polarizability of oxygen ions were calculated. The principle of additivity of glass properties was suitable for the calculation of refractive index between glass and compositional oxides. All the glasses were colorless and transparent in the visible to 6.5 μm middle infrared (MIR) region. These results are useful for designing new optical glasses with high refractive index and low wavelength dispersion in wide optical window.     

梯度光学功能玻璃研究进展

梯度折射率(GRIN)玻璃是指具有梯度折射率分布的光学功能玻璃,其在光学及光电学领域中具有广阔的应用前景.介绍了GRIN玻璃的形成原理及分类,综述了GRIN玻璃的制备技术及发展现状,讨论了它们各自存在的问题,提出了今后GRIN玻璃的研究方向.     

High-precision molding simulation prediction of glass lens profile for a new lanthanide optical glass

Precision glass lens molding (PGLM) is a recently developed method for fabricating glass optical components with high precision in large volumes. Lanthanum optical glasses are extensively used as optical materials owing to their superior optical properties, such as high refractive index, low dispersion, and high transparency. However, the transformation temperature of currently available high refractive index glass is generally above 650 °C and poses a challenge in manufacturing ultra-hard molds, durable coatings, and high-temperature molding equipment using PGLM. In this study, a preparation method for obtaining high refractive index, low -melting -point lanthanide optical glass (B-ZLaT198) used in PGLM was developed to reduce the transformation temperature. The developed method also characterizes the glass refractive indices and thermal-mechanical properties. To achieve the high-precision prediction of a molding shape in a simulation, a viscoelastic constitutive model of glass was established based on a micro-deformation uniaxial compression creep test. Moreover, by solving the Tool-Narayanasway-Moynihan model parameters based on the specific heat capacity fitting of optical glass at different heating and cooling rates, the input parameters of the structural relaxation model (SRM) for simulation prediction of aspheric glass lens profile deviation in the annealing stage were obtained. Finally, the profile deviation of the aspheric lens was predicted using a finite element model simulation. The results showed that the simulation’s predicted profile of an aspheric lens using the SRM model was in good agreement with that of experimental molding profile. In addition, using the SRM provided a higher prediction accuracy than that of the thermal expansion model in the annealing stage. Adopting the SRM was necessary for the annealing simulations of molding pressing and also verified the accuracy of the proposed viscoelastic characterization method for calculating the thermomechanical parameters of optical glasses.     

Microhardness and optical property of chalcogenide glasses and glass-ceramics of the Sn–Sb–Se ternary system

The microhardness of chalcogenide glasses (ChGs) of the Sn–Sb–Se (SSS) ternary system was investigated, and the correlation of microhardness with the mean coordination number of the SSS ChGs was determined. To prepare infrared-transparent SSS glass-ceramics (GCs), two SSS ChGs (A, Sn_6.23Sb_14.11Se_79.66; B, Sn_9.8Sb_17.22Se_72.98; by molar composition) were selected and thermally treated at 433 and 448 K, respectively. The improved microhardness (with values that increased by 11.5% and 7.3% for SSS ChG A and B, respectively) of the resulting SSS GCs is attributed to the formation of Sb₂Se₃ nanocrystals.     

Gradient refractive index structure of phosphor-in-glass coating for packaging of white LEDs

A gradient refractive index (GRIN) structure, with a gradual increase in the refractive index from the glass substrate, was successfully obtained by multilayer screen printing for white light-emitting diodes (w-LEDs) packaging. Each phosphor-in-glass (PiG) coating consisted of B₂O₃–SiO₂–ZnO glass matrix and yellow phosphor. The gradually increased refractive index (1.62, 1.72, and 1.82) of glass matrices were obtained from higher molecular weight of La₂O₃ and WO_3. After sintering at 600°C, no obvious interface was observed and the phosphor particles were mixed thoroughly in the glass matrix. When the phosphor content was 50 wt%, the white-light emission was obtained. Compared with those based on the nongradient and low-refractive PiG coating, the luminous efficacy of w-LEDs constructed by the PiG coating with GRIN was enhanced. It shows that the GRIN structure is beneficial to improve the luminous efficacy of w-LEDs.     

Large third-order optical nonlinearity of chalcogenide glasses within gallium-tin-selenium ternary system

We explore the third-order optical nonlinear properties of arsenic- and germanium-free chalcogenide glasses (ChGs) within a gallium-tin-selenium (Ga-Sn-Se, GSS) ternary system at wavelength of 1.064 μm in the picosecond region. A classical characterization showing the values of the absorption and the linear index will be given. Then, using D4σ-Z-scan technique, both nonlinear refractive index (n₂) and nonlinear absorption coefficient (β) of the GSS ChGs will be measured. A comparison of the results is made with other families of chalcogenide glasses considering the figure of merit calculation. The first results show that GSS system would give better NL performance promising high potential for n₂(β)-based photonic devices performed under clean production and green/sustainable chemistry.     

The hydrophobicity and optical properties of the HfO2-deposited glass

The HfO₂ thin film was deposited on the glass substrate by physical vapor deposition and exhibited good surface flatness. The coating had smaller grain size with increasing RF power. A control of lower oxidation state of Hf (Hf²⁺) is a way to enhance the hydrophobicity of the HfO₂-deposited glass. The nonlinear refractive index of HfO₂ film on the glass substrate was measured by Moiré deflectometry, and was of the order of 10^–8 cm² W^–1. As the RF power increased, the transparent HfO₂-deposited glass showed a blue-shift and lower transmission in the near-IR region. On comparing with the pure glass, the HfO₂-deposited glass exhibited hydrophobicity and had optical selection in the Vis–IR region for improving optical application.     

Preparation and characterization of light-focusing plastic rod by swollen-gel polymerization

A new method for preparing light-focusing plastic rod with gradient refractive index (GRIN) profile was fabricated by using the swollen-gel polymerization technique. Monomer pair systems of methyl methacrylate (MMA) with reactive benzyl methacrylate and unreactive bromonaphthalene, benzyl phenyl acetate, benzyl salicylate, triphenyl phosphate, and dibromobenzene were investigated. It was found that refractive index difference and numeric aperture (NA) values of MMA with an unreactive agent are larger than those of a reactive agent system, and a high NA value of 0.336 in a system of MMA/BN = 2/1 was obtained. A distortion-free image can be observed through GRIN rods fabricated by using the swollen-gel polymerization method. Optical characteristics of the GRIN rod were also investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 849–854, 1997     

Synthesis of highly refractive and transparent poly(arylene sulfide sulfone) based on 4,6-dichloropyrimidine and 3,6-dichloropyridazine

A highly refractive and transparent poly(arylene sulfide sulfone) (PASS) containing pyrimidine (or pyridazine) unit has been developed. The polymer was prepared by a polycondensation reaction of 4,4′-dimercaptodiphenyl sulfone (DMDPS) and 4,6-dichloropyrimidine (DCPM) (or 3,6-dichloropyridazine (DCPD)). They showed good thermal stabilities such as a relatively high glass transition temperature of 193–202 °C and a 5% weight loss temperature (T_5%) of 370–372 °C. The optical transmittance of the polymer at 450 nm is higher than 81%. The heterocycles unit and plural –S– linkages provides the polymer with a high refractive index of 1.737–1.743 at 633 nm and a low birefringence of 0.003–0.004.     

Effect of withdrawal rate on the evolution of optical properties of dip-coated yttria-doped zirconia thin films

In this work, the Swanepoel method is described and applied for determining various optical parameters and thicknesses of dip–coated yttria–doped zirconia thin films. Using this method the influence of the withdrawal rate on optical parameters was studied. The characterization of the deposited thin films was carried out by optical microscopy and FT–IR spectrophotometry. As expected, coating thickness was closely related to the withdrawal rate and consequently influenced optical parameters such as refractive index, extinction coefficient, and absorption coefficient. Regarding the average refractive index of the prepared thin films, n is in the 2.0 – 2.2 range, the higher refractive index average value being obtained with films deposited at 25 mm min⁻¹ (n = 2.19). The value of the optical band gap was also studied, this increased with withdrawal rate and was quite similar to values reported by other investigators at 50, 25 and 10 mm min⁻¹. Thus, this study proposes analysing the influence of the withdrawal rate for the manufacture of different types of thin films with previously specified optical parameters.     

Controlled variation of the refractive index in ion-damaged diamond

A fine control of the variation of the refractive index as a function of structural damage is essential in the fabrication of diamond-based optical and photonic devices. We report here about the variation of the real part of the refractive index at λ = 632.8 nm in high-quality single-crystal diamond damaged with 2 and 3 MeV protons at low-medium fluences (10¹³–10¹⁷ ions cm^? 2). After implanting the samples in 125 × 125 μm² areas with a raster scanning ion microbeam, the variation of optical thickness of the implanted regions was measured with laser interferometric microscopy. The results were analyzed with a model based on the specific damage profile. The technique allows the direct fabrication of optical structures in bulk diamond based on the localized variation of the refractive index, which will be explored in future works.     

Effects of alkali metal ion on imprinting GRIN microstructure in GeS2-Ga2S3-MCl (M=Na,K, Cs) glasses for visible to mid-infrared microgratings

Gradient refractive index (GRIN) micro-optics present unique opportunities for control of the chromatic properties, new degrees of freedom for optical design as well as the potential for use in new optical system applications. GRIN microgratings were imprinted in GeS₂-Ga₂S₃-MCl (M = Na, K, Cs) chalcohalide glasses by microthermal poling, and the effects of the type and concentration of alkali cations on their performance were investigated. Two effective imprinting formation regions of the GRIN microstructure based on the poling saturation voltage (U_s) and glass composition are observed at fixed poling time and temperature. The U_s increases from 140 to 750 and 2600 V in accordance with the activation energy (E_a) of alkali ions (Na⁺ to K⁺ and Cs⁺) increasing from 45.15 to 58.62 and 92.58 kJ/mol for studied samples. The saturated numbers of diffraction order (N_s) of the gratings in these samples are 7, 9 and 6, respectively, the highest number being provided by the K⁺-containing sample. This is in accordance with imprinting-induced phase differences (0.14λ, 0.19λ and 0.09λ) measured in the fabricated samples containing Na⁺, K⁺ and Cs⁺ ions. Furthermore, the U_s of samples decreases from 1500 to 300 V with four concentrations of K⁺ from 10 to 30%, associated with their E_a of K⁺ decreasing from 69.62 to 53.46 kJ/mol, while N_s increases from 8 to 14, which is attributed to the increase of the phase difference in the GRIN structures. The controllable GRIN microstructures are realized by adjusting the type and concentration of alkali cations in chalcohalide glasses, which is expected to drive the design of broadband GRIN microgratings.     

Preparation and characterization of gradient refractive index plastic rods with small calibers

A series of gradient refractive index (GRIN) plastic rods with diameters of 2–4 mm were fabricated using the centrifugal diffusion polymerization (CDP) technique. Methyl methacrylate (MMA) was used as the monomer having a lower refractive index, and poly‐(methyl methacrylate) (PMMA) was used as a prepolymer dopant. The reactive benzyl methacrylate (BzMA), and an unreactive agent chosen from bromonaphthalene (BN) and diphenyl sulfide (DS) with higher refractive index were used as the second component of the feed mixture. Effects of feed composition, centrifugal conditions, and initiator concentration on the optical characteristics of plastic GRIN rods are investigated. Refractive index profiles and image transmission qualities of the GRIN rods prepared in this investigation are estimated.