Disperse red 13 (DR13) azoaromatic chromophores were incorporated into sol-gel derived TiO2/organically modified silane matrix to achieve a hybrid material with low propagation loss and ultrafast optical response. The planar waveguide and nonlinear optical properties of the as-derived hybrid films were studied by a prism coupling technique and an optical Kerr shutter technique with an 800-nm femtosecond laser, respectively. Results indicate that the response time of the bulk sample doped with 0.1% DR13 molecules is less than 208 fs, and the third-order nonlinear refractive index is estimated at about 1.141×10−15 cm2/W. The planar waveguide film with a low propagation loss less than 1 dB/cm for both transverse electric and transverse magnetic modes at a wavelength of 1312 nm can be easily obtained by a spin-coating process. It can be concluded from the above results that the as-prepared hybrid materials under present conditions are expected to have potential in ultrafast optical applications.
A single layer sol-gel derived TiO2 thin films and 6 periods SiO2/TiO2 multilayer coating were designed and prepared on GaAs substrates as anti-reflection coating or near-IR-reflective coating for high power semiconductor laser applications. Crack free TiO2 thin films having thickness of 80-150 nm, and refractive indices of 1.8-2.1 have been obtained by simply sol-gel method upon heating at different temperatures. The obtained TiO2 thin films on GaAs substrates have shown reflectance of <EQ 1 percent in the wavelength of about 808 nm. Thin films of TiO2 and SiO2 were also used to fabricate near IR reflector ion GaAs substrates. The reflector consisted of 6 SiO2/TiO2 bi-layers, designed with a high-reflective band in the wavelength of 1064 nm. A minimum transmittance of <EQ 2 percent in the wavelength range between 950 and 1100 nm has been obtained in the present multilayer SiO2/TiO2 coating.
Erbium oxalate and neodymium oxalate nanoparticles/titania/organically modified silane composite sol-gel thin films for photonic applications have been prepared by combining an inverse microemulsion technique and the sol-gel technique at low temperature. Transmission electron microscopy observation shows that the size of these oxalate nanoparticles is in the range from 10 to 40 nm. Up- conversion emission properties of these composite thin films on silicon substrates have been studied. A relatively strong room-temperature green up-conversion emission at 544 nm has been measured for the composite films dispersed with erbium oxalate nanoparticles upon excitation at 993 nm. An up- conversion emission in violet color from neodymium oxalate nanoparticles upon excitation with a yellow light emission, two UV emissions at 341 nm and 376 nm and a weak blue emission at 467 nm have been obtained. The mechanism of the up-conversion emission has been explained by means of an energy level diagram. The lifetimes of the violet emissions have been measured.
Neodymium oxide nanoparticles/TiO2/ORMOSIL composite sol- gel thin films have been prepared by combining an inverse microemulsion technique and the sol-gel technique at low temperature. Transmission electron microscopy and scanning electron microscopy have been used to characterize the size and structural properties of the neodymium oxide nanoparticles and composite thin films. Photoluminescence and up-conversion emission properties of these composite thin films deposited on silicon substrates have been studied. A relatively strong room-temperature photoluminescence emission at 1064 nm corresponding to the 4F3/2 yields 4I11/2 transitions from these composite thin films has been observed as a function of the heat treatment temperature. An intense up-conversion emission in violet (402 nm corresponding to 4D3/2 yields 4I13/2 transitions) color from the composite thin films baked at different temperatures upon excitation with a yellow light (587 nm) has been observed. In addition to this violet emission, an UV emission at 372 nm and a weak blue emission at 468 nm have been obtained. The mechanism of the up-conversion emission has been explained by means of an energy level diagram. The lifetimes of the violet emissions have been measured.
TiO2/organically modified silane (ORMOSIL) optical waveguide thin films have been prepared at low temperature by the sol-gel technique by using y- Glycidoxypropyltrimethoxysilane and tetrapropylorthotitanate as precursors. Atomic force microscopy has been used to characterize the morphology and structural properties of the waveguide films. Waveguide properties of these composite thin films on III-V compound semiconductor substrates such as their refractive index, thickness, and propagation loss have been studied. It was experimentally demonstrated that grating structures could easily be fabricated for these composite thin films by using the embossing technique and we have successfully fabricated the grating by this method without baking. It was found that this method is specifically useful for the fabrication of diffractive grating and optical planar waveguides on sol-gel derived glass film coated on temperature sensitive substrates such as III-V compound semiconductors. As a preliminary result, the ridge waveguide and grating with a period of 1.102 micrometer and depth of 57.2 nm have been successfully fabricated.
We report the preparation and photoluminescence spectral analysis of Tb3+ and Eu3+ doped Zn2SiO4 powders in sol-gel sol-gel process. On exposure to an UV source, these rare earth ions doped zinc silicate materials have shown prominent luminescent green and red colors, due to the electronic transitions of 5D4 yields 7F5 (Tb3+) and 5D0 yields 7F2 (Eu3+) respectively. The green emitting transition of Tb3+ material has been a magnetic dipole in nature and the red emitting transition of Eu3+ material has been due to an electric dipole in nature with a hypersensitivity in its luminescence. Systematic characterization has been carried out to understand the fluorescence efficiency of these two materials by measuring their excitation, photoluminescence, time-resolved luminescence spectra and lifetimes of the emission transitions (5D0 yields 7F0,1,2,3,4&5) of Eu3+ at two different excitation wavelengths of 226 nm and 395 nm. However, for the emission transitions (5D4 yields 7F6,5,4,3,2&1) of Tb3+ doped material, one excitation wavelength of 229 nm was used. Structural characteristics of these materials was carried out with an XRD and TEM measurements. The computed color coordinates suggest that both the phosphors have all desirable features for CRT screen applications.
BaTiO3 thin films are prepared on ITO-coated Corning 1737 glass. The solution is prepared from a double metal ethoxide and the films are deposited by spin coating and annealing at 700°C for 2 hours in an O2 atmosphere. The films are characterized using x-ray diffraction, atomic force microscopy, micro-raman, UV-VIS spectroscopy, and Sawyer-Tower Bridge. The pure perovskite phase of BaTiO3 is identified by x-ray diffraction. The tetragonality is revealed from Raman study by identifying the symmetrical dependent Raman shift at about 306 cm-1. The ferroelectricity of the film is confirmed by the P-E hysteresis loop. The films are highly transparent, with an absorption edge at 3.73eV. These desirable features indicate that the films have potential in electronic display and electro-optical applications.
We report the preparation of sol-gel derived planar waveguides from high titanium content hybrid materials. By incorporating organic molecules into the inorganic TiO2- SiO2 sol-gel glass matrix, porous-free waveguide films are obtained with low temperature heat treatment. The single spin-on thickness is measured to be more than 1.7 micrometers , enough to support light guiding and the refractive index of the film is found to depend on the heat treatment temperature. We also studied the microstructural and optical properties of the waveguide films using atomic force microscopy, ellipsometry, thermal gravimetric analysis, and UV-visible spectroscopy. Based on these experimental results, we found that heat-treatment at a temperature about 100 degrees C is sufficient to produce a relatively dense film with high transmission in the visible and near IR range. We believe that this process is very useful for the fabrication of passive photonic circuits on temperature sensitive substrates such as III-V compound semiconductors. Meanwhile, it has also been noted that a purely inorganic and crack-free silica-titan films could be obtained after baking the hybrid material film at 500 degrees C or higher.
Temperature-dependent luminescence spectra, lifetimes and energy transfer in Eu3+ and other rare earths co- doped sol-gel SiO2 glasses, were investigated in the temperature range from 10K to 300K. Due to the addition of the other rare earths as co-dopants, luminescence spectra of Eu3+ have shown significant changes not only in spectral intensities but also in emission peak features. Evaluation of the temperature-dependent energy transfer rates and lifetimes and the computation of critical energy transfer distances by employing two different energy transfer model schemes, have provided evidence for such luminescence behavior in the nanometer-size confined glass matrices.
The cracking of sol-gel derived films on Si(100), Si(111), and glass substrates has been studied experimentally using optical microscopy, scanning electron microscopy and optical scattering method, as well as theoretically using the static method and the dynamic method. The experimental observations show that the primary cracking directions of the sol-gel derived film depend strongly on the symmetry of the substrate. As all the studied substrates have a uniform biaxial elastic modulus, the static method cannot explain such cracking behavior. However, the most probably directions of the primary cracks can be determined by considering the anisotropy of the longitudinal and the transversal elastic waves, and these directions are in good agreement with the experimental observations.
In this paper, we present the fabrication of sol-gel derived silica based films on InP using both inorganic and composite material precursors. Thin silica films with thicknesses less than 0.5 μm, are achieved using an inorganic precursor by means of multiple spin coatings and rapid thermal processing at an annealing temperature of 450°C. The cracking pattern of the inorganic silica film on InP is analyzed. Thick films are derived from composite materials by multiple spin coatings with only furnace baking at 150°C. In addition, the different properties of each type of films and their potential applications in terms of monolithic integration are discussed.
Silica/Titania optical waveguides have been prepared by the sol-gel technique using Glycidoxypropyltrimethoxysilane and tetrapropylorthotitanate as the starting materials. Scanning electron microscopy, atomic force microscopy, thermal gravimetric analysis, differential thermal analysis, and UV- visible spectroscopy have been used to characterize the morphology, the optical and structural properties of the waveguide films. The waveguides are also characterized by measuring their refractive index, thickness, and propagation loss as a function of titanium content and thermal treatment. The obtained results show that after an annealing at 500°C or above, an inorganic silica/titania crack-free film could be obtained. The single layer spin- coated film has high transparency in the visible range and is more than 0.5 micron thick. The propagation loss of the waveguide films was also estimated by using the scattered- light measurement method and was found to be around 1.0 dB/cm at the wavelength of 632.8 nm.
We present an investigation of third-order optical nonlinearity in surface modified PbS and CdxPb1-xS nanoparticles using the Z-scan technique with femtosecond laser pulses at 780-nm wavelength. The samples include PbS nanoparticles in microemulsion with PbS concentration range from 0.3-2.5 X 10-3 M and CdxPb1-xS nanoparticles in microemulsion with x from 0 to 1. An extended Z-scan theory based on the Huygens- Fresnel princeps is employed to extract the nonlinear refraction index from the experimental Z-scan data with a large nonlinear phase shift. The nonlinear refractive index in PbS nanoparticle microemulsion is found to increase linearly with PbS concentration between 0.3 X 10-3 and 1.9 X 10-3 M. The highest concentration microemulsion gives a nonlinear refractive index of 1.8 X 10-11 cm2/W, which is approximately 4 orders of magnitude higher than those of commercially available bulk semiconductors, such as ZnS and CdS, measured at the same conditions. In CdxPb1-xS nanoparticles, Cd0.33Pb0.67S exhibits relatively larger refractive nonlinearity. For all samples, nonlinear absorption remained unmeasureable up to 0.9 GW/cm2. The observed large refractive nonlinearity in these nanoparticles may mainly be attributed to the optical Stark effect and contribution from the surface-trapped states in the nanoparticles.
We report the implementation of a low loss core-cladding waveguide structure of an a-axis Nd:MgO:LiNbO3 single crystal fiber and the demonstration of a frequency-doubled laser made from such a cladded crystal fiber. The laser-heated pedestal grown a-axis single crystal fiber, which has an elliptical cross sectional area of about 200 micrometer X 150 micrometer, was further treated with a Mg-ion indiffusion process. An electron probe microanalysis was used to measure the Mg-ion concentration distribution of the Mg diffused layer. After a number of trials, the diffusion parameters suitable for forming a core-cladding waveguide structure have been obtained. The optical and structural properties of the cladded crystal fibers were also characterized. A diode pumped external cavity frequency doubled laser has been made from the cladded crystal fiber. At room temperature, CW green laser output with a power of 10 (mu) W at the wavelength of 0.532 micrometer has been obtained. The origins of the relatively low frequency-doubled conversion efficiency will also be discussed.
We report the preparation of high optical quality sol-gel waveguide films made from high titanium content organically modified silane (ORMOSIL) and the fabrication of optical channel waveguides in the deposited sol-gel films. The waveguide films were deposited on a solid substrate (such as silicon) by spin-coating and low temperature baking, and the channel waveguides were fabricated using laser writing and reactive ion etching (RIE). The properties of the sol-gel waveguide films were characterized using atomic force microscopy (AFM), ellipsometry, and UV-visible spectroscopy (UV-VIS). AFM and ellipsometry results showed that a dense and porous-free waveguide film could be obtained at the heat treatment temperature of 100 degrees celsius. The influence of the RIE parameters including O2 content, rf power, and pressure on etching rate of the sol-gel waveguide films have been investigated. After a number of exploratory experiments, suitable etching parameters for the case of photoresist mask layer have been obtained.
A novel planar-binary optical see-through visor, in which three binary optical elements, namely two couplers and one compensator, are designed to be fabricated on a planar glass slide substrate, is presented in this paper. One binary focusing coupler serves to image and couple the light into the optical plate so that the light can travel within the planar passage via total internal reflection. The other coupler directs the light out of the plate, and the compensator makes it possible for the user to see directly through the visor at the same time. Harmonic diffractive technology is employed to reduce the chromatic displacement in the visible range. The schematic of the structure and simulation results are given in this paper. Our results indicate that it is promising to utilize the planar-binary optics to cover the visible band.
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