Fused Silica Glass Research Articles

Removal Modeling and Experimental Verification of Magnetorheological Polishing Fused Silica Glass

Compared to conventional polishing methods, magnetorheological polishing has no subsurface damage and a has good polishing effect, which is suitable for fused silica glass surface processing. However, the existing magnetorheological polishing material removal model has low processing efficiency and uneven removal, which cannot realize the deterministic processing of parts. The material removal (MR) model of fused silica glass is established by convolving the dwell time with the material removal function. The residence time is Fourier transformed. The consequence of process variable such as machining time, workpiece rotational frequency, machining gap and X-direction deflection on the MR of workpiece interface are analyzed. Experiments verify the validity of the material removal model. The surface precision PV value of the workpiece surface under the optimal process parameters was decreased from 7.959 nm to 0.609 nm for machining. The experiment results indicate that the established MR model can be implemented as the deterministic MR of the optical surface and ameliorate the surface accuracy of the workpiece surface.

Increased fatigue resistance in transparent lead zirconate titanate thin films with interdigitated electrodes

This work compares the fatigue behavior of fully transparent lead zirconate titanate films with a composition at the morphotropic phase boundary on fused silica glass or sapphire, respectively, fitted with coplanar interdigitated top electrodes and no bottom electrodes to that of the same systems in a traditional metal–insulator–metal parallel plate capacitor geometry. While the polarization hysteresis in the latter geometry decreases rapidly during bipolar electrical cycling, systems with coplanar electrodes show no notable fatigue up to 107 cycles. The difference is explained based on the columnar microstructure of the films: for coplanar electrode geometries, the grain boundaries of the columnar structure act as trapping sites for oxygen vacancies, preventing the build-up of agglomerates that cause fatigue by domain wall pinning.

Understanding the tool influence function during sub-aperture belt-on-wheel glass polishing.

The tool influence function (TIF) during sub-aperture belt-on-wheel polishing has been evaluated as a function of various process conditions (belt use/wear, dwell time, displacement, belt velocity, and wheel modulus and diameter) on fused silica glass workpieces using C e O 2 polishing media. TIF spots are circular or elliptical in shape with a largely flat bottom character. The volumetric removal rate varies significantly with belt use (or wear), stabilizing after ∼15m i n of use. A modified Preston model, where the pressure dependence is adjusted using a different scaling of the wheel modulus (E w0.5), largely predicts the volumetric removal rate over the range of process conditions evaluated. The relatively high volumetric removal rate of 30-60m m 3/h using a fixed C e O 2-in-resin-host belt offers a rapid, and hence, more economical, initial polish of aspheric and freeform optics.

Manufacture of Three-Dimensional Optofluidic Spot-Size Converters in Fused Silica Using Hybrid Laser Microfabrication

We propose a hybrid laser microfabrication approach for the manufacture of three-dimensional (3D) optofluidic spot-size converters in fused silica glass by a combination of femtosecond (fs) laser microfabrication and carbon dioxide laser irradiation. Spatially shaped fs laser-assisted chemical etching was first performed to form 3D hollow microchannels in glass, which were composed of embedded straight channels, tapered channels, and vertical channels connected to the glass surface. Then, carbon dioxide laser-induced thermal reflow was carried out for the internal polishing of the whole microchannels and sealing parts of the vertical channels. Finally, 3D optofluidic spot-size converters (SSC) were formed by filling a liquid-core waveguide solution into laser-polished microchannels. With a fabricated SSC structure, the mode spot size of the optofluidic waveguide was expanded from ~8 μm to ~23 μm with a conversion efficiency of ~84.1%. Further measurement of the waveguide-to-waveguide coupling devices in the glass showed that the total insertion loss of two symmetric SSC structures through two ~50 μm-diameter coupling ports was ~6.73 dB at 1310 nm, which was only about half that of non-SSC structures with diameters of ~9 μm at the same coupling distance. The proposed approach holds great potential for developing novel 3D fluid-based photonic devices for mode conversion, optical manipulation, and lab-on-a-chip sensing.

Thermally stable high numerical aperture integrated waveguides and couplers for the 3 μm wavelength range

The femtosecond laser direct write technique was used to fabricate mid-infrared compatible waveguide couplers into Suprasil 3001, a fused silica glass with an OH content of as low as ≤1 ppm. Smooth positive step-index change multi-scan waveguides were produced with a high index contrast of 1 × 10−2, measured directly using quadriwave lateral shearing interferometry. Waveguides were annealed at 400 °C for 15 h and found to be highly stable, with only <5% reduction in positive index change. Brillouin microscopy and cathodoluminescence are introduced as novel tools that complement Raman mapping and electron microscopy for the investigation of the laser-induced structural changes within the glass matrix, and it was found that although a uniform step index profile is observed across the entire guiding region, different physical mechanisms underpin the index change in the upper and lower sections of the waveguide cross-section, respectively. Waveguides were optimized for mode-matching with optical fibers for the 3.2 μm wavelength range, and evanescent four-port directional couplers with coupling ratios ranging from 5:95 to 50:50 were designed and fabricated. This demonstration opens the door to the development of fully integrated and temperature-stable hybrid chip/fiber systems for the important mid-infrared spectral range.

Temperature and thermal stress analysis of ultrashort laser processed glass

When glass absorbs high energy from ultrashort-pulsed lasers, a very rapid melting-cooling event occurs. Images taken by a Scanning Electron Microscope (SEM) reveal a surface feature which elucidates the glass is heated to above 2000 °C. A series of voids along the laser path is also observed and analyzed by SEM and High-angle Annular Dark-filed Scanning Transmission Electron Microscopy (HAADF-STEM). Molecular Dynamic simulation predicting observable voids in fused silica glass requires the temperature to be above 10,000 Kelvin. This suggests that the thermal effect from nonlinear absorption along cannot explain the void generation. Thermal stress analysis based on three different types of glasses revealed that stress generated by laser heating is highly correlated to thermal expansion coefficient. Such thermal stress may be a key factor for laser cutting. • SEM images on the surface of ultrashort-pulse laser processed glass elucidate the glass is heated to above 2000 °C. • SEM images along the cross section of laser path reveal a series of voids. • MD simulation predicts the temperature required to form such voids by thermal effect along is above 10,000 Kelvin. • Higher thermal stress is generated on the glass with higher thermal expansion after the laser process.

Low-loss optofluidic waveguides in fused silica enabled by spatially shaped femtosecond laser assisted etching combined with carbon dioxide laser irradiation

We demonstrate the fabrication of low-loss optofluidic waveguides encapsulated in fused silica glass using femtosecond laser microfabrication followed by carbon dioxide laser irradiation. Spatially-shaped femtosecond laser-assisted chemical etching is first used to fabricate microchannels with circular cross-sections and a string of open extra-access ports in the glass. Further, the carbon dioxide laser direct writing on the glass surface is used to create a thermal reflow effect of etched glass microstructures for simultaneously polishing all internal surfaces of channels and sealing the extra-access ports. With this effect, the inner surface roughness of the etched microchannels can be reduced to ∼ 40 nm. Finally, a single-mode microfluidic optical waveguide with a propagation loss of ∼ 0.78 dB/cm at 1310 nm is obtained inside the glass by filling a mixture solution of decane and liquid paraffin into a laser-polished microchannel.

The effects of PEG molecular weight on fused silica glass sintering by using nano silicon oxide powder

The effects of PEG molecular weight on fused silica glass sintering by using nano silicon oxide powder

Rapid Fabrication of Silica Microlens Arrays via Glass 3D Printing.

Rapid manufacturing of high purity fused silica glass micro-optics using a filament-based glass 3D printer has been demonstrated. A multilayer 5 × 5 microlens array was printed and subsequently characterized, showing fully dense lenses with uniform focal lengths and good imaging performance. A surface roughness on the order of Ra = 0.12 nm was achieved. Printing time for each lens was <10 s. Creating arrays with multifocal imaging capabilities was possible by individually varying the number of printed layers and radius for each lens, effectively changing the lens height and curvature. Glass 3D printing is shown in this study to be a versatile approach for fabricating silica micro-optics suitable for rapid prototyping or manufacturing.

Compact packaged silicon photonic Bragg grating sensor based on a ball lens interface

We demonstrate a ball-lens based optical interface for coupling between a single mode fiber and a silicon grating coupler from the back side of a photonic integrated circuit (PIC). This allows compact packaging solutions and keeps the PIC top side accessible, e.g. for interacting with the environment in case of sensing applications. Different configurations employing 300 μm diameter ball lenses made of both LASF-35 glass and sapphire were investigated. Without any modifications to the grating coupler, the peak coupling efficiency (for TE polarization and operating wavelength around 1550 nm) was experimentally found to be only between 1.4 dB and 2.2 dB lower when interfacing with a ball lens from the back side compared to coupling from the top side using a cleaved fiber. Furthermore, no noticeable change in the bandwidth was found. The potential of the ball lens interface was proven by realizing a compact (diameter less than 1.5 mm) optical temperature sensor probe based on a phased shifted silicon photonic Bragg grating structure on a PIC. The probe consisted of a single mode fiber which was terminated with a 1.25 mm ceramic ferrule onto which a ball lens holder and a PIC was glued. The holder was realized in fused silica glass with a femtosecond laser direct-write technology and served to accurately position the ball lens with respect to the fiber and PIC. The assembly allowed to cleanly read out the Bragg grating spectrum in reflection, using a single fiber interface and was compatible with commercial interrogator systems. A Bragg wavelength shift of 73 pm/°C was found in a tested temperature range between 15 °C and 60 °C.

Compositional optimization of high-solid-loading ceramic cores via 3D printing

In this study, the effects of ZrO 2 mineralizer on the curing behavior of a silica-based core slurry and the microstructure and properties of the core were analyzed to optimize the properties of the samples. The results show that ZrO 2 addition aggravates the light scattering effect during the curing process, which increases the mis-cured region. However, ZrO 2 readily reacts with the fused silica glass in the matrix to form ZrSiO 4 , which inhibits the initiation and propagation of cracks and improves the high-temperature mechanical properties of the 60 vol% high-solid-loading core slurry. The content of ZrO 2 mineralizer in the slurry should be controlled within the range of 2.0–2.5 vol% for optimal mechanical performance.

Compressing High Energy Lasers through Optical Polymer Films

The thin-film post-compression technique has the ability to reduce the pulse duration in PW-class lasers, increasing the peak power. Here, the nonlinear response of an increasingly available optical thermoplastic demonstrates enhanced spectral broadening, with corresponding shorter pulse duration compared to fused silica glass. The thermoplastic can be used close to its damage threshold when refreshed using a roller mechanism, and the total amount of material can be varied by folding the film. As a proof-of-principle demonstration scalable to 10-PW, a roller mechanism capable of up to 6 passes through a sub-millimeter thermoplastic film is used in vacuum to produce two-fold post-compression of the pulse. The compact design makes it an ideal method to further boost ultrahigh laser pulse intensities with benefits to many areas, including driving high energy acceleration.

Evaluation of the helium hermeticity reliability of copper through-glass vias

This work aims to understand and assess the helium hermeticity reliability of metallized copper (Cu) through-glass vias (TGVs) made in Corning® HPFS® Fused Silica glass substrate. To assess this, the Cu TGV wafers were subjected to numerous stringent environmental reliability tests that includes high temperature storage (HTS) at 125 °C, highly accelerated stress testing (HAST), 130 °C/85 % RH and thermal shock (−40 °C/125 °C). Using a helium leak rate of >1.0 × 10−8 atm·cm3/s as the failure criteria, it was found that all the Cu TGV wafers used in this study significantly outperformed specification requirements, irrespective of the harsh environmental conditions that they were subjected to. This finding clearly attests to the robustness and suitability of Cu TGV wafers used in this study for stringent helium hermeticity requirement applications. At the completion of the tests, no failures were found for all samples subjected to thermal shock and HTS even after 9000 cycles and 4600 h respectively. For HAST samples that failed after exposure times of 400 h and 1500 h, it was found that the root cause for their failure was due to the erosion of Cu at the titanium (Ti)–Cu interface, caused by the formation of CuO and/or Cu2O. This led to sidewall debonding of the Ti–Cu interface, resulting in helium leak rates > 1.0 × 10−8 atm·cm3/s. Additionally, higher HAST exposure time was found to lead to increased degradation of the Ti–Cu interface.

Scanning-resonance optical sensing based on a laterally graded plasmonic layer—optical properties of Ag[formula omitted]Al[formula omitted] in the range of [formula omitted] to 1

Plasmonic AgAl/Si3N4 sensor layer structure was deposited on a fused silica glass slide by dual DC magnetron sputtering. The composition of the AgxAl1−x layer was laterally graded in which x linearly changes from x=0 to x=1 over a distance of 20 mm. The Si3N4 layer serves both as a resonator and a protective layer providing homogeneous chemical properties on top of the inhomogeneous AgAl layer. The structure was illuminated through a hemi-cylinder for variable-angle measurements in the Kretschmann–Raether configuration using a focused spot that enabled the change of x by moving it along the gradient of the composition. Optical properties of AgxAl1−x in the whole composition range were obtained. The positions of resonant peaks were shifted by changing the angle of incidence and the lateral position of the spot in a flow-cell configuration. The optical sensing performance of the bilayer system was investigated for x=0 and x=1. Based on the capabilities of ellipsometry limit of detection in refractive index unit values of ≈4−8⋅10−6 can be achieved in the resonant positions utilizing both p- and s-polarizations. Due to the flexible tunability of the resonant wavelengths by moving a focused spot, the above sensitivity is available in-situ, over the spectral range of 265-1504 nm.

Formation of silicone thin films by ArF excimer laser induced photo‐desorption

AbstractLow molecular weight silicones were ejected from silicone rubber target irradiated by a 193 nm ArF excimer laser through the photo‐desorption. The ejected silicones were successfully deposited on a fused silica glass substrate in air. An approximately 0.3 mm of the target‐substrate distance was required for the deposition. The deposited silicones became a thin film, showing an interference color when the ArF excimer laser was irradiated for a long time. Chemical bonding state of the formed thin films was analyzed by the Fourier transform infrared spectroscopy. The thin films were slightly different from the original silicone rubber structure, still it was composed of Si‐O‐Si bonds and Si‐CH3 bonds. Also, OH bonds were clearly produced in the silicone thin films. As a result, contact angle of water on the silicone thin films was measured to be approximately 20 degrees, indicating a hydrophilic property.

Fused silica as an optical material [Invited

Fused silica glass, with its large transparency range, low thermal expansion, high resistance to optical damage, high refractive index homogeneity, and ease of finishing has found use as an optical material in applications as varied as space shuttle windows, optical fiber, and deep UV lens elements. Its widespread role as an optical material has been enabled by manufacturing the glass from pure liquid precursor compounds, thereby minimizing impurities, and maximizing refractive index homogeneity. As a technical material, silica glass exhibits anomalous properties with respect to volume as a function of temperature and cooling rate, among other properties; these anomalies remain under investigation to this day. This article describes the manufacture of silica glasses and some of their varied optical applications. Silica is often used in demanding environments, an example of which is its use as a lens material for lithography systems using high photon excimer lasers. Static and dynamic properties of silica glass are discussed here.

Morphology evolution of Vickers indentation in fused silica glass etched by atmospheric pressure plasma jet

Nondestructive machining of optical components and smoothing of surface/subsurface damage generated by pre-processing is a major challenge for ultra-tight machining. The study analyzes the crack change during smoothing by quantitative layer-by-layer removal of Vickers indentations through atmosphere pressure plasma jet; the indentation change process is modeled and analyzed using Level Set Method (LSM) simulation. The results show that plasma jet processing can smooth the subsurface damage of fused silica optical components, and the LSM simulation verifies that the processing of cracks in fused silica components by plasma jet is dominated by each isotropic etching, and there are also each anisotropic etching during the change of cracks; and the depth of adjacent cracks can be judged by the moving direction of adjacent crack boundaries.

Ultrafast bandgap narrowing and cohesion loss of photoexcited fused silica.

Coupling and spatial localization of energy on ultrafast timescales and particularly on the timescale of the excitation pulse in ultrashort laser irradiated dielectric materials are key elements for enabling processing precision beyond the optical limit. Transforming matter on mesoscopic scales facilitates the definition of nanoscale photonic functions in optical glasses. On these timescales, quantum interactions induced by charge non-equilibrium become the main channel for energy uptake and transfer as well as for the material structural change. We apply a first-principles model to determine dynamic distortions of energy bands following the rapid increase in the free-carrier population in an amorphous dielectric excited by an ultrashort laser pulse. Fused silica glass is reproduced using a system of (SiO4)4- tetrahedra, where density functional theory extended to finite-temperature fractional occupation reproduces ground and photoexcited states. Triggered by electronic charge redistribution, a bandgap narrowing of more than 2eV is shown to occur in fused silica under geometry relaxation. Calculations reveal that the bandgap decrease results from the rearrangement of atoms altering the bonding strength. Despite an atomic movement impacting strongly the structural stability, the observed change of geometry remains limited to 7% of the interatomic distance and occurs on the femtosecond timescale. This structural relaxation is thus expected to take place quasi-instantly following the photon energy flux. Moreover, under intense laser pulse excitation, fused silica loses its stability when an electron temperature of around 2.8eV is reached. A further increase in the excitation energy leads to the collapse of both the structure and bandgap.

Reusable microfluidic chip processed by femtosecond double-pulse-assisted polarization-selective etching in fused silica glass

Reusable microfluidic chip processed by femtosecond double-pulse-assisted polarization-selective etching in fused silica glass

Inkjet‐Printed Piezoelectric Thin Films for Transparent Haptics

AbstractTransparent thin‐film piezoelectric transducers are attractive for haptic displays. However, for their widespread use in consumer electronics, innovative and cost‐effective processing methods need to be developed. In this contribution the effectiveness of the deposition of lead zirconate titanate thin films by inkjet printing for the fabrication of haptic devices is demonstrated. The 1,3‐propanediol solvent is used to prepare effective inkjet‐printing inks from chemical solution deposition solutions. The printed thin‐film structures on fused silica glass substrates are 900 nm thick and strongly {100} oriented perovskite phase is detected in X‐ray diffraction patterns. To fabricate devices, interdigitated capacitors and SU‐8 insulation layers are deposited on top of the printed lead zirconate titanate. Dimensions of the final device are 15.7 × 3.4 mm2. A standing antisymmetric Lamb wave is observed at 63.3 kHz, with out‐of‐plane displacement reaching 2 µm at an applied voltage of 100 V. This value exceeds the limit at which the texture rendering function can be induced in the device. Good functional performance of the device is linked with good electromechanical properties of the printed piezoelectric, with permittivity ε ′ and piezoelectric coefficient e33,f values of 1000 and 7.7 C m−2, respectively, which are comparable to films prepared by standard spin‐coating process.