Mark P. Andrews

Ultraviolet light imprinted sol-gel silica glass waveguide devices on silicon

Abstract We describe a new simplified process for inexpensive fabrication of low-loss (0.1 dB/cm) glass waveguides on silicon by ultraviolet light imprinting in photosensitive, organically modified sol-gel silica glass films prepared by one-step dip-coating process. The fabrication process is appealing because the buffer layer between waveguide and substrate is eliminated, and waveguides can be made in a few steps using low-cost equipment. Also, a 1 × 8 power splitter is produced by this process. The splitter exhibits relatively uniform output and a configuration loss of 0.9 dB at 1.55 μm wavelength.

Ultraviolet light imprinted sol-gel silica glass low-loss waveguides for use at 1.55 μm

The fabrication and characterization of UV-light-imprinted solgel silica glass waveguides on glass and silicon substrates are described. Waveguide fabrication parameters are evaluated. Appropriate combinations of UV light exposure time, sol-gel film thickness, and postbake time produce waveguides suitable for use at a 1.55-?m wavelength. Propagation losses in these waveguides are less than 0.3 dB/cm.

EPR spin trapping and 2-deoxyribose degradation studies of the effect of pyridoxal isonicotinoyl hydrazone (PIH) on *OH formation by the Fenton reaction.

The search for effective iron chelating agents was primarily driven by the need to treat iron-loading refractory anemias such as beta-thalassemia major. However, there is a potential for therapeutic use of iron chelators in non-iron overload conditions. Iron can, under appropriate conditions, catalyze the production of toxic oxygen radicals which have been implicated in numerous pathologies and, hence, iron chelators may be useful as inhibitors of free radical-mediated tissue damage. We have developed the orally effective iron chelator pyridoxal isonicotinoyl hydrazone (PIH) and demonstrated that it inhibits iron-mediated oxyradical formation and their effects (e.g. 2-deoxyribose oxidative degradation, lipid peroxidation and plasmid DNA breaks). In this study we further characterized the mechanism of the antioxidant action of PIH and some of its analogs against *OH formation from the Fenton reaction. Using electron paramagnetic resonance (EPR) with 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap for *OH we showed that PIH and salicylaldehyde isonicotinoyl hydrazone (SIH) inhibited Fe(II)-dependent production of *OH from H2O2. Moreover, PIH protected 2-deoxyribose against oxidative degradation induced by Fe(II) and H2O2. The protective effect of PIH against both DMPO hydroxylation and 2-deoxyribose degradation was inversely proportional to Fe(II) concentration. However, PIH did not change the primary products of the Fenton reaction as indicated by EPR experiments on *OH-mediated ethanol radical formation. Furthermore, PIH dramatically enhanced the rate of Fe(II) oxidation to Fe(III) in the presence of oxygen, suggesting that PIH decreases the concentration of Fe(II) available for the Fenton reaction. These results suggest that PIH and SIH deserve further investigation as inhibitors of free-radical mediated tissue damage.

Sol-gel waveguide fabrication parameters: an experimental investigation

Waveguides have been fabricated by a hybrid organic- inorganic glass sol-gel process and ultraviolet-light exposure. The ad- justment of chemical composition of the materials provides precise se- lection of the refractive index from 1.48 to 1.52 at the wavelength of 632.8 nm. The effect of ultraviolet-light exposure and heat treatment on the refractive index is studied. Ultraviolet-light inscription has been em- ployed to produce ridge waveguides with smooth sidewalls.

Overview of sol-gel guest-host materials chemistry for optical devices

This paper gives an overview of opportunities for sol-gel glass guest-host materials chemistry in the area of glass integrated optics, glass integrated optics on silicon, from the perspective of optical devices and components. Our discussion locates sol-gel glass processing among several available and competing processes such as flame hydrolysis deposition and chemical vapor deposition for producing glass optical devices and components. For the most part, these are high temperature processes. Hybrid sol-gel glass chemistry (HSGG) is reviewed as an adaptable, potentially low cost, high volume, very low temperature alternative. HSGG offers an outstanding range of materials tunable in properties from ones that are closely related to organic polymers, to ones that are indistinguishable from high temperature inorganic glasses. HSGG gives the designer material compositions and properties that can be adapted to an enormous range of photonics attractive for their use in hybrid opto-electronic circuits. Reliability issues, packaging and interconnect challenges to the implementation of these materials are enumerated for the example of electro-optic modulation.

Organoaluminophosphate sol-gel silica glass thin films for integrated optics

We report on the fabrication and characterization of waveguide thin films on silicon by ultraviolet light imprinting in a new photosensitive, organically modified aluminophosphate sol-gel silica glass prepared by a one-step dip-coating process. Appropriate combinations of ultraviolet light exposure time, sol-gel film thickness and postbake parameters produce waveguides suitable for optical telecommunication applications.

Gratings fabrication by ultraviolet light imprinting and embossing in a sol-gel silica glass

We present simple, low temperature methods for inexpensive fabrication of gratings in a photosensitive, organically modified silicate (ORMOSIL) system for integrated optical applications. The material is prepared by the sol-gel method. Gratings are made by UV imprinting through a mask and by an embossing technique. In the first case, UV exposure induces a refractive index change of (Delta) n equals 0.005 in the film and results in an index modulation type grating. Relief type gratings are made by mechanical embossing. Gratings are compared and characterized in terms of diffraction efficiency and grating period.

Visible laser self-focusing in hybrid glass planar waveguides.

We report that self-focusing occurs with simultaneous self-inscription of a cylindrical waveguide when 514.5-nm light from a cw argon-ion laser propagates in a solgel-derived silica methacrylate hybrid glass planar waveguide. Spatially localized free-radical polymerization of methacrylate substituents is initiated in the path of the guided wave. This causes intensity-dependent refractive-index changes that lead to self-lensing and focusing. A channel waveguide evolves in the matrix, which supports fundamental and higher-order optical modes and suppresses diffraction of the beam.

Sol-gel glass waveguides with Bragg grating

A vectorial coupled mode theory is used to analyze sol-gel ridge waveguides with UV-light-imprinted Bragg gratings. The effect of device parameters on the grating reflectivity is investigated. It is shown that 100% reflectivity for both TE and TM modes can be achieved using short (1 to 2 mm) gratings. The measured reflectivity in a ridge waveguide with a grating agrees with the theoretical predictions for TE and TM modes.

UV-light-imprinted surface, ridge, and buried sol-gel glass waveguides and devices on silicon

New processes are developed to produce surface, ridge and buried sol-gel glass waveguides by photo-inscription using a ultraviolet light source. The fabricated waveguides demonstrate very low propagation losses (approximately 0.1 dB/cm). Several integrated optical devices such as cascaded Y-branch power splitters, directional couplers, Mach-Zehnder interferometer wavelength division multiplexers have also been produced.