Search

A probe was developed to detect biomolecular binding events on a substrate in the microwave regime in real time and without labels. The probe consists of a coplanar transmission line fabricated on a glass slide that can detect dielectric changes in close proximity of the substrate-liquid interface. The probe behavior was evaluated by adsorbing polyelectrolyte monolayers of alternating charge. Biomolecular detection was demonstrated by immobilizing protein A on the glass surface and detecting rabbit IgG molecules in a flow channel. The sensitivity of the probe was conservatively estimated to be ~100 pg/mm 2 .

A technique based on photothermal deflection spectroscopy has been developed for measuring the absolute absorption of polymers. The technique utilizes the frequency dependence measurement of the deflection signals to retrieve polymers' thermal properties and experimental parameters that are necessary to convert the deflection signals to the absolute absorption coefficients. All the measurements are done on the same experimental setup and the same sample without the need of obtaining either the materials' thermal properties or the reference absorption coefficients from other sources. This technique has been applied to several polymers and the results are reported.

We demonstrate a GaAs/AlGaAs multiple-quantum-well in-line fiber optic intensity modulator. Based on evanescent wave coupling between a GaAs/AlGaAs anti-resonant reflective optical waveguide and a side-polished single mode fiber, this device concept combines the inherent advantages of in- line fiber devices with high-performance GaAs integrated optoelectronics. The GaAs waveguide utilizes distributed Bragg reflector mirrors, which are designed to provide maximum reflection at a given more angle, to phase-match to the low-index fiber. Intensity modulation of the transmitted light through the fiber is achieved by changing the complex propagation constant of the GaAs waveguide through the quantum-confined Stark effect. Typical device shows an on/off ratio of 4:1, with an applied voltage of 9V. Calculations show that with a longer interaction region, an on/off ratio of more than 40dB is achievable with the same applied voltage.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The weak absorption of waveguide materials can be measured by Photothermal Deflection Spectroscopy (PDS) with two orders of magnitude or higher sensitivity than conventional UV-VIS absorption spectroscopy. While it is easy to obtain relative absorption spectra for thin polymer films with PDS, extracting absolute absorption coefficients is more involved. The PDS measured signals depend on both thermal and optical absorption properties of materials. Knowledge of thermal properties is necessary to extract absorption coefficients. We report a methodology to obtain from PDS independently the thermal properties and absolute absorption coefficients.

A GaAs/AlGaAs in-line fiber optic filter for wavelength division multiplexing applications is demonstrated. The device consists of a GaAs/AlGaAs anti-resonant reflecting optical waveguide (ARROW) evanescently coupled to a single mode fiber. At certain discrete wavelengths, light is coupled from the fiber to the ARROW, due to phasematching conditions. Sharp resonances are observed around the design wavelength of 830 nm. The 3 dB cutoff bandwidth for TE polarization is 0.5 nm and the rejection ratio is 9 dB.

We are developing a traveling electro-optic modulator for analog microwave modulated fiber optic links used in radar applications. The modulator is a polymer in-line fiber device that has a rugged and low loss interface to single mode fibers and can be engineered to provide linear modulation over a large dynamic range. In the development of the modulator we take advantage of a variety properties available in polymers. The ability to deposit a conformal electro-optic thin film is used to fill the gaps between high-frequency co-planar electrodes and thus obtain a good overlap between the electric field produced by the the microwave electrodes and the fields in the optical fiber and the electro-optic waveguide. Reactive ion etching of the electro-optic polymer is used to trim the thickness of the polymer waveguide to obtain operation at a specific wavelength. The thermo-optic effect is used to fine tune the operation point of the modulator to obtain a large dynamic range. The geometry of the modulator permits operation close to the absorption peak of the electro-optic polymer and this provides the opportunity to take advantage of the resonant enhancement of the nonlinearity in the vicinity of an absorption band.

We review our recent research in the field of photochromic polymeric structures for optical data storage and nonlinear optics. We unity some of the sub-themes of azopolymer structures in the light of photo-induced movement of azobenzene molecules. In particular, we discuss photo-induced effects in supramolecular assemblies containing azobenzene molecules (e.g. Langmuir-Blodgett-Kuhn structures and ultrathin silane layers). Reorientation of azobenzenes in these structures will be compared to that observed in spin-cast films. Photoisomerization and photo-induced orientation of azobenzene molecules is also studied at the molecular level by means of azosilane molecules chemisorbed on Silicon Oxide substrates. We establish a correlation between polymer architecture and sub-glass transition temperature (Tg) light-induced molecular movement in high Tg nonlinear optical azo-polyimide polymers. We show that the isomerization reaction itself depends on the polymer molecular structure, and we present evidence of light-induced molecular movement 325 °C below Tg of a rigid NLO azo-polyimide polymer containing no flexible connector or tether.

A micromachined optical 'trap' to capture and move micron sized dielectric particles is presented. The trap consists of four single mode optical fibers mutually aligned to have a common optical beam intersection at the center of a micromachined housing. The intersection of the beams forms an optical 'cross-hair' which captures dielectric microparticles with a strong optical gradient force field, and holds them for further manipulation, visualization, and/or analysis. The stability and magnitude of the trapping force fields are comparable to the single beam 'optical tweezers' technique, but are considerably more versatile.

One might say this paper is about something old, something new, something borrowed, something blue -- finding chromophoric brides to be wed to polymeric husbands. Several dyes have been synthesized that are red, magenta, or blue in color and have large ground-state dipole moments. Dyes synthesized in our laboratory were characterized by differential scanning calorimetry and UV-VIS spectroscopy. First molecular hyperpolarizabilities ((beta) o) of the dyes were calculated using MOPAC (V6). Some of the dyes were dissolved in poly(methyl methacrylate), corona poled above the glass transition temperature, and cooled to room temperature to freeze in the polar order. Second-order nonlinear optical properties of these guest-host films were compared by optical frequency doubling measurements.

This paper discusses the development of two materials as AR coatings for thinned backilluminated charge-coupled devices. The first material is the heavy metal oxide Ta205 deposited as a spin on layer using sol-gel technology. The second material is Si3N4. Both these films have the high index of refraction and low absorption coefficients needed to produce good AR coatings in the near UV down to 300 nm. The goal of the program was to produce a coating which would yield devices with quantum efficiencies of greater than 50 at 300 nm. Both these materials satisfy this goal. Data on test devices will be reported. . 1.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Reflection-mode interference modulators can be used in electrical-to-optical interconnects. Prototype devices were implemented using poled nonlinear polymer films. The modulators were characterized and analyzed. It is shown that a modulation depth exceeding 10% is feasible using existing nonlinear polymers.

The electro-optic properties of polymeric materials are characterized using Fabry-Perot etalons in which the polymeric layer acts as the spacer layer. This technique is particularly useful since the etalon converts small electric field induced changes in the index of refraction of the spacer layer to changes in the overall transmittance and reflectance of the structure. In this paper we show that using angle tuning, the transmission characteristics of the Fabry-Perot etalons fabricated on glass substrates can be sufficiently characterized to allow for determination of the electro-optic coefficients of the spacer layer material. We also present experimental results of novel reflection mode etalons fabricated on Si. These structures exhibit a large change in reflectance as a function of the optical path length inside the etalon cavity. When fabricated with an electrooptic spacer layer, the reflectance can be modulated by applying an electric field. Reflection mode devices can also be used to study the properties of new eleciro-optic materials and also show promise for use as Si compatible modulators.

A method to produce guided wave second harmonic generation (SHG) in coated multimode optical fibers is described and analyzed. The fiber cores are coated with a highly nonlinear hemicyanine dye by the Langmuir/Blodgett technique. This technique allows precise control over the film thickness to one monolayer (-3 nm). Deposition ratio data indicate that the deposition forms a noncentrosymmetric (Z-type) film. The SHG signal increases as a function of the film thickness for up to 80 monolayers (-240 nm) of dye.Analysis for calculating the propagation constants and energy distributions of the fundamental and harmonic modes is used to determine the requirements for phase matching in the composite fiber-film system. For most cases of interest the effective index of refraction for a given film mode in the coated region may be closely approximated by the propagation constant in a planar waveguide of equal thickness. The conditions for phase matching and selective excitation of modes for improved SHG efficiency are proposed.Efficient SHG in coated fibers could prove useful in frequency doubling of lasers. They would be more compatible with fiber optic communications systems than currently used single crystal and channel waveguide doublers. In addition, demonstration of SHG suggests that other second order nonlinear effects (i.e. linear electro-optic effect, parametric amplification) may be produced in a Langmuir/Blodgett (L/B) nonlinear film coated fiber system.