Curtis E. Banks

Organic and inorganic crystals for electro-optic modulators with low driving voltage

The focus of this paper is the characterization of electro- optic properties of single crystal thin films of organic material NPP grown by the plate-guided method. Characterization was performed using the longitudinal a.c. modulation technique. Half-wave voltage V(pi ), figure- of-merit F, and electro-optic coefficient r63 were estimated to be 3.24 kV, 0.98x10-10 m/V and 25.8x10-12 m/V respectively. We found that crystalline z-axis is off the normal to the plane of the film at an angle of 7 degree(s). We also proposed a transverse version of a thin film electro-optic modulator with low driving voltage, which is based on a single-arm thin film waveguide interferometer.

Acoustic emission felicity ratio measurements in carbon composites laminates using fiber Bragg grating sensors

In light of ongoing efforts to reduce weight but maintain durability, designers have examined the use of carbon composite materials for a number of aerospace and civil structures. Along with this has been the study of reliable sensing and monitoring capabilities to avoid catastrophic failure. Fiber Bragg Grating (FBG) sensors are known to carry several advantages in this area one of which is their proven ability to detect acoustic emission (AE) lamb waves of various frequencies. AE is produced in these materials by failure mechanisms such as resin cracking, fiber debonding, fiber pullout and fiber breakage. With such activity there is a noticeable change in Felicity Ratio (FR) in relation to the increase of accumulated damage. FR is obtained directly from the ratio of the stress level at the onset of significant emission and the maximum prior stress at the same AE event. The main objective of this paper is to record the FRs of a carbon/epoxy laminate using FBG sensors and establish its trend as a method for determining accumulated damage in a carbon composite structure.

Nonlinear optical waveguides based on metal nanocluster composites produced by ion beam implantation

We present the results of analysis of microstructural and optical properties of composite nonlinear optical waveguides made by ion implantation of LiNbO3 with MeV ions of silver. Light guiding properties were studied by the prism coupling method, and nonlinear optical susceptibility was characterized using the Z-scan method. Special attention was paid to the influence of a host material and heat treatment on light guiding, optical absorption, and third order susceptibility.

Experimental investigation on acousto-ultrasonic sensing using polarization-maintaining fiber Bragg gratings

This report discusses the guided Lamb wave sensing using polarization-maintaining (PM) fiber Bragg grating (PM-FBG) sensor. The goal is to apply the PM-FBG sensor system to composite structural health monitoring (SHM) applications in order to realize directivity and multi-axis strain sensing capabilities while reducing the number of sensors. Comprehensive experiments were conducted to evaluate the performance of the PM-FBG sensor attached to a composite panel structure under different actuation frequencies and locations. Three Macro-Fiber-Composite (MFC) piezoelectric actuators were used to generate guided Lamb waves that were oriented at 0, 45, and 90 degrees with respect to PMFBG axial direction, respectively. The actuation frequency was varied from 20 kHz to 200 kHz. It was shown that the PM-FBG sensor system was able to detect high-speed ultrasound waves and capture the characteristics under different actuation conditions. Both longitudinal and lateral strain components in the order of nano-strain were determined based on the reflective intensity measurement data from fast and slow axis of the PM fiber. It must be emphasized that this is the first attempt to investigate acouto-ultrasonic sensing using PM-FBG sensor. This could lead to a new sensing approach in the SHM applications.

Fabry-Perot Interferometer-Based Electrooptic Modulator using LiNbO3 and Organic Thin Films

Investigation of electro-optic modulation in nonlinear materials placed within a Fabry-Perot modulator cavity is presented. Enhanced modulation at lower driving voltages is demonstrated in several materials including, LiNbO3 as well as thin films of organic compounds like COANP and NPP. Associated mechanical factors contributing to modulation are also described.

Electrical field effects in phthalocyanine film growth by vapor deposition

Phthalocyanine films have been synthesized by vapor deposition on quartz substrates. Some substrates were coated with a very thin gold film for introducing electrical fie.d These films have been characterized by x-ray diffraction and scanning electron microscopy. The films have excellent chemical and optical stability. However, the surface of these films grown without electrical field shows whisk-like morphology. When films are deposited under an electrical field, a dense film with flat surface is obtained. A change of film in growth orientations and solid state phase is also observed for the film synthesized under electrical fields.

Growth and characterization of single-crystal organic thin films for electro-optic modulators

Organic materials with large electro-optic coefficients are promising for fabrication of fast electro-optic modulators with low driving voltage. In this paper we describe the growth of micron-thick single crystal films of various electro-optic organic materials from melt using the plate- guided method. The compounds such as mNA, COANP, NPP, PNP, MBANP and DAST will be considered. The films are grown using a homemade facility, which allows to control melting and recrystallization rate and to observe the process with an optical polarizing microscope. A single crystal films will make up a planar optical waveguide integrated with a coupling prism. The light will be injected into the film using the prism. Then, after traveling a certain distance within the film, the light will be decoupled. Combination of high electro-optic coefficients of the film (10 to 100 pm/V) with relatively long travel distance of the light beam (5 mm and more) potentially gives a driving voltage of the phase modulation of the beam of 5 V and less. This is very important for the incorporation of the modulator into a standard low voltage electronic circuitry. The phase modulation can be converted into amplitude modulation using various interferometer schemes such as Mach-Zehnder (M-Z) scheme with external arm, M-Z with internal arm, polarimetric waveguide interferometer, and dual-mode single- arm interferometer. We will provide some experimental data showing the advantage of the dual-mode single-arm scheme. Potential modulation rate of the system can be 10 dB and higher.

Transmission measurements of the third-order susceptibility of gold

Gold nanoparticle composites are known to display large optical nonlinearities. In order to assess the validity of generalized effective medium theories (EMTs) for describing the optical properties of metal nanoparticle composites, we have used the z-scan technique to measure the third-order susceptibility of gold nanoparticle composites across the entire range of fill fractions. These materials range from low concentration statistically random gold sols, to aggregated thin (two-dimensional) composite films, to quasi-bulk thin films above the percolation threshold. These measurements allow the nonlinearity of gold to be determined both directly and by deduction from applicable effective medium theories. We compare our results with predictions which ascribe the nonlinear response to a Fermi-smearing mechanism. We demonstrate that the nonlinear susceptibility changes sign due to a phase shift between the applied field and the local field, and that this sign change occurs at the percolation threshold. Further for films whose thickness is less than an optical wavelength we introduce a 2D form of the Maxwell Garnett model.

Fabrication of MEMS using liquid jet dispensing technique

We describe a simple yet efficient technique of delineation of various polymer MEMS structures using computer driven liquid jet dispenser. A syringe-type dispenser with a replaceable needle is filled with a polymer solution and mounted on a vertical translation stage. The substrate is mounted on two-coordinate horizontal translation stage. Additional vertical translation arm is connected to the plunger of the syringe. Vertical translation provides positioning of the needle at a certain height over the substrate. Delineation is accomplished when the syringe plunger, being pushed down by the vertical translation arm, dispenses the liquid on the substrate at a programmable flow rate simultaneously with horizontal motion of the substrate with respect to the needle. Horizontal motion is done along a programmable trajectory at a programmable sped. Comparing to conventional methods, the proposed device consumes three order of magnitude less amount of material for the fabrication of similar MEMS structures. In addition, we describe a supplement to the liquid delineation system in the form of a microscope objective head connected to a noncoherent UV source with a multimode optical fiber. The head can serve as a tool for UV curing of the polymer material deposited with the jet dispenser as well as a separate UV writing tool. In conclusion, we describe the calculation technique for the distribution of the electric field in electrically or optically controlled ferroelectric polymer MEMS fabricated by the proposed technique.

Upconverted photobleaching and nonlinear effects of optical beam self-action in dye-doped polymer waveguides

We report on optical beam self-action in a waveguide made of poly(methyl methacrylate) doped with laser dye DCM upon its upconverted photobleaching produced by radiation of a low power CW He-Ne laser. Nonlinear effects of self-action produce spatially stable beam structures usually interpreted as dark spatial solitons in media with negative Kerr-like nonlinearity. We demonstrate experimentally that the proposed mechanism of self-action is more likely upconverted photobleaching, i.e. photobleaching by short wavelength radiation resulting from frequency upconversion of the primary red laser light. Upconversion is not a multi-photon process. It possibly occurs as a result of inhomogeneous line broadening and excitation of thermally populated higher vibrational energy states in the ground state of the dye molecules. Theoretical model of beam propagation is based on the Shrodinger-type nonlinear propagation equation complemented by the rate equation for photobleaching. The result of simulations are in good agreement with experimental data. Possible applications of the studied effects include photonic switching and optical interconnects.