The absorption spectra of methyl red (MR) dissolved in methanol, ethanol, dimethyl sulfoxide, and hexane were measured. It was found that the peaks of the absorption spectra of MR solutions shifted toward shorter wavelengths with increasing solvent polarity. Using the Z-scan method, the nonlinear optical properties of the four kinds of MR solutions were determined at wavelength 441.6 nm. The effective nonlinear indexes of refraction (n2) of MR solutions increased with the increasing thermo-optical coefficients of the solvents. In addition, the optical limiting effects of the MR solutions were investigated at 441.6 and 535 nm, and the results indicate that they possessed strong optical limiting effects.
A polymer based biochip for rapid 2-D separations of peptides, proteins, and other biomedically relevant molecules was
designed and fabricated. Like traditional 2D polyacrylamide gel electrophoresis (2D-PAGE) methods, the device will
allow molecules to separate based on isoelectric point (pI) and molecular weight (MW). The design, however, integrates
both an initial capillary isoelectric focusing (cIEF) step followed by capillary electrophoresis (CE) in multiple parallel
channels, all on a single microfluidic chip. Not only is the "lab-on-a-chip" design easier to use and less expensive, but
the miniaturization of the device produces very rapid separations, on the order of seconds. Fluorescence detection will
be used in the preliminary stages of testing, but the device is also equipped with integrated electrodes in the
electrophoresis channels to perform multiplexed electrochemical detection for quantitative analysis. We present the chip
design and fabrication, as well as the initial test results demonstrating cIEF and CE with one analyte. Furthermore, we
introduce preliminary work on the use of a polyacrylamide gel in the electrophoresis channels.
Thermooptic switches are viable options for rapidly and reliably switching and routing optical signals in planar
lightwave circuits. We present modeling and fabrication of a thermooptic switch made of the polymer SU-8, an epoxy
resin commonly used as a MEMS structural material. SU-8 is a good candidate material for use in planar waveguides
due to its high refractive index, good transmission properties in the visible and infrared, and excellent thermal and
mechanical stability. Furthermore, it has great advantages in fabrication since it is used as a negative photoresist, and
so can be patterned directly using photolithography. Light is guided by a refractive index gradient generated by
embedded MEMS microheaters, which activate the thermal nonlinearity of the polymer. The thermooptic change in
refractive index imparts an inhomogeneous phase shift to the beam in the waveguide, which guides the input into one of
two or more outputs. The switch design and operation parameters have been optimized using simulations of the
thermal profile using finite element modeling and of the optical propagation using the beam propagation method.
The finite difference beam propagation method (FD-BPM) is an effective model for simulating a wide range of optical waveguide structures. The classical FD-BPMs are based on the Crank-Nicholson scheme, and in tridiagonal form can be solved using the Thomas method. We present a different type of algorithm for 3-D structures. In this algorithm, the wave equation is formulated into a large sparse matrix equation which can be solved using iterative methods. The simulation window shifting scheme and threshold technique introduced in our earlier work are utilized to overcome the convergence problem of iterative methods for large sparse matrix equation and wide-angle simulations. This method enables us to develop higher-order 3-D wide-angle (WA-) BPMs based on Pade approximant operators and the multistep method, which are commonly used in WA-BPMs for 2-D structures. Simulations using the new methods will be compared to the analytical results to assure its effectiveness and applicability.
A polymer based biochip for rapid 2D separations of peptides, proteins, and other biomedically relevant molecules was designed and fabricated. Like traditional 2D polyacrylamide gel electrophoresis (2D-PAGE) methods, the device will allow molecules to separate based on isoelectric point (pI) and molecular weight (MW). Our design, however, integrates both an initial capillary isoelectric focusing (cIEF) step followed by capillary electrophoresis (CE) in multiple parallel channels, all on a single microfluidic chip. Not only is the "lab-on-a-chip" design easier to use and less expensive, but the miniaturization of the device produces very rapid separations. Compared to traditional 2D-PAGE, which can take hours to complete, we estimate separation times on the order of seconds. Fluorescence detection will be used in the preliminary stages of testing, but the device also is equipped with integrated electrodes in the electrophoresis channels to perform multiplexed electrochemical detection for quantitative analysis. We will present preliminary results of the chip development and testing.
The finite difference beam propagation method (FD-BPM) is an effective model for simulating a wide range of optical waveguide structures. We present results of simulations combining this method with finite element modeling of thermal effects using Comsol FEMLAB software. These simulations were developed and are used to examine propagation of optical signals in polymer waveguides in which inhomogeneous temperature profiles are induced using MEMS microheaters, for example, for use in switching applications. Thermal modeling combined with values of the thermo-optic nonlinearity yields three-dimensional refractive index profiles in the active regions of a variety of waveguide structures. The change in the refractive index profile of cladding induces mode deformations and transmission losses due to leakage at the core/cladding interface, in addition to phase shifts in the propagating beams. These effects are used to design thermo-optic switches in both multimode and single mode waveguides, and study the direct effect on propagation due to changes in the applied heater power. In addition, we demonstrate the utility of applying the method to assessing losses due to thermally induced inhomogeneities in planar lightwave circuits such as optical interconnects.
Polydiacetylene microcrystals in a water suspension or a polymer matrix were prepared by a simple precipitation procedure in order to obtain a thin samples with good optical quality maintaining the characteristics of crystalline materials. The nonlinear refraction, n2, and nonlinear absorption, (beta) , around the exciton peak were measured by z-scan method using a tunable picosecond laser. The signs of the n2 are positive/negative at wavelengths shorter/longer than the exciton peak and strong saturable absorption, which (beta) is negative, are observed around the peak. The largest n2 was obtained to be plus 0.024 cm2/GW (Re(chi(3) equals plus 1.4 multiplied by 10-9 esu) at 640 nm for a gelatin composite film containing 24 wt percent of polydiacetylene microcrystals.
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