The TWIST platform is an optical evanescent wave sensor which enables a label-free immunoassay-based portable
instrument. The approach is based on input grating coupler sensors serving as functionalized sensing devices. Binding of
the target analyte to the receptor-coated grating is detected by wavelength interrogation in the telecom spectral range.
We have demonstrated that high performance volumetric sensing can be achieved using a compact, low-cost telecom
laser as light source. The system footprint including light source, detectors and digitizers is compact. The platform is
amenable to multiplexed operation. We demonstrated a two-output system which enables detection of an analyte with an
on-chip reference signal.
We demonstrate a post-growth in-situ chlorine passivation for suppressing surface-dominant transport in Si nanowires
(SiNWs). The leakage current of bridged SiNWs suppressed more than five orders of magnitude as a result of chlorine
passivation while the shape and structural properties of the bridging NWs remain unaffected by the post-growth in-situ
HCl passivation. The chlorine passivated SiNW surfaces were found to be beneficial to enhance the high immunity to
environmental degradation.
The growth of crystalline 1D nanowires of semiconductors on non-epitaxial surfaces holds the promise to overcome
many of the current challenges of heteroepitaxial material synthesis and device fabrication for a wide range of electronic
and photonic applications. Nano-heteroepitaxial bridging of CVD grown nanowires potentially enables a low cost and
mass-manufacturable approach to nanowire based device fabrication. Here we report the synthesis and bridging of lateral
silicon nanowires between a pair of vertical non-single crystal surfaces and application of this technique in the design
and fabrication of waveguide-integrated photodetectors. The device consists of a number of 1D nanowires laterally
grown across gaps etched into rib optical waveguides with an amorphous silicon oxynitride core and silicon oxide
claddings. A pair of phosphorous-doped polysilicon electrodes was deposited on the walls of the waveguide gap for
electrical interfacing of the nanowires to collect the photocurrent under optical excitation. Characterization results
demonstrated good waveguide characteristics, high electrical isolation between the electrodes, low leakage current and
distinct photoresponse from the bridged nanowires. This implementation of silicon nanowires on polysilicon combines
the characteristics of crystalline 1D nanowires with the flexible fabrication processes on non-single-crystal silicon
platforms facilitating advances in silicon photonics and beyond.
A planar optical waveguide with an input grating coupler was used as an affinity-based
biodetection device. Nanoimprint lithography was used to integrate the grating patterns with
low loss silicon oxynitride thin-film waveguides. A widely tunable laser source at 1550nm was
used to characterize the device sensitivity to bulk medium changes, to thin film adsorption, and
to streptavidin protein. For each test, a comparison was performed between the sensitivity of
wavelength interrogation and the more standard angular interrogation approach. The effects of
surface reflections on the measured coupling curves were observed and interpreted, with
mitigation options being considered.
We have evaluated several methods for generating multi-color emission for IR scene projector applications. The baseline requirements we employed were the ability to simulate color temperatures in the range 300-3000 K, minimum radiance levels consistent with existing IR sensor requirements, 1000 Hz frame rates and manufacturability. The analysis led us to down select two independent approaches that are capable of meeting HWIL multicolor requirements. We describe and discuss each of the approaches, their expected performance as well as their limitations.
This work focuses on the effects of custom-designed, two-dimensional grating structures on the sensitivity of optical
waveguides biosensors in the input grating coupler configuration. Calculations suggest that suitably designed diffractive
structures with optimum pitch in two orthogonal directions can increase the sensitivity of devices when compared to a
conventional one-dimensional grating under the same conditions. A set of six diffractive structures designed for 1550 nm
wavelength were fabricated by thermal nano-imprint lithography on silicon oxynitride waveguides; the silicon master
stamp was patterned by deep UV stepper lithography. Preliminary experimental results indicate a sensitivity
enhancement of a factor two due to the 2D diffractive couplers.
Grating-based optical waveguide devices offer label-free biodetection capabilities relying on optical
response to adsorption of analytes and corresponding changes of refractive index. Various
configurations of this measurement approach were explored with the goal of obtaining a
miniaturized system. In particular, we evaluated the use of a two-dimensional grating coupler both
experimentally and theoretically. Design criteria for optimized sensing structures are presented.
Silicon oxynitride optical waveguides with a grating coupler were used for a label-free detection approach that measures the change of refractive index at the grating surface. Two approaches were used for the grating fabrication: (i) commercially available linear gratings were used as stamps for imprint lithography and the pattern was transferred by dry-etching; (ii) polystyrene microspheres self-assembly in an ordered close-packed array was exploited to obtain a two-dimensional grating with hexagonal symmetry. Optical coupling into slab waveguides of both visible (633nm) and tunable infrared (1550 nm) lasers was characterized as a function of incident angle in a custom-made automated apparatus. Sensitivity to different aqueous solutions was demonstrated with low loss waveguides fabricated using low-frequency plasma-enhanced chemical vapor deposition. The exploitation of the tunability of telecom infrared lasers and of the two-dimensional hexagonal grating coupler has the ultimate goal of providing a high performance, compact sensor that does not require mechanical moving parts.
Organic light emitting diode (OLED) based displays are well suited for fabrication on flexible polymer substrates. In order to achieve the vision of a highly flexible, rollable display, significant progress must be made in understanding and overcoming the mechanical limitations of the component materials. Methodologies and metrics for evaluating thin film components as well as full devices on flexible substrates need to be developed and standardized. A new technique for bend testing is described here and compared to a more traditional technique. One thin film component of flexible OLEDs that must be very mechanically robust is the permeation barrier. It is desirable to have a rapid method to characterize the onset of cracking upon bending of a barrier-coated substrate. We have developed a convenient method that allows characterization of mechanical cracking of flexible permeation barriers. In addition, transparent conductors with mechanical properties superior to those of ITO are desired for improved flexibility of displays. We report dramatically improved mechanical properties of multilayer ITO-Ag-ITO films that also exhibit excellent electrical and optical properties. Finally, we show preliminary results from bend tests of complete OLED devices on polymer substrates. The results demonstrate that in addition to evaluating component materials, other factors must be considered for integrated devices, and further investigation on this subject is needed.
We demonstrate arrays of light guides that are fabricated in sheets and laminated together to form tapered plastic fiber optic bundles that can be used to produce large seamlessly tiled displays.
A large seamless display that could be set up rapidly, operated effectively, and moved quickly would be a great value to the military. Such a display system would be even more beneficial if it consisted entirely of easily available, commercial, off-the-shelf components, not dependent on a single supplier. We have designed a seamlessly tiled projection system to meet these needs. The system consists entirely of easily available, commercial, off-the-shelf equipment. We created software that records the location of projected images as detected by a digital camera, computes the movements necessary to align the images, and drives the projection lenses to align the seamlessly tiled display. We developed a method for rapid mechanical mounting of the projectors and camera. We chose commercial folding stands and a mirror-based alignment method that accelerated the mechanical setup. In field trials, our prototype was operational within one-half hour of opening the shipping cases.
We have developed a mechanical, optical and digital system based only on commercially available equipment to allow a seamlessly tiled projection display system to be set up and aligned very rapidly. Using a digital camera and motorized projectors, our prototype system can be unpacked, aligned, and put into use within a half-hour. To minimize the number of projectors for a given pixel count, we do not overlap the projected fields and we do not move the images by digital displacement within the projected field. We use motorized lens mounts to displace the images to proper positions for tiling, a method that does not induce keystone distortion. The movement is under control of a digital camera using an image-processing system, making it unnecessary for an operator to control the movement of the lenses.
KEYWORDS: Composites, Actuators, Particles, Glasses, Polymers, Photonic crystals, Crystals, Simulation of CCA and DLA aggregates, Spectroscopy, Reflectivity
Physically robust photonic bandgap (PBG) composites based on electrostatically stabilized polymeric colloidal particles are presented. The glass transition (Tg)of the composites can be varied over a large temperature range through the selection of the monomer(s) used to fabricate the composite. Composites with a subambient Tg exhibited a mechanochromic response and were integrated with a peizoelectric actuator to produce a prototype device which exhibited a fully reversible tunable rejection wavelength, capable of a ca. +/- 86 nm (172 nm full range)stop band shift.
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