A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

/pdf/lanthanide-luminescence-for-functional-materials-and-bio-1w9cppwf8r.pdf

Lanthanide luminescence for functional materials and bio-sciences

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

Chemical methods developed over the past two decades enable preparation of colloidal nanocrystals with uniform size and shape. These Brownian objects readily order into superlattices. Recently, the range of accessible inorganic cores and tunable surface chemistries dramatically increased, expanding the set of nanocrystal arrangements experimentally attainable. In this review, we discuss efforts to create next-generation materials via bottom-up organization of nanocrystals with preprogrammed functionality and self-assembly instructions. This process is often driven by both interparticle interactions and the influence of the assembly environment. The introduction provides the reader with a practical overview of nanocrystal synthesis, self-assembly, and superlattice characterization. We then summarize the theory of nanocrystal interactions and examine fundamental principles governing nanocrystal self-assembly from hard and soft particle perspectives borrowed from the comparatively established fields of micro...

Self-Assembly of Colloidal Nanocrystals: From Intricate Structures to Functional Materials

Chemistries that Facilitate Nanotechnology Kim E. Sapsford,† W. Russ Algar, Lorenzo Berti, Kelly Boeneman Gemmill,‡ Brendan J. Casey,† Eunkeu Oh, Michael H. Stewart, and Igor L. Medintz*,‡ †Division of Biology, Department of Chemistry and Materials Science, Office of Science and Engineering Laboratories, U.S. Food and Drug Administration, Silver Spring, Maryland 20993, United States ‡Center for Bio/Molecular Science and Engineering Code 6900 and Division of Optical Sciences Code 5611, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States College of Science, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, United States Department of Biochemistry and Molecular Medicine, University of California, Davis, School of Medicine, Sacramento, California 95817, United States Sotera Defense Solutions, Crofton, Maryland 21114, United States

Functionalizing nanoparticles with biological molecules: developing chemistries that facilitate nanotechnology.

Most of the existing displays and optical shutters based on liquid crystals work in combination with linear polarizers. This implies that often more than half of the light is lost due to optical loss in the polarizers and/or the fact that the incoming light is unpolarized. For a number of shutter and filter applications it is important to have a high transmission, while it is not necessary to have a very high contrast. When considering nematic liquid crystals for use in fast optical shutters or filters, a number of possibilities exist. Dual-frequency liquid crystals offer faster switching possibilities because they can be switched from one state to another with a low frequency voltage and switching back can be achieved with the aid of a high frequency voltage. One of the limiting factors for the switching speed of dual-frequency nematics is the appearance of backflow. As in vertically aligned nematic devices, a certain threshold voltage exists above which the switching speed increases drastically [1]. Above the backflow threshold, the liquid crystal ends up in a meta-stable twisted orientation as shown in the figure below.

/pdf/fast-polarization-insensitive-optical-shutters-using-dual-19hgad0cs1.pdf

Fast polarization insensitive optical shutters using dual frequency liquid crystals

We show tuning of the resonance wavelength of Silicon-On-Insulator ring resonators with a liquid crystal cladding layer. In-plane switching of the liquid crystal director causes a shift towards longer wavelengths. The magnitude of the shift is 0.7 nm. We confirm our experiments with simulations using a fully anisotropic mode solver and explain the tuning mechanism. Keywords-Liquid crystals, silicon-on-insulator, tunable filters

https://biblio.ugent.be/publication/1146503/file/1146515.pdf

Tuning silicon-on-insulator ring resonators in in-plane switching liquid crystal cells

We study theoretically the spectral and polarization threshold characteristics of Vertical-Cavity Surface-Emitting Lasers with nematic and cholesteric liquid crystal overlay: LC-VCSELs. In the first case, we demonstrate the possibility of selecting between two orthogonal directions of linear polarization (LP) of the fundamental mode (x or y LP) by choosing appropriate NLC length and to achieve strong polarization discrimination: threshold gain difference as large as several times the threshold gain. We also demonstrate an active control of light polarization by electro-optically tuning the LC director and show that either polarization switching between x and y LP modes or continuous change of the LP direction is possible. For cholesteric LC-VCSEL we show that it becomes a coupled system with different spectral, threshold and polarization characteristics than the ones of the stand-alone VCSEL. Due to the existence of a band gap for circularly polarized light in the liquid crystal, lasing occurs in almost circularly polarized modes at the LC side.

VCSELs with nematic and cholesteric liquid crystal overlays

We report a low-voltage optical phase shifter using liquid crystal actuation integrated in IMEC's iSIPPSOG platform fabricated using inkjet printing as a deposition mechanism. A π phase shift is obtained at 3Vrms, almost 3π is obtained at 9Vrms. (Abstract)

Low power phase shifter using liquid crystal on an integrated silicon photonics platform

The increasing demand for high data rates and low power consumption puts silicon photonics at the edge of its capabilities. The heterogeneous integration of optical ferro-electric materials on silicon enhances the functionality of the silicon on insulator (SOI) platform to meet these demands. Lead zirconate titanate (PZT) thin films with a large Pockels coefficient and good optical quality can be directly integrated on SOI waveguides for fast electro-optic modulators. In this work, the relative permittivity and dielectric loss of PZT thin films deposited by chemical solution deposition on SOI substrates are analyzed at high frequencies. We extract ε
 r
 =1650−2129 and tan (δ) = 0.170 − 0.209 for the PZT thin films in the frequency range 1-67GHz. We show the possibility of achieving bandwidths beyond 60GHz via a Mach-Zehnder modulator with V
 π
  = 7V, suitable for next generation data communication systems.

Jeroen Beeckman

Papers

Fast polarization insensitive optical shutters using dual frequency liquid crystals

Tuning silicon-on-insulator ring resonators in in-plane switching liquid crystal cells

VCSELs with nematic and cholesteric liquid crystal overlays

Low power phase shifter using liquid crystal on an integrated silicon photonics platform

High frequency characterization of PZT thin-films deposited by chemical solution deposition on SOI for integrated high speed electro-optic modulators