Near-field characterization of a Bloch-surface-wave-based 2D disk resonator.

We present, to the best of our knowledge, the first experimental investigation of a two-dimensional disk resonator on a dielectric multilayer platform sustaining Bloch surface waves. The disk resonator has been patterned into a few tens of nanometer thin (∼λ/25) titanium dioxide layer deposited on the top of the platform. We characterize the disk resonator by multi-heterodyne scanning near-field optical microscopy. The low loss characteristics of Bloch surface waves allowed us to reach a measured quality factor of 2×103 for a disk radius of 100 µm.

Concurrent polarization retrieval in multi-heterodyne scanning near-field optical microscopy: validation on silicon form-birefringent grating.

We demonstrate a concurrent polarization-retrieval algorithm based on a multi-heterodyne scanning near-field optical microscopy (MH-SNOM) measurement system. This method relies on calibration of the polarization properties of the MH-SNOM using an isotropic region of the sample in the vicinity of the nanostructures of interest. We experimentally show the effectiveness of the method on a silicon form-birefringent grating (FBG) with significant polarization diversity. Three spatial dimensional near-field measurements are in agreement with theoretical predictions obtained with rigorous coupled-wave analysis (RCWA). Pseudo-far-field measurements are performed to obtain the effective refractive index of the FBG, emphasizing the validity of the proposed method. This reconstruction algorithm makes the MH-SNOM a powerful tool to analyze concurrently the polarization-dependent near-field optical response of nanostructures with sub wavelength resolution as long as a calibration area is available in close proximity.

Subwavelength cylindrical grating by holistic phase-mask coordinate transform.

A periodic grating with an integer number of periods is fabricated at the resist-coated wall of a cylinder by exposing a circularly symmetrical planar high index phase mask to a cylindrical wave. This extends the spatial coherence features easily achievable in a planar 2D space to the 3D space of cylindrical waves and elements.

Concentric ring metal grating for generating radially polarized light.

A subwavelength concentric ring metal grating for visible light (λ=632.8 nm) is designed and fabricated by electron-beam lithography to transform circularly polarized light into radially polarized light. Experimental results are compared to theoretical predictions and the advantages and disadvantages of the element with alternative methods are discussed.

Atomic layer deposited titanium dioxide and its application in resonant waveguide grating.

We demonstrate good optical quality TiO(2) thin films grown by atomic layer deposition at 120 degrees C. The optical properties were studied using spectroscopic ellipsometry and prism coupling methods. The refractive index was 2.27, and the slab waveguide propagation loss was less than 1dB/cm at 1.53microm. A high quality resonant waveguide grating was fabricated using a thin TiO(2) layer on top of a SiO(2) grating.

Giant enhancement of second-harmonic generation in multiple diffraction orders from sub-wavelength resonant waveguide grating.

We demonstrate a purely dielectric resonant waveguide structure that enhances the efficiency of second-harmonic generation by a factor of at least 5500 compared to a flat reference surface in the same geometry. We also show that the structure emits second-harmonic radiation in four different directions when the sample is illuminated with fundamental radiation incident at the resonant angle of the sample.

Angled sidewalls in silicon slot waveguides: conformal filling and mode properties.

Effect of angled sidewalls on the filling and properties of silicon slot waveguides is discussed. We demonstrate complete filling of slot waveguide structures with oxide material systems using the atomic layer deposition technique and discuss use of various slot filling materials. Properties of the optical modes in angled-sidewall slot waveguides are studied. Enhanced vertical confinement is obtained with certain waveguide parameters. The reduced effective mode area enhances e.g. nonlinear effects in the waveguide. We discuss the use of atomic layer deposition in realization of filled slot waveguides optimized for all-optical functionalities.

A wide-angle antireflection surface for the visible spectrum.

A surface consisting of periodically arranged nanopyramids producing wide-angle broad-band antireflection properties is presented. The reflectance of silicon dioxide is reduced below 0.45% over the visible spectral range (380-760 nm) for viewing angles from 0 degrees to 40 degrees . The surface is designed by using rigorous diffraction theory and fabricated first in silicon by exploiting its strong crystalline orientation and by using the wet etching process. The structure is transferred from silicon to transparent silicon dioxide by using nano-imprint lithography and proportional reactive ion etching.

Liquid phase deposition of polymers on arbitrary shaped surfaces and their suitability for e-beam patterning.

We present a straightforward low cost liquid phase deposition method to coat arbitrary-shaped dielectric substrates with uniform electron beam sensitive polymer films. Furthermore, we investigate the use of electron beam lithography to pattern the coated pre-form substrates. The polymers studied are poly-methyl-methacrylate with different molecular weights, poly(methyl methacrylate-co-ethyl acrylate) and methyl methacrylate. The polymer coverage over the whole surface area is shown to be uniform and the thickness of the film dependent on the concentration of the polymer liquid used. As the uniform polymer layer is deposited on non-flat surfaces, we show that with an electron beam various surfaces, e.g. microlens arrays, can be re-patterned accurately with nanoscale features. Furthermore, we show the required dose for electron beam exposure to be dependent on the concentration and on the molecular weight of the polymer used.

Electric field imprinting of sub-micron patterns in glass-metal nanocomposites.

We demonstrate that the dissolution of 10 nm metal nanoparticles localized in the subsurface layer of silicate glass by static electric field can be employed to alter the optical density and surface profile of the glass-metal composite with spatial resolution of 200 nm. The developed technique, which can be referred to as electric field imprinting (EFI), offers an attractive alternative to conventional micro- and nano-pattering techniques.

Enhanced optical absorptance of metals using interferometric femtosecond ablation.

The enhanced optical absorptance in metals was recently demonstrated using femtosecond laser-induced surface structuring. This structuring was obtained by simply focusing the light to the sample surface. Here we demonstrate more efficient absorptance enhancement using interferometric ablation. This interferometric ablation technique produces deeper surface structures and, consequently, higher absorption than structures obtained by just focusing the light to the surface. We also show the measured reflectance spectra over visible region for unaltered and structured stainless steel and copper samples.

Effects of abrupt surface-profile transitions in nonparaxial diffractive optics.

It is shown that the failure of the thin-element approximation of diffractive optics may, in the first approximation, be attributed to local diffraction effects caused by the abrupt vertical transitions in binary surface-relief profiles. We determine the field disturbance caused by a single-step transition (of given height) by rigorous diffraction theory. Associating such a disturbance with each individual transition point in the profile, we obtain a computationally efficient refinement of the thin-element approximation for the analysis and design of diffractive elements in the nonparaxial domain. The results agree well with those obtained by global application of rigorous diffraction theory, provided that the smallest features in the binary profile are larger than approximately one optical wavelength.

Deterministic diffractive diffusers for displays.

A LCD backlighting device that uses a diffractive light extractor has been developed for applications in which pointlike light sources are employed. The novel system eliminates the images of light sources, which appear as bright lines emanating from each source in the conventional diffractive approach. In addition, the system illuminates the LCD uniformly: Modulation of the diffractive structure as a function of position is used to control the output field of this extended planar light source.

Electron-beam-fabricated asymmetric transmission gratings for microspectroscopy.

Asymmetric transmission gratings operating in the resonance domain are designed by modeling of the dose-controlled electron-beam lithography process with Gaussian convolution. We aim to exceed some efficiency limit eta(s) over a specified spectral range and to maximize eta(s). The resultant continuous-profile gratings are fabricated by electron-beam lithography and proportional reactive-ion etching into SiO(2). We demonstrate gratings with good signal-to-noise ratio and a diffraction efficiency greater than 40% for wavelengths from 400 to 750 nm.

Beam shaping in the nonparaxial domain of diffractive optics.

We address the problem of shaping the radiant intensity distribution of a highly nonparaxial coherent field by means of a diffractive element located in the plane of the beam waist. To be capable of wide-angle energy redistribution the element must necessarily contain wavelength-scale transverse features, and consequently it must be designed on the basis of rigorous diffraction theory. We consider, in particular, wide-angle Gaussian to flat-top beam shaping in one dimension. Scalar designs are provided and their validity is evaluated by rigorous diffraction theory, which is also used for optimization deep inside the nonparaxial domain, where the scalar designs fail. Experimental verification is provided by means of electron-beam lithography.

Secretion of the Hormoconis resinae glucoamylase P enzyme from Trichoderma reesei directed by the natural and the cbh1 gene secretion signal.

Secretion of the Hormoconis resinae glucoamylase P (GAMP) enzyme from Trichoderma reesei using either the natural N-terminal extension of the premature glucoamylase P or the cellobiohydrolase I (CBHI) signal peptide was examined. The expression conditions for the heterologous glucoamylase P (gamP) gene in T. reesei were standardized by targeting one copy of a plasmid fragment, containing the gamP gene, to the cbh1 locus of the host. The results showed that the transient N-terminal extension of the premature GAMP acts as an efficient secretion signal in T. reesei and leads to a higher yield of extracellular glucoamylase activity than does the signal peptide of CBHI.