JEOS:RP - Journal of the European Optical Society Rapid publications
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Image formation in a multilayer using the Extended Nijboer-Zernike theory
Get PDFWe study the image formation by a high-numerical-aperture optical imaging system in the presence of a multilayer structure in the region around the image plane. Earlier references to this subject in the literature use numerical solutions of the diffraction integrals. In this paper, we use a numerical approach based on the semi-analytic Extended Nijboer-Zernike (ENZ) theory to solve the diffraction integrals in the presence of a multilayer structure. The specific ENZ calculation scheme uses the complex Zernike expansion of the complex amplitudes of forward and backward propagating plane wave components in a certain layer of the multilayer stack. By its nature, the ENZ approach enables an accurate and fast calculation of the vector field in the stratified image region. Examples of multilayer imaging that are encountered in high-numerical-aperture optical systems and in optical lithography for semiconductor manufacturing are presented and the accuracy of the ENZ approach is examined
Aberrational vignetting and eikonal theory
Get PDFIf an aperture stop is located inside of the real optical system, then variation of an entrance pupil depends on inclination of the incident beam of light rays. This effect called “aberrational vignetting†depends on aberration of the part of the optical system, which is located between the aperture stop and the entrance pupil. A theory of aberrational vignetting has been developed, using the eikonal theory
Tunable optical properties of silicon-on-insulator photonic crystal slab structures
Get PDFA photonic crystal slab structure with one-dimensional periodicity, obtained by preferential etching of a silicon-on-insulator wafer, is numerically investigated in 3-D. The etched grooves are considered to be filled either with an isotropic or with a Nematic Liquid Crystal (NLC) material. The molecular director is calculated using a consistent model of NLC reorientation under an external voltage. Different structures together with a broad range of voltage values are numerically simulated by means of a three-dimensional finite-difference time-domain method. The shifting of the photonic bandgap induced by the applied voltage, as well as its sensitivity in terms of refractometric applications, are discussed for a range of different structure geometries
Nonlinear-dispersive similariton of passive fiber
Get PDFUsing the spectral-interferometry method for short pulse complete characterization, we demonstrate the nature and distinctive properties of the similariton generated in single mode fiber without gain due to the combined impacts of nonlinearity and dispersion. The nonlinear-spectronic character of such a similariton, with the key specificity of linear chirping, leads to its self-spectrotemporal imaging, important for applications to signal analysis - synthesis problems in ultrafast optics
Analysis of calcium carbonate for differentiating between pigments using terahertz spectroscopy
Get PDFCalcium carbonate that is used as an art pigment exhibits strong absorption at approximately 3 THz. In this study, the authors investigated the relationship between the absorption and the condition of calcium carbonate crystals. By employing terahertz time-domain spectroscopy (0.5–4 THz), they verified that terahertz absorption energy depended on the crystal direction and crystal shape of the powder sample due to large birefringence. Further, the authors observed the difference in the crystal structure (calcite or aragonite) and the presence of impurities in natural calcium carbonate such as shells through terahertz absorbance spectra. The absorbance peak value of calcite at around 3 THz was four times as large as the peak value of aragonite. The absorbance spectral width increased because of the presence of these impurities. From the above observation, this study demonstrated that a certain kind of calcium carbonate crystal could be distinguished by terahertz spectroscopy
Tuning optical properties of opal photonic crystals by structural defects engineering
Get PDFWe report on the preparation and optical characterization of three dimensional colloidal photonic crystal (PhC) containing an engineered planar defect embedding photoactive push-pull dyes. Free standing polystyrene films having thickness between 0.6 and 3 microns doped with different dipolar chromophores were prepared. These films were sandwiched between two artificial opals creating a PhC structure with planar defect. The system was characterized by reflectance at normal incidence angle (R), variable angle transmittance (T), and photoluminescence spectroscopy (PL). Clear evidence of defect states were observed in T and R spectra, which allow the light to propagate for selected frequencies within the pseudogap (stop band)
Light and gas confinement in hollow-core photonic crystal fibre based photonic microcells
Get PDFWe review the recent progress on the understanding of optical guidance mechanisms in hollow-core photonic crystal fibres, and on the quantum and nonlinear optical applications of photonic microcells based on this fibre form. Two classes of hollow-core photonic crystal fibre are identified: one guides via a photonic bandgap and the other guides by virtue of an inhibited coupling between core and cladding mode constituents. For the former fibre type, we explore how the bandgap is formed using a photonic analogue of the tight-binding model and how it is related to the anti-resonant reflection optical waveguide guidance. For the second type of fibre, which can guide over a broad wavelength range, we examine the nature of the inhibited coupling. We describe a technique for the fabrication of photonic microcells that can accommodate vacuum pressures, and we finish by showing the latest results on electromagnetically induced transparency in a rubidium filled hollow-core photonic crystal fibre, the CW-pumped hydrogen Raman laser and the generation of multi-octave spanning stimulated Raman scattering spectral combs
Multi-particle three-dimensional coordinate estimation in real-time optical manipulation
Get PDFWe have previously shown how stereoscopic images can be obtained in our three-dimensional optical micromanipulation system [J. S. Dam et al, Opt. Express 16, 7244 (2008)]. Here, we present an extension and application of this principle to automatically gather the three-dimensional coordinates for all trapped particles with high tracking range and high reliability without requiring user calibration. Through deconvolving of the red, green, and blue colour planes to correct for bleeding between colour planes, we show that we can extend the system to also utilize green illumination, in addition to the blue and red. Applying the green colour as on-axis illumination yields redundant information for enhanced error correction, which is used to verify the gathered data, resulting in reliable coordinates as well as producing visually attractive images
Surface mapping of carrier density in a GaN wafer using a frequency-agile THz source
Get PDFWe developed a method for mapping the carrier density on a semiconductor substrate surface based on terahertz (THz)-reflective measurement. Reflectivity in the THz-frequency region away from the optical phonon frequency is sensitive to the carrier density in semiconductors. However, reflectivity in the optical phonon frequency regions is around 1.0, independent of the carrier density. We developed a THz-reflective spectral imaging system using a frequency-agile, ultra-widely tunable THz source (1 - 40 \THz). Different reflective images were obtained from GaN samples of carrier density 2.5x10^{16}cm^{-3}, 1.0x10^{18}cm^{-3}, and 1.5x10^{18}cm^{-3} using 22.7 and 26.5 THz. The image contrast reflected the GaN crystals' carrier density
Guided-wave photodetectors in germanium on optical chips in silicon-on-insulator
Get PDFWe report the integration of near-infrared waveguide photodetectors in polycrystalline Germanium with Silicon on Insulator optical chips for power monitor applications. We discuss design and fabrication of the devices as well as their characterization in terms of dark current, responsivity and signal to noise ratio