Investigation of speckle suppression beyond human eye sensitivity by using a passive multimode fiber and a multimode fiber bundle.

A method of speckle suppression without any active device is expected for pico-projectors. The effectiveness of the passive method of speckle reduction using a single multimode fiber and a multimode fiber bundle was actually measured and theoretically analyzed. The dependences of the speckle contrast and speckle suppression coefficient on the parameters of multimode fiber and projection systems were investigated. Our results shown that the efficiency of speckle suppression was limited because only the radial direction of the objective lens aperture was used. An improvement using both of the radial and azimuthal directions of the objective lens aperture is required.

Speckle suppression in scanning laser displays: aberration and defocusing of the projection system.

Aberration and defocusing effects in the mechanism of speckle suppression in laser projection displays were studied using the Fresnel approximation and the thin lens model. The analysis was performed with the assumption that aberrations change only the phase (and not the amplitude) in the rear principal plane of the display projection system. The analysis showed that aberrations should not have any influence on speckle contrast. It also showed that a screen shift relative to the image plane (defocusing) results only in a rescaling of the scanning beam autocorrelation function, which is equivalent to refocusing the objective lens to a new position of the screen. The optimal beam shape for optimal speckle suppression was also studied. A homogeneous field intensity distribution in the spatial frequency domain was found to provide close to the best speckle suppression.

Local plasmon resonance at metal wedge.

A local plasmon resonance on a metal wedge is studied by using the Meixner approach [J. Meixner, IEEE Trans. Antennas Propag.AP-20, 442 (1972)]. It is found that the singular field behavior of a local plasmon resonance as a function of the distance from the edge of the wedge is sensitive to the wavelength and wedge angle, and ranges from a dramatic increase in amplitude close to its theoretical limit to pure oscillatory behavior with only minor amplitude variation. Field singularities for gold, silver, and aluminum wedges are calculated. It is shown that, unlike an ideal-conductor wedge, the real part of the power index of the electric field singularity does not decrease monotonically as a function of the wedge angle, but has a minimum for some angle depending on the wavelength and material parameters. If the dielectric surrounding the wedge has a positive permittivity equal to the absolute value of that of the metal, and hence satisfies the plasmon resonance condition, then the electric field has a peculiar behavior for a wedge whose shape is close to the flat surface.

Speckle suppression in scanning laser display.

The theory of speckle noise in a scanning beam is presented. The general formulas for the calculation of speckle contrast, which apply to any scanning display, are obtained. It is shown that the main requirement for successful speckle suppression in a scanning display is a narrow autocorrelation peak and low sidelobe level in the autocorrelation function of the complex amplitude distribution across a scanning light beam. The simple formulas for speckle contrast for a beam with a narrow autocorrelation function peak were obtained. It was shown that application of a diffractive optical element (DOE) with a Barker code phase shape could use only natural display scanning motion for speckle suppression. DOE with a Barker code phase shape has a small size and may be deposited on the light modulator inside the depth of the focus of the reflected beam area, and therefore, it does not need an additional image plane and complicated relay optics.

Numerical simulation of characteristics of near-field microstrip probe having pyramidal shape.

A pyramid-type microstrip probe (PTMP) with metal tips is proposed for scanning near-field microscopes to obtain high spatial resolution of a few nanometers and high optical efficiency. Properties of an ordinary PTMP and the PTMP with a single metal tip are investigated by using a rigorous finite-integral technique simulation (MICROWAVE STUDIO package) and analyzing characteristics of working modes of the probe. Numerical simulation has demonstrated that an ordinary PTMP and the PTMT with a single metal tip exhibit large far- and near-transmission coefficients, field enhancement, and high spatial resolution. These high parameters imply that both types of microstrip probe may be utilized for optical and magnetic data storage, nanolithography, and other types of nanotechnology that use light for modification of a thin surface layer.

Mode propagation in optical nanowaveguides with dielectric cores and surrounding metal layers.

The mode spectrum in an optical nanowaveguide consisting of a dielectric-core layer surrounded by two identical metal layers is investigated. A simple model based on mode matching to predict the properties of mode propagation in such optical nanowaveguides is proposed. It is shown that quasi-TM00 and quasi-TM10 modes supported by an optical microstrip line do not have a cutoff frequency, regardless of the size of the metal strips, the thickness of the dielectric slab, and the cross-sectional shape. The transverse size of the TM00 mode supported by a nanosized microstrip line was found to be approximately equal to the transverse dimension of the microstrip line. In closed rectangular and elliptical nanowaveguides, i.e., in which all dielectric surfaces are covered with metal films, the cross-sectional shape of the waveguide should be stretched along one side to produce propagation conditions for the fundamental mode.