Variation Of Spot Size Research Articles

Design of fiber-matched uncladded rib waveguides on InP with polarization-independent mode matching loss of 1 dB

A waveguide taper design for uncladded rib or channel waveguides on InGaAsP-InP with polarization-independent coupling loss to the fiber is proposed. The spot size variation of the guided mode along the taper is investigated numerically by a two-dimensional finite difference method. By introducing thin guiding layers below the waveguide it is shown that the taper structure can be designed to have relaxed fabrication tolerances and a mode matching loss to the fiber of 1 dB.

A quantitative genetic analysis of an aposematic colour pattern and its ecological implications

The phenotypic and genetic variability of the aposematic colour pattern of the two-spot ladybird was investigated. There was significant variation in spot size (relative to elytron length) among wild populations of ladybirds. A quantitative genetic analysis revealed high heritability estimates for a number of individual colour pattern elements on the pronotum and elytra. The genetic covariances between the elytral spot and the pronotal spots were generally negative and all of the covariances among the pronotal spots were positive. This pattern of covariances could be explained if natural selection acts so as to maximize the combined anti-predator effect of the pronotal and elytral colour patterns by optimizing the rate of melanin production. An optimization process could also account for the significant levels of additive genetic variation found for each of the pattern elements considered. There was no evidence of any sex-linked gene expression for colour pattern, although female colour pattern may be influenced by maternally inherited factors.

Phenotypic Variation in Adult Mycalesis Hübner (Lepidoptera: Nymphalidae: Satyrinae) from the Australian Wet‐dry Tropics

ABSTRACTPhenotypic variation in the wing underside eyespot elements and size variation in female forewing length were analysed in three Australian butterflies of the tropical genus Mycalesis Hübner over 2 years at Cardwell (18°16′S), north‐eastern Queensland. Variation in spot size is strongly seasonal with distinctive wet‐season and dry‐season forms. Adult females of all three species are characterised by smaller ocelli during the dry cooler winter, whereas individuals with larger ocelli predominated throughout the wet hotter summer‐autumn months. Phenotypic change is less pronounced and more gradual in M. sirius, and most dramatic in M. perseus with the dry‐season form also lacking the conspicuous wing underside lines and bands. Dry‐season forms are typically larger (at least in M. perseus and M. terminus), less active, aggregate in moist refugia and often reproductively dormant during the dry season. Wet‐season forms usually reproduce directly and rarely diapause or aggregate. Seasonal polyphenism in these satyrines may be a dry season survival strategy, minimising risk of predation through crypsis during the period when females diapause and aggregate.

Variable spot-size waveguide for laser printing

A variable-spot-size Ti-LiNbO(3) waveguide that permits electro-optical longitudinal shifting of the focal point is described. A 70% spot-size increase is observed for the ±60-V power supply. This spot-size variation technique is used in a basic experiment on halftone laser printing.

Radiographic detail and variation of the nominal focal spot size: the "focal effect".

It is not generally appreciated that there is a gradation of the focal spot size from the anode to cathode end of an x-ray field that can dramatically affect radiographic detail from one end of a radiograph to the other. The authors name this gradation the "focal effect." Gradations in radiation intensity and focal spot size were measured from anode end to cathode end of a 14 x 17-inch field and were visually demonstrated with lymphangiograms and line-pair patterns. The degradation in spatial resolution along the anode-cathode axis was found to be as much as 75%, depending on the orientation of the patient with respect to the x-ray tube. Radiographic detail is, therefore, significantly improved (even when the large focal spot is used) by exploiting the focal effect and placing the body part requiring the best radiographic detail at the anode end of the table.

Non‐gaussian beams in direct coupling from laser diodes into optical waveguides via small gaps

AbstractIn a direct coupling from a laser diode into an optical waveguide, some mathematical models about field profile, spot size, and phase variation of the optical beam within the small diode‐waveguide gap can be used to fit the experimental data much better than those of the Gaussian beam. These models are expected to be useful in the numerical simulation of the losses of the diode‐to‐waveguide or diode‐to‐fiber coupling.

Spot size variation in non-adiabatic single mode fibre tapers

In an adiabatic taper, spot size is determined by the fundamental local mode alone. In non-adiabatic tapers, some of the power in the fundamental mode is coupled into cladding local modes, so that spot size is determined by a superposition of all these modes and can depart significantly from the adiabatic result. Both analytical and numerical solutions are presented.

A semiempirical model for the laser-induced molten zone in the laser recrystallization process. II

An extension to large laser power values of the semiempirical model for the laser-induced molten zone is given. The influence of the wafer preheating temperature and the thickness of thin capping layers on the molten zone is discussed. The variation of the size of the molten zone as caused by a change of the laser spot size is studied. An optimal laser power is determined to minimize the variation of the size of the molten zone as a result of a variation of the laser spot size. The difference between the laser power required to reach melt temperature in a silicon on insulator wafer and the laser power required to obtain complete melting is determined. A method to calculate the power required to reach the onset of complete melting in the case of a circular pseudostationary laser spot is proposed. The influence of the absorptances in liquid and in solid silicon, the thickness of the insulating layer, the thickness of the silicon overlayer, and the preheating temperature on the difference between the two threshold powers is treated.

Two-parameter characterisation of single-cladded, dispersion-shifted single-mode fibres

It is shown with numerical examples that single-cladded, dispersion-shifted, single-mode fibres with arbitrary refractive-index profiles have spectral spot size and dispersion variations predictable from only two parameters. These are the Laplace spot-size value ?L and fibre dispersion value Mf specified at the wavelength ? = 1.55 ?m.

Focusing of electromagnetic waves through a dielectric interface

Given a time-harmonic electric-current distribution over a finite planar aperture situated in front of a dielectric half-space, the transmitted field in the dielectric half-space is calculated by the plane-wave-spectrum technique. We concentrate on the current distribution that focuses the electromagnetic energy into a small spot in the dielectric medium, such as in hyperthermia applications. Numerical results are given to illustrate the variation of spot size and of focal-point electric-field intensity as functions of polarization, scanning, and the permittivity of the half-space. We find that (1) the maximum electric-field intensity is not at the focal point but rather at a point closer to the aperture; for a small aperture, this focal shift may be more than one wavelength; (2) when the dielectric half-space is introduced, the 3-dB spot size changes according to the ratio of the wavelength in the half-space to that in the original aperture medium; and (3) the electric-field intensity at the focal point is greatest when the permittivity of the half-space is less than that of the aperture medium, not when the two media are electrically matched.

Characterisation of graded single-mode fibres by fundamental-mode spot size variation

In the letter the accuracy of ESI parameters extracted from spectral spot size behaviour is examined. Different spot size definitions are considered and it is found that the equivalent cutoff wavelength, even for profiles far from a step, agrees reasonably with the mathematically defined cutoff wavelength.

Measured x-ray spectra from 25 to 110 kVp for a typical diagnostic unit.

Diagnostic x-ray spectra were measured with a NaI(T1) spectrometer system. A digital computer was used to correct the observed spectrum and to find the true spectrum by solving a matrix equation. X-ray spectra for various diagnostic x-ray units were measured under different conditions of focal spot size, duration of exposure, tube current, and kVp. Half-value layer, effective photon energy, and mean energy were measured and compared for similar x-ray units. The principal variation in x-ray spectra was related to differences in kVp and tube filtration. Focal spot size and mAs variation did not significantly influence the measured x-ray spectra.

Short time-constant thermal self-defocusing of laser beams

Time constants as low as 20 μs have been observed when the beam of a helium-neon laser is focused on a small spot on a thin dye sample and the thermal self-defocusing effects observed. The short time constant arises mainly from the small spot size, but to some extent from axial heat flow to the cell ends. The analysis takes into account the axial heat flow, the variation of spot size within the cell, and diffraction defocusing. Agreement between analysis and experiment is good except for cases of the smallest spot sizes, in which case convective turbulence was observed.

Mathematical model to describe vidicon operation

A theoretical development is presented that describes the operation of a vidicon. Output current is determined for an arbitrary distribution of intensity and wavelength of illumination falling on the face of the vidicon. The nonlinear behavior of the photoconductor is taken into account. The effect of progressive erasure of the stored charge on the rear of the photoconductor with the motion of the electron beam is included. The readout beam is assumed to be Gaussian with either a circular or elliptical cross section. The effect of the electron beam on lines other than that being scanned is included. Variation in electron beam spot size across the face of the vidicon is also considered. Correlation with published output data is presented. The apparent phase shift of objects, especially at high beam currents, can be significant. Numerical results for the cases of line and sinusoidal targets are discussed in detail.

A correction to the visually estimated intensities for the spot-size variation in the upper-level Weissenberg photographs

A correction to the visually estimated intensities for the spot-size variation in the upper-level Weissenberg photographs

A correction to the visually estimated intensities for the spot-size variation in the upper-level Weissenberg photographs

A method to correct the visually estimated intensities for the spot size variation in an upper-level Weissenberg photograph has been suggested. The method is applicable to elongated as well as contracted reflection spots. The success of the method has been demonstrated in a practical case.

Stability of a light beam in a beam waveguide

Long-distance, high-capacity transmission using a light beam in a beam waveguide is an attractive project for optical communications. However, the transmission of energy in the form of a beam gives rise to a new problem, that is, the stability of a sharp beam. In this paper, the stability problems of a Gaussian beam in a beam waveguide are presented. The deflection and the spot-size variation of a beam in the waveguide with known imperfections, such as transverse displacements of lenses, variation in focal length, and so on, are studied. If the transverse displacements of the lenses are periodic in space, instability of the beam path may occur. The unstable condition is derived. The variation of the spot size at the lenses is obtained in terms of small perturbations of the ideal waveguide. If the incident beam from a laser is not matched to the mode of the waveguide, the spot size at the lenses varies periodically. Statistical results for the models of a waveguide with random lenses, having random transverse position, random spacing, and random focal length, are also given.