JEOS:RP - Journal of the European Optical Society Rapid publications
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Theoretical investigation of amplified spontaneous emission in an active structure by extended (3x3) transfer matrix formalism: the case of a non-uniform longitudinal distribution of emitters
Get PDFWe use an extended (3x3) Transfer Matrix Formalism (TMF) to investigate the properties of Amplified Spontaneous Emission (ASE) in an active structure that exhibits a non-uniform spatial distribution of emitters along its longitudinal axis. The spectral density of power of the internal and emitted fields, both filtered into the transfer function of the structure, are expressed analytically in structural dimensionless parameters. We show that a periodically modulated distribution of emitters inside a cavity, in spite of their being spatially non-coherent, are responsible for a cross-interference product that can lead to an unexpected resonant enhancement of the spectral selectivity
Retroreflector array as a tapped delay-line filter for ultra-short optical pulses
Get PDFA retroreflector array can be used to act as an optical tapped delay-line filter for temporal optical signals. Here, we demonstrate the basic operation and present a theoretical description. Our theory is based on the mathematical formalism for finite impulse response filters. A relationship to the classical Talbot bands experiment is established. By adding a mask to the retroreflector array, one can implement arbitrary filter operations. As a specific example, a differentiation in frequency domain is demonstrated by using a simple binary mask. The proposed devise maybe useful for the optical filtering and shaping of ultra short pulses
Switching and instabilities of optical vortices in nonlinear dual-core photonic crystal fibre couplers
Get PDFWe study switching of an optical vortex launched into one core of a
dual-core waveguide coupler in a photonic crystal fibre with
self-focusing nonlinearity. We analyse how the beam power and the
angular momentum associated with the vortex mode transfer to the
second core of the coupler in both linear and nonlinear regimes. We
describe three major scenarios of the vortex dynamics and reveal
novel symmetry-breaking instabilities associated with the vortex
nonzero angular momentum
Comparison of beam combiners for a synthetic aperture imaging telescope
Get PDFFuture astronomical space missions will comprise a constellation of several optical telescopes to detect exo-planets by interferometric nulling of starlight. The Darwin mission of the European Space Agency (ESA) and NASAs Terrestrial Planet Finder Interferometer both consist of a free-flying collection of telescopes and a beam combiner. As such, the constellation provides a co-phased array of telescopes that can also be used
for aperture synthesis imaging. This imaging technique relies on recording intensity interference patterns, in which the layout of the beam combination optics and the detector play a key role. Several designs for beam combination have been proposed in the literature. In this article, we compare these beam combiners by rigorously simulating the imaging process of a weak stellar source, taking into account the photon arrival statistics, an imperfect detection process and the image reconstruction from the recorded data. The results are presented as the to be expected reconstruction error in the luminous intensity distribution function of a wide-field stellar source versus the provided amount of photons. Using these results, the optimum design of the combination beam combiner and detector array can be identified
Transverse magneto-optical Kerr effect measured using phase modulation
Get PDFAn ellipsometric configuration for measurement of complex transverse magneto-optical Kerr effect is described that uses photoelastic modulator (PEM). The real and imaginary parts of the complex transverse Kerr effect are represented as small perturbations of ellipsometric angles and . The measurement based on null ellipsometry and zone averaging gives high signal typical for modulation techniques and insensitivity to other magnetisation components and system imperfections. The method is demonstrated by the measurement of transverse component during magnetisation reversal in thin cobalt film
Effective spectral optical functions of lamellar nanogratings
Get PDFSpectral properties of lamellar sub-wavelength gratings (nanogratings) are described by effective medium approximation (EMA). Analytical spectral formulae for ordinary and extraordinary effective optical functions are derived for nanogratings consisting of material described by Sellmeier, damped harmonic oscillator, and Drude formulae. Spectral origin for birefringence of dielectric nanogratings and linear dichroism for absorbing ones is discussed for model cases and gratings consisting of real natural materials. Simple approximation by zero-order diffraction is compared with rigorous modeling based on Rigorous Coupled Wave Analysis (RCWA). Limits of applicability of effective medium approximation is discussed in the spectral domain
Resonant second harmonic generation in random dielectric structures
Get PDFWe show that resonant second harmonic generation can be btained in random dielectric structures. The scheme is based on internal resonances due to the optical counterpart of Anderson localization. By making use of different localization lengths at the fundamental and at the second harmonic frequencies, we predict a conversion efficiency that is four orders of magnitude higher than a bulk material and even one order of magnitude higher than an ideal phase matched slab of the same size. The method is highly insensitive to fabrication tolerances, and provides excellent angle tunability
Illustrations of optical vortices in three dimensions
Get PDFOptical vortices (phase singularities) arise from interference and are threads of darkness embedded within light fields. Although usually visualised in terms of their points of intersection with an observation plane, appreciation of their true form requires a view in three dimensions. Through numerical simulation we re-examine three situations where optical vortex lines evolve as an additional parameter is varied. Our specific examples are: the addition of a fourth plane wave of varying amplitude into a superposition of three plane waves, the increase of height of a non-integer spiral phase step, and finally the perturbation that creates, and then dissolves, a vortex link in a specific combination of Laguerre-Gauss modes
Compact supercontinuum source for the visible using gain-switched Ti:Sapphire laser as pump
Get PDFWe demonstrate the use of a miniature gain-switched Ti:Sapphire laser for efficient generation of visible supercontinuum light in a highly nonlinear microstructured optical fiber. This allows for a compact setup that puts out nanosecond pulses of light that cover the spectral range from 410 to 1300 nm. It offers a low-cost alternative to the mode-locked-laser-pumped systems as a source of visible supercontinuum light
Joint probability distributions for optical parametric down-conversion
Get PDFWe derive multi mode joint generating functions, photon-number distributions, integrated-intensity distributions and related quantities for spontaneous and stimulated parametric down-conversion in relation to experiments