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The signal analysis-synthesis problems at a few femtosecond time scale demand the generation and study of broadband similaritons. We generate similariton of ~100 nm bandwidth and characterize it experimentally to reveal its nature and distinctive properties, and to describe it mathematically. We carry out the complete characterization of the broadband similariton by means of its chirp measurement through the technique of spectral compression and frequency tuning in the sum-frequency generation process. Our studies are of interest in view of applications of similariton to the solution of signal analysis and synthesis problems in ultrafast optics, particularly for similariton-induced temporal lensing and similariton-based spectral interferometry. Our developed method of similariton chirp measurement can also serve for the fiber characterization.

We demonstrate pulse compression by generating nonlinear-dispersive similariton in fiber and its chirp cancellation in a dispersive delay line, consisting of a pair of fused-silica dispersive prisms. The initial pulse with 11 nm bandwidth and 146 fs autocorrelation duration was used to form the similaritons with different bandwidths. We have synthesized approximately transform-limited pulses of down to 25 fs autocorrelation duration, i.e. 17 fs duration, from a similariton of 77 nm bandwidth. All obtained results are in a good agreement with the numerical simulations.

We introduce a self-reference method of parabolic temporal lensing and aberration-free spectrotemporal imaging for the direct measurements of femtosecond waveforms, with the goal of designing an ultrafast optical oscilloscope. Our method is based on dispersive stretching of the signal pulse and afterwards cancellation of the dispersion-induced phase in a quadratic nonlinear process by adding a reference parabolic phase (instead of Kerr lensing of traditional spectral compression). We have implemented the method through sum-frequency generation using the self-shaped nonlinear-dispersive similariton as a reference pulse and have demonstrated it experimentally for the direct measurements of amplitude- and phase-modulated pulses on a femtosecond time scale.

Polyion complexes formed by monolayers of quaternary ammonium amphiphiles containing the 4-nitro-4‘-alkoxy azobenzene chromophore spread at the surface of aqueous solutions of a number of anionic polyelectrolytes were investigated. In general, Π−A isotherms were found to depend on the nature of the polyion present in the subphase, with monolayers of complexes involving polycarboxylates tending to exhibit larger limiting areas than those formed with polysulfonates or polysulfates. Monolayers of the polyion complexes can be transferred to hydrophilic solid substrates to yield Z-type LB films, although some peeling off for more than 10 layers is an impediment. X-ray reflectivity measurements indicate that relatively smooth and uniform films are obtained up to about 10 layers. Average layer thicknesses are, however, significantly smaller than extended molecular lengths, implying that the amphiphiles are strongly inclined from the surface normal. Polarized FT-IR measurements also indicate poor molecular orientation perpendicular to the surface. Preliminary SHG measurements for LB films of two systems, 12Q/CMC−Na and 12Q/PAA, confirm the presence of noncentrosymmetric out-of-plane chromophore ordering. Stable signals are observed for elevated temperatures up to 130 °C and for a period of 4 months at room temperature. To the best of our knowledge, this represents the first report of stable SHG in LB films of polyion complexes.

A complete theoretical analysis of a modified grating-frustrated coupler involving a second grating in an input channel is presented. We show that this second grating allows for improved performance of the device, especially in terms of backreflected light. The condition for zero backreflection is found analytically, and a physical interpretation of the results is given.

We have calculated the photo-emf in square profile graded band-gap semiconductor structures under local illumination. It is shown that the photo-emf is a linear function of the position of a light strip on the photosensitive surface and it changes the sign when the light strip passes across the center of the structure. The coordinate sensitivity of Ga1—xAlxAs graded-gap structure can be larger than 1.4 × 106 V/Wm.

The purpose of this short article is to derive an analytic formula for a variance swap delta. It shows that the delta is determined by the volatility skew and the vega of vanilla options only. Copyright © 2009 Wilmott Magazine Ltd

A complete theoretical analysis of a modified grating-frustrated coupler with a second grating in the input channel is presented. We show that this second grating allows for a reduction to zero of backreflected light and transmits all the radiation near the Bragg wavelength to a drop port.

Linear diffraction gratings that provide strongly asymmetric diffraction without surface modulation are created and studied. The spatial phase shift of the refractive-index grating relative to the absorption grating is the origin of nonreciprocal behavior.