A new approach to design waveguides for supercontinuum generation through dispersive wave emission from optical wave-breaking is proposed in this work. In two steps, the spectral broadening is analytically related to the dispersion curve, and the cross-section of a waveguide is optimized in a few iterations to fit such dispersion profile and, consequently, the target output bandwidth. This strategy does not only improve the efficiency of design tasks, but also provides new insights into the underlying nonlinear processes.
KEYWORDS: Dispersion, Photonic crystal fibers, Light sources, Control systems, Erbium, Fabrication, Scanning electron microscopy, Solitons, Photonic crystals, Process control
The interplay between chromatic dispersion and nonlinear effects is patent. Once a photonic crystal fiber (PCF) preform
has been prepared, changing the parameters that control the fabrication process it is possible to adjust the dispersion
properties of the fiber. In addition, it is very useful to develop postprocessing techniques that enable a fine adjustment of
the dispersion along a section of PCF. The tapering of PCF, using a fusion and pulling technique, has been established as
a rather useful technique to engineer the dispersion properties along tens of centimeters. Some of our recent experiments
demonstrate that the use of erbium doped PCF enables an optical control of the dispersion through optical pumping of
the rare earth ions. Our interest is focused on the exploitation of nonlinear PCF for the development of fiber light
sources. Thus, we will present several experiments on supercontinuum and photon pairs generation, through degenerated
four-wave mixing (FWM), in order to illustrate the control that one can achieve on the optical spectra of these light
sources as a function of different dispersion control approaches.
We recognize some photonic-crystal-fiber structures, made up of soft glass, that generate ultrawide (over an octave),
very smooth and highly coherent supercontinuum spectrum when illuminated with femtosecond pulsed light around
1.55 μm. The design of soft-glass microstructured fiber geometry with nearly ultraflattened, positive and low dispersion
is crucial to accomplish the above goals.
We examine quasiperiodic multilayers arranged according to m-bonacci sequences that combine ordinary positive index materials and dispersive metamaterials with negative index in certain frequency ranges. When the averaged refractive index, in volume, of the multilayer equals zero, the structure does not propagate light waves and exhibits a forbidden band. In this contribution we recognize some approximated analytical expressions for the determination of the upper and lower limits of the above mentioned zero-average refractive index band gap.
We investigate the appearence of non-Bragg band gaps in 1D fractal photonic structures, specifically the Cantor-like lattices combining ordinary positive index materials and dispersive metamaterials. It is shown that these structures can exibit two new type of photonic band gaps with self-similarity properties around the frequencies where either the magnetic permeability or the electric permittivity of the metamaterial is zero. In constrast with the usual Bragg gaps, these band gaps are not based on any interference mechanisms. Accordingly, they remain invariant to scaling or disorder. Some other particular features of these polarization-selective gaps are outline and the impact on the light spectrum produced by the level of generation of the fractal structure is analyzed.
We study the group-velocity dispersion properties of a novel class of Bragg fibers. They are radially-symmetric microstructured fibers having a high-index core (silica in our case) surrounded by a cylindrical multilayer omnidirectional mirror as cladding, which is formed by a set of alternating layers of silica and a lower refractive-index dielectric. The interplay between the unusual geometric dispersion shown by the multilayer cladding of the fiber and the material dispersion corresponding to the silica core allows us to achieve an achromatic flattened dispersion behavior in the 0.8 μm wavelength window and even an ultraflattened behavior in the 1.5 μm range for some specific designs.
A new method for the computation of the tristimuli values that correspond to the impulse response along the optical axis provided by an imaging optical system working under polychromatic illumination is evaluated. A comparison between this method and the classical one of Hopkins and Yzuel shows that for systems with pupil functions of general profile it needs less computation time to obtain the same degree of accuracy.
This paper gives the theoretical basis for the development of a novel modal method to describe 3D dielectric structure modes. To this end, the vector wave equation, which determines the magnetic field, is written in terms of a linear operator, whose eigenvectors satisfy orthonormality relation. The key of our method is to obtain a matrix representation of the wave equation in a basis that is defined by the modes of an auxiliary system. Our proposed technique can be applied to systems with arbitrary 3D real or complex refractive-index distributions. In this work we have focused on thin-film photonic crystal waveguides with an asymmetrical core.
A novel analysis of specially designed photonic crystal fibers accounts for the existence of endlessly single-mode structures with flattened dispersion. Our approach permits to control the fiber dispersion in terms of its geometrical parameters.
We have combined a fusion-pulling technique and a standard metal-coating technique to fabricate in-line single-mode fiber filters, polarizers and sensors. The reduction of the core and cladding diameters in a tapered fiber causes the evanescent field to extend beyond the outer boundary. Thus, when a metal film is evaporated on a tapered fiber, the surface plasma modes cause coupling to the fiber mode.
We define a matching function that describes the amplitude variations produced over supergaussian beams, by cladding optical fibers that, if uncladded, can sustain this type of beams as Eigenmodes.
A technique is presented for improving 3-D resolution in confocal scanning microscopy. The technique is based on the equal contribution to the image of the illuminating and the collecting lenses. It is proposed, then, to apodize such lenses with complementary filters. The combined action of both filters produces a narrowness of the point spread function of the system both in the image plane, and along the optical axis.
We discuss the formation of self-images in an optical fiber with quadratic refractive index variations, and in its lens tandem equivalent setup. We identify two family sets of self-images. The first family set has geometrical magnification less or greater than unity. The other family set is obtained by longitudinal replication, with unit magnification of the first family set.
The boundary perturbation method is applied to investigate the changes in the lowest modes of optical fibers sustaining super-Gaussian beams due to the cladding with a constant refractive index. This contribution illustrates the exploitation of quantum-mechanical analogies and methods in the study of optical phenomena.
A method for the calculation of the axial illuminance and chromaticity as polychromatic merit functions of optical imaging systems is presented. We show that the Wigner distribution function of the pupil of the system allows us to obtain all the monochromatic components needed for the calculation of these parameters. From this single phase-space representation, the merit functions can be obtained in a polar fashion for a variable spherical and longitudinal chromatic aberrations. Numerical examples for an axially apodizing filter are shown.
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