In this work we introduce a new category of diffractive lenses called multifocal binary Gabor zone plates (MGZP). These lenses are designed by integrating in a single plate multiple binary Gabor zone plates with distinct harmonic terms. We demonstrate how this binding allows the creation of a desired multifocal distribution that can be customized in the lens design to generate multiple focal points with adjustable focal distances of variable intensity. Numerical examples are presented of a bifocal and to a trifocal lenses with equi-energetic foci.
We present the multiple trapping of microspheres using structured diffractive lenses in a setup of optical tweezers. Diffractive lenses are experiencing a wide development due to their successful implementation in areas such as ophthalmology or biophysics. The implementation of multifocal diffractive lenses in an experimental arrangement of optical tweezers affords the generation of multiple traps in a stable and controlled manner. We carried out the multiple trapping of polystyrene microspheres of radius ∼ 2 − 2.4 μm immersed in distilled water. An infrared laser and a multifocal diffractive lens enabled a set of axial foci. The structured lens is generated in a spatial light modulator (SLM) calibrated for a 2π phase shift at λ = 1064 nm and the tailored beam is focused by a high numerical aperture objective. Each focal point generated by the lens acts as a separate optical trap, whereby the confinement of an individual microsphere is possible. The versatility provided by structured diffractive lenses allows increasing the number of optical traps by modifying the lens profile. In addition, such strategy increases the flexibility in the experimental arrangement of optical tweezers.
We present the massive migration of metallic nanoparticles (NPs) due to their interaction with thermal gradients. A single-mode optical fiber is introduced into an ethanol solution with silver NPs of size between 0.5 1 µm- radius. When the laser radiation of λ = 455 nm leaving the optical fiber illuminates the suspended silver NPs, they absorb part of the energy and remit it as heat to the surrounding environment. This causes the formation of a thermal gradient in each particle and the medium. When the NPs are near the temperature gradient generated in the medium, they move to the high or low-temperature zone, the direction depending on the distance between the NPs and the tip of the optical fiber. The phenomenon that describes this behavior is called ∆α photophoresis. The particles present a considerable absorption on the illuminated side, generating a temperature difference relative to the non-illuminated side. The heat is conducted through the medium that surrounds the particles, giving rise to a momentum exchange between the molecules of the medium and the NPs. This exchange causes either an attraction or a repulsion of the NPs relative to the end optical fiber. The displacement of the NPs stems from the influence of the ∆T force, whose direction is equal to the propagation of the beam, and the force ∆α, with the opposite direction on each NP. We also study the appropriate optical and thermal conditions that enhance the migration of the silver NPs.
In this work, we report the achievement of images obtained with radial Walsh filters. Derived from Walsh functions, radial Walsh filters are phase binary diffractive optical elements characterized by a set of equal-area concentric rings that take the phase values 0 or π, corresponding to +1 or -1 transmittance values of the corresponding Walsh function. Then, a radial Walsh filter can be re-interpreted as an aperiodic zone plate with self-similar multi-focusing properties under monochromatic illumination and, therefore, multi-imaging capabilities. We have implemented these unconventional lenses with a spatial light modulator and the first images obtained with this type of lenses are presented and evaluated.
In this contribution we present a new family of diffractive lenses which are designed using the m-bonacci sequence.
These lenses are a generalization of the Fibonacci Zone Plates previously reported. Diffractive elements of this type are
called aperiodic zone plates because they are characterized by a radial profile that follows a given deterministic aperiodic
sequence (Cantor set, Thue-Morse, Fibonacci...). Aperiodic lenses have demonstrated new interesting focusing and
imaging properties that have found applications in different fields such as soft X-ray microscopy and spectral domain
optical coherence tomography. Here, we show that m-bonacci zone plates are inherently bifocal lenses. We demonstrate
that the relative separation of their foci depends on the m-value of the sequence and also can be correlated with the
generalized golden ratio. As a particular case, the properties of the m-bonacci sequence with m=2 and m=3, called
Fibonacci and Tribonacci Zone Plates respectively are discussed.
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.
Fresnel zone plates are conventional focusing and imaging elements used for X-ray and extreme ultraviolet radiation. The distribution of the transmissive and opaque circular rings in a Fresnel zone plate is periodic along the squared radial coordinate. In this communication we present a novel family of zone plates in which this periodicity is broken. These aperiodic zone plates present interesting focusing properties. We found two different kinds of designs. One of them produces a bifocal device with predictable separation between the foci. The other one produces a focal distribution along the optical axis with a fractal structure which is governed by the lacunarity of the zone plate. Different parameters allow a flexible design of both kinds of zone plates.
Using group theory arguments and numerical simulations we demonstrate the existence of spatial solitons in non linear photonic systems with discrete point-symmetry. This new approach permits a systematic classification of all non-linear solitonic solutions. New spatial effects can be derived and numerically tested in the context of two-dimensional photonic crystal fibers, optical lattices or, equivalently, in that of Bose-Einstein condensates in periodic potentials.
KEYWORDS: Visualization, Optical spheres, Virtual reality, Wave propagation, Communication and information technologies, Software development, Diffraction, Superposition, Opacity, Radio propagation
Information and Communication Technologies have demonstrated to be extremely effective in the transmission of scientific knowledge. Nowadays, the development of software and hardware makes it possible to simulate physical processes as close to reality as required. Furthermore, complex physical processes benefit from graphical simplicity in order to emphasize the main points for a complete understanding. In this work we focus our attention on the interference of coherent scalar waves in homogeneous media. Digital simulations have been designed in order to help the students to understand this phenomenon. Examples of interference of plane waves and cylindrical waves are visualized in sapce-time scales as the main advantage over traditional teaching resources.
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.
Cantor ring diffractals describe rotationally symmetric pupils based on a polyadic Cantor set. The influence on the axial irradiance of several fractal descriptors including fractal dimension, number of gaps and stage of growth of such pupils are investigated. The analysis is performed through a new method for the computation of axial PSF's that uses a Wigner distribution function obtained from the pupil.
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.
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