In solid core Microstructured Optical Fibers (MOFs), guidance of light is due to a finite number of layers of holes surrounding a solid core. Because the potential barrier is finite, all modes are leaky, blurring the distinction between guided and non-guided modes. Through simulations using a multipole formulation, we clarify the definition of modal cutoff in MOFs. We establish that the fundamental mode of MOFs undergoes a transition between modal confinement and non-confinement similar to modal cutoff. An asymptotic analysis gives us a better understanding of mode properties on each side of the cutoff but also near cutoff and leads us to define a cutoff point and a cutoff region for the fundamental mode. Three operation regimes with very different mode properties can be distinguished. Only two of these are of practical interest, one with strong mode confinement and another with broader field distributions. The former is of interest for single-mode guidance with strong confinement, whereas the latter, the cutoff region, is where highly adjustable chromatic dispersion can be achieved. We provide a map of the parameter space (MOF "phase diagram") summarizing the operating regimes of MOFs, and show for a few examples how this map can be used for deterministic MOF design.
In the recent years, many experimental and theoretical achievements have shown that meta-materials can simulate homogeneous materials with optical index less than unity or even negative. For example, a dielectric photonic crystal, used at the edge of a band gap, can generate phenomena of ultra-refraction (positive index less than unity) or negative refraction (negative index). Some applications of these phenomena will be shown, specially the design of directive antenna in the microwaves region. More recently, experimental and theoretical studies have been published on left-handed materials. These materials, which have a permittivity and a permeability equal to -1, have been the subject of controversies about their alleged property of making perfect lenses. It will be shown that such a perfect lens cannot exist. However, this kind of meta-material could be used for making better lenses than the best classical ones, a fact which could explain some experimental results. The vital influence of the size of the elementary cell on the performance of the lens will be pointed out. Finally, it will be shown that surprisingly, a left-handed material can be interpreted as a means to go through the mirror, as Alice in the novel of Lewis Carrol...
We describe a multipole theory of photonic crystal or more generally microstructured optical fibers (MOF). We review basic MOF properties such-as losses and number of modes-obtained with our method and expose considerations and results on dispersion management taking into account the losses.
Based on the analogy between Schrödinger and Helmholtz equations (or in other words between electron and photon), the concept of photonic crystal has been introduced very recently after an experimental evidence of the existence of transmission gaps in periodic dielectric structures used in the microwave region.. Due to the importance of photonic bad gap structures in practical applications such as inhibition of spontaneous emission in semi-conductor lasers, many experimental and theoretical efforts have been made in the last years in order to investigate the properties of photonic crystals, or to improve the construction of such structures in the visible region. Following a presentation of these structures, it will be shown that the electromagnetic theory is able to provide accurate predictions on the gaps, for both periodic and doped crystals.
Surface characterization has a vital importance in many fields of research and technology. In the recent years, increasing efforts have been made in order to use light scattering rather than classical optical and mechanical tools for the purpose of characterization. After a brief recall on the classical optical means, a presentation of recent achievements in the field of characterization from surface scattering analysis will be made. Two kinds of surfaces and two kinds of characterizations will be distinguished.
By evaporating an infinitely thin layer of perfectly conducting metal on the small facet of the groove of a dielectric echelette grating then by superimposing an adequate inhomogeneous layer on top of the large facet, it is shown that a theoretical efficiency of 100% is obtained in a transmitted order. A numerical proof of this theoretical prediction is achieved using a computer code based on a rigorous finite-elements method. The curves of efficiency near the blazing effect show remarkable widths.
It is shown that the concept of localiton, introduced in the frame of localization of light by randomly rough surfaces, can be extended to other kinds of structures like impedance sheets or a set of random dielectric rods. Rigorous numerical calculations show the structure of these new localiton. Finally, the possibility of observing such a localized field from experimental measurements is suggested.
A code based on Maxwell equations has been developped in order to investigate the problem of scattering by deterministic and random rough surfaces. Numerical data on absorption and enhanced backscattering phenomena are shown.
The possibility of concentrating all the transmitted energy into one spectral order is established for a triangular groove dielectric grating for which a thin layer of per fectly conducting metal is evaporated on the small facet. The reflected energy is then only equal to the Fresnel reflectance (i. e. " 4 ). When an antireflection coating is evaporated on the large facet the transmitted efficiency can reach 100 into the first order.
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