Photonic crystal fibers guide light by corralling it within a periodic array of microscopic air holes that run along the entire fiber length Largely through their ability to overcome the limitations of conventional fiber optics—for example, by permitting low-loss guidance of light in a hollow core—these fibers are proving to have a multitude of important technological and scientific applications spanning many disciplines The result has been a renaissance of interest in optical fibers and their uses

https://science.sciencemag.org/content/sci/299/5605/358.full.pdf

Photonic crystal fibers

This Review summarizes the simultaneous transmission of several independent spatial channels of light along optical fibres to expand the data-carrying capacity of optical communications. Recent results achieved in both multicore and multimode optical fibres are documented.

/pdf/space-division-multiplexing-in-optical-fibres-9acl86j916.pdf

Space-division multiplexing in optical fibres

http://ab-initio.mit.edu/~oskooi/papers/Oskooi10.pdf

Meep: A flexible free-software package for electromagnetic simulations by the FDTD method

We present a novel waveguide geometry for enhancing and confining light in a nanometer-wide low-index material. Light enhancement and confinement is caused by large discontinuity of the electric field at highindex-contrast interfaces. We show that by use of such a structure the field can be confined in a 50-nm-wide low-index region with a normalized intensity of 20 mm 22 . This intensity is approximately 20 times higher than what can be achieved in SiO2 with conventional rectangular waveguides. © 2004 Optical Society of America OCIS codes: 030.4070, 130.0130, 130.2790, 230.7370, 230.7380, 230.7390, 230.7400. Recent results in integrated optics have shown the ability to guide, bend, split, and f ilter light on chips by use of optical devices based on high-index-contrast waveguides. 1–5 In all these devices the guiding mechanism is based on total internal ref lection (TIR) in a highindex material (core) surrounded by a low-indexmaterial (cladding); the TIR mechanism can strongly confine light in the high-index material. In recent years a number of structures have been proposed to guide or enhance light in low-index materials, 6–1 1 relying on external ref lections provided by interference effects. Unlike TIR, the external ref lection cannot be perfectly unity; therefore the modes in these structures are inherently leaky modes. In addition, since interference is involved, these structures are strongly wavelength dependent. Here we show that the optical field can be enhanced and conf ined in the low-index material even when light is guided by TIR. For a high-index-contrast interface, Maxwell’s equations state that, to satisfy the continuity of the normal component of electric f lux density D, the corresponding electric field (E-field) must undergo a large discontinuity with much higher amplitude in the low-index side. We show that this discontinuity can be used to strongly enhance and confine light in a nanometer-wide region of low-index material. The proposed structure presents an eigenmode, and it is compatible with highly integrated photonics technology. The principle of operation of the novel structure can be illustrated by analysis of the slab-based structure shown in Fig. 1(a), where a low-index slot is embedded between two high-index slabs (shaded regions). The novel structure is hereafter referred to as a slot waveguide. The slot waveguide eigenmode can be seen as being formed by the interaction between the fundamental eigenmodes of the individual slab waveguides. Rigorously, the analytical solution for the transverse E-field profile Ex of the fundamental TM eigenmode of the slab-based slot waveguide is

/pdf/guiding-and-confining-light-in-void-nanostructure-2oa0yk6hqm.pdf

Guiding and confining light in void nanostructure.

The history, fabrication, theory, numerical modeling, optical properties, guidance mechanisms, and applications of photonic-crystal fibers are reviewed

Photonic-Crystal Fibers

Perturbation theory permits the analytic study of small changes on known solutions, and is especially useful in electromagnetism for understanding weak interactions and imperfections Standard perturbation-theory techniques, however, have difficulties when applied to Maxwell's equations for small shifts in dielectric interfaces (especially in high-index-contrast, three-dimensional systems) due to the discontinous field boundary conditions---in fact, the usual methods fail even to predict the lowest-order behavior By considering a sharp boundary as a limit of anisotropically smoothed systems, we are able to derive a correct first-order perturbation theory and mode-coupling constants, involving only surface integrals of the unperturbed fields over the perturbed interface In addition, we discuss further considerations that arise for higher-order perturbative methods in electromagnetism

/pdf/perturbation-theory-for-maxwell-s-equations-with-shifting-2ycjz0ykhw.pdf

Perturbation theory for Maxwell's equations with shifting material boundaries

We present the light-propagation characteristics of OmniGuide fibers, which guide light by concentric multi-layer dielectric mirrors having the property of omnidirectional reflection. We show how the lowest-loss TE01 mode can propagate in a single-mode fashion through even large-core fibers, with other modes eliminated asymptotically by their higher losses and poor coupling, analogous to hollow metallic microwave waveguides. Dispersion, radiation leakage, material absorption, nonlinearities, bending, acircularity, and interface roughness are considered with the help of leaky modes and perturbation theory, and both numerical results and general scaling relations are presented. We show that cladding properties such as absorption and nonlinearity are suppressed by many orders of magnitude due to the strong confinement in a hollow core, and other imperfections are tolerable, promising that the properties of silica fibers may be surpassed even when nominally poor materials are employed.

/pdf/low-loss-asymptotically-single-mode-propagation-in-large-3w3vne40ah.pdf

Low-loss asymptotically single-mode propagation in large-core OmniGuide fibers.

A method for converting electromagnetic (EM) energy between guided modes of a photonic crystal waveguide (800) having a waveguide axis (810), the method including: (i) providing the photonic crystal waveguide (800) with a mode coupling segment (820) comprising at least one bend (830) in the waveguide axis (810), wherein during operation the mode coupling segment (820) converts EM energy in a first guided mode to a second guided mode; (ii) providing EM energy in the first guided mode of the photonic crystal waveguide (800); and (iii) allowing the EM energy in the first guided mode to encounter the mode coupling segment to convert at least some of the EM energy in the first guided mode to EM energy in the second guided mode.

Electromagnetic mode conversion in photonic crystal multimode waveguides

In general, in one aspect, the invention features systems, including a photonic crystal fiber including a core extending along a waveguide axis and a dielectric confinement region surrounding the core, the dielectric confinement region being configured to guide radiation along the waveguide axis from an input end to an output end of the photonic crystal fiber. The systems also includes a handpiece attached to the photonic crystal fiber, wherein the handpiece allows an operator to control the orientation of the output end to direct the radiation to a target location of a patient.

Photonic crystal fibers and medical systems including photonic crystal fibers

We present a method for dispersion-tailoring of OmniGuide and other photonic band-gap guided fibers based on weak interactions (“anticrossings”) between the core-guided mode and a mode localized in an intentionally introduced defect of the crystal. Because the core mode can be guided in air and the defect mode in a much higher-index material, we are able to obtain dispersion parameters in excess of 500,000 ps/nm-km. Furthermore, because the dispersion is controlled entirely by geometric parameters and not by material dispersion, it is easily tunable by structural choices and fiber-drawing speed. So, for example, we demonstrate how the large dispersion can be made to coincide with a dispersion slope that matches commercial silica fibers to better than 1%, promising efficient compensation. Other parameters are shown to yield dispersion-free transmission in a hollow OmniGuide fiber that also maintains low losses and negligible nonlinearities, with a nondegenerate TE01 mode immune to polarization-mode dispersion (PMD). We present theoretical calculations for a chalcogenide-based material system that has recently been experimentally drawn.

/pdf/dispersion-tailoring-and-compensation-by-modal-interactions-sygiravmtm.pdf

Ori Weisberg

Papers

Perturbation theory for Maxwell's equations with shifting material boundaries

Low-loss asymptotically single-mode propagation in large-core OmniGuide fibers.

Electromagnetic mode conversion in photonic crystal multimode waveguides

Photonic crystal fibers and medical systems including photonic crystal fibers

Dispersion tailoring and compensation by modal interactions in OmniGuide fibers.