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Lecture

Optical Fiber Modes and Diffraction

In course

PHYS-317: Optics I

L'optique est un vieux domaine qui touche à beaucoup de sujets modernes, des techniques expérimentales aux applications courantes. Ce premier cours traite plusieurs aspects de base de l'optique: propagation, dispersion, interférence, diffraction, polarisat ...

Description

This lecture covers the modes in optical fibers, including step index multimode fibers and the calculation of fields using the Helmholtz equation. It also explores diffraction phenomena, such as Fresnel and Fraunhofer diffraction, with detailed geometric methods and intensity calculations.

Instructor

Benjamin Dwir

Academic title: Dr. Birth date: 24.10.1959 Nationality: Swiss At EPFL since: 1988

Official source

Ontological neighbourhood

Physics

Optics: Fourier optics

Related concepts (32)

Diffraction

Diffraction is the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660.

Fraunhofer diffraction

In optics, the Fraunhofer diffraction equation is used to model the diffraction of waves when plane waves are incident on a diffracting object, and the diffraction pattern is viewed at a sufficiently long distance (a distance satisfying Fraunhofer condition) from the object (in the far-field region), and also when it is viewed at the focal plane of an imaging lens. In contrast, the diffraction pattern created near the diffracting object and (in the near field region) is given by the Fresnel diffraction equation.

Fresnel diffraction

In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of the Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near field. It is used to calculate the diffraction pattern created by waves passing through an aperture or around an object, when viewed from relatively close to the object. In contrast the diffraction pattern in the far field region is given by the Fraunhofer diffraction equation. The near field can be specified by the Fresnel number, F, of the optical arrangement.

Diffraction from slits

Diffraction processes affecting waves are amenable to quantitative description and analysis. Such treatments are applied to a wave passing through one or more slits whose width is specified as a proportion of the wavelength. Numerical approximations may be used, including the Fresnel and Fraunhofer approximations. Because diffraction is the result of addition of all waves (of given wavelength) along all unobstructed paths, the usual procedure is to consider the contribution of an infinitesimally small neighborhood around a certain path (this contribution is usually called a wavelet) and then integrate over all paths (= add all wavelets) from the source to the detector (or given point on a screen).

Kirchhoff's diffraction formula

Kirchhoff's diffraction formula (also called Fresnel–Kirchhoff diffraction formula) approximates light intensity and phase in optical diffraction: light fields in the boundary regions of shadows. The approximation can be used to model light propagation in a wide range of configurations, either analytically or using numerical modelling. It gives an expression for the wave disturbance when a monochromatic spherical wave is the incoming wave of a situation under consideration.

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