The normalized frequency V is also an important quantity. Whose relation with the numerical aperture is: Is the sine of the maximum acceptance angle:įigure 3.7 - Numerical Aperture representationĪnother important parameter is the NORMALIZED REFRACTIVE INDEX DIFFERENCE: The numerical aperture measures the light gathering capacity of a fibre and The cone of acceptance of light into the core is defined by the acceptance angle of the fibre, whose maximum value can be calculatedĪssuming that the refractive index of the medium outside the fibre is 1 (air) Index n 2 where n 1 > n 2assuring that light rays are reflectedīased on the principle of total internal reflection, only rays with incidentĪngles greater than the critical angle, at the CLADDING-CORE interface,įigure 3.6 - Representation of the acceptance angle. The medium for light propagation, while the cladding (the exterior layer) has a lower refractive The core (the interior layer ) with refractive Optical fibres are cylindrical waveguides made of two concentric layers of Total internal reflection occurs.Īnimation 4 - Refraction-reflection theory (total reflection). Īnimation 3 - Refraction-reflection theory (criticalįor angles of incidence greater than the critical angle, the rays are TOTALLY Parallel to the interface and the ANGLE OF REFRACTION reaches 90 °, and the corresponding angle of incidence is called the critical angle. If n1>n2, at a certain angle of incidence, the refracted wave propagates When a light ray encounters the interface of a medium, the light ray is refracted and its direction of propagation changes according to Snell's law of refraction.Īnimation 2 - Refraction-reflection of waves. In a transparent medium, the speed of light is affected by a factor n, In space light propagates with velocity c =3x10 8 m/s. Zone of the frequency spectrum (frequencies between 10 14 Hz Optical Fibres communication elements operate in the micrometer wavelength Longer wavelengths correspond to the infrared region (IR). Visible light extends from 380 nm ( violet)įor smaller wavelengths ultra-violet radiation (UV) occurs. We will assume a ray description of light. In this unit you will be introduced to the basic concepts of propagation in Chapter 3 – Light Propagation in Optical Fibres
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