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The Planar Optical Waveguide
Published in Martin J. N. Sibley, Introduction to Electromagnetism, 2021
Use of this angle in Snell’s law gives an angle of refraction of 90°. This means that there is a transmitted ray travelling along the boundary. The critical angle is the minimum angle for which total internal reflection occurs. If θi is greater than θc, ρ will be complex but |ρ| will be unity, total internal reflection still takes place and there is a transmitted wave. We have already seen that the transmitted E field is given by Et=τEiexp(jβ2xx+jβ2yy)z
Understanding Light in Optical Microscopy
Published in John Girkin, A Practical Guide to Optical Microscopy, 2019
A full mathematical treatment of the way that an electromagnetic wave interfaces with a transparent surface also shows that even at normal incidence some small fraction of light is reflected. This is known as Fresnel reflection and depends on the two different refractive indices as well the angle at which the light hits the surface. For glass this provides a reflection of around 4% for light at normal incidence and this increases with angle and a higher refractive index. This is the reason why all optical surfaces within a microscope are coated, reducing the Fresnel reflection, which would otherwise give ghost images within the system. When the light is travelling between materials from a high to a low refractive index the level of reflection increases with the angle until a point is reached at which all the light is reflected. This is known as total internal reflection and is the physics behind optical fibres.
Chapter 3 Physics of the Senses
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
Figure 3.17 is a little misleading because it implies that all of the light that reaches the boundary is refracted and continues into the second medium. This is not true, and some percentage of the incident light is reflected away from the surface. The reflected light, which has been omitted from the figure for clarity, leaves at an angle which is simply the reflection of the incident angle in the normal to the boundary plane. The relative intensities of the incident, reflected and refracted light depend on the properties of the media and on the angle of incidence. An investigation of Snell’s law by substituting some values of the angle of incidence and the relative indices will quickly reveal that it is easy to get a value for sin θ2 that has a magnitude of greater than unity. There is no angle that satisfies this requirement, and the physical consequence is that all incident light is reflected back into the first medium (total reflection). It is possible to use the principle of total reflection to keep light trapped within a medium, if the angle at which the light strikes its surfaces is always greater than the critical angle for total reflection. This is called total internal reflection, and is the basis of the design of optical fibres.
Steering light in fiber-optic medical devices: a patent review
Published in Expert Review of Medical Devices, 2022
Merle S. Losch, Famke Kardux, Jenny Dankelman, Benno H. W. Hendriks
Optical fibers are commonly integrated into medical devices for remote light delivery and collection because of their high flexibility, low propagation loss, compatibility, and tolerance to electromagnetic interference [1]. The usefulness of fiber-optic devices has been shown for various medical applications, such as temperature, pressure and shape sensing [2–7], tissue illumination and modification [8–10], and spectral tissue sensing [8–10]. A conventional optical fiber is made up of a core that carries the light, a cladding, and a buffer coating. The refractive index of the cladding is slightly lower than the refractive index of the core. Because of this difference in refractive index, light incident on the core-cladding interface with an angle greater than a certain threshold, known as the critical angle, is reflected back into the core – a phenomenon known as total internal reflection. Thanks to total internal reflection, light can travel along the longitudinal axis of the optical fiber core to the distal end of a device.
Scattering of plane-wave through fluid medium of finite width between self-reinforced and triclinic half spaces
Published in Waves in Random and Complex Media, 2021
Shishir Gupta, Snehamoy Pramanik, Abhijit Pramanik
The angle is known as a critical angle where the refracted waves move horizontally. It happens because of When then where and denote the incident and reflected waves respectively. In this case, will be the critical angle. The characteristic of incidence angle is that it is equal to the critical angle in case the refracted angle is . At the position, where reflected and refracted beam becomes the total reflection, that is known as critical angle. When the angle of incidence reaches a certain critical value, the refracted ray lies along the boundary. This angle of incidence is known as a critical angle which is the largest angle of incidence for which refraction can still occur. For any angle of incidence greater than critical angle, wave will undergo total internal reflection. The actual value of critical angle is dependent upon the combination of materials present on each side of the boundary.
Distributed fiber optics sensors for civil engineering infrastructure sensing
Published in Journal of Structural Integrity and Maintenance, 2018
Optic fiber uses total internal reflection to guide a light transmitted along its longitudinal axis (e.g. Agrawal, 2007). That is, optical fiber is a circular waveguide, in which light is guided within a glass or silica core. An optical waveguide is a dielectric structure that transports energy at wavelengths in the infrared or visible portions of the electromagnetic spectrum (Synder & Love, 1983). The cross-section of an optical fiber is small and is generally separated into three layers, as shown in Figure 2. The central region is the core with a given refractive index and it is surrounded by cladding with a lower refractive index. The refractive index of the cladding is reduced by different levels of impurities with the same silicon dioxide.