Refraction refers to the change in direction that a beam of light, a sound wave or an electromagnetic wave undergoes when it passes from one medium with a certain density into another medium with a different density and the refractive indices of the two media are different. The law of refraction can be used to determine the angle of the incident and refracted rays.
The law of refraction states that the ratio of the refractive indices of the two substances is equal to the ratio of the sine of the angle of incidence to the sine of the angle of refraction (sin a/sin b = n2/n1).
If the angle of incidence becomes shallower, total internal reflection may occur. Such a total reflection occurs only at the transition from an optically denser medium with the larger refractiveindex to an optically thinner medium with a lower refractive index. In terms of optical fibers, this means that the light beam from the core glass is refracted at the cladding glass and thus cannot exit the core glass.
Between the angles of incidence that lead to refraction and total reflection, there is another angle of incidence at which the light beam passes exactly on the boundary line of the two media. This ray is called the limiting ray, the angle is called the limiting angle and depends on the refractive indices of the two media. If the two media are air (refractive index 1) and glass with a refractive index of 1.5, then the critical angle is 41.8°.
Refraction can refer not only to the transition between two media with different refractive indices, but also to a change in density within a medium. Thus, the refractive index changes directly with the density change. The effect of continuous change of refractive indices is exploited in gradient fiber. The effect of refraction is also applied to compact discs( CD) and DVDs for reading out the stored data. While thedye of the storage layer is burned at certain points when the information is stored and thus becomes darker, the refraction of light at these points is different from that at the lighter, unburned points when the data is read out.