The concepts of reflection and refraction are very important in the design of Optical Fibres and has a key part in how Optical fibres work. The law of reflection states that a beam of light striking a flat surface (the incidence ray) would be reflected at the same angle at the normal, the medium dividing the incidence ray and the reflective ray and is perpendicular to the surface of reflection. That would also mean that the angle of incidence (from the incidence ray to the normal) is also equivalent to the angle of reflection (from the reflective ray to the normal). Refer to Diagram 1.

Diagram 1

Snell's Law, named after the Dutch mathematician Willebrord van Roijen Snell, states that the product of the refractive index and the sine of the angle of incidence of a ray in one medium is equal to the product of the refractive index and the sine of the angle of refraction in a successive medium. This can be represented algebraically by n1 sin1 = n2 sin2, where n1, n2 are the two values of refractive index and 1,2 are the angles of the incidence and refraction. Refer to Diagram 2.

Diagram 2

We shall now move on to Critical Angles.

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