| Popis: |
Light, like all its counterparts across the electromagnetic spectrum, has a wave-particle duality, that is, it has the properties of a wave and a particle, and the particles we call photons. It suits us when we are considering the subject of communications to usually think of light as a wave, which leads to an easier understanding of the properties of reflection, refraction and polarization. Considering light in its particle form has more benefit when we look at the subject of producing light in LEDs and lasers. In this chapter we looks at the basics of light transmission including the units and parameters of measurement and the upper speed limit of light. We shall also try to define the upper and lower limits of the electromagnetic spectrum and focus on the radio and optical ‘windows’ that allow for communications. In particular we look at the spectral response of four media, air, water, plastic and glass and identify the ‘bands’ of lowest attenuation, in the infra-red and visible light spectrum, that allow for successful communications links. |
