Optical medium

For light-based digital storage media, see Optical disc.

An optical medium is material through which electromagnetic waves propagate. It is a form of transmission medium. The permittivity and permeability of the medium define how electromagnetic waves propagate in it. The medium has an intrinsic impedance, given by

\eta = {E_x \over H_y}

where $E_x$ and $H_y$ are the electric field and magnetic field, respectively. In a region with no electrical conductivity, the expression simplifies to:

\eta = \sqrt{\mu \over \varepsilon}\ .

For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted Z₀, and

Z_0 = \sqrt{\mu_0 \over \varepsilon_0}\ .

Waves propagate through a medium with velocity $c_w = \nu \lambda$ , where $\nu$ is the frequency and $\lambda$ is the wavelength of the electromagnetic waves. This equation also may be put in the form

c_w = {\omega \over k}\ ,

where $\omega$ is the angular frequency of the wave and $k$ is the wavenumber of the wave. In electrical engineering, the symbol $\beta$ , called the phase constant, is often used instead of $k$ .

The propagation velocity of electromagnetic waves in free space, an idealized standard reference state (like absolute zero for temperature), is conventionally denoted by c₀:^[1]

c_0 = {1 \over \sqrt{\varepsilon_0 \mu_0}}\ ,

where

\varepsilon _{0}

is the electric constant and

~ \mu_0 \

is the magnetic constant.

For a general introduction, see Serway^[2] For a discussion of man-made media, see Joannopoulus.^[3] Types of optical mediums

1 Homogenous medium 2 Heterogeneous medium 3 Transparent medium 4 Translucent medium 5 Opaque body

Notes and references

↑ With ISO 31-5, NIST and the BIPM have adopted the notation c₀.
↑ Raymond Serway & Jewett J (2003). Physics for scientists and engineers (6th ed.). Belmont CA: Thomson-Brooks/Cole. ISBN 0-534-40842-7.
↑ John D Joannopouluos, Johnson SG, Winn JN & Meade RD (2008). Photonic crystals : molding the flow of light (2nd ed.). Princeton NJ: Princeton University Press. ISBN 978-0-691-12456-8.

Optical medium

Notes and references

See also