Wednesday, 7 September 2016

Basic Principle of Fiber Optic Communication

An Optical Fiber is a cylindrical dielectric waveguide i.e. nonconducting waveguide that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer, both of which are made of dielectric materials.

Fiber optic communication uses light to send information from one point to another. I will tell you about what happens once the light is inside the optical fiber.

The main principle for propagation inside a Fiber is total internal reflection. Thus, whenever a ray of light travelling from a denser to a rarer medium is incident on the interface between the two media at an angle greater than the critical angle of incidence, there is no refracted ray. The ray is totally internally reflected. This is something we all are well aware of.

Besides this, we have to think of two important factors that play an important role when the signal propagates inside the fiber: loss due to absorption and dispersion. The material of the fiber can absorb some amount of the signal and can result in transmission less than 100%. This absorption is found to be wavelength dependent, meaning that absorption would be more at certain wavelengths compares to others. This loss can be compensated by using amplifiers. However, if the loss is very large, several amplifiers have to installed at periodic intervals. This makes the circuit bulky and not very cost effective when operated on a small scale basis.

Also, dispersion causes the signal to lose its monochromatic nature and split into a band of several close wavelengths. This result in overlap of adjacent wavelengths while propagation and hence reduces the transmission capacity of the fiber or the amount of information that can be sent into one channel is limited. An optimum wavelength that balances both loss and dispersion is 1550 nm and most fiber optic networks work at this wavelength.

No comments: