FIBER OPTIC COMMUNICATION

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks in the developed world.
The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal.

Fibers:

Step-index fibers, graded-index fibers.
Fiber modes, single-mode fibers, multimode fibers.
Dispersion, mode coupling, and loss mechanics.
Glass materials, fiber fabrication, and characterization
techniques.

Sources and Transmitters:

Light-emission processes in semiconductors.
Light-emitting diodes (LEDs).
Semiconductor lasers, (laser diodes: LDs).
Modulation response.
Source-fiber coupling.

 

Detectors and Receivers:

Photodetectors, receivers.
Receiver noise and sensitivity.

Optical Amplifiers

Erbium doped fiber amplifiers

Semiconductor optical amplifiers

Raman amplification

Systems:

System design: power budget and rise-time budget.
Single-Wavelength Fiber-Optic Networks (FDDI, SONET)
Wavelength-Division Multiplexing (WDM)

Total internal reflection

When light traveling in an optically dense medium hits a boundary at a steep angle (larger than the critical angle for the boundary), the light is completely reflected. This is called total internal reflection. This effect is used in optical fibers to confine light in the core. Light travels through the fiber core, bouncing back and forth off the boundary between the core and cladding. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out. This range of angles is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding.
In simpler terms, there is a maximum angle from the fiber axis at which light may enter the fiber so that it will propagate, or travel, in the core of the fiber. The sine of this maximum angle is the numerical aperture (NA) of the fiber. Fiber with a larger NA requires less precision to splice and work with than fiber with a smaller NA. Single-mode fiber has a small NA.