1.5 Fibre Optics Flashcards
What is Total Internal Reflection
When the Angle of Incidence is greater than the Critical Angle, all the light is reflected back.
What property of the fibre optic core allows Total Internal Reflection?
With Total Internal Reflection, the light is reflected back into the medium of higher refractive index.
The core must be of a high refractive index.
What is a Multi-Mode Core?
Large core, allows more than one mode of light. Short distance.
What is a Sigle Mode Fibre?
Small core, only carries one mode of light. Longer distance.
What is the Numerical Aperature of fibre optic cables?
The angle at which the fibre will accept incoming light for a multimode fibre.
Draw a basic Optical Communication System diagram
What are two main types of light sources for optical communications systems and what is the difference?
LED - inefficient, used for multi-mode
Laser Diode - more efficient, used for single mode
How does a fibre optic receiver work?
Photodetector converts light into electricity by the photoelectric effect.
What are the 3 major causes of loss in fibre optic cable?
Mode-Coupling Losses
Bending
Dispersion
What are Mode-Coupling Losses?
Irregularities in cladding, imperfections from splicing, or bubbles in the core cause scattering or escaping of light.
What are Bending Losses?
Bending in the cable can cause the angle of incidence to change. If the angle of incidence becomes less than the critical angle, we will not have Total Internal Reflection and light will escape.
Name 3 advantages of Fibre Optic.
Low attenuation
Difficult to intercept
High data rate
Immune to EM interference
Name 2 disadvantages to Fibre Optic Cable.
Splicing is difficult.
Cost.
