Optical Fibre Theory Flashcards
Define the term “Propagation”?
Propagation is a process by which light or sound waves travel.
What are the two types of Optical Fibre?
Single Mode (SM) fibre type
Multi-Mode (MM) fibre type
Explain why refraction occurs?
Refraction occurs because light travels at different speeds in different materials
What does NA stand for?
Numerical Aperture (NA);
By what means does light travel along an Optical Fibre?
Stepped Index
Graded Index;
What the typical sizes of Multimode Optical Fibre?
- 50/125 or 50/125/250
- 62.5/125 or 62.5/125/250
?80/125 or 80/125/250?
?100/140 or 100/140/280?
?200/240 or 200/240/480?
What is the typical size for Single Mode Optical Fibre?
• 8/125 or 8/125/250
?9/125 or 9/125/250?
?10/125 or 10/125/250?
Outside Vapour Deposition is one method of fibre manufacture, what is the other?
Modified Chemical Vapour Deposition (MCVD).
or
Outside Vapour Deposition (OVD)
Multimode is often referred to as OM, what does this stand for?
OM = Optical Multimode
What is the attenuation of 62.5/125 optical fibre cable operating within the First Window of Operation?
850nm / 3.5(dB/km)
What is the attenuation of 50/125 optical fibre cable operating within the Second Window of Operation?
1300nm / 1.5(dB/km)
Multimode optical fibre has two different core construction, what are these?
Stepped index
Graded index
Modal Dispersion is associated with which type of Multimode optical fibre?
Multimode - Step Index
What effect does Graded Index optical fibre have on light rays?
The effect of Graded Index fibre is to drastically reduce the Modal Dispersion of multimode fibres by slowing down the rays with shorter paths relative to those with longer paths through the fibre.
State the benefits of Multimode optical fibre?
- Bend Radius/Flexibility
* Cheaper Tx/Rx Equipment
State the drawbacks of using Multimode optical fibre?
- Lower Bandwidth
- Expensive Cable
- Short distance only
Single mode is often referred to as OS, what does this stand for?
OS = Optical Single Mode
What is the difference between OS1 and OS2 optical fibre cables?
OS1 is specified for upto 2km (Internal)
OS2 is Specified for over 2km (external)
Explain the term “Chromatic Dispersion”?
Chromatic dispersion (CD) is caused by the fact that single mode glass fibres transmit light of different wavelengths at different speeds.
State the benefits of Single mode optical fibre?
- Longer Distances
- Higher Bandwidth
- Cheaper Cable
State the drawback of Single mode optical fibre?
- Less bend radius tolerances
- Finer connector tolerances
- Expensive Tx/Rx equipment
What is the attenuation of OS2 optical fibre cable operating within the Third Window of Operation?
1550nm / 0.4(dB/km)
What three key parameters which categorise the performance of an Optical Fibre?
- Launch Power
- Attenuation
- Bandwidth
What unit of measurement is used to denote attention?
Decibels (dB)
What are the four causes of attenuation in optical fibres?
- Attenuation through absorption
- Attenuation through scattering
- Waveguide attenuation through macro bending
- Waveguide attenuation through micro bending
Ty-wraps are not to be used for affixing optical fibre cables as this can cause which type of bend?
Micro Bends
Define the term “Macro Bending”?
These are fibre bends with a radius of curvature of the order of millimetres.
Going over the bend radius
Define the term “Bandwidth”?
Bandwidth describes the information-carrying capacity of a fibre optic system, usually measured in bits per second (Mb/s or Gb/s)
Which type of optical fibre provides the highest bandwidth?
8/125 single-mode has a much higher bandwidth.
