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Introduction to optical fibres
Why use optical fibre?Advantages
• Higher bandwidth than copper
• Smaller, lighter than copper
• Does not suffer from electromagnetic interference
• Long distance communication
• Intrinsically safe
Disadvantages
• Cannot carry power
• Cost of equipment (test, termination and transmission)
• Highly skilled to install optical fibre
History of optical fibres• 1870 John Tyndall showed that
light could be guided in a thin stream of water.
• 1960 introduction of lasers 1962 introduction of semiconductor lasers.
• 1970 introduction of glass that gives loss of 20 dB/km giving low enough loss for communications.
Light guiding within an optical fibre
Refractive index
materialin light of speedairin light of speed
vcn
reflection internal for total c
5.1102103
18
18
msxmsx
vc
Glassn = 1.5
Air n =1
Glassn = 1.5
Air n = 1
Overview of a simple optical network
Transmitter Patch panel
Patch panel Receiver
Backbonecable
Media converter
Attenuator
Patch cable
Pigtail
Coupleror WDM
Types of optical fibre
62.5/125 mm Optical fibre• Known as OM1• Optical Multimode 1
• Core of optical fibre has diameter of 62.5 mm (0.00625 cm)
• Cladding of optical fibre has diameter of 125 mm (0.0125 cm)
50/125 mm Optical fibre• Either OM2 or OM3 • Optical Multimode 2 or
Optical Multimode 3-laser enhanced
• Core of optical fibre has diameter of 50 mm (0.005 cm)
• Cladding of optical fibre has diameter of 125 mm (0.0125 cm)
9/125 mm Optical fibre• Known as OS1 • Optical Single-mode 1
• Core of optical fibre has diameter of 9mm (0.0009 cm)
• Cladding of optical fibre has diameter of 125 mm (0.0125 cm)
Difference between multimode and single mode optical fibre
• Multimode fibre; light can take many paths down the core of the optical fibre e.g. m0, m1, m2 etc
• This is due to the large size of the optical core either 50 or 62.5 mm.
• Singlemode fibre; light can only take one path down the core of the optical fibre.
• This is due to the small size of the optical core of 9 mm.
Cladding
Core
Cladding
Core
Cladding
Cladding
m0
m1
m2
m0
Wavelength
Frequency [Hz]102 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 11 10 12 10 13 10 14 10 15 10 16 10 17 10 18
3000km 30km 300m 3m 3cm 0.3mm 3 mm 30nm 0.3nm
NFrange
HFrange
Microwavesrange
Opticalrange
X / gammarange
Wavelengths of light used (l)
• Wavelength is defined as the distance between the one point of the wave and the next corresponding point on the wave.
• For multimode the main wavelengths used are 850 nm (first window) and 1300 nm (second window).
• For singlemode the main wavelengths used are 1310 nm (second window) and 1550 nm (third window).
• 1 nm is equivalent to 0.000001 mm
1 wavelength
Wavelength
Frequency [Hz]102 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 11 10 12 10 13 10 14 10 15 10 16 10 17 10 18
3000km 30km 300m 3m 3cm 0.3mm 3 mm 30nm 0.3nm
NFrange
HFrange
Microwavesrange
Opticalrange
X / gammarange