The Origin of Splicing
Early Optical Communications
The French used semaphores to transmit messages in the 1790s
Later systems also sent optical signals through the air
• But clouds, rain, and other atmospheric disturbances can disrupt optical signals sent through the air
• Electric signals through wires avoid that problem
Guiding Light With Water
Light in a stream of water stays inside the water and bends with it
This was first demonstrated in the 1840s
• Image from glenbrook.k12.il.us/gbssci
Refraction (Bending) of Light
Ray A comes from straight up and does not bend much
Ray B comes at a shallow angle and bends a lot more
• Image from seafriends.org.nz
The View From Underwater
Underwater, the light always shines down steeply, even when the Sun is low in the sky
The whole sky appears in a limited round area called “Snells Window”
• Image from seafriends.org.nz
Light Coming Out of Water
Animation on link Ch 1b on my Web page (samsclass.info)
• http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=66
Total Internal Reflection
There is a critical angle at which no light can be refracted at all, so 100% of the light is reflected
• Light is trapped in the water and cannot escape into the air
• This works with any dense medium, such as plastic or glass, the same way it works with water
Image from glenbrook.k12.il.us
How Light Travels in Fiber
Image from ece.umd.edu/~davis
Bare Fiber
During 1920-1950, thin, flexible rods of glass or plastic were used to guide light
Such “bare” fibers require air outside each fiber
• Image from Wikipedia
Fiber With Cladding
Developed in 1954 by van Heel, Hopkins & Kapany
Cladding is a glass or plastic cover around the core
Protects the total-reflection surface contamination
Reduces cross-talk from fibers in bundles
Medical Imaging
By 1960, glass-clad fibers were available for medical instruments, to look inside the body
The glass was unable to transmit light far enough for communications, because of impurities
• Attenuation (loss of light) was 1 decibel per meter
Decibels
Decibels are a logarithmic scale of power
• Abbreviated dB
A loss of 10 decibels means only 10% of the light gets through
A loss of 20 dB means 1% of the light gets through
• Sunglasses stop 99% of light, so they cause a loss of 20 dB
For communications, loss must be no more than 10 or 20 decibels per kilometer
Optical Fiber in 1966
Charles Kao developed a fiber that could transmit 1 GHz (One billion bits per second)
But attenuation was 1000 dB/km, so it could not transmit light far enough for practical communications
Corning
Corning scientists developed low-attenuation silica glass fibers in 1970
Corning Video: At The Speed of Light
• Link Ch 1c on my Web page (samsclass.info)
Singlemode and Multimode Fiber
Singlemode fiber has a core diameter of 8 to 9 microns
Multimode fiber has a core diameter of 50 or 62.5 microns
Both have a cladding diameter of 125 microns
Optical Fiber in 1977
Telephone signals used infrared light with a wavelength of 850 nm to send data at 6.2 Mbps and 45 Mbps
Loss was 2 dB per km
Repeaters were required every few kilometers
• The repeaters were electro-optical – converting the light to electricity and then back to light
TAT-8
In 1988 AT&T laid the first fiber-optic transatlantic telephony cable
3,148 miles long
Connected North America to France
Repeaters every 40 miles
565 Mbps bandwidth
Used 1300 nm light
Attenuation 0.4 dB/km
• Info from link Ch 1e www.greatachievements.org/?id=3706
Fiber Amplifier
Special fiber with Erbium atoms in it is used to amplify light without changing it to an electrical signal first
Uses stimulated emission, the same principle that makes lasers work
• Image from rp-photonics.com (Link Ch 1g)
Wavelength Division Multiplexing (WDM)
Several signals can be sent through the same fiber simultaneously by using different wavelengths (colors) of light
That means more bandwidth—more data per second
Freeway Analogy
TAT-8 in 1980
• 565 Mbps
• Electro-optical repeaters
TAT-12/13 in 1996
• 2.5 Gbps
• Optical amplifiers
1998
• 20 Gbps
• WDM with 8 wavelengths
Image from www2.rad.com (Link Ch 1j)
Dense Wavelength Division Multiplexing (DWDM)
Uses up to 100 wavelengths through a single fiber
Bandwidth up to 1 Tbps (1000 Gbps)
Lennie Lightwave’s Guide To Fiber Optics: Basics
From jimhayes.com/lennielw
Fiber Optics History
Fiber optics began about 30 years ago in the R&D labs (Corning, Bell Labs, ITT UK, etc.)
First installed in Chicago in 1976
By the early 1980s, fiber networks connected the major cities on each coast.
The 1980s
By the mid-80s, fiber was replacing all the telco copper, microwave and satellite links
In the 90s, CATV started using fiber to enhance the reliability of their networks
• CATV companies also discovered they could offer phone and Internet service on that same fiber and greatly enlarged their markets
Computers and LANs
Started using fiber about the same time as the telcos
Industrial links were among the first as the noise immunity of fiber and its distance capability make it ideal for the factory floor
Mainframe storage networks came next, the predecessors of today’s fiber SANs (storage area networks.)
Other Applications
Aircraft, ship and automobile data buses
CCTV for security
Links for consumer digital stereo
Today fiber optics is either the dominant medium or a logical choice for every communication system
Which Fiber Optics?
“Outside Plant” fiber optics are used in telephone networks or CATV
“Premises” fiber optics are usedin buildings and campuses
Just like “wire” which can mean lots of different things - power, security, HVAC, CCTV, LAN or telephone - fiber optics is not all the same.
Installing Fiber Optics
Fiber is harder to install than 100 Mbps copper Ethernet cable
But fiber is MUCH faster, so the infrastructure won’t need to be upgraded so soon
• And gigabit Ethernet is harder to install
LAN copper cable is delicate. It only has a 25 pound pulling tension limit and kinks will ruin the high speed performance
• Fiber has more strength and greater tolerance to abuse than copper wire
Safety First!
The light in the fiber can burn your retina
NEVER look into a fiber unless you know no light is present - use a power meter to check it
The infrared light is invisible
Fiber Shards
When you cleave fiber, there are small scraps of glass produced.
These scraps are very dangerous!
The cleaved ends are extremely sharp and can easily penetrate your skin
They are even worse in your eyes, mouth, etc.
Safety Rules
Wear glasses or safety glasses
Dispose of all scraps properly: put them on black tape and then into a properly marked trashcan
Work on a black pad which makes the slivers of glass easier to spot
Do not drop scraps on the floor
Do not eat or drink anywhere near the work area
Chemical Safety
Fiber optic splicing and termination use various chemical adhesives and cleaners
Follow the instructions for use carefully
Isopropyl alcohol, used as a cleaner, is flammable
Zero Tolerance for Dirt
Airborne particles are about the size of the core of Single Mode fiber
• They absorb lots of light and may scratch connectors if not removed
• Dirt on connectors is the biggest cause of scratches on polished connectors and high loss measurements
Hygiene Rules
Work in a clean area – avoid dust
Keep dust caps on all connectors
Use lint free pads and isopropyl alcohol to clean connectors
Last modified 1-20-06
May 29th, 2006 at 10:37 am
Hi, this is a comment.
To delete a comment, just log in, and view the posts’ comments, there you will have the option to edit or delete them.
May 29th, 2006 at 9:30 pm
Hey Jack thanks!
May 29th, 2006 at 9:31 pm
Early Optical Communications
The French used semaphores to transmit messages in the 1790s
Later systems also sent optical signals through the air
• But clouds, rain, and other atmospheric disturbances can disrupt optical signals sent through the air
• Electric signals through wires avoid that problem
Guiding Light With Water
Light in a stream of water stays inside the water and bends with it
This was first demonstrated in the 1840s
• Image from glenbrook.k12.il.us/gbssci
Refraction (Bending) of Light
Ray A comes from straight up and does not bend much
Ray B comes at a shallow angle and bends a lot more
• Image from seafriends.org.nz
The View From Underwater
Underwater, the light always shines down steeply, even when the Sun is low in the sky
The whole sky appears in a limited round area called “Snells Window”
• Image from seafriends.org.nz
Light Coming Out of Water
Animation on link Ch 1b on my Web page (samsclass.info)
• http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=66
Total Internal Reflection
There is a critical angle at which no light can be refracted at all, so 100% of the light is reflected
• Light is trapped in the water and cannot escape into the air
• This works with any dense medium, such as plastic or glass, the same way it works with water
Image from glenbrook.k12.il.us
How Light Travels in Fiber
Image from ece.umd.edu/~davis
Bare Fiber
During 1920-1950, thin, flexible rods of glass or plastic were used to guide light
Such “bare” fibers require air outside each fiber
• Image from Wikipedia
Fiber With Cladding
Developed in 1954 by van Heel, Hopkins & Kapany
Cladding is a glass or plastic cover around the core
Protects the total-reflection surface contamination
Reduces cross-talk from fibers in bundles
Medical Imaging
By 1960, glass-clad fibers were available for medical instruments, to look inside the body
The glass was unable to transmit light far enough for communications, because of impurities
• Attenuation (loss of light) was 1 decibel per meter
Decibels
Decibels are a logarithmic scale of power
• Abbreviated dB
A loss of 10 decibels means only 10% of the light gets through
A loss of 20 dB means 1% of the light gets through
• Sunglasses stop 99% of light, so they cause a loss of 20 dB
For communications, loss must be no more than 10 or 20 decibels per kilometer
Optical Fiber in 1966
Charles Kao developed a fiber that could transmit 1 GHz (One billion bits per second)
But attenuation was 1000 dB/km, so it could not transmit light far enough for practical communications
Corning
Corning scientists developed low-attenuation silica glass fibers in 1970
Corning Video: At The Speed of Light
• Link Ch 1c on my Web page (samsclass.info)
Singlemode and Multimode Fiber
Singlemode fiber has a core diameter of 8 to 9 microns
Multimode fiber has a core diameter of 50 or 62.5 microns
Both have a cladding diameter of 125 microns
Optical Fiber in 1977
Telephone signals used infrared light with a wavelength of 850 nm to send data at 6.2 Mbps and 45 Mbps
Loss was 2 dB per km
Repeaters were required every few kilometers
• The repeaters were electro-optical – converting the light to electricity and then back to light
TAT-8
In 1988 AT&T laid the first fiber-optic transatlantic telephony cable
3,148 miles long
Connected North America to France
Repeaters every 40 miles
565 Mbps bandwidth
Used 1300 nm light
Attenuation 0.4 dB/km
• Info from link Ch 1e www.greatachievements.org/?id=3706
Fiber Amplifier
Special fiber with Erbium atoms in it is used to amplify light without changing it to an electrical signal first
Uses stimulated emission, the same principle that makes lasers work
• Image from rp-photonics.com (Link Ch 1g)
Wavelength Division Multiplexing (WDM)
Several signals can be sent through the same fiber simultaneously by using different wavelengths (colors) of light
That means more bandwidth—more data per second
Freeway Analogy
TAT-8 in 1980
• 565 Mbps
• Electro-optical repeaters
TAT-12/13 in 1996
• 2.5 Gbps
• Optical amplifiers
1998
• 20 Gbps
• WDM with 8 wavelengths
Image from www2.rad.com (Link Ch 1j)
Dense Wavelength Division Multiplexing (DWDM)
Uses up to 100 wavelengths through a single fiber
Bandwidth up to 1 Tbps (1000 Gbps)
Lennie Lightwave’s Guide To Fiber Optics: Basics
From jimhayes.com/lennielw
Fiber Optics History
Fiber optics began about 30 years ago in the R&D labs (Corning, Bell Labs, ITT UK, etc.)
First installed in Chicago in 1976
By the early 1980s, fiber networks connected the major cities on each coast.
The 1980s
By the mid-80s, fiber was replacing all the telco copper, microwave and satellite links
In the 90s, CATV started using fiber to enhance the reliability of their networks
• CATV companies also discovered they could offer phone and Internet service on that same fiber and greatly enlarged their markets
Computers and LANs
Started using fiber about the same time as the telcos
Industrial links were among the first as the noise immunity of fiber and its distance capability make it ideal for the factory floor
Mainframe storage networks came next, the predecessors of today’s fiber SANs (storage area networks.)
Other Applications
Aircraft, ship and automobile data buses
CCTV for security
Links for consumer digital stereo
Today fiber optics is either the dominant medium or a logical choice for every communication system
Which Fiber Optics?
“Outside Plant” fiber optics are used in telephone networks or CATV
“Premises” fiber optics are usedin buildings and campuses
Just like “wire” which can mean lots of different things - power, security, HVAC, CCTV, LAN or telephone - fiber optics is not all the same.
Installing Fiber Optics
Fiber is harder to install than 100 Mbps copper Ethernet cable
But fiber is MUCH faster, so the infrastructure won’t need to be upgraded so soon
• And gigabit Ethernet is harder to install
LAN copper cable is delicate. It only has a 25 pound pulling tension limit and kinks will ruin the high speed performance
• Fiber has more strength and greater tolerance to abuse than copper wire
Safety First!
The light in the fiber can burn your retina
NEVER look into a fiber unless you know no light is present - use a power meter to check it
The infrared light is invisible
Fiber Shards
When you cleave fiber, there are small scraps of glass produced.
These scraps are very dangerous!
The cleaved ends are extremely sharp and can easily penetrate your skin
They are even worse in your eyes, mouth, etc.
Safety Rules
Wear glasses or safety glasses
Dispose of all scraps properly: put them on black tape and then into a properly marked trashcan
Work on a black pad which makes the slivers of glass easier to spot
Do not drop scraps on the floor
Do not eat or drink anywhere near the work area
Chemical Safety
Fiber optic splicing and termination use various chemical adhesives and cleaners
Follow the instructions for use carefully
Isopropyl alcohol, used as a cleaner, is flammable
Zero Tolerance for Dirt
Airborne particles are about the size of the core of Single Mode fiber
• They absorb lots of light and may scratch connectors if not removed
• Dirt on connectors is the biggest cause of scratches on polished connectors and high loss measurements
Hygiene Rules
Work in a clean area – avoid dust
Keep dust caps on all connectors
Use lint free pads and isopropyl alcohol to clean connectors
Last modified 1-20-06
May 29th, 2006 at 9:33 pm
Optical Fiber
Fiber v. Copper
Optical fiber transmits light pulses
• Can be used for analog or digital transmission
• Voice, computer data, video, etc.
Copper wires (or other metals) can carry the same types of signals with electrical pulses
Advantages of Fiber
Fiber has these advantages compared with metal wires
• Bandwidth – more data per second
• Longer distance
• Faster
• Special applications like medical imaging and quantum key distribution are only possible with fiber because they use light directly
Elements of a Fiber Data Link
Transmitter emits light pulses (LED or Laser)
Connectors and Cables passively carry the pulses
Receiver detects the light pulses
Repeaters
For long links, repeaters are needed to compensate for signal loss
Optical Fiber
Core
• Glass or plastic with a higher index of refraction than the cladding
• Carries the signal
Cladding
• Glass or plastic with a lower index of refraction than the core
Buffer
• Protects the fiber from damage and moisture
Jacket
• Holds one or more fibers in a cable
Singlemode Fiber
Singlemode fiber has a core diameter of 8 to 9 microns, which only allows one light path or mode
• Images from arcelect.com (Link Ch 2a)
Multimode Step-Index Fiber
Multimode fiber has a core diameter of 50 or 62.5 microns (sometimes even larger)
• Allows several light paths or modes
• This causes modal dispersion – some modes take longer to pass through the fiber than others because they travel a longer distance
• See animation at link Ch 2f
Multimode Graded-Index Fiber
The index of refraction gradually changes across the core
• Modes that travel further also move faster
• This reduces modal dispersion so the bandwidth is greatly increased
Step-index and Graded-index
Step index multimode was developed first, but rare today because it has a low bandwidth (50 MHz-km)
It has been replaced by graded-index multimode with a bandwidth up to 2 GHz-km
Plastic Optical Fiber
Large core (1 mm) step-index multimode fiber
Easy to cut and work with, but high attenuation (1 dB / meter) makes it useless for long distances
Sources and Wavelengths
Multimode fiber is used with
• LED sources at wavelengths of 850 and 1300 nm for slower local area networks
• Lasers at 850 and 1310 nm for networks running at gigabits per second or more
Sources and Wavelengths
Singlemode fiber is used with
• Laser sources at 1300 and 1550 nm
• Bandwidth is extremely high, around 100 THz-km
Fiber Optic Specifications
Attenuation
• Loss of signal, measured in dB
Dispersion
• Blurring of a signal, affects bandwidth
Bandwidth
• The number of bits per second that can be sent through a data link
Numerical Aperture
• Measures the largest angle of light that can be accepted into the core
Attenuation and Dispersion
See animation at link Ch 2e
Measuring Bandwidth
The bandwidth-distance product in units of MHz×km shows how fast data can be sent through a cable
A common multimode fiber with bandwidth-distance product of 500 MHz×km could carry
• A 500 MHz signal for 1 km, or
• A 1000 MHz signal for 0.5 km
From Wikipedia
Numerical Aperture
If the core and cladding have almost the same index of refraction, the numerical aperture will be small
This means that light must be shooting right down the center of the fiber to stay in the core
See Link Ch 4d
Fiber Types and Specifications
From Lennie Lightwave (www.jimhayes.com/lennielw/fiber.html)
Popular Fiber Types
At first there were only two common types of fiber
• 62.5 micron multimode, intended for LEDs and 100 Mbps networks
There is a large installed base of 62.5 micron fiber
• 8 micron single-mode for long distances or high bandwidths, requiring laser sources
Corning’s SMF-28 fiber is the largest base of installed fiber in the world (links Ch 2j, 2k)
Gigabit Ethernet
62.5 micron multimode fiber did not have enough bandwidth for Gigabit Ethernet (1000 Mbps)
LEDs cannot be used as sources for Gigabit Ethernet – they are too slow
So Gigabit Ethernet used a new, inexpensive source:
• Vertical Cavity Surface Emitting Laser (VCSEL)
Multimode Fiber Designed for VCSELs
First came laser-rated 50 micron multimode
• Bandwidth 500 MHz-km at 850 nm
Then came laser-optimized 50 micron multimode
• Bandwidth 2000 MHz-km at 850 nm
• Distinctive aqua-colored jacket
See links Ch 2g, 2h, 2i
Don’t Mix Fiber Types
You can’t mix singlemode and multimode fiber – you lose 20 dB at the junction (99% of the light!)
Mixing 50 micron and 62.5 micron multimode is not as bad, but you lose 3 dB (half the power) which is usually unacceptable
Flash Cards
To memorize this stuff, I use online flash cards
• Go to samsclass.info
• Click on CNIT 211
• Click on Flashcards
• Choose Ch 2a: Fiber Types
Fiber Manufacture
Three Methods
Modified Chemical Vapor Deposition (MCVD)
Outside Vapor Deposition (OVD)
Vapor Axial Deposition (MCVD)
Modified Chemical Vapor Deposition (MCVD)
A hollow, rotating glass tube is heated with a torch
Chemicals inside the tube precipitate to form soot
Rod is collapsed to crate a preform
Preform is stretched in a drawing tower to form a single fiber up to 10 km long
• Image from thefoa.org
Outside Vapor Deposition (OVD)
A mandrel is coated with a porous preform in a furnace
Then the mandrel is removed and the preform is collapsed in a process called sintering
• Image from csrg.ch.pw.edu.pl
Vapor Axial Deposition (VAD)
Preform is fabricated continuously
When the preform is long enough, it goes directly to the drawing tower
• Image from csrg.ch.pw.edu.pl
Drawing
The fiber is drawn from the preform and then coated with a protective coating
Index of Refraction
When light enters a dense medium like glass or water, it slows down
The index of refraction (n) is the ratio of the speed of light in vacuum to the speed of light in the medium
Water has n = 1.3
• Light takes 30% longer to travel through it
Fiber optic glass has n = 1.5
• Light takes 50% longer to travel through it
Fiber Applications
Step-index Multimode
Large core size, so source power can be efficiently coupled to the fiber
High attenuation (4-6 dB / km)
Low bandwidth (50 MHz-km)
Used in short, low-speed datalinks
Also useful in high-radiation environments, because it can be made with pure silica core
Graded-index Multimode
Useful for “premises networks” like LANs, security systems, etc.
62.5/125 micron has been most widely used
• Works well with LEDs, but cannot be used for Gigabit Ethernet
50/125 micron fiber and VSELS are used for faster networks
Singlemode FIber
Best for high speeds and long distances
Used by telephone companies and CATV
Fiber Performance
Attenuation
Modern fiber material is very pure, but there is still some attenuation
The wavelengths used are chosen to avoid absorption bands
• 850 nm, 1300 nm, and 1550 nm
• Plastic fiber uses 660 nm LEDs
Image from iec.org (Link Ch 2n)
Three Types of Dispersion
Dispersion is the spreading out of a light pulse as it travels through the fiber
Three types:
• Modal Dispersion
• Chromatic Dispersion
• Polarization Mode Dispersion (PMD)
Modal Dispersion
Modal Dispersion
• Spreading of a pulse because different modes (paths) through the fiber take different times
• Only happens in multimode fiber
• Reduced, but not eliminated, with graded-index fiber
Chromatic Dispersion
Different wavelengths travel at different speeds through the fiber
This spreads a pulse in an effect named chromatic dispersion
Chromatic dispersion occurs in both singlemode and multimode fiber
• Larger effect with LEDs than with lasers
• A far smaller effect than modal dispersion
Polarization Mode Dispersion
Light with different polarization can travel at different speeds, if the fiber is not perfectly symmetric at the atomic level
This could come from imperfect circular geometry or stress on the cable, and there is no easy way to correct it
It can affect both singlemode and multimode fiber.
Modal Distribution
In graded-index fiber, the off-axis modes go a longer distance than the axial mode, but they travel faster, compensating for dispersion
• But because the off-axis modes travel further, they suffer more attenuation
Equilibrium Modal Distribution
A long fiber that has lost the high-order modes is said to have an equilibrium modal distribution
For testing fibers, devices can be used to condition the modal distribution so measurements will be accurate
Mode Stripper
An index-matching substance is put on the outside of the fiber to remove light travelling through the cladding
• Figure from fiber-optics.info (Link Ch 2o)
Mode Scrambler
Mode scramblers mix light to excite every possible mode of transmission within the fiber
• Used for accurate measurements of attenuation
• Figure from fiber-optics.info (Link Ch 2o)
Mode Filter
Wrapping the fiber around a 12.5 mm mandrel
• Exceeds the critical angle for total internal reflection for very oblique modes
• The high-order modes leak into the cladding and are lost
• That creates an equilibrium modal distribution
• Allows an accurate test with a short test cable
Figure from fiber-optics.info (Link Ch 2o)
Decibel Units
Optical Loss in dB (decibels)
If the data link is perfect, and loses no power
• The loss is 0 dB
If the data link loses 50% of the power
• The loss is 3 dB, or a change of – 3 dB
If the data link loses 90% of the power
• The loss is 10 dB, or a change of – 10 dB
If the data link loses 99% of the power
• The loss is 20 dB, or a change of – 20 dB
dB = 10 log (Power Out / Power In)
Absolute Power in dBm
The power of a light is measured in milliwatts
For convenience, we use the dBm units, where
-20 dBm = 0.01 milliwatt
-10 dBm = 0.1 milliwatt
0 dBm = 1 milliwatt
10 dBm = 10 milliwatts
20 dBm = 100 milliwatts
Last modified 1-27-06
May 30th, 2006 at 3:38 pm
The English Language. Have you ever wondered why foreigners have trouble with the English Language?. Let’s face it. English is a crazy language. There is no egg in the eggplant No ham in the hamburger. And neither pine nor apple in the pineapple. English muffins were not invented in England. French fries were not invented in France. We sometimes take English for granted But if we examine its paradoxes we find that Quicksand takes you down slowly, Boxing rings are square. And a guinea pig is neither from Guinea nor is it a pig. If writers write, how come fingers don’t fing. If the plural of tooth is teeth. Shouldn’t the plural of phone booth be phone beeth, If the teacher taught, Why didn’t the preacher praught. If a vegetarian eats vegetables. What the does a humanitarian eat? Why do people recite at a play, Yet play at a recital? Park on driveways and Drive on parkways. You have to marvel at the unique lunacy. Of a language where a house can burn up as it burns down. And in which you fill in a form by filling it out. And a bell is only heard once it goes! English was invented by people, not computers, and it reflects the creativity of the human race (Which of course isn’t a race at all) That is why when the stars are out they are visible, but when the lights are out they are invisible, and why it is that when I wind up my watch it starts, but when I wind up this observation, it ends.