1. Introduction to Computers
Fiber Optic Cables

2. Cable Construction
Core usually made of high quality ultra-pure glass or clear plastic
Surrounding the core is a reflective cladding which will keep the light inside the core and keep it traveling through the cable
Surrounding the core and cladding are layers of strengthening materials and protective materials
This keeps the core from breaking or or getting dirty

3. Types of Fiber Optic Cables
Single Mode
Allows one ray of light (Called a mode)
Very thin core microns (millionth of a meter)
Can transmit large amounts of data over long distances. It has been tested to transfer 10 gigabits per second over 80 kilometers
Multimode
Uses multiple rays of light
Each mode is slightly different frequencies, allowing the transmission of multiple signals at the same time
Much thicker; around microns
Cladding is designed to reflect each mode at a different angle to keep frequencies separate
Can’t be nearly as long. Around 2 km for 100 Mbps, 1 km for 1000 Mbps, and 500 m for 10 Gbps

4. Fiber Optic Cable Advantages and Disadvantages
Immune to electromagnetic interference
Strongly resists eavesdropping since there is no outside electromagnetic signal. Only way to capture data is to patch into the cable
Extremely high bandwidth
Allows for extremely long cables
Less flexible and harder to install
Much more expensive, about 10 times as much as UTP
Quite fragile and inflexible
Attaching connectors is not as easy and requires more specialized equipment

5. Fiber Optic Connectors
There are many different connectors we can use for fiber optic cables. Although some are only used for multimode or single mode cables, the ones we will look at can all be used for either
ST connector -
Uses a ceramic ferrule to ensure proper core alignment and prevent light ray deflection
Have a keyed bayonet-type connector, sometimes called push and twist
As part of the assembly process, it is necessary to polish the exposed fiber tip to make sure light is passed from one cable to the next without dispersion
SC connector -
Characterized by its square connection
Also uses a ceramic ferrule and the core needs to be polished
However, it uses a spring loaded ceramic ferrule instead of a keyed bayonet

6. More Fiber Optic Connectors
LC Connector
Uses a locking tab similar to an RJ-45 connector
About half the size of other fiber optic connectors, making it popular for uses in cramped spaces
Like the other connections, uses a ceramic ferrule and needs to have its exposed core polished during manufacturing
Separates the transmitting and receiving signal into two wires on one connector
MT-RJ Connector
Uses a locking tab as well as metal guide pins to ensure proper allignment

7. Fiber Optic Issues
Fiber optic cable is much less forgiving than copper cable. For the signal to pass through the fiber on one side of the connector or splice must line up exactly with the other side
Even if the connector is successfully locked into the jack, if it is the wrong connector or misaligned you could lose up to 90% of your bandwidth
Dirty connectors can also severely hamper a cable’s effectiveness, so cleaning them should be a priority
For connectors where the ferrule is accessible a lint-free cloth soaked in denatured alcohol works well. If the ferrule is recessed you will need a specialized cleaning tool. You will also need a specialized cleaning tool for the fiber optic jack

8. Insertion loss and ORL
Whenever a connector is installed on the end of a fiber optic cable there will be some signal loss. This is called insertion loss
Also, problematically some light that is loss will be reflected back down the cable to the source, which can damage the transmitter or corrupt the data being sent. This is called back-reflection or optical return loss (ORL)
Manufacturers must polish the connector to ensure minimum loss

9. Polishing grades
The better the polish, the more light will pass through without reflection
Physical Contact (PC) polishing is usually used for single mode fiber. It’s end is curved so on the cores of the fiber touch
Super Physical Contact (SPC) and Ultra Physical Contact (UPC) use a higher grade of polishing and have a higher curvature than PC
Angled Physical Contact (APC)
has an 8 degree angle cut into
the ferrule. This provides great
protection from ORL if used
with another APC connector

10. Fiber Optic Cabling Issues
The fiber optic core is very fragile and can easily be damaged. Even bending a fiber optic cable too far can cause it to break
Wavelength mismatch will cause almost total signal loss. Wavelength mismatch would occur if connecting single mode fiber to multimode fiber or connecting cables of the same type but different core diameters

11. Attenuation and Loss Budgeting
Fiber optic cable suffers attenuation in a very predictable and calculable way. Cable length, connectors and splices all contribute to the signal loss
If you add the average signal loss of all the factors together you get your loss budget
You then calculate your link loss margin by subtracting the calculated attenuation from the total power of the transmission source. Your link loss margin should be at least 3 decibels
This ensures that the cable will continue to function as its components age

12. Fiber Optic Loss Budget Calculation
Connectors or splices 0.3 dB loss each
Multimode cabling 1-3 dB per kilometer, depending on thickness and quality
Single mode cabling dB per kilometer, depending on thickness and quality

13. Video About the Science Behind Fiber Optic and the Transatlantic Cable