Fiber Optic Cables Notes

Definition: Fiber-optic cable is a thin strand of glass or plastic coated with a protective plastic jacket.
Flexibility: The glass fibers are thin enough to bend easily.
Functionality: Traps a beam of light within the fiber, acting as a 'pipe' to carry light around corners.
Data Transmission: Supports high data rates, theoretically up to $50 ewline Gbps$ .
Signal Distance: Can carry a light signal up to approximately $2 ewline km$ before requiring signal strengthening.

Immunity to Interference:
- Not affected by electromagnetic fields.
- Immune to electromagnetic interference (EMI) and radio frequency interference (RFI).
- Suitable for noisy environments with electrical motors.
Durability:
- Does not corrode.
- Well-suited for high humidity and underwater environments.
Security:
- Difficult to splice into without detection.
- Considered a highly secure medium.

Cost: Relatively expensive in terms of materials and installation compared to copper cabling.

Basic Communication Model:
- Transmitter and receiver connected by optical fiber cabling.

Light-emitting diodes (LED):
- Use less power and are less expensive than lasers.
- Most common light source.
- Commonly used with multimode fiber (MMF).
- Provide bandwidth of approximately $250 ewline MHz$ .
Laser diodes:
- Used with single-mode fiber (SMF) for long-distance transmission.
- Use laser light, which is more powerful; light waves are radiated in phase (crests and troughs aligned).
- Optimized for alignment or coherence.
- Creates a signal with less attenuation and dispersion than noncoherent light.
- Provide much higher bandwidth, up to a theoretical maximum of $10 ewline GHz$ .

Signal Separation and Bandwidth:
- Each signal is separated by being reflected at different angles within the fiber.
- LEDs provide a bandwidth of approximately $250 ewline MHz$ .

Used with single-mode fiber (SMF), which allows only one path (mode) for light propagation.
Transmits only one optical signal.
Single-mode fiber can transmit signals over much longer distances than multimode fiber (MMF).
Use laser light, which is more powerful because laser light waves are radiated in phase, meaning the crests and troughs of all light waves are perfectly aligned.
Optimized for alignment or coherence, which creates a signal with much less attenuation and dispersion than noncoherent light.
Provide much higher bandwidth, up to a theoretical maximum of $10 ewline GHz$ .

Core:
- A solid fiber of highly refractive clear glass or plastic that serves as the central conduit for light.
- Diameter and consistency of the core vary depending on the specification of the fiber.
Cladding:
- A layer of clear glass or plastic with a lower index of refraction.
- Causes light to refract or bend back into the core completely (total internal reflection).
- The cladding of each fiber completely contains light signals within each core, preventing crosstalk.
Coating:
- A reinforced plastic outer jacket that protects the cable from damage.

Fiber optic cable is very thin; diameters are specified in micrometers ( $\\mu m$ ).
The thinnest fiber-optic cable (SMF) typically has a core diameter of $5$ to $10 ewline \mu m$ ( $0.005$ to $0.010 ewline mm$ ).
The thicker multimode fiber-optic cable ranges from $50$ to $100 ewline \mu m$ in core diameter.
Human hair is approximately $100 ewline \mu m$ thick.
Fiber-optic cable is specified in terms of its core and cladding diameter (e.g., $62.5/125 ewline \mu m$ cable, where $62.5$ refers to the core diameter and $125$ refers to the cladding diameter).
The core diameter is also known as the aperture because it determines the maximum angle from which the cable can accept light.

Step-Index Fiber:
- The standard type of optical fiber.
- Consists of only two transparent layers (core and cladding).
- Cannot compensate for the multimode signal dispersion effect.
Graded-Index Fiber:
- The core has several transparent layers, each with a different refractive index.
- Allows light modes to travel at different speeds through the core.
- Modes traveling down the core’s center travel slower than those refracting off the cladding.
- All modes reach the far end of the fiber more uniformly.
Single-Mode Fiber (SMF) Cable:
- SMF cables require laser diode transmitters.
- Can support longer transmission distances than MMF.
- Distances range from a few miles to as many as $20$ miles.
- SMF cables are generally step-index fibers.
- Because only one mode travels along the fiber, the problem of diffusion does not occur in SMF cables.

Installation Challenges:
- Difficult to install correctly and requires well-trained, careful installation technicians.
- Problematic installation combined with time-consuming connections makes it the most expensive cable to install.
- Many organizations hire specialists to install fiber optic networks.

Connections and splices are complicated to make. Each end must be:
- Cut off at perfect right angles.
- Ends polished by hand or machine.
- Cable precisely aligned to the connector.
Fiber connectors must perform at a higher level of precision.

Many different types, and many are proprietary.
- ST—Bayonet mounted
- SC—Stick and click into the device
- LC—Similar to SC connectors but smaller
- FC—Screw into the device
- MT-RJ—Snap into the device; transmit and receive fibers are locked together.
The Electronic Industries Alliance and Telecommunications Industry Association (EIA/TIA)-568 standard specifies two connector types: ST and SC.