Basic Fiber Optic Concepts

Advantages of Fiber Optics • A signal can be sent over long distances (200 Km/125 miles)

without the need for regeneration • Not sensitive to electromagnetic or radio frequency

interference • Does not conduct electricity • Greater data capacity than copper, coax, or wireless • Much lighter and smaller than copper cable, enabling more

fiber strands in a given cable diameter • Extremely reliable, very flexible, not sensitive to vibrations • Capable of operating over a large temperature range • Long service life

What is an optical fiber?

Types of optical fibers

What is a “mode”? • Refers to Mode of Propagation:

Multimode Fiber

This photograph illustrates the path light takes as it travels down a glass rod when the light is injected at an angle. This is an example of a “mode” of light.

Multimode Fiber

Step Index Multimode Fiber

Graded Index Multimode Fiber The core of graded-index multimode fiber possesses a non-uniform refractive index. This forces the rays of light to progress through the fiber in a sinusoidal manner. As with step index fiber, each mode has a different distance to travel depending on their path through the fiber optic glass.

Multimode Fiber Summary

• Tolerant of lower cost light sources, such as Light Emitting Diodes (LEDs)

• Simple, inexpensive connectors • Relatively high attenuation and low bandwidth limits • Typically uses short wavelengths (850nm, 1300nm) • Not applicable for long distances • Typically used to connect adjacent devices together

Singlemode Fiber Singlemode fiber has a core diameter that is so small that only one “mode” is possible

Singlemode

Multimode

Comparison of Multimode vs Singlemode

Singlemode Fiber Summary

• Uses higher cost, higher quality light sources (lasers)

• Capable of long distances without regeneration (> 200 Km / 125 Miles)

• Nearly infinite bandwidth • All outside plant fiber being deployed today

is singlemode

Fiber Optic Physical Components

Fiber Optic Cables Fiber optic strands are grouped together and bundled to form cables. The jacket of each strand is color coded, and typically grouped in units of 12.

Fiber Optic Cables In “loose tube” cables, each group of 12 fibers is enclosed in a color coded sheath called a “buffer tube”

Fiber strands in groups of 12

Buffer tubes

Fiber Optic Cables Ribbon fiber cables combine multiple fiber strands into a flat “ribbon” and stack them inside a buffer tube (also referred to as a “central core”). This allows for more fibers within a given cable diameter.

Outer Jacket

Water-Blocking Tape

Water-Blocking Tape Ripcord Strength member

Fiber Ribbon Buffer Tube Corrugated Steel Armor

Fiber Optic Cables

Larger ribbon fiber cables can have multiple buffer tubes/central cores:

Fiber Optic Cables Water is the enemy of outside plant cables. The empty spaces inside the cable sheath may be filled with water blocking gel, powder, or a water-swellable tape material that expands upon contact with water.

Water-Swellable Tape

Fiber Optic Cables

Splicing

Splicing is the process where two separate fiber optic strands are joined together. This can be a mechanical connection…

Splicing … or the splice can be a fusion splice, where the two ends of the fiber are placed in a splicing machine and are then melted, or fused, together. A sleeve is then placed over the fused area to protect and strengthen it.

Splicing Fibers that have been fusion spliced are then organized in a splice tray, which is subsequently protected by an enclosure

Fiber Optic Termination

Outside plant fiber optic cables ultimately terminate in a central office or cabinet. The termination point is often referred to as a patch panel, bulkhead, or frame. On the subscriber side, the fiber may terminate in a small patch panel, or in most cases in an Optical Network Terminal (ONT).

Fiber Optic Termination

Fiber Frame

Rack mount fiber panel

Rack mount panel with integrated splice tray

Optical Network Terminal (ONT)

Fiber Optic Connectors

Fiber optic connectors are used where the cable ends and the electronics begin, such as the central office, cabinets, or a subscriber’s location. Although there are approximately 100 different fiber optic connector types in use throughout the world, the telecommunications industry has largely standardized on just a few:

Fiber Optic Connectors

Fiber Optic Connectors

Fiber Optic Connectors Pre-terminated drop cables may use the Corning OptiTap connector (or equivalent). The connector plugs into a port in a pre-connected Tether. The goal is reduced labor costs for drop installations by eliminating fusion splicing.

Connector Ferrule Shapes & Polishes

Some early style connectors, particularly those that rotate when fastened, have air gaps between the connection surfaces. The air gap introduces loss. Later designs enabled the connectors to snap tightly together with flat end faces, allowing the fiber cores to make Physical Contact (PC) and reducing loss. Concave end surfaces were determined to reduce loss even further. Polishing the end surface to a slight angle allows reflections at the connector to bounce back and be absorbed in the fiber cladding.

The tip of the fiber optic connector is called a Ferrule. The shape and configuration of the ferrule varies depending on the type of connector and its intended purpose.

Connector Ferrule Shapes & Polishes The connector and ferrule type are typically listed together to describe the connector, such as: • SC-APC is an SC type connector with an angle polish ferrule • LC-UPC is an LC type connector with an Ultra Physical Contact

ferrule Connectors are also color-coded. Beige is typically a multimode connection, blue is a singlemode connection, and green is an angle polish connection.

Patch Cords

• Patch Cords are short lengths of fiber cable with connectors on each end. They are used to connect the electronic equipment with the outside plant cables (via the patch panel, bulkhead, etc.), or to connect electronic equipment to other nearby electronic equipment

• Patch cords may have different types of connectors on each end

Lasers

Lasers

Light Amplification by Stimulated Emission of Radiation • May be built-in to the equipment, or may be

one of several pluggable varieties • Pluggable lasers can be custom tailored to the

intended use • May be single direction or bi-directional

Lasers

• Small Form-factor Pluggable (SFP) lasers fit into a socket on the electronics

• A wide variety of SFPs are available for various distance and wavelength requirements

• SFPs may contain more than one fiber connector

• Earlier variants were called GBICs • XFPs are higher performance SFPs capable of

10 Gigabits per second speeds

SFP Lasers

Fiber Optic Deployment Topologies

Point to Point

Ring

Collapsed Ring

Fiber To The Node (FTTN)

Traditional copper distribution cables

Fiber To The Premise (FTTP)

Also known as: • Fiber To The Home (FTTH) • Fiber To The (whatever) (FTTx)

• Can be either PON or Active

Passive Optical Network (PON)

Single Splitter:

Passive Optical Network (PON)

Multiple Splitters:

Active (also referred to as Active Ethernet)

PON and Active Many manufacturers can accommodate PON and Active in the same equipment

Terminology Common terms for the service provider electronic equipment in a FTTx network: • Optical Line Terminal (OLT) • Optical Network Unit (ONU) • (or just “the shelf”)

Terminology Common terms for the subscriber-side electronic equipment in a FTTx network: • Optical Network Terminal (ONT) • Optical Network Unit (ONU) • Network Interface Device (NID)

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