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Fiber Optics In Telecommunication

The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics.

With development of Internet technologies, traditional telecommunication system based on copper networks is becomming limited day by day. As a method of transmitting information from one place to another, optical fiber transmission is first developed in 1970s, and quickly expanded in last 30 years, no matter the transmission distance or the area covered.

By sending pulses of light through an optical fiber, fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over traditional electrical transmission, optical fibers have largely replaced copper wire communications in core networks. Optical fiber is now world widely used to transmit telephone signals, Internet communication, and cable television signals.

The process of communicating using fiber-optics involves the following basic steps:

  1. Coverting electrical voice, data, and vedio signal into optical signal
  2. Transmitting optical signal into the fibers
  3. Relaying the signal along the fiber
  4. Ensuring that the signal does not become too distorted or weak
  5. Receiving the optical signal, distributing and converting it into an electrical signal

The fiber optic components related to these process contain optical  fiber cables, connectors, adapters, attenuators, couplers, splitters, WDMs, active transmission devices, cable management racks, cabinets, enclosures, and boxes etc.


Optical Fibers

An optical fiber (or optical fibre) is a flexible, transparent fiber made of extruded glass (silica) or plastic, typically surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection, which make fiber functions as a waveguide, or “light pipe”, to transmit light between the two ends of it.

Optical fibers are widely used in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data rates) than wire cables, because signals travel along them with less loss and are also immune to electromagnetic interference. 

There are two general categories of optical fiber: single-mode and multimode (see Figure 2).

single-mode & multimode fiberMultimode fiber was the first type of fiber to be commercialized. It has a much larger core than single-mode fiber, allowing hundreds of modes of light to propagate through the fiber simultaneously. Additionally, the larger core diameter of multimode fiber facilitates the use of lower-cost optical transmitters (such as light emitting diodes [LEDs] or vertical cavity surface emitting lasers [VCSELs]) and connectors.

Single-mode fiber, on the other hand, has a much smaller core that allows only one mode of light at a time to propagate through the core. While it might appear that multimode fibers have higher capacity, in fact the opposite is true. Singlemode fibers are designed to maintain spatial and spectral integrity of each optical signal over longer distances, allowing more information to be transmitted.

Its tremendous information-carrying capacity and low intrinsic loss have made single-mode fiber the ideal transmission medium for a multitude of applications. Single-mode fiber is typically used for longer-distance and higher-bandwidth applications. Multimode fiber is used primarily in systems with short transmission distances (under 2 km), such as premises communications, private data networks, and parallel optic applications.

fiber Types

The international standard for outer cladding diameter of most single-mode and multimode optical fibers is 125 microns (µm) for the glass and 245 µm for the coating. This standard is important because it ensures compatibility among connectors, splices, and tools used throughout the industry.

Standard single-mode fibers are manufactured with a small core size, approximately 8 to 10 µm in diameter. Multimode fibers have core sizes of 50 to 62.5 µm in diameter.


Fiber Cables – Construction

Glass fiber is coated with a protective plastic covering called the “primary buffer coating” that protects it from moisture and other damage. More protection is provided by the “cable” which has the fibers and strength members inside an outer protective covering called a “jacket”. Most indoor fiber optic cables are tight buffer design, usually they consist of the following components:

  • Tight buffer optical fiber
  • Kevlar which is used to further strength the cable structure, making it resist high tension
  • FRP which is non-metallic strengthen member
  • Cable outer jacket

So, based on these basic components, indoor fiber cables are available with following standard structures:

  • 900um Buffer cable
  • Simplex fiber cable
  • Duplex Fiber Cable
  • Distribution Bundle Fiber Cable
  • Breakout Fiber Cable
  • Ribbon Fiber Cable

indoor fiber cable

To meet different installation enverionment, the cable jackets will be flame retardant and built with LSZH, riser(OFNR) or Plunem(OFNP) rated PVC materials.

Indoor Optical Fiber Cables are mainly used in building wiring applications. As patch cables, they could be installed in network racks, cabinet, patch panels, and other fiber enclosures. As backbone fiber cables, they could be installed in walls, between floors, in plenum air handling ducts and under data center floors.

Fiber Cables – Single-mode or Multimode? 50/125 or 62.5/125?

For identification purposes, multimode fiber, and also singlemode fiber, is often referred to by its performance level identified by ISO/IEC (International Organization of Standards and International Electrotechnical Committee), which is based on the fibers bandwidth capabilities.

 Fiber Types and Typical Specifications

(OM/OS refers to TIA types, B refers to IEC types, G refers to ITU types)

 Core/Cladding

 Attenuation

Bandwidth

 Applications/Notes

 Multimode Graded-Index

 

@850/1300 nm

 

 50/125 microns (OM2)

3/1 dB/km

500/500 MHz-km

Laser-rated for GbE LANs

 50/125 microns (OM3)

3/1 dB/km

2000/500 MHz-km

Optimized for 850 nm VCSELs

 50/125 microns (OM4)

3/1 dB/km

3600/500 MHz-km

Optimized for 850 nm VCSELs, higher speed

 62.5/125 microns (OM1)

3/1 dB/km

200/500 MHz-km

LAN fiber

 100/140 microns

3/1 dB/km

150/300 MHz-km

Obsolete

Single-mode

 

@1310/1550 nm

 

9/125 microns (OS1 B1.1 or G.652)

 0.4/0.25 dB/km

 HIGH!

Singlemode fiber, most common for Telco/CATV/high speed LANs

~100 Terahertz

 9/125 microns (OS2, B1.2 or G.652)

 0.4/0.25 dB/km

 HIGH!

Low water peak fiber

~100 Terahertz

 9/125 microns (B2 or G.653)

 0.4/0.25 dB/km

 HIGH!

Dispersion shifted fiber

~100 Terahertz

 9/125 microns (B1.2 or G.654)

 0.4/0.25 dB/km

 HIGH!

Cutoff shifted fiber

~100 Terahertz

 9/125 microns (B4 or G.654)

 0.4/0.25 dB/km

 HIGH!

Non-zero dispersion shifted fiber

~100 Terahertz

Multimode Step-Index

 

@850 nm

@850 nm

 

 200/240 microns

 4-6 dB/km

 50 MHz-km

Slow LANs & links

POF (plastic optical fiber)

 

 @ 650 nm

  @ 650 nm

 

 1 mm

 ~ 1 dB/m

 ~5 MHz-km

Short Links & Cars

  • Single-mode 9/125 fiber is refered to as OS1 or OS2, now commonly used is OS2 type.
  • Multimode 62.5/125 fiber is referred to as OM1.
  • Multimode 50/125 fiber is referred to as OM2, OM3 and OM4. OM4 has greater bandwidth than OM3 and OM3 has greater bandwidth than OM2.

OM3 fiber is designed to accommodate 10 Gigabit Ethernet up to 300 meters, and OM4 can accommodate it up to 550 meters. Therefore, many users are now choosing OM3 and OM4 over the other glass types. In fact, nearly 80% of 50 micron fiber sold is OM3 or OM4.

If you require higher data rates or plan on upgrading your network in the near future, laser optimized 50 micron (OM3 or OM4) would be the logical choice.

 

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