Optical Fiber

& OF Cables

THE PRESENTATION

Brief Flow of the Presentation.1. What are Optical Fibers?

2. Advantages / Disadvantages of OF….

3. Various Types of OF Cables. Their Construction , Specifications etc…

4. Some Test Equipments & Instruments used in OF Communications.

What this presentation is about?This presentation is about giving a broad idea about the concepts of Optical Fiber and OF Cables, (OPGW, Lashed cables, ADSS, Under Ground & Duct Cables ) without going into the deep technicalities. So that as and when OF is being discussed the person who has attended this presentation is able to understand and follow the discussion.

WHAT ARE OPTICAL FIBERS ?

Q.) And how deep is the Pacifica ocean?

Ans) At the deepest point called the Marina Trench, The pacific ocean is all of just 13km deep…..!!!!!

Optical Fibers are thins long (km) strands of ultra pure glass (silica) or plastic that can to transmit light from one end to another without much attenuation or loss.

The glass used to make Optical Fibers is so pure that if the Pacific Ocean was filled with this glass then we would be able to see the ocean bottom form the surface….!!!!

This is to be believed as repeater distances on long haul routes for optical fibers vary from 50 to 150 km.

Working of Optical fibers?

The light source (LAZER) at the transmitting (Tx) end is modulated by the electrical signal and this modulated light energy is fed into the Optical Fiber.

At the receiving end (Rx) this light energy is made incident on photo-sensors which convert this light signal back to electrical signal.

1. VERY HIGH INFORMATION CARRING CAPACITY.

2. LESS ATTENUATION (order of 0.2 db/km)

3. SMALL IN DIAMETER AND SIZE & LIGHT WEIGHT

4. LOW COST AS COMPARED TO COPPER (as glass is made from sand..the raw material used to make OF is free….)

5. GREATER SAFETY AND IMMUNE TO EMI & RFI, MOISTURE & COROSSION

6. FLEXIBLE AND EASY TO INSTALL IN TIGHT CONDUICTS

7. ZERO RESALE VALUE (so theft is less)

8. IS DILECTRIC IN NATURE SO CAN BE LAID IN ELECTICALLY SENSITIVE SURROUNDINGS

9. DIFFICULT TO TAP FIBERS, SO SECURE

10. NO CROSS TALK AND DISTURBANCES

ADVANTAGES OF OPTICAL FIBERS

1. The terminating equipment is still costly as compared to copper equipment.

2. Of is delicate so has to be handled carefully.

3. Last mile is still not totally fiberised due to costly subscriber premises equipment.

4. Communication is not totally in optical domain, so repeated electric –optical – electrical conversion is needed.

5. Optical amplifiers, splitters, MUX-DEMUX are still in development stages.

6. Tapping is not possible. Specialized equipment is needed to tap a fiber.

7. Optical fiber splicing is a specialized technique and needs expertly trained manpower.

8. The splicing and testing equipments are very expensive as compared to copper equipments.

DISADVANTAGES OF OPTICAL FIBERS…

Composition of optical fibreComposition of optical fibre

Silica based glass or plastic filaments are spun and packed into bundles of several hundreds or thousands. Bundles may be put together as rods or ribbons and sheets.

These bundles are flexible and can be twisted and contorted to conduct light and images around corners

The thin glass center of the fibre where the light travels is called the “core”.

The outer optical material surrounding the core that reflects the light back into the core is called the “cladding”.

In order to protect the optical surface from moisture and damage, it is coated with a layer of buffer coating.

Cross section of a bundle

7.9

Figure 7.14 Fiber construction

Operation of the fibre optic systemOperation of the fibre optic system

Light is ejected into the glass core at the correct angle and transmitted; it will reflect back repeatedly with internal reflections, even when the rod is curved. Light cannot escape from a fibre optics cable. A bundle of rods of fibres is capable of taking an image projected at one end of the bundle and reproducing it at the other end.

Reflected path of light in the glass rod

Two main types of cablesTwo main types of cablesStep Index Fibre Step Index Fibre This cable has a specific index of refraction for

the core and the cladding.  It causes deformations due to the various paths lengths of the light ray.  This is called modal distortion. It is the cheapest type of cabling. Within the cladding and the core, the refractive index is constant.

Graded Index Fibre Graded Index Fibre

In graded index fibre, rays of light follow sinusoidal paths. Although the paths are different lengths, they all reach the end of the fibre at the same time. Multimode dispersion is eliminated and pulse spreading is reduced. Graded Index fibre can hold the same amount of energy as multimode fibre. The disadvantage is that this takes place at only one wavelength.

APPLICATIONS OF OPTICAL FIBERS…

1. LONG DISTANCE COMMUNICATION BACKBONES

2. INTER-EXCHANGE JUNCTIONS

3. VIDEO TRANSMISSION

4. BROADBAND SERVICES

5. COMPUTER DATA COMMUNICATION (LAN, WAN etc..)

6. HIGHT EMI AREAS

7. MILITARY APPLICATION

8. NON-COMMUNICATION APPLICATIONS (sensors etc…)

COMPARISION WITH OTHER MEDIA / TECHNOLOGIES

VARIOUS TYPES OF OPTICAL FIBER CABLES

1. OPGW Cable

2. ADSS type OF Cable

3. Self-Support AERIAL figure 8 type OF Cable

4. LASHED type OF Cable

5. UNDERGROUND / BURRIED type OF Cables

6. DUCT Type OF Cable

Thank YouThank You

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