Optical Fiber

Optical Fiber Cable(OFC)

What is the principle of optical Fibre?

In 1854, john tyndall, experiment prove that light beam can travel inside the water and can follow a specific path by using internal reflection same thing used in optical fiber. An optical fiber is a flexible, transparent fiber made by glass(silica). Optical fiber provide a medium for transmission of information in the form of light. The optical fibers basically work on the principle of total internal reflection.

Construction of optical fiber

optical fiber has 4 main component
1-Core
This is the main layer that is made up by silica(or glass) in which our light signal will travel from source to destination by the process of total internal reflection
2-Cladding
This is layer of silica(or glass) that cause necessary reflection to allow light to travel through the core of fiber.
Note:-Refractive index of cladding is less then core.
3-Coating
This is the thicker surrounds layer around the cladding. It is made up by Carbon, Polymide, Silicone etc.
4-Electo Chromium Coated Steel(ECCS) Tape
This is a steel strip which is used for optical fiber cable armouring. It has very hight tensile strength. It protect from attacks from rodents.
5-Buffer
It used to encapsulate one or more optical fiber and also providing protection from physical damage. Generally it is filled with a gel such as Synthetic Thixotropic Gel. It is mostly made up from Polybutylene terephthalate(PBT)
6-Jacket
It protect our optical fiber from external environment condition and physical damage.jacket is usually made of PolyEthylene(PE), HDPE, PVC etc.

Note:-Fiber optic cable carry a number of strands of fiber optic and these strands can be grouped as Tight buffer cable or Loose Tube buffer cable.

Tight buffer cable

A Tight buffer cable consists of one or more bundled fiber strands covered by an outer often jacket the outer jacket contain multiple layer to add structure to the cable and provide water resistance.

Loose Tube buffer cable

Loose Tube buffer cable fiber strands are contained within a buffer tubes allowing the strands to move freely while also providing additional protection for strands. The addition of buffer tubes and other protective layer causes the cable diameter to be larger and cable to less flexible.
But a Tight buffer cable is more easily damaged than loose buffer cables therefore tight buffer cable are more appropriate for indoor use and loose buffer cables for outdoor use.

Fiber optic cable types

1-single mode optical fiber(SMF)

In single mode optical fiber only one wave(light) can travel through the fiber.
It is basically used for long distance transmission of the signal.

2-Multi-mode optical fiber(MMF)

In Multi-mode optical fiber we can pass more than one light wave from source to destination at same time.
In case of Multi-Mode optical fiber the diameter of core is more then diameter of cladding.

Multi-mode fiber are two type step-index multi-mode and graded index multi-mode

Graded index multi-mode fiber

• In graded index multi-mode fiber is a type of optical fiber where the refractive index is higher at the axis of the core and then it decreases gradually towards the core-cladding interface.
• In graded index multi-mode fiber light travels forward in the form of sinusoidal oscillation.

Step-index multi-mode fiber

• In step-index fiber a uniform refractive index exists within the core and a sharply decresed refractive index exists in the core-cladding interface.
• In step-index fiber light travels forward in a zig-zag path along the axis of fiber.

Different types of optical fiber used commercially

Multimode fiber cable is prefixed with 'OM' and Single mode fiber cable is prefixed with 'OS'. Presently single mode optical fiber have 2 types:-OS1 and OS2. Whereas Multimode have 6 type:-OM1, OM2, OM3, OM4, OM4+ and OM5.
The size of fiber measure in micron(µm). It is very small unit of measurement as 1µm=1X10^-6 metre and the diameter of human hair is between 20 to 200µm. As in case of multimode fiber more than one signal can travel through fiber core, therefore multimode fiber has a much larger core size as compare to single mode.Presently multimode fiber core have two main size 50 micron and 62.5 micron(it is used in case of OM1).
Generally the size is show by the companies as 62.5/125/250(Fiber size)
Here, First set of number 62.5 refer to diameter core, second set of number 125 refer to diameter of outside of the fiber cable’s that is cladding. Third set of number 250 for coating
In companies datasheet this data is indicated as
Typical Core Diameter :-62.5 ± 2.5 µm
Cladding Diameter:-125 ± 0.7 µm
Primary Coating Diameter:-245 ± 7 µm

Types of optical fibers

Single-mode(SM) optical fiber 9/125µm

• Generally yellow in colour. It also indicated as OS
• It is used mainly a long distance communication upto 10Km. It has low attenuation as Compare to the multimode fiber

62.5/125µm(OM1)

• Generally orange in colour
• lenght-1GB upto 275meter.
• Bandwidth:-200MHz(depend on quality fiber)

50/125µm(OM2)

• Generally orange in colour
• lenght-1GB upto 550meter
• Bandwidth:-500MHz(depend on quality fiber)

50/125µm(OM3)

• Generally Aqua in colour
• lenght-for 1GB upto 550meter, for 10GB upto 300meter, for 40GB upto 100meter
• Bandwidth:-2000MHz(depend on quality fiber)

50/125µm(OM4)

• Generally Aqua in colour
• lenght-for 1GB upto 550meter and for 10GB upto 400meter, for 40GB upto 150meter, for 100GB upto 150meter
• Bandwidth:-4700MHz(depend on quality fiber)

50/125µm(OM4+)

• Generally violet in colour
• lenght-for 1GB upto 550meter, for 10GB upto 800meter, for 40GB upto 300meter, for 100GB upto 300meter
• Bandwidth:-4900MHz(depend on quality fiber)

50/125µm(OM5)

• Generally green in colour
• lenght-for 1GB upto 550meter, for 10GB upto 400meter, for 40GB upto 150meter, for 100GB upto 150meter
• It is used for Short Wavelenght Division Multiplexing(SWDM) for a wavelength of 840nm to 953nm.
Note:-By the help of SWDM technology we can transmit 4 fiber data into one fiber

NOTE:-All outdoor fiber cables are black jacketed to protect from the sun harmful ultraviolet rays

Source of transmit signal in optical fiber

For transmitting signal we use Led in OM1 and OM2 and after that from OM3 we start using LASER(Light Amplification by Stimulated Emission of Radiation) such as VCSEL(Vertical cavity surface emitting laser)

Mode Field Diameter(MFD)

Mode Field Diameter(MFD) is a measure of light intensity, MFD as the effective area of fiber in which light signal propagating. Therefore it is combination of core and a little bit part of cladding.

Why is MFD important ?

It provides information about the cable performance and the amount of signal loss while propagating in the fiber due to micro bending, splicing and impurity in fiber.
MFD information given in company datasheet
Typical Mode Field Diameter@1310nm:-9.2 ± 0.4 µm
Typical Mode Field Diameter@1550nm:-10.4 ± 0.5 µm

Type of optical fiber on the base of construction

1-uni-tube
In case of uni-tube optical fiber we do not have CSM(Central strength Member).
2-Multi-tube
CSM(Central strength Member) is a rod at the center of Multi-tube fiber, which is mostly made of Fiber Reinforced Plastic(FRP). for making FRP we used E-Glass fiber with high heat resistance, which provide excellent strength and stiffness to the cable.

Type of armouring in the cable

Multi-tube steel tape armoured cable
here armouring is done by steel wire , which provide excellent mechanical streangth. It is mostly used as cable with steel tape is light weight that steel wire
Multi-tube steel wire armoured cable
here armouring is done by steel wire , which provide excellent mechanical streangth. But its weight increase largely.
Multi-tube dielectric armoured cable
here armouring is done by dielectric(IGFR) which due of which it is suitable in the area where rodent are peresent. It is a lightweight armoured cable.
Multi-tube FRP armoured cable
here armouring is done by FRP road.

Applications of fiber optics

• Simplex fiber and duplex fiber are design to use indore application such as for desktop connectivity from modem and to establish a link between electronic equipment.
• Jelly filled optical fiber is designed endure outside temperature and high moisture condition.
• Dry loose tube cable are offering easy handling and very good durability for a broad range of application. As these cable are also light in weight therefore these are streamline cable.
• Armoured cable used for rodent protection in direct burial if you required.
• Jelly filled optical fiber is designed endure outside temperature and high moisture condition.
• Mostly single mode is used in telecommunication network, cable T.V(CATV) network and 5G network mainly depend on optical fiber. As optic cable transmit large amount of data at very high speed. As optical fiber use light as a signal therefore they do not affected by EM wave and it provide us high security transmission for a long distance
• Multimode fiber mostly used inside data center, in a LAN(Local Area Network) and CAN(Campus Area Network). As Multimode fiber provide us greater bandwidth and speed.