Fibre Optic Transmission Chapter 1 Fibre Optic Transmission

Chapter coverage Introduction to Fibre-Optic Transmission Advantages of Fibre-Optic Communication Propagation modes, Single-Mode & Multi-Mode Fibres Light Sources, Photo Detectors Fibre Optic Transmission Optical Modulation Direct Modulation, External Modulation Optical Amplification WDM basics WDM Bandwidth Capacity SONET Standard SONET Network Architecture

Introduction to fiber optic transmission Definition : Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber.

Details of Optic Transmission Fiber optic is the fastest and most cost effective means for high capacity data transmission over large distance. It uses fiber glass material for data transmission and the data transferred in the form of light. Data loss is very less 0.2dB/Km No regeneration and amplification is required up to 10,000 km.

Structure of Fibre Optic

Advantages Bandwidth - Fiber optic cables have a much greater bandwidth than metal cables. Low Power Loss - An optical fiber offers low power loss.  This allows for longer transmission distances.  Interference - Fiber optic cables are immune to electromagnetic interference.  It can also be run in electrically noisy environments also.  Size & Weight - Fiber optic cables are much thinner and lighter than metal wires.   Security - Optical fiber are difficult to tap.  As they do not radiate electromagnetic energy, emissions cannot be intercepted.  As physically tapping the fiber takes great skill to do undetected, fiber is the most secure medium available for carrying sensitive data.

Disadvantages Cost - Cables are expensive to install but last longer than copper cables.  Transmission - transmission on optical fiber requires repeating at distance intervals.  Fragile - Fibers can be broken or have transmission loses when wrapped around curves of only a few centimeters radius.  However by encasing fibers in a plastic sheath, it is difficult to bend the cable into a small enough radius to break the fiber.  Protection - Optical fibers require more protection around the cable compared to copper.

Propagation in optical fiber Propagation means how the light travels in the fiber optic cables from source to target. There are 2 types of propagation mode in fiber optics cable They are : 1) Single Mode 2) Multimode

Single Mode This mode is called as single mode because the light is travelling in the lateral direction. There is only one angle that is straightway as the core of the diameter is very less. Source Destination

Multimode Multimode fiber optic cable has a large diameter core, so multiple modes of light propagate in it. It has more data carrying capacity due to multiple reflection inside. Source Destination

Light Source It is the heart of fiber optical system. A hybrid device converts electrical signal to optical signal and launches these optical signals into optical fiber for data transmission. There are two types of light source devices in fiber optics : - LED & LD

LED : - It is a light emitting diode LED : - It is a light emitting diode. It is a two led semiconductor light source. It is used for multimode system with 100-200 Mb/s rates. It works on low voltage and is inexpensive.

LD : - It is Laser Diode. It is mainly used in single mode systems LD : - It is Laser Diode. It is mainly used in single mode systems. Its light emission range is from 5 to 10 degrees. It Require Higher complex driver circuitry than LEDs therefore it is very expensive. It is also much more temperature sensitive than LEDs.

Light Detectors : - These are photodetectors Light Detectors : - These are photodetectors. It is the device used to convert optical signals to electrical signals. Photodetector Parameters : - Responsivity Wavelength bandwidth Damage Threshold

Optical Modulation : - The information can be transmitted on the optical carrier by varying any property of light like intensity, frequency etc. with respect to time. It is called as optical modulation. The most common optical modulation is intensity. There are two types of optical modulation: - DirectM ExternalM

DirectM :- In this technique the direct current which is supplying the light source is modulated. This is done by making small changes to biased current of the laser.

2) External Modulation : - It is used for longer distance communication links. Here the signals are externally modulated by electro absorption modulators.

Optical Amplification An optical amplifier is a fiber optic device used to amplify optical signals directly without conversion into electrical signals.

WDM Basics Multiplexing is a technique of sending multiple signals on a carrier at the same time in the form of single complex signal then recover the original signal at the end by separating the signals. WDM(Wavelength Division Multiplexing) is a type of multiplexing

WAVELENGTH DIVISION MULTIPLEXING

SONET : - It means Synchronous Optical Network. It is used for optical transmission. SONET used time domain multiplexing so as to send the bandwidth signals into one high-capacity signal that can be sent over optical fiber.

SONET Layers: -

The classes of SONET networking equipment are as follows: - O-E-O Regenerators 2) Add-drop multiplexers (ADMs) 3) Terminal Multiplexers(TMs)

Videos What are Fiber Optics ? https://www.youtube.com/watch?v=7h2xr-pi5VQ 2. What is SONET ? https://www.youtube.com/watch?v=UWpYyxXz0gs