By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 1/28 Fibre Optic Communications Saroj Regmi Lecture 06 CT0004NI Principles of Comms Systems

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 2/28 Last Lecture: 05 Satellite Communications Introduction to Satellites, Components of a Human-Made Satellite, Launching a Satellite, Orbital Altitudes, Satellites in Orbit, Satellite Systems, GSO, MEO and LEO Satellites, Satellite Payload.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 3/28 Today’s Lecture: 06 Fibre Optic Communications Introduction to Optical Communications, Technological Developments, System & Data Link Considerations, System Components, Optical Fibre Principle of Operation, Types of Optical Fibre, Optical Fibre Transmission Characteristics, Wavelength Division Multiplexing.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 4/28 Reflection from sunlight, smoke signals, etc. “Flashing light signalling” used by the military to transmit information (Morse Code). Optical Communications

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 5/28 Technological Developments The invention of laser during the 1950s, The invention of glass optical fibres during the 1960s,  Initiallyα = 1000 dB/km  1970s α = 20 dB/km  1980s α < 1 dB/km (for single mode glass optical fibres),  1990s α 0.1 dB/km (for single mode glass optical fibres). Where: α = attenuation

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 6/28 Optical Fibre Communication Systems Initial installations in the late 1970s to early 1980s, Transcontinental and Sub-sea communications, In lakes and around continents under the sea.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 7/28 Fibre Optic Data Link Design Considerations Bandwidth / Data Rate, Power Budget:  Source power and detector sensitivity minus losses. Component Compatibility based on the wavelength used.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 8/28 Optical Fibre Communication System Components Transmitter Receiver

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 9/28 Generic Optical Fibre Communication System

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 10/28 Active Opto-Electronic Components Light Sources used are:  Laser (Light Amplification by Stimulated Emission of Radiation),  LED (Light Emitting Diode). Light Detectors:  With internal amplification - Avalanche Photodiodes (APD),  Without internal amplification.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 11/28 Comparison Between Light Sources ParameterLEDsLasers EfficiencyLowerHigher Response TimeSlowerFaster Data Transmission RateLowerHigher Output SpectrumBroaderNarrower Light BeamNot coherentCoherent Bit RateLowerHigher Launch Power LowerHigher Distortion at Output HigherLesser Transmission Distances ShorterLonger DispersionHigherLower Heating ProblemsLowerBigger ConstructionSimplerComplicated Life TimeLongerShorter

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 12/28 Principle of Operation of an Optical Fibre Based on the laws of refraction and reflection: Incident light n 1 > n 2 Reflected light Refracted light Where:n 1 and n 2 are the refractive indices of the two media, = critical angle, = angle of incidence.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 13/28 Core made of glass or plastic, Cladding made of glass or plastic, Jacket made of plastic elastic material. The refractive index of the core (n 1 ) is higher than the refractive index of the cladding (n 2 ) to ensure total internal reflection: n 1 > n 2 The Structure of an Optical Fibre

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 14/28 Light is injected in the core of the fibre up to a maximum angle, known as the acceptance angle, The acceptance angle in within a cone shaped zone, known as Numerical Aperture, NA. Acceptance Angle & Numerical Aperture Where:n 0 = the refractive index of air (n 0 ≈ 1), n 1 = the refractive index of the core, n 2 = the refractive index of the cladding.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 15/28 Multimode Step Index Optical Fibre:  An optical fibre with refractive index for the core, n 1, and the cladding, n 2, where n 1 > n 2. Uniform refractive index throughout.  It can support many hundreds of modes, i.e. rays of light.  Suffers from dispersion, i.e. broadening of the pulse. Optical Fibre Structures

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 16/28 Optical Fibre Structures (…2) Multimode Graded Index Optical Fibre:  An optical fibre whose core refractive index decreases as a function of the radial distance from its centre.  The refractive index of the core at its centre is the highest slowing the mode which travels parallel to the optical axis of the fibre.  This fibre causes the modes which have been injected closer to the critical angle of the fibre to travel faster thus resulting in all the modes reaching the end of the fibre at the same time.  Considerable decrease in dispersion effects.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 17/28 Singlemode Step Index Optical Fibre:  Step refractive index arrangement but the core is only 50μm.  Only a single ray can propagate thus no dispersion effects. Optical Fibre Structures (…3)

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 18/28 Light Distribution Within the Fibre Core

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 19/28 Three Common Types of Optical Fibre Where: GOF = Glass Optical Fibre POF = Plastic Optical Fibre

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 20/28 Optical Fibre Transmission Characteristics 1 st window (880 nm) 2 nd window (1310 nm) 3 rd window (1550 nm)

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 21/28 Amplifier Fibre Long distance communication is achieved using either electrical or optical amplifiers.  Electrical: Required the optical signal to be converted to electrical to be amplified and then back to optical again for transmission.  Optical: Can amplify the optical signal without needing to convert them to electrical. Amplification

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 22/28 Wavelength Division Multiplexing (WDM) A number of channels is used simultaneously to transmit a number of independent information channels over the same fibre.  WDM is a viable system concept. Technology available. Very good design understanding. Systems are deployed continuously. Current configurations deliver 1.6 Tbps (160 x 10 Gbps). Worldwide research on 40 Gbps per wavelength. Future evolution towards 40 Gbps per wavelength and beyond.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 23/28 Information Capacity:  Optimum use of fibre,  Avoids “bottle neck” in electronics. Operational:  Dynamic routing,  Wavelength routing,  Management and control in the optical layer. Advantages of WDM Linear propagating conditions, Sufficient channel separation to prevent cross talk. Requirements of WDM

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 24/28 WDM Systems Monitor Points Demux 2 n 1 n-1 Wavelength Converter 2 n 1 n-1 Multiplexer Wavelength Converter NT Network Terminals NT Today, dense wavelength-division multiplexing (DWDM) systems combine 4 to 120 channels using a wavelength multiplexer (MUX). A demultiplexer (DEMUX) separates the received channels to individual receivers in network terminals (NTs).

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 25/28 WDM Systems (…2) 1 1 Multiplexer Demultiplexer  n  n Fibre Optical Amplifier Routing Node WDM is achieved using multiplexers and demultiplexers.

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 26/ nm1545 nm Channels: 16 Spacing: 0.8 nm DWDM Spectrum

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 27/28

By: Dr. N. Ioannides (Feb 2010)CT0004NI - L.06 – Fibre Optic Communications - pp 28/28 Summary Introduction to Optical Communications, Technological Developments, System & Data Link Considerations, System Components, Optical Fibre Principle of Operation, Types of Optical Fibre, Optical Fibre Transmission Characteristics, Wavelength Division Multiplexing.