Laser Technology and Principles

Course Information

• Course Title: Information Technology
• Course Code: IT438
• Communication Technology
• Instructor: Kamal Hamza, PhD
• Fall Semester 2024-2025
• Acknowledgement: Presentation contains some figures and text from Data Communications and Networks, by W. Stallings

Introduction

• Communication: The basic process of exchanging information from a source to a destination.
• Sending, receiving, and processing information/signals from one point to another.

Communication Systems Components

• Any system requires a transmitter, receiver, and a communication channel.
• The Transmitter prepares the data (information) to be transmitted in an appropriate format.

Communication System Components (cont.)

• Information Source: Generates the message (e.g., voice, pictures, keyboard). If the message isn’t electrical, a transducer converts it to an electrical signal. The source can be analog or digital.
• Source Encoder/Decoder: Maps the signal to a digital form and removes redundancy for a more efficient representation.
• Channel Encoder/Decoder: Maps the input signal into a different digital signal that minimizes noise.
• Modulator: Transmits the signal effectively over the channel. Most schemes adjust the amplitude, phase, or frequency.

Examples of Guided Comm. Channels

• Twisted Pair: Insulated wires twisted together for reduced interference and better signal retention. Often bundled into cables. Typically found in interior building wiring.
• Coaxial Cable: Inner and outer conductors separated by an insulator with a woven outer shield. Used in cable television and broadband communications
• Optical Fiber: Light-transmitting, thin filament of glass or plastic core. Light propagates largely through total internal reflection, in the core.

Examples of Unguided Comm. Channels

• Microwaves, Satellites, Radiowaves, Infra-Red

Why Different Types of Communication Systems?

• Nature of the channel (e.g., fiber optic cables for underwater).
• Nature of the application (mobile applications require wireless systems).
• Required level of quality.
• Cost.

Problems that Face Communication Systems

• Noise: Undesired effects from environment; usually beyond control.
• Interference: Signal superposition; may stem from system design flaws.
• Jamming: Deliberate interference to disrupt or destroy signal.

Data Versus Signal

• Data (Information): Application-generated information sent to a receiver.
• Signal: Representation of data within the communication system (e.g., electricity in a microphone).

Types of Data and Signal

• Analog data/analog signal: Traditional phone systems and similar.
• Analog data/digital signal: Voice over IP (VoIP) and digital music.
• Digital data/analog signal: Early internet connections and optical networks.
• Digital data/digital signal: Ethernet, Wi-Fi, and modern networks.

Signal Representation in the Time Domain

• Continuous signal: Signal intensity changes smoothly over time.
• Discrete signal: Signal intensity maintains a constant level for a period and then changes.
• Sine Wave: A smooth periodic oscillation with regular shape. Common in signal representation including sound waves, light waves. Used for representing analog signals in communication systems.
• Square Wave: Quickly switches between high and low values (on/off); used for digital signals (e.g., binary data).

Signal Representation in the Frequency Domain

• Electromagnetic signal comprises multiple frequencies; frequency range constitutes a signal’s spectrum.

Noise and Interference

• Practical system signals are blurred by noise and interference.
• Can be analyzed in time and frequency domains.

Signal Bandwidth

• Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies.
• Measured in Hertz.
• Bandwidth in different communication systems: Telecommunications, Radio Broadcasts, Video and TV transmission, Wi-Fi & 5G.

Fiber Optics Communication Technology

• Main components of an optical transmission system: Optical fiber links, Transmitters, Receivers, Amplifiers, Network medium
• Light Propagates by total internal reflection.
• Advantages of fiber optical links: High Bandwidth Capacity, Reduced Signal Attenuation (Loss), Immunity to Electromagnetic Interference, Security, Lightweight and Thin, Durability and Longevity, Reduced Latency, Scalability, Environmental Benefits, High Reliability.
• Types of optical fiber: Single-mode fiber, Multimode fiber.
• Attenuation in optical fiber: Attenuation coefficient (dB/km), Fiber length (km). Attenuation is loss as signal travels.
• Dispersion is the widening of pulse duration as it travels through a fiber.
• Various types of dispersion: Modal, Chromatical.
• Types and characteristics of different Optical Couplers

Nonlinearities in Fiber

• Nonlinearities in fiber occur when the light intensity in the fiber becomes high enough to cause the fiber's refractive index to change or induce other non-linear effects.
• This can lead to attenuation, distortion, and cross-channel interference. A specific example of this is called Four-Wave Mixing.

Optical Amplifiers

• Types of optical amplifier: Erbium-doped fiber amplifier (EDFA), Raman amplifier, Semiconductor optical amplifier (SOA).

Passive Star Couplers (PSC)

• Optical devices used in fiber optic networks to split or combine optical signals.
• Passive and rely on the physical properties of the fiber to distribute light signals.
• Commonly used for broadcast and select networks, or combining signals.
• Examples of coupling ratios for 8x8 and 16x16 PSC.

Transponders

• Critical components in DWDM systems between terminal equipment and the DWDM system.
• Functions include signal conversion (electrical or optical), regeneration, and wavelength assignment.
• Terminal-side wavelengths (850nm, 1310nm, 1550nm); DWDM side wavelengths (15xx nm).

Wavelength Converters (WC)

• Converts the wavelength of an input signal to another wavelength.
• Types of Wavelength Conversion: Opto-electronic (OE-WC), Coherent Effects.
• Comparison of these two methods.

Wavelength-Routed Networks (and similar)

• Optical Circuit Switching Networks (OCS).
• Setting up a circuit (path) between sender and receiver
• Stations connected via a set of nodes to form connections.
• Lightpath (wavelength).
• Problem of routing and wavelength allocation.
• Solution Strategies: Routing problem (shortest path using Dijkstra), Fault Tolerant routing, Wavelength Assignment problem(Random, first-fit, etc.)
• Other concepts: Optical Packet Switching (OPS), Speed-Mismatch Problem.
• Contention resolution.
• Optical buffers, Wavelength converters. Optical Burst Switching (OBS).

Multiplexers/Demultiplexers

• Multiplexers combine multiple optical signals with different wavelengths into one beam.
• Demultiplexers separate the combined optical signals into individual wavelengths at the receiver end.
• Adding and dropping functionality in DWDM networks.