Optical Fiber Lecture Notes

Introduction

• Optical Fiber Definition: Flexible glass or plastic fiber transmitting light from one end to the other.
• Advantages over Metal Wires:
  • Less loss in signal transmission
  • Immune to electromagnetic interference
• Applications:
  • Fiber-optic communications
  • Illumination and imaging (fiberscopes)
  • Fiber optic sensors and fiber lasers

Structure and Types

• Composition: Core surrounded by transparent cladding with lower refractive index.
• Total Internal Reflection: Keeps light in the core, acting as a waveguide.
• Types of Fibers:
  • Multi-mode Fibers:
    • Wider core diameter
    • Used for short-distance communication and high power applications
  • Single-mode Fibers (SMF):
    • Used for communication links longer than 1,050 meters

Joining Optical Fibers

• Importance: Low loss joining is crucial for communication.
• Techniques:
  • Fusion splice (permanent connection using an electric arc)
  • Mechanical splice (temporary connection)
  • Optical fiber connectors for semi-permanent connections

Fiber Optics Field

• Definition: Applied science and engineering involving optical fibers.
• Coined by: Narinder Singh Kapany

Historical Development

• 1840s: Light guiding by refraction demonstrated by Daniel Colladon and Jacques Babinet.
• 1953-1956: Development of image transmission through optical fibers.
• 1965: Charles K. Kao & George A. Hockham propose reducing attenuation for practical communication.
• 1970: Breakthrough with low attenuation fiber by Corning Glass Works.
• 1980s-2000s: Advancements in fiber manufacturing speeds and capabilities.

Uses of Optical Fibers

• Communication:
  • Medium for telecommunication and networking
  • Long-distance communication with fewer repeaters
• Military: Use in drones immune to electromagnetic interference
• Sensors:
  • Remote sensing applications
  • Measure strain, temperature, pressure
• Power Transmission:
  • Transmit power using photovoltaic cells
• Other Uses:
  • Illumination (fiber optic lamps)
  • Imaging optics (endoscopes)
  • Structural health monitoring

Principle of Operation

• Waveguide Theory:
  • Dielectric waveguide transmitting light via total internal reflection
• Refractive Index:
  • Determines speed of light in material
  • Important for signal speed calculations

Mechanisms of Attenuation

• Transmission Loss: Reduction in light intensity as it travels through fiber.
• Causes:
  • Scattering (Rayleigh scattering)
  • Absorption (UV-Vis-IR)
• Loss Budget: Calculating total loss over a fiber link including connectors and splices.

Manufacturing

• Materials:
  • Common: Silica glass, fluoride glass, phosphate glass
  • Plastic optical fibers for short distances
• Process: Preform construction and drawing fiber from the preform.
• Coatings: Protect fiber, minimize attenuation due to microbending.

Practical Issues

• Installation:
  • Bend radius considerations
  • Tension resistance for installation
• Termination and Splicing:
  • Use of connectors and splicing techniques
  • Fusion and mechanical splicing methods
• Free-space Coupling: Aligning fibers with devices or other fibers.

Recent Advancements

• Photonic Crystal Fibers: Use diffraction effects for light guidance.
• Data Transmission Speeds: Significant milestones achieved, enhancing capacity.

Note: These notes cover key points and details for a comprehensive understanding of optical fibers based on the provided transcript.