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Lasers & Fiber Optics

Lasers & Fiber Optics. Engr. Hyder Bux Mangrio Engr. Fayaz Hassan Mangrio. Introduction. L&FO labs Lab #01: Introduction to Fiber optics Communication System Lab #02: Optical Sources Lab #03: Optical Detectors Lab #04: Optical fiber attenuation losses Lab #05: Analog voice transmission

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Lasers & Fiber Optics

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  1. Lasers & Fiber Optics Engr. Hyder Bux Mangrio Engr. Fayaz Hassan Mangrio

  2. Introduction L&FOlabs • Lab #01: Introduction to Fiber optics Communication System • Lab #02: Optical Sources • Lab #03: Optical Detectors • Lab #04: Optical fiber attenuation losses • Lab #05: Analog voice transmission • Lab #06: Understanding basic function of S122A splicer • Lab #07: Perform Fusion/Mechanical Splicing

  3. Introduction • Lab #08: Understanding the basic function of OTDR • Lab #09: Perform fiber measurement on OTDR • Lab #10: Fiber attenuation measurement using Cut-Back method • Lab #11: Optical Field Spectrum Analyzer • Lab #12: Overview of Power meter & Light Source

  4. Information • Email: hyder.bux@faculty.muet.edu.pk • Webpage: https://sites.google.com/a/faculty.muet.edu.pk/hydermangrio/ • Optical Communication Laboratory • Consultation Timings: Monday(8am to 3pm) & Friday (8am to 1pm)

  5. Laboratory • There will be at least 13 labs covering in 13 weeks course. Each lab will be approximately 2 hours long. The lab report / Handout is due to the lab assistant before next lab.

  6. What is lightwave technology? • Lightwave technology uses light as the primary medium to carry information. • The light often is guided through optical fibers (fiberoptic technology). • Most applications use invisible (infrared) light. (HP)

  7. Why lightwave technology? • Most cost-effective way to move huge amounts of information (voice, data) quickly and reliably. • Light is insensitive to electrical interference. • Fiber optic cables have less weight and consume less space than equivalent electrical links. (HP)

  8. Use Of Lightwave Technology • Majority applications: • Telephone networks • Data communication systems • Cable TV distribution • Niche applications: • Optical sensors • Medical equipment

  9. LW Transmission Bands 193 229 353 461 THz Frequency Near Infrared UV Wavelength (vacuum) 1.0 0.6 1.8 1.6 1.4 1.2 0.8 0.4 0.2 µm HeNe Lasers 633 nm Longhaul Telecom Regional Telecom Local Area Networks 1550 nm CD Players 780 nm 1310 nm 850 nm

  10. Introduction to Fiber Optics • Fiber optics is a medium for carrying information from one point to another in the form of light. Unlike the copper form of transmission, fiber optics is not electrical in nature. • A basic fiber optic system consists of a transmitting device that converts an electrical signal into a light signal, an optical fiber cable that carries the light, and a receiver that accepts the light signal and converts it back into an electrical signal.

  11. Introduction to fiber Optics

  12. Optical Sources • Two main types of optical sources • Light emitting diode (LED) • Large wavelength content • Incoherent • Limited directionality • Laser diode (LD) • Small wavelength content • Highly coherent • Directional

  13. Light Emitting Diodes (LED) • Spontaneous emission dominates • Random photon emission • Spatial implications of random emission • Broad far field emission pattern • Dome used to extract more of the light • Spectral implications of random emission • Broad spectrum

  14. Laser Diode • Stimulated emission dominates • Narrower spectrum • More directional • Requires high optical power density in the gain region • Optical Feedback: Part of the optical power is reflected back into the cavity • End mirrors • Lasing requires net positive gain • Cavity gain • Depends on external pumping • Applying current to a semiconductor pn junction • Cavity loss • Material absorption • Scatter • End face reflectivity

  15. Optical Detectors • Inverse device with semiconductor lasers • Source: convert electric current to optical power • Detector: convert optical power to electrical current • Use pin structures similar to lasers • Electrical power is proportional to i2 • Electrical power is proportional to optical power squared • Called square law device • Important characteristics • Modulation bandwidth (response speed) • Optical conversion efficiency • Noise • Area

  16. HOW DOES FIBRE OPTIC WORK ? • Carries Signals as Light Pulses • signals converted from electrical to light (and visa-versa) by special equipment • e.g. fibre-optic “transceiver” (transmitter / receiver)

  17. FIBRE CONSTRUCTION 8, 50, 62.5 Core Glass 125 Cladding Glass

  18. PRIMARY BUFFER Primary Buffer 250 Cladding 125 Core (62.5)

  19. SECONDARY BUFFER Secondary Buffer 900 Primary Buffer 250 Cladding 125 Core (62.5)

  20. FIBRE MATERIAL • Silica Glass • used for high-speed data applications • Plastics • used for low-speed data / voice applications • Composite Constructions • used for low-speed and specialized applications

  21. FIBRE TRANSMISSION • Multi-Mode • graded-index • used for short / medium distance applications • step-index • early fibre type - no longer used • Single-Mode • a.k.a Mono-Mode • used for long-distance / very high-speed applications • e.g. cross-country and transatlantic communications

  22. LIGHT TRANSMISSION MultiMode Step Index MultiMode Graded Index SingleMode

  23. 50 µm 62.5 µm 100 µm 8 µm 125 µm 125 µm 125 µm 140 µm MultiMode Graded Index SingleMode COMMON FIBRE SIZES

  24. Advantages/Disadvantages of Fiber Optics • Advantages • Enormous potential bandwidth • Small size and weight • Electrical Isolation • Signal security • Low transmission loss • Potential low cost

  25. Advantages/Disadvantages of Fiber Optics • Disadvantages • High cost for connector and interfacing • Requires specialized and sophisticated tools for maintenance and repairing • Higher initial cost in installation

  26. Light-Source • What is light? • Properties of Light. • Refractive Index • Law of Refraction • Law of Reflection • Total Internal Reflection

  27. Refractive Index • The guidance of the light beam which acts as a transmission channel for information (through the optical fiber) takes place because of the phenomenon of total internal reflection (TIR), which is dependent on the refractive index of the medium. The refractive index (n) of a medium can be written as:

  28. Total Internal Reflection • A ray of light incident on a denser medium i.e. n1<n2 According to Snell’s Law and the law of reflection we have n1 sin θ1 =n2 sin θ2 and θ1=θ3

  29. Total Internal Reflection • The angle of incidence, for which the angle of refraction is 90º, is known as the critical angle and is denoted by θc .Thus, when θ1=θc =sin-1(n2/n1) θ2=90. When the angle of incidence exceeds the angle of critical (i.e.,θ1>θc), there is no refracted ray and we have total internal reflection.

  30. Total Internal Reflection

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