Ecc3601 lecture 2

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Modulation to Optical Modulation

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Ecc3601 lecture 2

  1. 1. ECC3601: OPTICAL COMMUNICATION Lecture 2: Introduction to Optical Communication (Part 2) Makhfudzah bt. Mokhtar, PhD. Department of Computer and Communication Systems Faculty of Engineering University Putra Malaysia
  2. 2. LEARNING OUTCOMES At the end of this lecture, students should be able to: -Define ‘light’ and ‘photon’ -Explain the property of light in terms of particle and wave -Identify light as the information carrier signal -Identify the significance of optical communication -Follow the evolution of optical communication
  3. 3. What is Light? Light is an electromagnetic radiation that is responsible for the sense of sight Light From Wikipedia, the free encyclopedia
  4. 4. Radiation can be defined as small (subatomic) particles with kinetic energy that are radiated or transmitted through space. The behaviour of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. What is radiation? Available at http://www.rerf.jp/general/whatis_e/index.html
  5. 5. What is Photon? Light is transported by particles, called photons. They have no mass, but carry sizeable amount of energy. About 1019 photons of a laser beam hit a mirror per second. (© thn) light and its particles: photons Available at http://www.attoworld.de/Home/attoworld/ElectronsAndLight/LightAndPhotons/index.html
  6. 6. Light as a ‘particle’ and ‘wave’ Light has both wave and particle properties. Electromagnetic radiation can be considered to consist of particle-like packets of wave-energy called photons. These massless particles travel at the speed of light (300,000 kilometers per second in a vacuum). Every photon is characterized by wavelength (the distance from the crest of one wave to the crest of the next wave), by frequency (the number of wave cycles that pass by in a given period, measured in Hertz, which stands for cycles per second), and by the energy it carries (measured in electron volts). http://micro.magnet.fsu.edu/primer/java/wavebasics/index.html Is light a particle or wave? Available http://www.edinformatics.com/math_science/electromagnetic_spectrum.htm
  7. 7. The energy carried by a photon is proportional to the number of field oscillations per second, called frequency. The energy of infrared photons, which can build up a wave oscillating at a low frequency relative to visible light is therefore smaller than the energy of visible light photons. The more photons cross a unit area per second the larger the amplitude of oscillations of the electric and magnetic fields and the higher the intensity of the light wave. light and its particles: photons Available at http://www.attoworld.de/Home/attoworld/ElectronsAndLight/LightAndPhotons/index.html
  8. 8. Preparation for Quiz 1 -Find equation than relates wavelength, frequency and light speed (calculation based) -Find equation that relates energy and frequency of light (calculation based)
  9. 9. Light as information carrier signal Sun’s radiation Sender Message Receiver Eye - brain Hand motion, semaphore line -Slow information transfer -Limited transmission distance (1790s) -Higher probability of error Sun’s radiation Sender Message Receiver Eye - brain Smoke signal -Longer transmission distance
  10. 10. Photophone (1880) Sender Thin voicemodulated mirror Sun’s radiation Message-voice -Not successfully commercialized due to the invention of telephone Receiver Photoconducting selenium cell Lamp Sender Blinker light, traffic light Message Receiver Eye - brain -Low information capacity
  11. 11. (1960) Unguided laser radiation Sender Laser Modulated message (non-fiber) Receiver Photodiode -High capacity optic communication -Need for clear line-of-sight -Eye damage risk (1960s) Guided laser radiation Sender Laser Modulated message (Glass fiber) Receiver Photodiode -Light beam is guided (based on John Tyndall demonstration – 1854) -Very high attenuation, need for low attenuation of optical fiber
  12. 12. Evolution of optical fiber Optical Fibre Communication – ppt MeintSmit (OED)XaveerLeijtens (OED)Huug de Waardt (ECO)Eduward Tangdiongga (ECO)
  13. 13. The significance of optical communication system Mbps Increase of the bandwidth and decreases of the cost per transmitted bit. Ref.: S. Kartalopoulos, WDWM Networks, Devices and Technology Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar
  14. 14. The significance of optical communication system Increase of the bit rate distance product BL for different communication technologies over time. Ref.: G.P. Agrawal, Fiber-Optic Comm. systems A figure of merit of communication systems is the bit rate – distance product, BL, where B is the bit rate and L is the repeater spacing. Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar
  15. 15. Bit-rate distance product (BL) for different generations of optical communication systems. Ref.: G.P. Agrawal, Fiber-Optic Comm. systems * The increase of the capacity-distance product can be explained by the four major innovations. Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar
  16. 16. Evolution of lightwave system 1. Generation: The development of low-loss fibers (compared to glass fiber) and semiconductor lasers (GaAs) in the 1970‘s. A Gallium Arsenide (GaAs) laser operates at a wavelength of 0.8μm. The optical communication systems allowed a bit rate of 45Mbit/s and repeater spacing of 10km. Example of a laser diode. (Ref.: Infineon) Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar
  17. 17. 2. Generation: The repeater spacing could be increased by operating the lightwave system at 1.3μm. The attenuation of the optical fiber drops from 2-3dB/km at 0.8μm down to 0.4dB/km at 1.3μm. Silica fibers have a local minima at 1.3μm. Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar
  18. 18. 2. Generation: The transition from 0.8μm to 1.3μm leads to the 2nd Generation of lightwave systems. The bit rate- distance product can be further increased by using single mode fibers instead of multi-mode fibers. Single mode fibers have a distinctly lower dispersion than multi mode fibers. Lasers are needed which emit light at 1.3 μm. 3. Generation: Silica fibers have an absolute minima at 1.55μm. The attenuation of a fiber is reduced to 0.2dB/km. Dispersion at a wavelength of 1.55μm complicates the realization of lightwave systems. The dispersion could be overcome by a dispersionshifted fibers and by the use of lasers, which operate only at single longitudinal modes. A bit rate of 4Gbit/s over a distance of 100km was transmitted in the mid 1980‘s. Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar
  19. 19. 3. Generation: The major disadvantage of the 3. Generation optical communication system is the fact that the signals are regenerated by electrical means. The optical signal is transferred to an electrical signal and the signal is regenerated and amplified before the signal is again transferred to an optical fiber. Traditional long distance single channel fiber transmission system. Ref.: H. J.R. Dutton, Understanding optical communications Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar
  20. 20. 4. Generation: The development of the optical amplifier lead to the 4. Generation of optical communication systems. Schematic sketch of an erbium-doped fiber amplifier (EDFA). Ref.: S.V. Kartalopoulos, Introduction to DWDM Technology Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar
  21. 21. State of the Art optical communication system: Dense Wavelength Division Multiplex (DWDM) in combination of optical amplifiers. The capacity of optical communication systems doubles every 6 months. Bit rates of 10Tbit/s were realized by 2001. Ref.: S. Kartalopoulos, WDWM Networks, Devices and Technology Introduction to Optical Communication – Lecture slide Prof. Dr. Manoj Kumar

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