OFCbasics.ppt
- 1. Dr.D. SRIRAM KUMAR Professor / ECE NIT, Trichy - 15
- 2. is a method of transmitting information from one place to another by sending light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information.
- 3. The process of communicating using fiber- optics involves the following basic steps: Creating the optical signal using a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, and receiving the optical signal and converting it into an electrical signal.
- 5. 1880 – Alexander Graham Bell 1930 – Patents on tubing 1950 – Patent for two-layer glass wave-guide 1960 – Laser first used as light source 1965 – High loss of light discovered 1970s – Refining of manufacturing process 1980s – OF technology becomes backbone of long distance telephone networks in NA.
- 6. An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Light is kept in the "core" of the optical fiber by total internal reflection.
- 7. Thinner Less Expensive Higher Carrying Capacity Less Signal Degradation& Digital Signals Light Signals Non-Flammable Light Weight
- 8. Much Higher Bandwidth (Gbps) - Thousands of channels can be multiplexed together over one strand of fiber Immunity to Noise - Immune to electromagnetic interference (EMI). Safety - Doesn’t transmit electrical signals, making it safe in environments like a gas pipeline. High Security - Impossible to “tap info.”
- 9. Less Loss - Repeaters can be spaced 75 miles apart (fibers can be made to have only 0.2 dB/km of attenuation) Reliability - More resilient than copper in extreme environmental conditions. Size - Lighter and more compact than copper. Flexibility - Unlike impure, brittle glass, fiber is physically very flexible.
- 10. greater capacity (bandwidth up to 2 Gbps, or more) smaller size and lighter weight lower attenuation immunity to environmental interference highly secure due to tap difficulty and lack of signal radiation 10
- 11. Disadvantages include the cost of interfacing equipment necessary to convert electrical signals to optical signals. (optical transmitters, receivers) Splicing fiber optic cable is also more difficult.
- 12. expensive over short distance requires highly skilled installers adding additional nodes is difficult 12
- 13. Telecommunications Local Area Networks CableTV CCTV Optical Fiber Sensors
- 14. relatively new transmission medium used by telephone companies in place of long-distance trunk lines also used by private companies in implementing local data networks require a light source with injection laser diode (ILD) or light-emitting diodes (LED) fiber to the desktop in the future 14
- 16. Core – thin glass center of the fiber where light travels. Cladding – outer optical material surrounding the core Buffer Coating – plastic coating that protects the fiber.
- 17. The core, and the lower-refractive-index cladding, are typically made of high-quality silica glass, though they can both be made of plastic as well.
- 18. consists of three concentric sections 18 plastic jacket glass or plastic cladding fiber core
- 19. Photons (light “particles”) light represented by tiny bundles of energy (or quanta), following straight line paths along the rays.
- 20. PLANCK’S LAW Ep =hf Where, Ep – energy of the photon (joules) h = Planck’s constant = 6.625 x 10 -34 J-s f – frequency o f light (photon) emitted (hertz)
- 23. 7.23 Figure 7.11 Optical fiber
- 24. 7.24 Figure 7.12 Propagation modes
- 26. 7.26 Table 7.3 Fiber types
- 27. 7.27 Figure 7.14 Fiber construction
- 28. 7.28 Figure 7.15 Fiber-optic cable connectors
- 29. Two main categories of optical fiber used in fiber optic communications are multi-mode optical fiber and single-mode optical fiber.
- 30. Single-mode fibers – used to transmit one signal per fiber (used in telephone and cable TV). They have small cores(9 microns in diameter) and transmit infra-red light from laser.
- 31. Single-mode fiber’s smaller core (<10 micrometres) necessitates more expensive components and interconnection methods, but allows much longer, higher-performance links.
- 32. Multi-mode fibers – used to transmit many signals per fiber (used in computer networks). They have larger cores(62.5 microns in diameter) and transmit infra-red light from LED.
- 33. Multimode fiber has a larger core (≥ 50 micrometres), allowing less precise, cheaper transmitters and receivers to connect to it as well as cheaper connectors.
- 34. However, multi-mode fiber introduces multimode distortion which often limits the bandwidth and length of the link. Furthermore, because of its higher dopant content, multimode fiber is usually more expensive and exhibits higher attenuation.
- 35. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded- index fiber.
- 36. A step-index fiber has a central core with a uniform refractive index. An outside cladding that also has a uniform refractive index surrounds the core; however, the refractive index of the cladding is less than that of the central core.
- 37. In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This causes light rays to bend smoothly as they approach the cladding, rather than reflecting abruptly from the core-cladding boundary.
- 39. Single-mode fiber Carries light pulses along single path Multimode fiber Many pulses of light generated by LED travel at different angles
- 40. 40 fiber optic multimode step-index fiber optic multimode graded-index fiber optic single mode
- 42. light-emitting diodes (LEDs) laser diodes
- 43. LEDs produce incoherent light laser diodes produce coherent light.
- 44. LED is a forward-biased p-n junction, emitting light through spontaneous emission, a phenomenon referred to as electroluminescence. The emitted light is incoherent with a relatively wide spectral width of 30-60 nm.
- 45. LED light transmission is also inefficient, with only about 1 % of input power, or about 100 microwatts, eventually converted into «launched power» which has been coupled into the optical fiber. However, due to their relatively simple design, LEDs are very useful for low-cost applications.
- 46. Communications LEDs are most commonly made from gallium arsenide phosphide (GaAsP) or gallium arsenide (GaAs) Because GaAsP LEDs operate at a longer wavelength than GaAs LEDs (1.3 micrometers vs. 0.81-0.87 micrometers), their output spectrum is wider by a factor of about 1.7.
- 47. LEDs are suitable primarily for local-area-network applications with bit rates of 10-100 Mbit/s and transmission distances of a few kilometers. LEDs have also been developed that use several quantum wells to emit light at different wavelengths over a broad spectrum, and are currently in use for local-area WDM networks.
- 48. A semiconductor laser emits light through stimulated emission rather than spontaneous emission, which results in high output power (~100 mW) as well as other benefits related to the nature of coherent light.
- 49. Laser diodes are often directly modulated, that is the light output is controlled by a current applied directly to the device.
- 50. The main component of an optical receiver is a photodetector that converts light into electricity through the photoelectric effect.
- 51. The photodetector is typically a semiconductor-based photodiode, such as a p-n photodiode, a p-i-n photodiode, or an avalanche photodiode.
- 52. Metal-semiconductor-metal (MSM) photodetectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers.
- 53. -60 -50 -40 -30 -20 -10 0 10-1 10-5 10-9 10-13 10-17 Average Received Optical Power (dBm) Bit Error Rate APD PIN
- 54. Two popular connectors used with fiber-optic cable: ST connectors SC connectors
- 55. 55 OPT 471A © Russell A. Chipman Long Haul Fiber System Submarine networks Metro Long Haul CATV Metro Metro Access • Types of Systems • Pulse quality • Bit Error Rate • Noise