Unit 9. Exercise 1. Light Sources and Components – Definitions

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1. Forward Biased LED – Semiconductor diode with a positive voltage applied to the p-region and a negative voltage to the n-region.

2. Incoherent Light – Light in which the electric and magnetic fields of photons are completely random in orientation. Incoherent light is typically emitted from light bulbs and LEDs.

3. Laser – Acronym for light amplification by stimulated emission of radiation. The laser produces a coherent source of light with a narrow beam and a narrow spectral bandwidth (about 2cm). Lasers in fiber optics are usually solid-state semiconductor types. Lasers are used to provide the high-powered, tightly controlled light wavelengths necessary for high-speed, long-distance optical fiber transmissions.

4. Output Pattern – LED and laser semiconductors used in fiber-optic light sources are packaged to couple as much light as possible into the core of the optical fiber. The output pattern, or NA of the light source directly relates to the energy coupled into the core of the optical fiber.

5. Ouput Power – This power of light sources used in fiber-optic communication systems varies dramatically depending on the application. LEDs are typically designed to support transmission distances of up to 2km while laser light achieves distances in excess of 80km. Laser optical power output levels can exceed LED optical output power levels by more than 20dB.

6. Modulation Speed – One factor that can limit the performance/bandwidth of a fiber-optic communication system via the light source.

7. Core Diameter Mismatch – Occurs when there is a difference in the core diameters of the two optical fibers. A los may occur when the core diameter of the transmitting optical fiber is greater than the core diameter of the receiving optical fiber.

8. Current – Flow of electrons in a conductor.

9. PIN Photodiode – works like a PN photodiode; however, it is manufactured to offer better performance. The better performance comes in the form of improved efficiency and greater speed

10. Avalanche Photodiode – With respect to opticalfiber equipment, a specialized diode designed to use the avalanche multiplication of photocurrent. The photodiode multiplies the effect of the photons it absorbs, acting as an amplifier.

Page 2 Unit 9 Exercise 1 Light sources Essay

11. Responsivity – The ratio of a detector’s output to input, usually measured in units of amperes per watt. Also it’s themeasure of how well a photodiode converts a wavelength or range of wavelengths of optical energy into electrical current.

12. Optical Subassembly – The portion of a fiber-optic receiver that guides light from the optical fiber to the photodiode.

13. Dynamic Range – The difference between the maximum and minimum optical input power that an optical receiver can accept.

14. Operating Wavelength – The wavelength at which a fiber-optic receiver is designed to operate. Typically, an operating wavelength includes a range of wavelengths above the below the stated wavelength.

15. Fiber-Optic Coupler – A device that combines or splits optical signals.

16. Optomechanical Switch – Redirects an optical signal by moving fiber or bulk optic elements by means of the mechanical devices.

17. Optical Attenuator – Reduces the intensity of light waves, usually so that the power is within the capacity of the detector. There are three basic forms of attenuators: fixed optical attenuators, stepwise variable optical attenuators, and continuous variable optical attenuators. Attenuation is
normally achieved either by a doped fiber or an offset or core misalignment.

18. Optical Isolator – A component used to block out reflected and other unwanted light.

19. Wavelength Division Multiplexing – A method of carrying multiple channels through a fiber at the same time whereby signals within a small spectral range are transmitted at different wavelengths through the same optical-fiber cable.

20. Passive Optical Network – An optical network that does not electrically powered equipment or components to get the signal from one place to another.

21. FTTH – Fiber-to-the-home uses optical fiber from the central office to the home.

22. FTTB – Fiber-to-the-building uses optical fiber from the central office to the building and there are no electronics helping with the transmission in between.

23. FTTC – Fiber-to-the-curb fiber runs from the central office and stops at the curb.

24. FTTN – Fiber-to-the-node only has optical fiber from the central office to the node.

25. Feeder Cable – A voice backbone cable that runs from the equipment room cross-connect to the telecommunications cross-connect. A feeder cable may also be the cable running from a CO to a remote terminal, hub, head end, or node.

26. Distribution Cable – An optical fiber cable used “behind-the-shelf” of optical fiber patch panels; typically composed of 900 micron tight buffered optical fibers supported by aramid and/or glass-reinforced plastic (GRP).

27. Drop Point – Area where a terminal is to be installed.

28. Local Convergence Point – It’s the access point where the feeder cables are broken out into multiple distribution cables.

29. Network Access Point – Is located close to the homes or buildings it services. It’s the pint where a distribution cable is broken out into multiple drop cables.

30. Network Interface Device – Is typically mounted to the outside of the house or building. It’s an all-plastic enclosure designed to house the electronics that support the network.

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