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1.optical introduction
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- 22. What is anOptic Source? • The heart of a fiber optical data system • A Hybrid Device – Converts electrical signals into optical signals – Launches these optical signals into an optical fiber for data transmission. • Device consists of an interface circuit, drive circuit, and components for optical source. (LEDs, ELEDs, SLEDs, LDs, etc) 22
- 23. LEDs – LightEmitting Diode • Emits incoherent light through spontaneous emission. • Used for Multimode systems w/ 100-200 Mb/s rates. • Broad spectral width and wide output pattern. • 850nm region: GaAs and AlGaAs • 1300–1550nm region: InGaAsP and InP • Two commonly used types: ELEDs and SLEDs 23
- 24. SLEDs – SurfaceEmitting LEDs • Primary active region is a small circular area located below the surface of the semiconductor substrate, 20-50µm diameter and up to 2.5µm thick. • Emission is isotropic and in lambertian pattern. • A well is etched in the substrate to allow the direct coupling of emitted light to the optical fiber • Emission area of substrate is perpendicular to axis of optical fiber • Coupling efficiency optimized by binding fiber to the substrate surface by epoxy resin with matching refractive index 24
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- 26. ELEDs – EdgeEmitting LEDs • Primary active region is a narrow strip that lies beneath the semiconductor substrate • Semiconductor is cut and polished so emission strip region runs between front and back. • Rear face of semiconductor is polished so it is highly reflective while front face is coated with anti-reflective, light will reflect from rear and emit through front face • Active Regions are usually 100-150µm long and the strips are 50- 70µm wide which are designed to match typical core fibers of 50- 100µm. • Emit light at narrower angle which allows for better coupling and efficiency than SLEDs 26
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- 28. LDs – LaserDiodes • Emit coherent light through stimulated emission • Mainly used in Single Mode Systems • Light Emission range: 5 to 10 degrees • Require Higher complex driver circuitry than LEDs • Laser action occurs from three main processes: photon absorption, spontaneous emission, and stimulated emission. 28
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- 33. Splicing There are severalreasons for splicing a fiber cable, these include: To join two fibers due to a breakage. To connect some of the cores straight through a patch cabinet. To extend a cable run. To reduce losses, a fusion splice has much lower losses than two connectorized cables joined through a coupler. Or to attach a pre-terminated pigtail. 33
- 34. Definitions Splicer mechanical device forjoining two pieces of paper or film or magnetic tape Splice joint made by overlapping two ends and joining them Splicing process of the permanent connection of two pieces of optical fibers 34
- 35. Types of Splicing •Mechanical • Fusion (welding) 35
- 36. Fusion Splicing • Fusingthe two fibers • Flame heating sources - micro-plasma burners, oxy- hydric micro-burners, electric arc.. • Advantage - consistent and easily controlled heat with adaptability • Possible drawback - weakening of fiber in the vicinity of splice 36
- 37. Mechanical Splicing • bondingtwo fibers together in an alignment structure • Transparent adhesive - e.g. epoxy resin • Commonly used groove - V-groove • Alignment problems 37
- 38. Comparison Mechanical splicing Fusionsplicing Reflection losses (-45 db to -55 db) No reflection losses Insertion loss (0.2 db) Very low insertion loss (0.1 db to .15 db) cost – high Comparatively less 38
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- 40. V-groove optical fibersplicing 40
- 41. Optical Fiber Connectors •Some of the principal requirements of a good connector design are as follows: 1- low coupling losses 2- Interchangeability 3- Ease of assembly 4- Low environmental sensitivity 5- Low-cost and reliable construction 6- Ease of connection 41
- 42. Splicing Losses • Intrinsic -Freznel reflection • Extrinsic - foreign particles on surfaces • Reflection - incident and reflected beam travel on the same path 42
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- 47. Need of fiberoptic communication Fiber optic communication system has emerged as most important communication system Compared to traditional system because of following requirements: • 1. In long haul transmission system there is need of low loss transmission medium • 2. There is need of compact and least weight transmitters and receivers. • 3. There is need of increased span of transmission. • 4. There is need of increased bit rate-distrance product. A fiber optic communication system fulfills these requirements, hence most widely accepted 47