You can tell the students that yes, we will be using Visual Fault Locators that operate around 650 nm and are Class 2 Lasers, but will not do any permanent damage if exposed directly to the eye. When it comes to using VFLs, guidance will be provided on how to avoid direct eye exposure to the light.All other light sources today are low power Class 1 lasers that are not in the visible light spectrum, so no point in looking into them.
The rays of light going straight along the middle of the fiber will reach the far end of the fiber earlier than those which bounce around from side to side. This means that a pulse of light will spread out as it travels along the fiber. This pulse spreading due to light following different modes along the fiber is known as modal dispersion. If pulses of light are put into the fiber too close together, as they may be in 1000BASE-SX and 10GBASE-S, then the pulses of light may run into one another and bits of information may be lost. On the next slide, we’ll show the real world impact of this dispersion.
You may get challenged on something called Polarization Modal Dispersion (PMD) as a parameter that affects singlemode. In the Enterprise environment (< 5,000 m) this is not an issue.
You may have some students dispute failing photo 2. This is normal. The photos here were taken at 250x, which allows us to look on the ferrule to see if there is debris. You can also go to 400x magnification, but you risk not seeing the debris on the rest of the connector.
Merenja u telekomunikacijama
MERENJA U TELEKOMUNIKACIJAMA Mihajlo Prerad Certified Cable Test Technician TrainerMIHAJLO PRERAD - MERENJA Slide 1
Tri zakona mreže: #1 – Mreža Nikad neće biti sporija • Planirajte veće brzine, bolje vreme odziva, smanjeno kašnjenje #2 - Mreža Nikad neće biti manja • Planirajte više korisnika, veću količinu saobraćaja, više linkova #3 - Mreža Nikad neće biti ista • Planirajte fleksibilnost, izmenljivost i mogućnost brzih promenaMIHAJLO PRERAD - MERENJA Slide 22
Šta radi OTDR (Optical Time Domain Reflectometer)? OTDR Port konektor OTDR 1. Šalje svetlosne impulse Directional Coupler Two Laser Diodes Color 2. Proverava da li se svetlost Display odbija 3. Što dalje svetlost ode, više mu vremena treba a se vrati (meri dužinu) Processing & Control 4. Što dalje svetlost ode, signal koji se vrati je verovatno dosta slabiji Very Sensitive Photo (meri gubitke vlakna) Detector 5. Kada svetlost naiđe na konektor, deo se reflektuje Optical Fiber nazad Electrical (pronalazi konekcije)MIHAJLO PRERAD - MERENJA Slide 40