Working With Fiber Optics.doc

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Working With Fiber Optics
Fiber optic signal transmission can offer significant benefits for many applications. Here's what you need to know to make it work for your next project. THE GOAL Ensure that enough light reaches the receiver. CONNECTOR TYPES ST - straight tip connector. A popular fiber optic connector originally developed by AT&T. SC - subscription channel connector. A push-pull type of optical connector that features high packing density, low loss, low backreflection, and low cost. TYPES OF FIBER Multi-mode vs. single-mode A mode is a defined path in which light travels. A light signal can propagate through the core of the optical fiber on a single path (singlemode fiber) or on many paths (multi-mode fiber). The mode in which light travels depends on geometry, the index profile of the fiber, and the wavelength of the light. Single-mode fiber has the advantage of high information-carrying capacity, low attenuation, and low fiber cost, while multi-mode fiber has the advantage of low connection and electronics cost, which may lead to lower system cost. CALCULATING LOSS In fiber optics, signal loss is expected because the signal will weaken as it travels from the transmitter to the receiver. It stems from two primary sources: the length of the fiber and the end connectors and any splices that may be placed in the fiber strand.
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To determine the system's total optical loss, calculate the sum of the cable loss (as a function of desired transmission distance), splice loss, and connector loss. Then add a safety margin of 3 dB.
Typical Optical Loss Budget (dB)

1 km 850 nm (multi-mode) 1,310 nm (multi-mode) 1,310 nm (single-mode) 1,550 nm (single-mode) 4 2 0.5 0.2

5 km 20 10 2.5 1

10 km 20 5 2

20 km 10 4

40 km 20 8

60 km 30 12

TYPES OF LOSS SPLICE AND CONNECTOR LOSS Connector and splice losses have maximum values set by the fiber optic industry and are not frequency dependent. Connector loss per pair = less than 0.75 dB Splice loss = less than 0.3 dB INSERTION LOSS Loss (dB) = 10 • log10 (P1/P2) Where P1 is the output power of a continuous fiber and P2 is the output power after the fiber has been cut exactly in the middle and terminated with a splice or connector. NA MISMATCH LOSS Occurs when the numerical aperture of the transmitting fiber is larger than that of the receiving fiber. Must be considered if two different types of fibers are connected. CORE/CLADDING DIAMETER MISMATCH Occurs when the core diameter of the transmitting fiber is larger than the fiber at the receiving end. POWER BUDGET Power budget = transmitter power - receiver sensitivity

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The optical power budget must be greater than all of the cable plant losses (such as attenuation, losses due to splices and connectors, etc.) for the installation to work properly. MAKING SPLICES There are two types of splices: fusion and mechanical. Mechanical splices are alignment gadgets that hold the ends of two fibers together with some index matching gel or glue between them. The tools to make mechanical splices are cheap, but the splices are expensive. Fusion splices are made by welding the two fibers together usually with an electric arc. Good fusion splicers can cost $15,000 to $40,000, but the splices only cost a few dollars each. TERMINATION TOOL KIT A complete toolkit for making fiber terminations should include: • 2-inch scissors • Tweezers • Fiber cleaver • Alcohol wipes • Medium black marker • Tape • Enhanced UniCam installation tool • UniCam length gage • Adhesive • UniCam crimp tool • Stripping tool • 203-micron stripper • Jacket stripper • ST adapter • FC adapter • ST multi-mode (orange) jumper cable, 1 meter • ST single-mode (yellow) jumper cable, 1 meter
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• Visible Laser Light Source (VLLS) with power supply STEPS FOR MAKING TERMINATIONS Fiber preparation 1. Strip the casing from the fiber in small pieces. 2. Clean the exposed fiber with alcohol. 3. Cleave the fiber to the proper length. Connector preparation 4. Remove the dust cover and note the top of the connector. 5. Place the connector into the ST adapter making sure that the date and key slot are up. Mount the assembly into the connector tool. 6. Turn on the Visible Laser Light Source and notice the radiated light from the connector. Termination 7. Carefully insert the fiber into the back of the connector until the radiated light fades considerably. 8. Move the cam lever to the down position. 9. Raise the crimp arm up and then over into the crimping position and apply pressure. 10. Place the boot on the fiber, noting the correct orientation. NOTE: It's recommended that you test the output power to ensure acceptable performance.

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