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THE ORIGINAL PUSH-PULL CONNECTOR Fig. 2: Trace from a PON installation with a single splitter. which specified limits are exceeded in any parameter. Finally, the OTDR will identify problems which, while not suf- ficient to cause failure immediately, could result in performance impairment or complete failure in future. Such problems include excessive bends (macrobends), and other mechanical stresses in the fibre installation. How does an OTDR work? The OTDR sends a pulse of light at a precise wavelength through the fibre under test. Along the length of the fibre, minute particles embedded in the glass during its manufacture cause a small amount of light to be scattered. Some of this scattered light travels back to the OTDR; this is known as back- scatter. The OTDR includes an extremely accurate light sensor which can measure precisely the amount of light returning to it as backscatter, and also measure the time between emitting a More than pulse and receiving the backscatter from that pulse. 50'000 connector The glass used to manufacture optical fibre is extremely combinations pure, and these particles are evenly spaced and scatter light uniformly. Information about the regular backscatter behaviour The modular design of of manufactured fibre (before it is installed) is provided by the LEMO products provides manufacturer and programmed into the OTDR. The OTDR then more than 50'000 compares the backscatter it measures in an installed fibre under different combinations test with the backscatter that it expects from the manufacturer’s of connectors with a data in order to calculate an optical loss figure; and also to large choice of contact locate the cause(s) of losses along the length of fibre under test, configurations : through a calculation using the elapsed time between a pulse and its associated backscatter, and the speed of light. High and low voltage A simplified version of an OTDR trace is given in figure 1, Coaxial and triaxial Quadrax Thermocouple Fibre optic Fluidic and pneumatic Hybrid Custom solutions Cable assembly LEMO SA - Switzerland Phone: (+41 21) 695 16 00 Fig. 3: Trace from a PON installation with two closely Fao@lem+4co21) 695 16 02m1.o(x:fni cascaded splitters, showing the event table at the top of the display. Contact your local partner on www.lemo.com www.electronics-eetimes.com Electronic Engineering Times Europe January 2013 35


EETE JANUARY 2013
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