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Q: How do I know if I have enough optical budget for my application?
A: To determine the optical budget for a link, you need to know the transmit launch power from each end of the link and also the Rx sensitivity for each end of the link. Typically, this number is shown in dBm and is frequently a negative number with the Rx end obviously having the lower number. For example, if you have a Tx launch power of -2.5dBm and a Rx sensitivity of -11dBm, then your budget is the difference between these two numbers, so in this case you would have a budget of 8.5dB.
Q: How do I test to determine insertion loss on a link?
A: Insertion loss on a link is determined by the number of intermediate connections, splice points, and fiber attenuation. Every time a link goes through an intermediate connection the loss value can be anywhere from 0.1dB to 0.8dB depending on the connector type. Sometimes extremely good splices have no loss value, but typically technicians use a value of 0.2dB for each splice to be on the safe side. The type and age of fiber will indicate the insertion loss due to attenuation. We always recommend using bend-insensitive fiber to prevent attenuation due to tight bends that may occur on the fiber route path. For multimode fiber, the loss is about 3.0dB per km for 850nm sources, 1.0dB per km for 1300nm sources (3.5 and 1.5 dB/km max per EIA/TIA 568 standards). This roughly translates into a loss of 0.1dB per 100ft/30m for 850nm, 0.1dB per 300ft/100m for 1300nm. For single mode fiber, the loss is about 0.5dB per km for 1310nm sources, 0.4dB per km for 1550nm. (1.0dB/km for premises/0.5dB/km at either wavelength for outside plant max per EIA/TIA 568). This roughly translates into a loss of 0.1dB per 600ft/200m for 1310 nm, 0.1dB per 750ft/250m for 1550 nm.
Q: Why do some 40/100G ports require an MPO/MTP connector and others an LC?
A: OM3/4 multimode fiber links transmit data across multiple lanes and each lane requires a dedicated fiber. MPO/MTP adapters terminate multiple fibers from 8 to as high as 72 fibers. Most 40/100G single mode fiber links use LC connecters because the source and destination devices perform wavelength multiplexing to transmit the multiple lanes on dedicated wavelengths. Since multiple wavelengths can coexist at the same time on a single fiber, a duplex LC connector is all that is required.
Q: Why do multimode links cost more to tap than single mode fiber links?
A: Generally speaking, multimode fiber passive components are more complicated to manufacture and difficult to test, as a result, these items are generally a little more expensive. To learn more about this subject, read our BLOG, “10G TO 40/100G DATA CENTER MIGRATION“.