The dBm scale is logarithmic, meaning a small numerical change represents a large change in actual light power. This allows engineers to express a huge range of power levels, from microwatts to hundreds of milliwatts, using manageable numbers. Whenever tests are performed on fiber optic networks, the results are displayed on a power meter, OLTS or OTDR readout in units of “dB. ” Optical loss is measured in “dB” which is a relative measurement, while absolute optical power is measured in “dBm,” which is dB relative to 1mw optical power. Thus 1 mW = 0 dBm, 1 uW = -30 dBm, 1 nW = -60 dBm and two equal powers compared are 0dB (eg. power being the same, there is no loss. dB does not indicate how much power exists. At its core, the device consists of: The power meter does not evaluate. That is a measurement of absolute power, generally expressed in decibels referenced to a milliwatt of optical power (dBm).
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