Use the meter in dBm (absolute power) mode. Record the displayed Tx power and compare directly to the transceiver datasheet (don't guess acceptable levels). The measurement may be optical power from a test source, a transmitter or the input of receiver, measured in dBm, which is "absolute" power - absolute in that it refers to power calibrated to a national standard, so two people testing the same fiber output with different power meters calibrated to. A fiber-optic power meter is a quantitative measurement instrument, not a diagnostic tool by itself. Its sole function is to measure the optical power level arriving at a specific point in a fiber link, expressed in dBm or mW. At its core, the device consists of: The power meter does not evaluate. An optical power meter contains a photodiode (typically InGaAs for telecom wavelengths or germanium for legacy 850nm work) that converts incoming light into an electrical current. +10 dB is a factor of 10 (10 times log10 10 which is 1), +20dB is a factor of 100 (10 times log10 100 which is 2), +30dB a factor of 1000 (10 times log10 1000 which is 3)and so on. Measured in decibels (dB), loss degrades signal quality, limits distance, increases bit-error rate, and escalates infrastructure cost. Understanding and managing it is critical to. Accurately testing an optical Transceiver means proving two things: that the module is emitting the right power at the right wavelength, and that the link it's attached to delivers that signal without unexpected loss or reflections.
