For electricians, voltage is the primary thing measured. In fact
every electrical measurement is based on voltage, based on the
relationship V = IR. In fiber optics, the most basic measurement
is the optical power of the light at the end of a fiber. Optical
power measurement is the basis for loss measurements as well as
the power in an operating system at the source or receiver. So,
electricians use voltmeters. What do fiber optic technicians
use? Optical power meters are the primary fiber optic
measurement instrument, while optical loss test sets (OLTSs) and
optical time domain reflectometers (OTDRs) also measure power in
testing loss, which is similar to how an ohmmeter or ammeter
measures voltage and converts it to the appropriate units.
Optical power is based on the heating power of the light, and
some optical lab instruments actually measure optical power by
the heat absorbed by a detector. While this may work for high
power lasers, these detectors are not sensitive enough for the
low power levels typica