The proper calibration of an optical power meter requires the verification of two critical
parameters: absolute accuracy at a given reference power over a wavelength range and
linearity at a given wavelength over a power range. We discuss the key elements
involved in determining the uncertainty in the absolute accuracy and the non-linearity of
the power response under what are termed “reference conditions of calibration”. We
also discuss the underlying causes of erroneous measurements resulting from each of
the three subsystems constituting a power meter: detector element, collecting optics
and electronics.