I have used optic power meters. This in my experience has been with JDSU. In general power is power no mater what frequency. There are some terms that differ and measurement techniques. First thing is ground is "dark". Dark is "no input" or a short at RF frequencies. Attenuation in optical is often seen as any contaminant on the connection. In RF we often clean the connections with alcohol. In optical, clean connections are always required.