Detector and the wavelength
Normally the handheld optical power meter use InGaAs detector and the Silicon detector. The InGaAs detector can test the wavelength 800 to 1700nm,for Silicon detector it is 400-1100nm.But for handheld optical power meter,the manufactures can not calibrate every wavelength, they can only calibrate some normal used wavelengths such as 850nm,1300nm,1310nm,1490nm,1550,1625nm etc..and the quantity of calibrated wavelengths is fixed,most of them is six.But for Silicon detector,the normal calibrated wavelengths are 635nm,650nm,780nm,808nm.