In conclusion, an optical power meter is designed to measure the power of optical signals at specific wavelengths, primarily 850 nm for short-distance applications and 1300-1310 nm for medium-distance applications. To augment the absolute power measurements NIST provides nonlinearity, spectral responsivity, and uniformity measurements. Understanding this becomes really important when measuring power levels since different wavelengths get absorbed differently by materials, which affects. Si detectors tend to saturate at relatively low power levels, and they are only useful in the visible and 850 nm bands, where they offer generally good performance.