An optical power meter sensor
The major semiconductor sensor types are Silicon (Si), Germanium (Ge) and Indium Gallium Arsenide (InGaAs).
Additionally, these may be used with attenuating elements for high optical power testing, or wavelength selective elements so they only respond to particular wavelengths. These all operate in a similar type of circuit, however in addition to their basic wavelength response characteristics, each one has some other particular characteristics:
Si detectors tend to saturate at relatively low power levels, and they are only useful in the visible and 850 nm bands.
Ge detectors saturate at the highest power levels, but have poor low power performance, poor general linearity over the entire power range, and are generally temperature sensitive. They are only marginally accurate for "1550 nm" testing, due to a combination of temperature and wavelength affecting responsivity at e.g. 1580 nm, however they provide useful performance over the commonly used 850 / 1300 / 1550 nm wavelength bands, so they are extensively deployed where lower accuracy is acceptable. Other limitations include: non-linearity at low power levels, and poor responsivity uniformity across the detector area.
InGaAs detectors saturate at intermediate levels. They offer generally good performance, but are often very wavelength sensitive around 850 nm. So they are largely used for singlemode fiber testing at 1270 – 1650 nm.
related:
http://www.vedioedu.com/forum.php?mod=viewthread&tid=540404
http://122.96.27.11:8081/mydz/forum.php?mod=viewthread&tid=1939836
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