Detectivity

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Definition: the inverse of the noise equivalent power

Categories: article belongs to category light detection and characterization light detection and characterization, article belongs to category fluctuations and noise fluctuations and noise

Units: 1 / W; cm Hz^1/2 / W (specific detectivity)

Formula symbol: <$D$>

DOI: 10.61835/shj Cite the article: BibTex plain text HTML Link to this page! LinkedIn

The detectivity <$D$> of a photodetector is a figure of merit, defined as the inverse of the noise-equivalent power (NEP). The larger the detectivity of a photodetector, the more it is suitable for detecting weak signals which compete with the detector noise.

The specific detectivity <$D^*$> is the detectivity normalized to a unit detector area (1 m²) and detection bandwidth (1 Hz); one can calculate it by multiplying the detectivity with the square root of the product of detector area (in square centimeters) and the detector bandwidth (in Hz). That term is useful for comparing the performance of different detector technologies. If the detector bandwidth scales inversely with the active area, typically because of the limiting impact of the electrical capacitance, the specific detectivity will be independent of the active area.

For a given detector, one may decrease the noise level, thus reducing the noise-equivalent power and increasing the detectivity, by restricting its detection bandwidth (e.g. by adding a low-pass filter). Assuming white noise, one will then obtain the same specific detectivity as before.

In contrast to the responsivity, the detectivity is influenced by detector noise. Improving the responsivity improves the detectivity only if the noise level is increased less than the signal level.

More to Learn

responsivity noise-equivalent power photodetectors

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