detectivity (original) (raw)

Author: the photonics expert (RP)

Definition: the inverse of the noise equivalent power, or (specific detectivity) a quantity normalized to detector area and detection bandwidth

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

Related: responsivitynoise-equivalent powerphotodetectors

Units: W–1; cm Hz1/2 / W (specific detectivity)

Formula symbol: ($D$), ($D^{*}$)

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

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Contents

What is a Detectivity?

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.

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.

Specific Detectivity

The specific detectivity ($D^*$) is the detectivity normalized to a unit detector area (e.g. 1 cm2) and detection bandwidth (1 Hz). It can be calculated by multiplying the detectivity with the square root of the product of detector area (in square centimeters) and the detector bandwidth (in Hz): D^* = D \: \sqrt{A \: \Delta f}$$

This figure of merit is useful for comparing the performance of different detector technologies. If the detector bandwidth scales inversely with the active area — typically due to the limiting effect of the detector's electrical capacitance — then the specific detectivity will be approximately independent of the active area.

For a given detector, the noise level can be reduced — and consequently the noise-equivalent power (NEP) decreased and the detectivity increased — by restricting the detection bandwidth (for example, by applying a low-pass filter). Assuming the noise is white, the specific detectivity ($D^*$) remains unchanged, since both the signal and noise scale consistently with the bandwidth.

Frequently Asked Questions

This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).

What is the detectivity of a photodetector?

The detectivity ($D$) is a figure of merit defined as the inverse of the noise-equivalent power (NEP). A higher detectivity value means the detector is more suitable for detecting very weak optical signals.

What is the specific detectivity ($D^*$)?

The specific detectivity ($D^*$) is the detectivity normalized for a standard detector area (1 cm2) and detection bandwidth (1 Hz). This value allows for a fair comparison of the performance of different photodetector technologies, independent of sensor size.

How does detectivity differ from responsivity?

Responsivity quantifies the output signal generated per unit of input optical power, without considering noise. Detectivity incorporates detector noise, making it a measure of how well a detector can distinguish a weak signal from its inherent noise.

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