sensitivity (original) (raw)

Author: the photonics expert (RP)

Definition: (different meanings, depending on the context)

Categories: light detection and characterization, fluctuations and noise

Related: responsivitynoise-equivalent powerdetectivityalignment sensitivity of optical resonators

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

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Contents

The term sensitivity is used quite frequently in the area of photonics, and this with different meanings — mostly with qualitative ones. Some cases are discussed in the following sections.

Sensitivity of Photodetectors

Most frequently, the term is used in the context of photodetectors such as photodiodes and photomultipliers, but often without a clearly defined qualitative or even quantitative meaning.

In some cases, what is meant is actually the responsivity of a detector. This is essentially the ratio of output signal (e.g. a photocurrent) and the strength of the optical input (as an optical power).

In other cases, sensitivity is understood as the ability to detect weak signals. That ability is usually limited by detector noise. A quantitative measure for that aspect is the noise-equivalent power, which is essentially the optical input required to obtain the same output signal strength as that which results from detector noise. A related quantity — just the inverse of the noise-equivalent power — is the detectivity.

Note that by adding an electronic amplifier to the output of a photodetector one can effectively increase the responsivity, but not the detectivity. Similarly, some photodetectors have a particularly high responsivity, while others have a higher detectivity.

In the case of the human eye, there is no clearly defined output signal, nor a well-defined noise level, but sensitivity can again mean the ability to detect weak light signals. One may say, for example, that the human eye is more sensitive to green light than to red or blue light.

Sensitivity of Devices to Certain Parameters

Frequently, the term sensitivity is used in the discussion of how certain devices react to disturbing influences such as changes in temperature, humidity, mechanical influences like vibrations or bending, input wavelengths, signal powers, back reflections etc. Device designs may be optimized to minimize unwanted sensitivities.

In the context of optical resonators, the alignment sensitivity is often of interest. It essentially quantifies how much the position of resonator modes shift as a result of misalignments. That depends substantially on the chosen resonator design.

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 does 'sensitivity' mean for a photodetector?

For a photodetector, sensitivity can refer to its responsivity—the ratio of output signal to input optical power. Alternatively, it can mean the ability to detect very weak signals, which is limited by noise and quantified by the noise-equivalent power.

What is the difference between the responsivity and the detectivity of a photodetector?

Responsivity is the magnitude of the output signal per unit of input optical power. Detectivity, which is the inverse of the noise-equivalent power, measures the ability to detect weak signals in the presence of noise. An electronic amplifier can increase responsivity but not detectivity.

In what other contexts is the term 'sensitivity' used in photonics?

It is often used to describe how a device's performance reacts to external influences like temperature changes, vibrations, or back reflections. An example is the alignment sensitivity, which quantifies how resonator modes shift due to misalignments.

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