RP Photonics

Encyclopedia … combined with a great Buyer's Guide!

VLib
Virtual
Library

Photodetectors

Definition: devices used for the detection of light

German: Photodetektoren, Lichtdetektoren

Category: photonic devices

How to cite the article; suggest additional literature

Photodetectors are devices used for the detection of light – in most cases of optical powers. As the requirements for applications vary considerably, there are many types of photodetectors which may be appropriate in a particular case:

Various kinds of photodetectors can be integrated into devices like powermeters and optical power monitors.

Important Properties of Photodetectors

Depending on the application, a photodetector has to fulfill various requirements:

  • It must be sensitive in some given spectral region (range of optical wavelengths). In some cases, the responsivity should be constant or at least well defined within some wavelength range. It can also be important to have zero response in some other wavelength range; an example are solar-blind detectors, being sensitive only to short-wavelength ultraviolet light but not to sun light.
  • The detector must be suitable for some range of optical powers. The maximum detected power can be limited e.g. by damage issues or by a nonlinear response, whereas the minimum power is normally determined by noise. The magnitude of the dynamic range (typically specified as the ratio of maximum and minimum detectable power, e.g. in decibels) is often most important. Some detectors (e.g. photodiodes) can exhibit high linearity over a dynamic range of more than 70 dB.
  • In some cases, not only a high responsivity, but also a high quantum efficiency is important, as otherwise additional quantum noise is introduced. This applies e.g. to the detection of squeezed states of light, and also affects the photon detection probability of single-photon detectors.
  • The active area of a detector can be important e.g. when working with strongly divergent beams from laser diodes. For light sources with very high and/or non-constant beam divergence, it is hardly possible to get all the light onto the active area. An integrating sphere may then be used (with appropriate calibration) for measuring the total power.
  • The detection bandwidth may begin at 0 Hz or some finite frequency, and ends at some maximum frequency which may be limited by internal processes (e.g. the speed of electric carriers in a semiconductor material) or by the involved electronics (e.g. introducing some RC time constants). Some resonant detectors operate only in a narrow frequency range, and can be suitable e.g. for lock-in detection.
  • Some detectors (such as pyroelectric detectors) are suitable only for detecting pulses, not for continuous-wave light.
  • For detecting pulses (possibly on a few-photon level), the timing precision may be of interest. Some detectors have a certain “dead time” after the detection of a pulse, where they are not sensitive.
  • Different types of detectors require more or less complex electronics. Penalties in terms of size and cost may result e.g. from the requirement of applying a high voltage or detecting extremely small voltages.
  • Particularly some mid-infrared detectors need to be cooled to fairly low temperatures. This makes their use under various circumstances impractical.
  • For some applications, one-dimensional or two-dimensional photodetector arrays are needed – most often in the form of photodiode arrays. For detector arrays, some different aspects come into play, such as cross-pixel interference and read-out techniques.
  • Finally, the size, robustness and cost are essential for many applications.

Different detector types, as listed above, differ very much in many of these properties. In typical application scenarios, some requirements totally rule out the use of certain detector types, and quickly lead to a fairly limited choice. Note also that there are some typical trade-offs. For example, it is frequently difficult to combine a high detection bandwidth with a high sensitivity.

Suppliers

The RP Photonics Buyer's Guide contains 49 suppliers for photodetectors. Among them:

See also: photodiodes, p–i–n photodiodes, avalanche photodiodes, metal–semiconductor–metal photodetectors, velocity-matched photodetectors, phototubes, photomultipliers, photodiode arrays, powermeters, optical power monitors, single photon counting, noise specifications, noise-equivalent power, responsivity
and other articles in the category photonic devices

How do you rate this article?

Click here to send us your feedback!

Your general impression: don't know poor satisfactory good excellent
Technical quality: don't know poor satisfactory good excellent
Usefulness: don't know poor satisfactory good excellent
Readability: don't know poor satisfactory good excellent
Comments:

Found any errors? Suggestions for improvements? Do you know a better web page on this topic?

Spam protection: (enter the value of 5 + 8 in this field!)

If you want a response, you may leave your e-mail address in the comments field, or directly send an e-mail.

If you enter any personal data, this implies that you agree with storing it; we will use it only for the purpose of improving our website and possibly giving you a response; see also our declaration of data privacy.

If you like our website, you may also want to get our newsletters!

If you like this article, share it with your friends and colleagues, e.g. via social media:

arrow