radar, monitoring of laser power levels for materials processing, and laser metrology. Different
types of optical detectors are available, covering the ultraviolet, visible, and infrared portions of
the electromagnetic spectrum. Optical detectors convert incoming optical energy into electrical
signals. The two main types of optical detectors are photon detectors and thermal detectors.
Photon detectors produce one electron for each incoming photon of optical energy. The electron
is then detected by the electronic circuitry. Thermal detectors convert the optical energy to heat
energy, which then generates an electrical signal.
The detector circuit often employs a bias voltage and there is a load resistor in series with the
detector. The incident light changes the characteristics of the detector and changes the current
flowing in the circuit. The output signal is then the change in voltage drop across the load
In this module, we will describe some common optical detectors and their important
characteristics. We shall not attempt to cover the entire field of light detection, which is very
broad. Instead, we shall emphasize those detectors that are most commonly encountered in
Download here (pdf)