In optoelectronic systems, photodetectors play a very important role. It is like the "eye" of an optoelectronic system, measuring external light signals and converting them into electrical signals for subsequent signal processing. This paper studies some commonly used photodetectors, their working principle and performance.

The conversion of optical signals to electrical signals mainly utilizes the photoelectric effect of materials. Einstein was awarded the 1921 Nobel Prize in Physics for his successful explanation of the photoelectric effect using the quantum theory of light. Broadly speaking, the phenomenon that the electrical effect of material changes due to the incidence of light is the photoelectric effect. This mainly includes that the material emits electrons due to the incidence of light, the material changes its electrical conductivity due to the incidence of light, and the material changes its electromotive force due to the incidence of light.

Since photodetectors convert optical signals into electrical signals, there are naturally some parameters that characterize this conversion process.

dark current

Dark current represents the current of the detector when it is not illuminated by light. It is mainly caused by the irregular thermal motion of electrons. The thermal movement of electrons can usually only be suppressed by lowering the temperature, thereby reducing the dark current.

Response time

It mainly characterizes the responsiveness of the detector to modulated optical signals, that is, the frequency response of the detector. When the light signal arrives, the detector does not sense the light signal immediately, but has a hysteresis process corresponding to the rise time of the output current or voltage curve. This delay time is the response time.

Photodetectors also have some other parameters, such as operating wavelength, operating temperature, sensitivity, linearity, etc.

For more photodetector knowledge, please read this article: Requirements for the use of photodetectors.