photodetector (PD)

In optical fiber technology, a photodetector (PD) is the receiving element used to convert the transmitted light into electrical signals. A distinction is made between avalanche photo diodes( APD), PIN diodes, phototransistors and photodiodes.

Since there are no photodiodes that cover the entire wavelength spectrum from 600 nm to 1,600 nm, the material properties of the detectors determine the wavelength range. In terms of semiconductor material, a distinction is made between silicon, germanium and indium gallium arsenide( InGaAs).

Silicon detectors (Si) have a spectral range from 400 nm to 1,100 nm, with a maximum at 850 nm, i.e. exactly the wavelength of the first optical window of optical waveguides. These detectors are also used for plastic fibers with windows around 650 nm and 780 nm.

Germanium detectors (Ge) have a spectral range between 800 nm and 1,600 nm, with a maximum at 1,550 nm. Due to a high noise component, these detectors are relatively insensitive at -60 dBm.

In contrast, the noise of the indium gallium arsenide detectors is about -90 dBm. They cover the spectral range between 700 nm and 2,000 nm and have a less pronounced maximum between 1,300 nm and 1,700 nm.