PHOTODIODE

Selective detection of light signals of two different wavelength bands is accomplished by two separate pn junctions (13, 14) which are disposed on two different sides of a substrate (1) and are optically in series. The pn junction (13) lying in front in the light path responds to light of, e.g., 850 nm, but not to light in the range from 950 nm to 1,650 nm. The substrate acts as a filter and passes the light of longer wavelength while blocking the 850-nm light, 50 that the second pn junction (14) is only reached by light in the range from 950 nm to 1,650 nm. The device may be used in optical data communication.