ABSTRACT
This chapter presents a number of properties of photodiodes which are of particular importance for use in optical broadband (BB) transmission systems. Restrictions on the bandwidth of the detectable base band signals are composed as a result of the transit time of the charge carriers, the capacity of the depletion region, and the frequency-dependence of the multiplication factor M of avalanche photodiodes. In optical BB transmission links the following properties of the photodetectors are important: long lifetime, large band width, low noise, high quantum efficiency and low dark current. Optical transmission technology only uses photodetectors constructed on a semiconductor basis. The photodiode bandwidth is a very important factor when planning high-rate optical transmission systems. In order to measure the bandwidth of photodetectors independently of the modulation properties of the optical transmitter, a heterodyne process is used. Ge is used for many transmission systems in the optical long wavelength range.
