Silicon Avalanche photodiodes (Si APD) are the preferred optical detectors for applications where the wavelength lies between 400nm and 1100nm and where high speed and low optical power detection is required. The avalanche multiplication of the photo-generated carriers is responsible for the signal-to-noise ratio improvement when compared to a simple PN or PIN detector. BER or probability of detection in communication systems, maximum range and range resolution for Laser range finder or NEP in scanning video imager can be improved by using APD.
APD gain is the parameter that one has to choose in order to maximize system performance. The gain maximizing signal-to-ratio (SNR) or noise equivalent power (NEP) depends on system parameters; mainly background and signal optical power, operating temperature and operating wavelength and on the optical receiver itself; i.e. the transimpedance amplifier and APD characteristics.