“…In the case of an avalanche photo-diode (APD), which is the more relevant case, there is an additional, third type of noise, namely, the excess noise, induced by the APD, which is actually a multiplicative noise process pertaining to fluctuations in the random gain associated with the avalanche mechanism, as each primary electron-hole pair (generated by a photon absorbed in the photo-diode), may generate secondary electron-holes, which in turn can generate additional electron-holes, and so on. For more details, and additional aspects of the problem area, the interested reader is referred to some earlier work, e.g., [2], [3], [4], [5], [6], [7], [13], [14], [15], [16], [17], [18], [19], [20], and [22], which is by no means an exhaustive list of relevant articles (and a book).…”