Abstract

The photoelectric pulse generated by an avalanche photodiode (APD) as a result of a single injected photoelectron is regarded as a nonstationary random function of time (the impulse response function). A discrete stochastic model for the electron-hole motion and multiplication is defined on a spatio-temporal lattice and used to derive recursive equations for the mean, the variance, and the autocorrelation of the impulse response as functions of time. The power spectral density of the photocurrent in response to a Poisson-distributed stream of photons of uniform rate is evaluated. Correlation properties of the impulse response is studied for a conventional and multilayer (superlattice) APD with the same gain and carrier-ionization rate ratio. The conventional APD has a much more correlated response and a higher excess noise factor. Its response is slower; however, the signal-to-noise ratio (SNR) of its current response is greater. The photocurrent generated in the conventional APD from a stream of photons has a narrower power spectral density but a higher SNR. For both devices, the rms current is low at the onset of multiplication, sharply peaks at about the same time but does not die off as rapidly as the mean current. For a high-data-rate optical communication system, this type of noise will enhance inter­symbol interference and limit the bit error rate.

© 1991 Optical Society of America