In this contribution we present a rate equation model for the simulation of InAs/InP(100) quantum dots which are used as the active material of waveguide photodetectors. Unlike the normal rate equation models in literature which are built for carrier injection and photon emission, our model is modified for the carrier extraction and photon absorption. The simulation results are compared with previous experimental results. Experimental observations are explained in terms of fundamental properties of the quantum dots, e.g. the bias voltage dependent carrier extraction rate and absorption coefficient.