We report on the theoretical study of an integrated waveguidelphotodetector. We present the optical modeling of an integrated waveguide/photodetector based on the absorption of the evanescent optical field in an absorbing layer, deposited on the waveguiding layer.From this modeling, the expression of the electron-hole pair generation rate, for such a device, is established. Then, we apply this result to the calculation of the dynamic quantum efficiency of an integrated waveguidelp-i-n photodiode. The static and dynamic behaviors o f GaInAs p-i-n photodiodes monolithically integrated on a classical n-/n+ InP homostructure waveguide or on a GaInAsP/InP heterostructure waveguide are discussed and optimized structures are pointed out.