A new nonlinear model for commercial PIN photodiodes is presented in this paper.The gain and the third-order spurious-free dynamic range(SFDR3) of a basic microwave photonic link influenced by the nonlinearity of the photodiode(PD) are also studied. of applicability and simple conceptual basis,we anticipate that the model will be of value in understanding and evaluating the nonlinearity of microwave photonic links.Numerical studies indicate that the nonlinearity of PD degrades the microwave phot...