We have investigated the characteristics of an In0.4Ga0.6As self-organized quantum-dot (QD) resonant-cavity photodiode. The QD epitaxy and the design of the two-dimensional photonic crystal cavity are tailored for 1.3-μm wavelength operation. The input excitation to the photodiode is provided with an in-plane defect waveguide designed with the same photonic crystal. The measured spectral photocurrent characteristics reflect mode coupling between the waveguide and detector and the resonant cavity effect due to total internal reflection and photonic bandgap confinement. The photocurrent response is explained with a model involving the circulating fields in the cavity. The characteristics are also dependent of cavity size. Enhancement and narrowing (∼ 10 nm) of the photoresponse at λ∼1.3 μm are observed. A spectral dip, of ∼ 10-nm width, also observed at 1.3 μm is possibly due to the anticrossing mechanism, uniquely present in photonic crystal waveguides.