In this paper, a new type of resonant cavity enhanced (RCE) photodetector which divides the resonant cavity into three subcavities is proposed. The analysis shows that a narrower spectral response line-width (<1 nm) can be obtained with a high quantum efficiency up to 90%. This means that the quantum efficiency can be decoupled from both the response speed and the spectral linewidth with such a photo-detectors. This type of photo-detector may be proved useful for dense wavelength division multiplexing (DWDM) applications.