We present a simple and efficient approach for higher-order Berenger mode computation. We establish the physical mapping between radiation modes and complex Berenger modes, and theoretically prove that the higher-order substrate Berenger modes and cladding Berenger modes can converge to a cluster of complex modes with the same phase angle. This model can be explained by weighted optical path distance in both cladding and substrate, and can be implemented by adjusting parameters of perfectly matched layers. A germanium (Ge) photodetector is utilized to evaluate the merits of this method in terms of robustness, efficiency, and accuracy.