An accurate and fast behavior modeling procedure is presented for codesign of active optical device with circuitry. The developed method is based upon defining partial elements (PEs) and their measurement-based partial element equivalent circuits (M-PEEC), associating design rules with them, and characterizing them through the use of test structures. The test structures are designed such that they can include only sensitive combinations of predefined building blocks, and they are measured over a wide band of frequencies using network analysis techniques. Measurement-based partial element equivalent circuits of the building blocks are derived from the measured s-parameters of the test structures by nonlinear optimization methods. The method has been experimentally verified using metal-semiconductor-metal photodetectors. The method has also been verified with circuits using simulations, with good results obtained.