This paper presents the characterization and validation of a time-domain physical model for illuminated high-frequency active devices and shows the possibility of use of the electromagnetic analysis of FDTD not only for electromagnetic interaction and scattering but also for the device simulation as a good candidate for a microwave simulator. The model is based on Boltzmann's Transport Equation, which accurately accounts for carrier transport in microwave and millimeter wave devices with sub-micrometer gate lengths. Illumination effects are accommodated in the model to represent carrier density changes inside the illuminated device. The simulation results are compared to available experimental records for a typical MESFET for validation purposes. Simulation results show that the microscopic as well as the macroscopic characteristics of the active device are altered by the light energy. This fact makes the model an important tool for the active device design method under illumination control.

This paper presents the performance of a proposed GaAs MESFET photodetector with wide drain-to-gate distances for improving the optical coupling efficiency in subcarrier optical transmission. Principle and design parameters of the proposed MESFET are described. Link gain, CNR, and BER, are experimentally investigated as functions of the drain-to-gate distance. It is experimentally found that the proposed MESFET improves the link gain by 8.5 dB compared to the conventional structure at the subcarrier frequency of 140 MHz. Discussions are also included compared to PIN-PD.

This paper presents the performance of optically controlled MESFETs as photodetectors. The optical performance characteristics such as optic-to-electric responsivity, and BER for a π/4-QPSK signal are experimentally investigated. Measurements are performed by using MMIC compatible MESFETs. Experimental results are also evaluated in comparison with calculated PIN-PD limit. Optic-to-electric responsivity has high gain at lower received optical powers. It is shown experimentally that MESFET photodetectors improve the permissible optical power by 6 dB compared to the PIN-PD limit. Optically controlled MESFETs will provide a novel receivers for fiber-optic systems.