HBT Optoelectronic Mixer Design for Radio over Fiber System

Radio over fiber (RoF) system is the solution for the providing highly reliable communication service. This system is characterized by having both a fiber optic link and free-space radio path to exploit the synergy of two complementary technologies; the broadband mobile wireless access and fixed optical access. Optoelectronic mixing is required in RoF systems to detect the RF modulated optical signal and perform frequency up-conversion. In this work, three-terminal InP/InGaAs HBT with optical access has been used as the optoelectronic mixer (OEM) for front-end RoF optical receiver configuration. Thus in this configuration, the photodetection and frequency conversion can be achieved in p-i-n photodiode and HBT device, which considerably simplify the conventional method. The RoF OEM was successfully simulated using a nonlinear microwave simulator to perform harmonics balance analysis, which represented actual photodetection model and nonlinear dynamic optoelectronic mixing behavior. In this paper we reported the - 5.2 dB maximum internal mixing efficiency for 400 MHz IF modulated signal to 3.4 GHz upconverted RF signal with LO power is -2dBm, and that agreed with conventional theoretical analysis. In this article, the theory of operation, the device structure of the RoF OEM and its characteristic will be presented.