In this paper we’ll try to improve conversion gain of an integrated opto-electronic mixer, based on InP/InGaAs hetero junction bipolar transistors in both single and cascode configurations. For this purpose we’ll use a hybrid-Pi model, extracted from physical parameters of HBT transistors. For verification of our results and calibration of software simulator, at first, we compared our simulation results with empirically reported experiments for a prefabricated HBTOEM sample. Then we examine the simulator on our modified proposed HBT to prove its better gain performance. As a result of our improvements, down conversion power gain for the new proposed mixer in comparison with previously reported results is improved about 11dB, 16dB and 19dB respectively in optical modulation frequencies about 200MHz, 1GHz and 10GHz for single mixer. These values for cascode mixer are about 6dB, 10.5dB and 16dB respectively in optical modulation frequencies about 200MHz, 1GHz and 10GHz. These improvements are mainly because, current gain of HBT device has been improved from 130 to 318.