Arrayed Photomixers for THz Beam-Combining and Beam-Steering

In this study, generating and enhancing THz continuous/pulsed waves is achieved by fabricating a monolithic InP substrate chip of arrayed photomixers, where each photomixer includes an InP/InGaAs uni-traveling-carrier photodiode (U'I'CPD) with integrated 1 x 4 planar slot antennas (PSAs). Through optoelectronic time-aligned and -gradient delays of lightwaves that couple to arrayed photomixers, the radiated THz waves yield both quantitative gain and spatial directional gain. To generate continuous 300 GHz waves, each UTC-PD is excited at a photocurrent of 3 mA to attain -15.79 dBm THz power that exhibits 12 dB combined gain by four arrayed UTC-PDs. Whereas, -17.71 dBm THz pulse generation with a duration of 25 ps can be achieved at the same optical pump power. The results show that the power enhanced gain of THz pulses is around 10 dB, w hich is less than that of continuous THz waves, because a part of the generated frequency components of the THz pulse is significantly deteriorated by bandwidth-limited PSAs. Furthermore, by means of optoelectronic time-gradient delay with frequency-independent characteristics, we successfully demonstrate steering of continuous and pulsed THz waves repeatedly in a range of 30 degrees and 20 degrees, respectively. In conclusion, strengthening directional THz power by beam-combining and -steering with arrayed photomixers is a promising technique for effective generation of continuous/pulsed THz waves.