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 (UTC-PD) with integrated 1 × 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, which 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
$^\circ$
and 20
$^\circ$
, 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.