The unique advantages offered by terahertz (THz) waves have stimulated the emergence and advancement of novel THz systems for imaging, spectroscopy, communication, and radar applications. Currently, photonic-assisted THz technologies are on the rise due to the wide bandwidth and minimal loss of optical fibers. Additionally, their compatibility with C-band fiber-optic components in the microwave frequency region, not available for electrical technologies, further drives their development. However, because of the high free-space path loss, existing THz systems typically utilize high-gain antennas for fixed point-to-point applications. To expand their applicability in mobile environments, compact integrated transceivers with beam steering capabilities are indispensable. Therefore, this thesis focuses on developing and fabricating photonic integrated circuits (PICs) for photonic-assisted THz beam steering.

This thesis reports on the first indium phosphide (InP)-based THz leaky-wave antenna (LWA), supporting low-loss and monolithic integration with THz photodiodes (PDs). By adjusting the antenna’s operating frequency from 230 to 330 GHz, quasi-linear beam steering from −46° to 42° can be achieved. Experimental results demonstrate an average realized gain of ~11 dBi and a 3-dB beam width of ~10°.

Using a photonic THz transmitter based on this fabricated LWA, a mobile THz communication system that supports both single and multi-users is reported for the first time. Within the whole beam steering range, a data rate of 24 Gbit/s is achieved for a single mobile user at a wireless distance of 6 cm without using a THz amplifier for the transmitter. At longer wireless distances of up to 32 cm, data rates of up to 4 Gbit/s are achieved. Furthermore, this THz communication system could simultaneously support up to twelve users with a total wireless data capacity of 48 Gbit/s.

The thesis also reports on an optical beam forming network (OBFN) chip designed for a 1×4 photonic-assisted phased array operating at 300 GHz. Four optical phase shifters (OPSs), each consisting of two cascaded optical ring resonators (ORRs), are used to adjust the phase shift of THz waves in the optical domain. A phase shift range of 2π with a tuning efficiency of 0.058 W/π is experimentally characterized. Furthermore, a beam steering range of ~62° is successfully demonstrated.

The thesis also delves into the design, concept, and technological advancements of 2D THz beam steering approaches. A PIC concept based on an LWA array configuration is proposed. By incorporating an additionally integrated OBFN chip, a THz beam steering range of 60° in the E-plane of the antenna array can be achieved. Suppose this PIC is used instead of the single LWA for the mobile THz communication system, the wireless distance can be extended from 6 cm to 4.5 m for a data rate of 24 Gbit/s. Furthermore, a heterogeneous integrated III-V/Si platform is developed to enable vertical integration of a PD matrix on an OBFN chip for achieving a 2D photonic-assisted phased array. The optical modes are coupled from the waveguides of the OBFN chip into PDs through prism coupling without requiring any additional optical couplers. For fabrication purposes, an epitaxial-layer-transfer technology has been developed to transfer the only ~1.2 µm thick PD epitaxial layers from the original InP substrate onto the surface of an OBFN chip.