UCLA

Advances in silicon technologies and emerging on-chip antennas have provided a reliable solution for designing low-cost, high-speed integrated circuits. The birth of 5G systems and the definition of the 6G standard are evidence of the increasing interest in the exploration of terahertz frequencies for ultra-broadband wireless communication systems. Terahertz frequencies promise unlicensed wide-spectrum bandwidth for the next generation of wireless communication links.

Traditionally, terahertz systems have been realized optically by exploiting a photoconductive antenna with a femtosecond laser source. However, laser-based terahertz systems suffer from high cost, bulky measurement setups, and high power consumption, making them impractical for certain applications in communication, sensing, and imaging. In contrast, the transistor speed in silicon-based technologies has been improving over the last several decades, making electronic terahertz systems a low-cost and efficient alternative for optical systems. However, one of the main challenges in realizing efficient integrated terahertz systems in silicon is the generation and detection of signals beyond the maximum oscillation frequency (fmax) of a transistor, which does not exceed hundreds of gigahertz.

Considering all the progress made in electronic terahertz systems, researchers have remained pessimistic regarding the feasibility of terahertz propagation over relatively long distances due to high atmospheric absorption loss. This issue is even more critical for silicon-based terahertz radiators, where the amount of radiated power is 10s of dB below that of optical terahertz systems. Therefore, most studies in the terahertz domain have been limited to short-distance setups in a lab environment.

In this dissertation, a fully integrated laser-free terahertz impulse transceiver in silicon is presented that can radiate and detect arbitrary signals in millimeter-wave and terahertz bands with a 2 Hz frequency resolution. In the transmit mode, this chip radiates broadband impulses with 2.5-picosecond full width at half maximum, corresponding to a frequency comb with 1.052 terahertz bandwidth. In the receive mode, this design acts as a coherent detector that detects arbitrary signals up to 500 GHz with a peak sensitivity of -100 dBm with a 1 KHz resolution bandwidth. This receiver is utilized in conjunction with an impulse radiator to implement a dual-frequency comb spectroscopy system. A chip-to-chip dual-frequency comb is successfully measured and characterized in the 20--220 GHz frequency range. Additionally, this design can transmit picosecond impulses at 4 Gb/s data rate. Moreover, long-path terahertz communication channel characterization is introduced in the frequency range of 0.32-1.1~THz, where a specular link is created using a terahertz radiator, parabolic reflector antennas, a plane mirror, and a downconverter mixer. The terahertz channel is characterized up to a distance of 110~m. The measurement results demonstrate channel path loss, atmospheric absorption, and low-loss frequency windows suitable for long-range point-to-point wireless communication links in the terahertz regime.