Broadband Terahertz Signal Generation and Radiation Based on Direct Digital-to-Impulse Radiating Arrays in Silicon

Broadband terahertz (THz) signal generation and radiation has unique applications in 3-D hyper-spectral imaging, molecular sensing, and high-speed wireless communication. THz waves interact with the rotational and vibrational transitions of molecules with applications in material detection and biomedical sensing. They also penetrate through non-metallic and non-polar mediums that can be used to image concealed objects for security purposes. Conventional terahertz pulse generation techniques are based on the optical excitation of a III-V photoconductive antenna with a femtosecond optical laser pulse. This method of THz pulse generation and detection is widely used in THz time-domain spectroscopy systems. Although THz-TDS is a powerful technique, its dependence on bulky, expensive and power-hungry femtosecond lasers, optomechanical components, and costly photoconductive antennas compromises its speed, accessibility and scalability. In this dissertation, an on-chip laser-free direct digital-to-impulse (D2I) architecture is introduced that is capable of radiating a THz pulse by creating and exciting a broadband radiating resonator consisting of an on-chip antenna and a broadband matching network. This novel method converts a digital trigger edge to a radiated THz pulse with a high timing accuracy. A broadband matching network and an ON/OFF impulse-shaping technique are designed to maximize the amplitude of the pulse and minimize ringing. This method achieves a high DC-to-radiated efficiency by turning off the current switch shortly after turning it on. The deep nonlinear switching mechanism results in numerous harmonics from GHz to THz. Based on the high timing accuracy of the radiated THz pulses in D2I, a novel trigger-based beamforming architecture is introduced that enables broadband pulse beamforming in which all frequency content is steered simultaneously. This is in contrast with conventional phased-array architectures that have a limited bandwidth, where an RF signal is time-delayed. One of the main challenges of sampling a picosecond pulse in the time domain is ensuring that both the receiver and its antenna are broadband and have a linear phase response. Pyramidal horn antennas cannot be used to receive picosecond pulses, due to their limited bandwidth and nonlinear phase response. In addition, commercially available sampling oscilloscopes have a 3-dB bandwidth of less than 70 GHz, therefore cannot be used to sample a pulse with a FWHM of \textasciitilde 2 ps. To address this problem, we propose a direct time-domain measurement scheme based on femtosecond-laser-based THz sampling systems. Having a high-power, broadband frequency-comb source is critical in imaging and spectroscopy applications. By applying a periodic trigger signal, the D2I architecture radiates an impulse train in the time domain, which has a frequency-comb spectrum with a spacing of $1/T$. To perform spectroscopy, T can be controlled to sweep the whole spectrum. Further in this thesis, we will present our THz pulse radiating chips applied in imaging and spectroscopy experiments. This is the first time that a fully electronic chip is capable of generating and radiating harmonic tones at frequencies higher than 1 THz. Owing to the high scalability of the D2I architecture, combined with the broadband pulse beam-forming method, large arrays of D2I radiators can be built to radiate high-power, steerable narrow beams. In this thesis, ultra-short pulse radiating sources will be presented that were used to demonstrate laser-free broadband gas spectroscopy and THz imaging.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Engineering

Grantor

Rice University

Year dc:date.issued

2018

Author dc:creator

• Assefzadeh, Mahdi

Advisor dc:contributor.advisor

• Babakhani, Aydin

Committee member dc:contributor.committeemember

• Knightly, Edward

• THz
• silicon
• radiation
• integrated circuits
• phased arrays
• beamforming
• broadband
• picosecond pulse
• impulse

Statement dc:rights

• Copyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1911/105740

OAI identifier oai:identifier

oai:repository.rice.edu:1911/105740