Active Metamaterials for Terahertz Communication and Imaging
Abstract: In recent
years there has been significant interest in terahertz (THz) systems mostly due to their
unique applications in communication and imaging. One of the primary reason for this
resurgence is the use of metamaterials to design THz devices due to lack of natural
materials that can respond to this electromagnetic spectrum, the so-called ''THz gap''.
Even after years of intense ... read moreresearch, THz systems are complex and expensive, unsuitable
for mainstream applications. This work focuses on bridging this gap by building all
solid-state THz devices for imaging and communication applications in a commercial
integrated circuit (IC) technology. One such canonical device is a THz wave modulator
that can be used in THz wireless communication devices and as spatial light modulator
(SLM) for THz imaging systems. The key contribution of this thesis is a metamaterial
based THz wave modulator fabricated in a commercial gallium arsenide (GaAs) process
resonant at 0.46~THz using a novel approach of embedding pseudomorphic high electron
mobility transistors (pHEMTs) in metamaterial and demonstrate modulation values over
30%, and THz modulation at frequencies up to 10 MHz. Using the THz wave modulator, we
fabricated and experimentally demonstrated an all solid-state metamaterial based THz
spatial light modulator (SLM) as a 2x2 pixel array operating around 0.46 THz, by raster
scanning an occluded metal object in polystyrene using a single-pixel imaging setup.
This was an important step towards building an low-voltage (1V), low power, on-chip
integrable THz imaging device. Using the characterization result from the THz SLM, we
computationally demonstrated a multi-level amplitude shift keying (ASK) terahertz
wireless communication system using spatial light modulation instead of traditional
voltage mode modulation, achieving higher spectral efficiency for high speed
communication. We show two orders of magnitude improvement in symbol error rate (SER)
for a degradation of 20 dB in transmit signal-to-noise ratio (SNR). We have
computationally demonstrated a novel pictorial modulation technique showing N/log2(N)
improvement in bandwidth using a N-tile SLM compared to standard spatial modulation
using a single-pixel detector. Finally, we demonstrate a path to realize a terahertz
focal plane array (FPA) using a commercial 0.18 um CMOS foundry process. Through EM
simulation and circuit simulation we have demonstrated a metamaterial based THz
detectors at 230-325 GHz that can be used in a focal plane
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Electrical Engineering.
Advisor: Sameer Sonkusale.
Committee: Mohammed Afsar, Shuchin Aeron, Xiaocheng Jiang, and Edward Lee.
Keywords: Electrical engineering, Electromagnetics, and Physics.read less