Zhenguo Jiang

Coded-Aperture Imaging Using Photo-Induced Reconfigurable Aperture Arrays for Mapping Terahertz Beams

We report terahertz coded-aperture imaging using photo-induced reconfigurable aperture arrays on a silicon wafer. The coded aperture was implemented using programmable illumination from a commercially available digital light processing projector. At 590 GHz, each of the array element apertures can be optically turned on and off with a modulation depth of 20 dB and a modulation rate of ~ 1.3 kHz. Prototype demonstrations of 4 ×4 coded-aperture imaging using Hadamard coding have been performed. Continuous THz imaging with 8 ×8 pixels has also been demonstrated, using a slowly moving metal strip as the target. In addition, this technique has been successfully applied to mapping THz beams by using a 6 ×6 aperture array at 590 GHz. The imaging results agree closely with theoretical calculations based on Gaussian beam propagation, demonstrating that this technique is promising for realizing real-time and low-cost terahertz cameras for many applications. The reported approach provides a simple but powerful means to visualize THz beams, which is highly desired in quasi-optical system alignment, quantum-cascade laser design and characterization, and THz antenna characterization.

Terahertz focal plane arrays employing heterostructure backward diodes integrated with folded dipole antennas

In this paper, we present the design, simulation, fabrication and initial characterization results of terahertz (THz) focal plane arrays (FPAs) employing Sb-based heterostructure backward diodes (HBDs) integrated with lens-coupled folded-dipole antennas (FDAs). For single array element design, FDAs with high embedding-impedances have been designed for impedance matching to HBDs without additional matching network. Under impedance matching conditions, a maximum detector responsivity of ~21,000 V/W could be obtained for single array pixel at 200 GHz. In order to expand the single element design into full 2-D THz FPAs, the off-axis radiation patterns of the FDA mounted on an extended hemispherical silicon lens have been analyzed using the ray tracing technique. In addition, mutual coupling between two adjacent FDAs has been studied using full-wave simulation. The above results along with initial array fabrication and device characterization results have demonstrated the potential to achieve room-temperature, high-performance and large-scale FPAs for THz imaging applications.

Advanced Terahertz Sensing and Imaging Systems Based on Integrated III-V Interband Tunneling Devices

Owing to the unprecedented development in terahertz (THz) sources and detectors in the last decade, technologists and researchers have intensified their efforts to develop advanced THz sensing and imaging systems with superior performance and unique functionalities. One of the key elements to realize such systems is the ability to monolithically integrate high-performance semiconductor devices with THz antennas and other passive structures. In recent years, devices based on interband tunneling in III-V heterostructures have emerged as promising candidates for THz detection that offer extremely high nonlinearity, high sensitivity, low noise, fast response, and room temperature operation. In this paper, we first review the development of heterostructure backward tunnel diodes (HBDs) in the InAs/AlSb/AlGaSb material system that have been demonstrated with detection sensitivity that outperforms the current state of the art (e.g., the fundamental limit of Schottky diodes) and with noise-equivalent power (NEP) below 0.2 pW/Hz½. We then present the monolithic integration of HBDs with planar folded dipole antennas (FDAs) using submicrometer-scale airbridges to achieve optimized impedance matching for high-performance and compact THz detectors and focal-plane array (FPA) imaging systems. In addition, the potential of using HBDs for realizing THz systems with advanced functionalities such as spectroscopic FPAs (using frequency-tunable THz antennas) and polariametric detection/imaging systems will be discussed. Finally, the integration of HBDs into waveguides for more advanced THz sensing and imaging (e.g., a six-port reflectometer for near-field imaging) will be discussed.

A terahertz reconfigurable photo-induced fresnel-zone-plate antenna for dynamic two-dimensional beam steering and forming

We report a novel and simple approach to realize terahertz (THz) dynamic two-dimensional (2D) beam steering and forming antennas, based on reconfigurable photo-induced Fresnel zone plates (PI-FZPs). The FZPs are formed by directly illuminating a high-resistivity silicon wafer with the desired patterns using a digital light processing (DLP) projector, without any circuit or device fabrication. At 750 GHz, the THz beam from a diagonal horn antenna has been steered two dimensionally over a range from approximately -12° to +12° from the antenna boresight, by projecting different PI-FZP patterns. In addition, using PI-FZPs with different focal lengths, the THz beam size can be dynamically tuned. Both the beam steering and forming can be performed simultaneously without affecting the antenna performance, making this an enabling technology for emerging THz applications such as sensing, imaging, tracking, adaptive wireless communications and short-range high-speed interconnections.

Integration and fabrication of high-performance Sb-based heterostructure backward diodes with submicron-scale airbridges for terahertz detection

In this work, the authors report integration and fabrication of high-performance Sb-based heterostructure backward diodes (HBDs) with planar folded dipole antennas (FDAs) using submicron-scale airbridges for terahertz (THz) detection. By integrating HBDs into FDAs, high detector responsivity of 20 000 V/W at 200 GHz and 9500 V/W at 585 GHz could be potentially achieved due to the optimized impedance matching between the antenna and HBD detector. In order to minimize interconnect parasitics, the HBD integration is accomplished using submicron-scale airbridges. Electromagnetic simulations coupled to device models show that by introducing submicron-scale airbridges and optimizing the device layout, parasitic capacitance and spreading resistance can be significantly reduced. This allows performance nearly equal to the intrinsic device performance to be obtained. To achieve this level of performance, a novel fabrication and integration process has been developed. The process includes mix-and-match electron bea...

A 200 GHz lens-coupled annular-slot antenna with 50 GHz tuning range for reconfigurable terahertz detectors

A frequency-tunable lens-coupled annular-slot antenna using a Schottky varactor diode has been developed and characterized at 140-220 GHz. A tuning range of ~50 GHz (agree with simulation) has been demonstrated by varying the diodes DC bias. Antenna far-field patterns have been measured at 203 GHz, showing that the diode has only a minor effect on the antennas radiation properties. This type of tunable antenna is promising for realizing reconfigurable THz detectors and focal-plane arrays.

Emerging electronic devices for THz sensing and imaging

Continuing advances in scaling of conventional semiconductor devices are enabling mainstream electronics to operate in the millimeter-wave through THz regime. At the same time, however, novel devices and device concepts are also emerging to address the key challenges for systems in this frequency range, and may offer performance and functional advantages for future systems. In addition to new devices, advances in integration technology and novel system concepts also promise to provide substantial system-level performance and functionality enhancements. Several emerging devices and device concepts, as well as circuit-level concepts to take advantage of them, are discussed. Based on unconventional semiconductor device structures and operational principles, these devices offer the potential for significantly improved system sensitivity and frequency coverage. When combined in arrays, features such as polarimetric detection and frequency tunability for imaging can be achieved. As examples of emerging devices for millimeter-wave through THz sensing and imaging, heterostructure backward diodes in the InAs/AlSb/GaSb material system and GaN-based plasma-wave high electron mobility transistors (HEMTs) will be discussed. Based on interband tunneling, heterostructure backward diodes offer significantly increased sensitivity and extremely low noise for direct detection applications, and have been demonstrated with cutoff frequencies exceeding 8 THz. The plasma-wave HEMT is an emerging device concept that, by leveraging plasma-wave resonances in the two-dimensional electron gas within the channel of the HEMT, offers the prospect for both tunable narrowband detection as well as low-noise amplification at frequencies well into the THz. These emerging devices are both amenable to direct integration within compact planar radiating structures such as annular slot antennas for realization of polarimetric detection and frequency tuning for spectroscopy and imaging.

Quasi-Optical Terahertz Microfluidic Devices for Chemical Sensing and Imaging

We first review the development of a frequency domain quasi-optical terahertz (THz) chemical sensing and imaging platform consisting of a quartz-based microfluidic subsystem in our previous work. We then report the application of this platform to sensing and characterizing of several selected liquid chemical samples from 570–630 GHz. THz sensing of chemical mixtures including isopropylalcohol-water (IPA-H2O) mixtures and acetonitrile-water (ACN-H2O) mixtures have been successfully demonstrated and the results have shown completely different hydrogen bond dynamics detected in different mixture systems. In addition, the developed platform has been applied to study molecule diffusion at the interface between adjacent liquids in the multi-stream laminar flow inside the microfluidic subsystem. The reported THz microfluidic platform promises real-time and label-free chemical/biological sensing and imaging with extremely broad bandwidth, high spectral resolution, and high spatial resolution.

Investigation and Demonstration of a WR-4.3 Optically Controlled Waveguide Attenuator

We report the design and demonstration of a compact WR-4.3 (170-260 GHz, equivalent to WR-4 band in Electronics Industries Alliance band designation) optically controlled waveguide attenuator using an E-plane tapered high-resistivity micromachined silicon absorber. Variable attenuation is realized by illuminating the silicon absorber with different light intensities from a fiber-guided infrared laser diode. Finite element method simulation has shown that high attenuator performance can be potentially achieved. For a prototype demonstration, a WR-4.3 optically controlled attenuator has been designed and implemented using an E-plane split waveguide configuration. The attenuator has been characterized in the WR-4.3 waveguide band using a vector network analyzer and the results show that a 0.6-dB insertion loss, greater than 10-dB return loss, and an average of approximately 25-dB tuning range have been achieved over most of the WR-4.3 band (i.e., 170-230 GHz). This approach is promising for developing high-performance variable waveguide attenuators into the millimeter-wave and terahertz regime.

Tunneling-based heterostructure devices for millimeter-wave and THz sensing

Sensing and imaging at millimeter-wave and THz frequencies is promising for a wide range of applications, including security, industrial control, healthcare, and scientific metrology. The development of high-sensitivity, low noise detectors based on interband tunneling in III-V heterostructure devices, and their integration into subsystems is promising for realizing the potential of these applications. This paper describes recent work on both heterostructure backward diodes and tunneling field-effect transistors as sensitive detectors in the microwave through THz frequency ranges, as well as their integration into tunable pixel elements and focal plane arrays for imaging and sensing applications.