This PDF file contains the front matter associated with SPIE Proceedings Volume 12420, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Negative resistance millimeter wave semiconductor devices (including Tunnel, Gunn, IMPATT and, BARITT diodes) can generate high frequency microwave signals approaching the terahertz infrared regime for commercial telecommunications and military applications. These devices can be included in the drain or source regions of a MOSFET as one integral device to form Millimeter Wave to Terahertz Optoelectronic CMOS Transistors. Here, we will discuss the performance advantages of this novel technology: how it may even outperform traditional CMOSBased RF ASICs, System on Chip (SoC), or Silicon Photonics due to reduced series resistance and capacitance. Critical RF parameters, such as cutoff frequency (ft and fmax), are improved due to the switching speed improvements from the photonic and millimeter wave generation process. The integrated device produces less heat and can be thermally more stable. Also, photonic millimeter-wave devices can be designed to handle pulsed laser and millimeterwave signals simultaneously. Low operating voltages are possible due to the nature of the tunneling process and the close proximity of the components in the integrated device. We also show a path toward monolithic integration in a CMOS fabrication sequence. IMPATT and BARITT are reverse-biased diodes. Laser and LED are forward-biased diodes. The source or drain junction of a MOSFET is a reverse-biased diode. Photon and microwave generating diodes can be included in the drain or source regions of a MOSFET. Photon sensors can be fabricated in the substrate, well or drain regions. Millimeter wave diodes, laser or LED, Photon Sensors, and MOSFET are fabricated as one integral device to form the Millimeter-wave Photonic CMOS Transistors. A millimeter wave tunnel diode can be operated at a very low voltage, due to the tunneling process without thermal diffusion. Photonic Microwave CMOS functions with electric fields (it is a field effective device) compared with diode lasers, which rely on thermal diffusion and produce more thermal noises. With improved device models and circuit designs, nonlinear laser and millimeter wave communications can be a reality. The manufacturing costs for 3D All-Around-Gate FETs and Sub-5nm FINFETs can be very high. The Microwave Photonic CMOS process is 100% compatible with existing CMOS fabrication. In this report we will discuss the performance advantages and cost benefits of the technology.

We propose a theoretical phase noise analysis applicable for most of narrowband optoelectronic oscillators. In order to mathematically describe the phase noise spectrum, we directly convert a deterministic universal microwave envelope equation into a stochastic form by using a Langevin approach. The power density spectrum can be successfully obtained from the stochastic model, and it suggests ways to optimize the phase noise performance.

To exploit the extremely wide bandwidth in the THz region for ultra-high-speed wireless communication, UTCPD- based THz emitters enjoy a wide bandwidth and high linearity, but face challenges in increasing power due to saturation effects and thermal effects. We designed a 16-way WR3 power combiner for 12 dB gain using the Y-branch structure in the 300 GHz band. Additionally, a 37.7 dBi gain reflector-integrated diagonal horn antenna was developed for a pencil beam at 300 GHz. Furthermore, ongoing efforts are dedicated to manufacturing them with 3D printing technique.

We demonstrate a fully photonic sub-THz communication link using a PIN photodiode (PD) emitter and an optimized photoconductive antenna (PCA) as a heterodyne receiver. The novel receiver comprises an iron-doped indium gallium (InGaAs) PCA on a silicon lens and passive radio frequency (RF) circuitry, all packaged into a fiber-coupled module. A 3-dB-bandwidth of 11 GHz for the intermediate frequency was measured. We analyzed the capabilities of the receiver in a wireless communication link over a distance of 1 m with a PIN photodiode as the emitter. At a carrier frequency of 120 GHz, we demonstrate error free transmission for net data rates up to 10 Gbit/s with quaternary quadrature amplitude modulation (4-QAM) modulation.

In this paper, we present a novel RF interconnection technique for the integration of high-speed photodiodes allowing multi-band rectangular waveguide (RW) interface from a single device. It is based on the dielectric rod waveguide (DRW) technology, which is known to offer broad bandwidths. The signal from photodiode is coupled to a rectangular slab DRW by the near-field coupling from a planar transition. The DRW also offers mechanical compatibility with standard RWs. By achieving the fundamental mode excitation, a broad working bandwidth of 75 GHz to 330 GHz is achieved in the simulated model. This corresponds to four frequency bands of WR-10, WR-8, WR-5 and WR-3.

This paper showed the biological response of skin cells, and human newborn foreskin fibroblasts under the irradiation of a photonics-based 300 GHz terahertz source with a beam power of 20 ㎼ which has been usually used as terahertz source of non-destructive testing. We investigated the viability of the cells, cancer-induced biological signals, and aging under the irradiation of terahertz waves.

We report on the development and application of terahertz spectral imaging in burn diagnosis, using our new Portable HAndheld Spectral Reflection (PHASR) Scanner. The PHASR Scanner features a fiber-coupled housing, which provides an alignment-free strategy for the placement and operation of the THz optics. Image formation is achieved through telecentric beam steering over a planar surface through a custom f-θ scanning lens. Electronically Controlled Optical Sampling can be implemented for high THz trace acquisition rates and a simultaneously recorded error signal can be used to calibrate the signals for accurate measurement. This scanner allows for a constant spatial resolution over a wide field of view and rapid acquisition of full THz-TDS spectra in clinical and operating room settings.

A THz detector with both high sensitivity and fast time response has been required for industrial applications such as nondestructive testing (NDT), security, and spectroscopy. Through a collaboration with the Technical University of Denmark (DTU), we have recently developed a THz-sensitive point detector and imager based on metasurface and photomultiplier tube (PMT) and image intensifier (I.I.) technologies, respectively. A fast time response is one of the unique characteristics of these devices: the PMT-based point detector provides a nanosecond response time while the I.I.- based imager is capable of frame rates up to 1000 fps. These devices have a double split-ring resonator (DSRR) at the photocathode for THz-electron conversion (metasurface). In this paper, we discuss the two devices and report on the development and results for increasing their sensitivity for ultrafast, broadband THz pulses by sharpening the fieldenhancing antenna tips. This leads to a smaller tip diameter, which increases the electric field confinement and thus intensity at the tip, making the field emission more likely to occur at lower field strengths as a result. Both devices thus offer a sensitive and simple method to detect THz frequencies easily, with the I.I. offering a handheld, 9V batterypowered device.

Advantages of photoacoustic detection with a silicon cantilever microphone are demonstrated in the THz range. In our method, earlier membrane microphone is replaced with robust silicon cantilever microphone, which can tolerate high intensity of the input radiation in contrast to vulnerable membrane. The responsivity of the photoacoustic sensor was confirmed to be constant over almost six orders of magnitude of input power, which is not easy to achieve with any other detector of THz radiation. Another favorable feature of the photoacoustic sensor is its uniform spatial responsivity over areas of several millimeters in size. Finally, we measured nearly constant spectral responsivity of the photoacoustic sensor for the wavelength range of 0.3 μm to 200 μm.

Increases in data bandwidth requirements are constantly pushing wireless communications networks to frequencies. With operating frequencies starting to approach the Terahertz (THz) band, it is important to develop compact, chip-based THz radiation sources that are compatible with both the semiconductor industry and the Si photonics scene. In recent years, spintronic THz emitters, thin film heterostructures with a stack thickness of 5 nm capable of producing THz pulses via femtosecond laser pulse excitation have been the subject of much interest due to their efficiency, small footprint, and ease of integration with various platforms. Here, we present spintronic THz radiation emitters on Si and SiO₂ substrates integrated with optical waveguides that allow for modulation of the generated THz radiation power by up to 87% via variation of the optical pump polarization. As a result of the gradual trend towards higher frequencies, we envision such structures as being utilised for various on-chip applications alongside electronic and photonic circuits.

Stability of optical beats in a chaotically oscillating laser is compared to that of a free-running continuous-wave laser using a highly efficient plasmonic photomixer (Antenna). Numerical calculations were also performed for the multimode semiconductor laser with optical delayed feedback system. As a result, fundamental results on modes simultaneity in laser chaos is obtained.

We study that carriers in monolayer graphene can be accelerated to the Fermi velocity driven by high-power terahertz pulse E_THz without lattice heating at the charge-neutrality point. It is because that electron-phonon scattering rate is strongly suppressed due to the decreasing density of state near the Dirac point. Therefore, the carriers can be accelerated without energy transfer to optical phonons. As a result, carriers in graphene can travel at the Fermi velocity. At the Fermi lever larger than 110 meV, in contrast, excited carriers by E_THz heated the lattice of graphene and optical phonons are generated. The emitted optical phonons increase carrier-carrier scattering rate and drift velocity or carrier mobility can be reduced. This study indicates that the electron-optical phonon rate is affected by Fermi level in the graphene and provides insight for high-speed electronics of graphene-based applications.

Research has shown that breath exhaled from human lungs contains hundreds of volatile organic compounds (VOCs), from which illnesses and physical phenomena of organ systems can be detected. We can use exhaled nitric oxide (ENO) concentration to test whether a patient has a chronic obstructive pulmonary disease (COPD). One significant advantage of using exhaled breath to examine the existence of illness is that the examination is non-invasive, posing no extra risks to human bodies. In the past two decades, some studies applied electronic sensors in detecting the concentration of nitric oxide, and the sensors needed to operate at high temperatures. However, few studies are about optical detection with a measuring range from ultraviolet to visible light, and the range could cause harm to human skin. In this paper, we used tunable metamaterial to build a split-ring resonator (SRR) that resonates in the region of terahertz (THz) frequency. The resonant peak was designed to appear at 0.250 THz, which is the resonant peak of nitric oxide. In order to increase the total volume of gas adsorption, we laid a compound layer that consisted of a layer of zinc titanium oxide and a layer of graphene on the metamaterial's surface to enhance the sensitivity (ΔT/Δn) of the component from 2% to 12.6%. We hope to develop the research result into a component that monitors and examines the physical conditions of human bodies and expect to apply the component in the development of wearable electronic components.

With regards to composites, the need for non-destructive evaluation (NDE) of their inner structure, or constructions they form continuously rises. Nowadays, a great deal of attention has been paid to methods based on the use of Terahertz radiation (THz). It is related to the exceptional properties of THz radiation which allows for contactless, safe, and fast inspection of non-conductive materials. In the frame of this work the results of the use of the Terahertz imaging method, operated at the frequency of 300 GHz, are presented. The selected aramid fiber-reinforced composites with intentionally introduced defects were monitored. A thorough structural materials inspection was carried out in transmission mode. The obtained images were preprocessed and enhanced. Overall, the phenomenon of noninvasive monitoring using Terahertz radiation and the tremendous advances in this field were presented.

Applications of terahertz (THz) and sub-THz technology require portable, inexpensive, efficient, and reliable THz electronics. This stimulated the search for novel semiconductor materials for THz applications. This paper evaluates the potential of ultra-wide bandgap semiconductors (UWBGS) for THz and sub-THz applications. The wide bandgap is the consequence of strong bonds between the nearest neighbors in UWBGS, such as diamond, boron nitride, and aluminum nitride. This is the consequence of small atomic radii of carbon and nitrogen forming intimate contacts with their nearest neighbors. The resulting high energies of optical phonons in these materials lead to superior transport properties, including high breakdown voltages and long mean free paths of electrons in the conduction band and holes in the valence band. These factors make ultra-wideband semiconductors prime candidates for high-power and high-frequency applications. The analysis of the cutoff frequencies and quality factor of plasma oscillations show that diamond has a high potential as an active material for Terahertz Field Effect Transistors (TeraFETs) generating THz and sub-THz radiation, including radiation in the 300 GHz range, which is of special interest for 6G communications. Boron nitride should enable high cutoff frequencies of operation in collision-dominated regimes.

This work demonstrates the realization of terahertz (THz) spectroscopy on a subwavelength scale. We do so by using dielectric spheres as focusing elements and apertures as spatially constricting elements for THz radiation. Such a configuration forms intense, subwavelength-sized THz microjets. Two implementations are used to demonstrate the effectiveness of THz microjets, as follows: apertured THz plane waves and apertured THz microjets. Seven aperture diameters were chosen for each implementation to discern their capabilities at the subwavelength scale. We investigated the effectiveness of each implementation in mapping the material characteristics of the sample onto the THz beam. Such analyses show that apertured THz microjets were able to map material characteristics (via refractive index and extinction coefficient) onto the beam (via phase and amplitude) effectively and reliably. This is expected as the beam produced by apertured THz microjets has a small cross-sectional area (apertures) and high intensity (THz microjets). Here, we illustrate the capabilities of apertured THz microjets for a biological specimen, being lactose, to show the potential for biological applications. Overall, this work demonstrates the ability of apertured THz microjets to perform THz spectroscopy at a subwavelength scale. Such findings could bring about biological characterization with cellular-scale resolution.

Photomixing of internal mode beat in a Kerr micro-resonator frequency comb (microcomb) is a potential method to generate CW-THz wave with ultra-high frequency, low phase noise, and practicability for next-generation wireless communication. Here, we generated a 560-GHz CW-THz wave by photomixing of a soliton microcomb generated from a Si₃N₄ micro-resonator (frequency spacing = 560 GHz) with a uni-traveling-carrier photodiode (UTC-PD). Then, we evaluate the phase noise characteristics of generated CW-THz waves.

Thermoelectrically coupled nanoantennas (TECNAs) are a new class of infrared detectors based on the resonant absorption of freely propagating electromagnetic waves. When IR light illuminates the devices, radiation-induced antenna current heats the nanothermocouples. The temperature difference with respect to the cold junction at the substrate is converted to electrical signals by the Seebeck effect. The physical size of the nanoantenna determines the spectral response of the device. In this work, we show experimentally obtained spectral responses of TECNAs using Fourier-transform infrared spectroscopy (FTIR) and compare the results to simulations.

We have previously demonstrated a microwave photonic spectrometer based on laser speckle pattern imaging in which laser is modulated with the RF signal, transmitted through a long multimode optical fiber and the speckle pattern is measured [1]. The spectrometer is calibrated by associating a set of calibration RF tones to speckle patterns. Unknown signals can then be identified by correlation with the calibration set. The spectrometer is capable of achieving MHz-level resolution over a 17-GHz frequency range, which compares favorably with the best real-time microwave spectrum analyzers. However, the speed of the instrument is wanting in comparison to conventional RF electronics and the footprint is large due to the 100 meters of potted fiber. To increase speed, we incorporate a high-speed camera capable operating at up to 800 kHz frame rate, effectively increasing the data acquisition rate by a factor of 16,000. We present updated analysis of the spectrum recovery towards an increase in spectral recovery rate. Additionally, in the interest of miniaturization, we present the results of simulations of a 50-μm wide, 40-cm long multimode waveguides in silicon nitride or silicon that suggest that they can replace the 100-m long multimode fiber can be replaced by short waveguides without degradation in performance.

We have proposed a multiband operated superlative MIMO antenna structure. The simple T-shaped resonator-based design is numerically investigated for the 4 GHz to 20 GHz frequency range. The performance of the design is done in terms of reflectance coefficient, transmission coefficient, radiation pattern, gain, and electric field. The design provides the four-band behaviour. The results represent a minimum S11 of -27.27 dB, a peak gain of 9.66 dB, an E-field of 20041 v/m, and broad directivity. The design is fabricated using the Roger RT Duroid 5880. The presented structure's performance also examines ECC, TARC, DG, and CCL. The reliability of the design is checked by comparison among simulated and measured results. The design helps the airborne, Naval radar and many wireless communication applications.

In this paper, we report on terahertz spectral properties of polymer medical films cross-linked by electron beam irradiation. This is significant because it shows the potentials for novel technique to monitor of crosslinking state in polymer materials. We were able to clearly distinguished to cross-linked and noncross-linked medical films, which were manufactured with a PEO based synthetic polymer, in our conducted experiments. The THz-TDS method has potential as a useful nondestructive technique for polymer inspection and analysis.