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By adopting nanoelectrodes, the performances of THz photo-conductive antennas (PCAs) and photomixers (PMs) have been significantly improved. On the extension of our previous works, here we present a nanoelectrode PM for homodyne THz detection, free from low-temperature-grown semiconductors. It was realized by utilizing the electric field enhancement effect by the nanoelectrode, which may be applied...
With a vision of easily-accessible terahertz industrial applications, we are in pursuit of small and cost-effective terahertz technologies. Our various approaches for the enhanced performances, including arrayed devices and nano-based devices will be presented.
Recently, nano-structures have been adopted for the photonics-based THz emitters and detectors to enhance their output power and detection sensitivity. The notable improvements have been attributed to the plasmon enhanced absorption. However, we found that the field enhancement at the extremities of the nano-structure dominates over the plasmon effect, may be maximized by considering nano-scale ultrafast...
A wire-grid polarizer based on VO2/Al2O3 (0001) is fabricated. It is experimentally confirmed that the polarizer controls the amplitude of the transmitted THz wave by changing the temperature. The device performance was estimated through degree of polarization (DOP), extinction ratio (ER), and the temperature dependence of field amplitude modulation depth (MD). From the measurements, the fabricated...
Semiconductor devices based on photonics for the tunable continuous-wave THz generation and detection are explored. A tunable single-chip terahertz transceiver consists of beating source, broadband photomixer, and THz detector is developed. The realizable possibility of monolithically integrated single-chip THz transceiver which is main building block for the wide spread industrial applications will...
A 1.3-µm dual-mode laser diode with an integrated semiconductor optical amplifier has been developed as an optical beat source for a continuous-wave terahertz system via the photomixing method. It exhibits a high output power of over 80 mW and a wide optical beat frequency tuning range 250–1480 GHz.
A simple and compact method of generating modulated beating signals from a dual-mode laser via bias modulation of integrated micro-heaters is proposed and successfully demonstrated. The proposed scheme will enrich the continuous-wave terahertz system applications.
This paper reports on the development of terahertz (THz) bandpass properties with a transverse electromagnetic (TEM) mode by using two multiple-slit plates that serve as parallel-plate waveguides (PPWGs). The lower multiple-slit plate, which has a 500-µm period, shifts to the THz propagation direction by 270 µm to remove Bragg and Bragg-related resonances. The resonance frequency of the bandpass depends...
According to an air gap variation in a parallel-plate waveguide (PPWG), a tunable terahertz (THz) single resonance with a transverse-electromagnetic (TEM) mode can be demonstrated. When the air gap between the metal plates of the PPWG is controlled from 60 to 240 µm using a piezo-actuator, the resonant frequency is changed from 1.75 up to 0.62 THz, respectively. We also demonstrate the tunable THz...
Introducing antireflection slits at the boundaries of a finite-size coupled terahertz cavity in a metal air-gap waveguide can minimize reflections at the boundaries. The optimal design parameters for the minimal reflection were obtained using the one-dimensional antireflection coating theory and finite-difference time-domain simulations. We experimentally demonstrated that the optimized antireflection...
We present experimental and theoretical studies on terahertz (THz) notch filter having a wide THz frequency range and low-pass filter (LPF) having a 0.78 THz cutoff frequency. The notch filter has a dispersion-free and low-loss transverse magnetic (TM) mode. On the other hand, the cut off frequency of the LPF was determined using a Bragg stop band, which depends on slit period.
Using Terahertz Time-Domain Spectroscopy (THz-TDS), we measured the structural transition from hydroquinone (HQ) clathrates having the storage properties to crystalline a-form hydroquinone as a function of temperatures. We found that all three HQ clathrates, CO2-, CH4-, and CO2/CH4-loaded HQ clathrates, have the different vibrational lines and transform into the a-form HQ at around 102±7°C. The resonance...
We present experimental and finite-difference time-domain (FDTD) simulation studies on the THz Bragg stop bands carried out by using metal slit arrays positioned at the center of the air gaps in tapered parallel-plate waveguides (TPPWGs)[1]. The prosperities of THz stop bands determined in the simulations show excellent agreement with those observed experimentally. Recently, researchers have investigated...
We have fabricated a miniaturized optical fiber coupled THz endoscope system. The cross section of the endoscope head is only 2 × 4 mm and 6 mm long, which is small enough to be inserted into mouth. For a feasibility test, we measure reflective THz signals from the side wall of the mouth, tongue, and palm skin as well as from water for comparison.
We present terahertz field propagation through input- and output-side tapered parallel-plate waveguide (TPPWG). Coupling of the TPPWG having a 3° slop angle improved the measured THz amplitude by over 100%, unlike the cylindrical silicon lens used in the PPWG because TPPWG had almost no impedance mismatch to the propagating THz wave.
This research reports an experimental and simulation study of a silicon-lens-free tapered parallel-plate waveguide (TPPWG) to improve THz coupling to the plate separation gap. The TPPWG without any silicon lens is compared to the parallel-plate waveguide (PPWG) with a plano-cylindrical silicon lens. It was found that the input- and output-side TPPWG with a 3° tapered slop angle increased by about...
We developed optical fiber-coupled terahertz (THz) endoscope system which utilized a photoconductive generator and detector driven by a mode-locked Ti:sapphire laser. For a feasibility test, the endoscopic system was used to measure reflective THz signals from the side wall of the mouth, tongue, and palm of hand as well as from water for comparison. The absorption and refractive index of the side...
This presentation will give an overview of the THz metal waveguides which are single metal wire, copper coaxial cable, parallel-plate, and aluminum sheet. We investigated the propagation of single- and multi-mode terahertz (THz) radiation through a parallel-plate waveguide (PPWG) for various gap sizes of the plates and polarizations of the incoming THz field. Also we present experimental and theoretical...
Using terahertz time-domain spectroscopy (THz-TDS), we have measured the absorption spectra of alpha-hydroquinone and methane- and methanol-loaded beta-hydroquinone clathrates up to 3 THz frequency range. The alpha-hydroquinone exhibits 11 resonances whereas methane- and methanol-loaded beta-hydroquinone clathrates show only 1 resonance. The observed THz resonances represent the intermolecular and...
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