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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.
We present a terahertz (THz) radiation pumped by a passively mode-locked Yb-doped fiber laser using two fiber-pigtailed log-spiral-based low-temperature-grown (LTG) InGaAs photoconductive antenna (PCA) modules. The mode-locked fiber laser produces over 220 mW of the average optical power with positively chirped of 1.49 ps pulses. In order to generate THz radiation using the fiber-pigtailed PCA modules,...
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...
Despite the massive influx of mobile apps into the market, not everyone is "mobile literate." The steady growth of the mobile industry has highlighted the emerging need to advance mobile literacy. This study uses an individual level mobile app usage dataset to examine the potential of mobile platform-based social games as training tools for mobile literacy. We choose Anipang, a popular mobile...
We fabricated a nano-gap electrode large area THz emitter and measured the THz emission using a femtosecond laser based THz time-domain spectroscopy system. As a result of adopting the large-area emitter structure, the optical power density was significantly reduced at the active region, and the emission power was improved by 20 times.
We report an Yb-doped mode-locked fiber laser at 1.03 μm for time-domain terahertz spectroscopy. The total cavity length is 21.4-m long including free space. The 3 dB optical bandwidth of the mode-locked fiber laser is ∼ 3.5 nm. It can be used as an optical source for compact and potable THz radiation source.
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...
We designed and fabricated planar InGaAs Schottky barrier diode (SBD) array for terahertz (THz) imaging applications. We also characterized the performances of SBD array and successfully obtained THz images.
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.
We have investigated the direct modulation characteristics of a phase-shifted 1.3-µm dual-mode laser diode. Stable dual-mode operation and high spectral purity are maintained under 2.5-Gbps direct modulation.
We characterize InGaAs Schottky barrier diodes (SBDs) with a variation in the anode size. High-efficiency terahertz (THz) pulse detection of the InGaAs SBDs is performed in the cases of anode diameters of 2 µm and 3 µm. The uniformity of the fabricated 1 × 20 InGaAs SBD array is measured to be fine. The THz imaging results using the 1 × 20 InGaAs SBD array are presented.
We report a continuously tunable dual-wavelength laser based on the polymer Bragg gratings for continuous wave terahertz optical beat source generation. The polymer Bragg gratings are used to wavelength selective components in the laser cavity. The measured wavelength tuning range is about 19 nm. The side mode suppression ratio is achieved more than 30 dB for dual wavelength.
A travelling-wave photomixer was realized. The responsivity was 0.42A/W for 15µm length device. It showed a 3dB bandwidth of more than 200GHz, limited by transit-time of photo-generated carriers. Also, it showed a successful THz wave generation up to frequency range of more than 500GHz.
The photomixers enables continuous-wave, frequency-tunable terahertz (THz) emitter and detector by using conventional photonics technology. To increase the emission and detection efficiency, various antennas have been adopted. In this work, we provide experimental characterizations of various kinds of antenna-integrated photomixers by measuring reference THz pulse from an InAs crystal.
We have developed a semiconductor optical amplifier integrated λ/4 phase-shifted 1.3-μm dual-mode laser as an optical beat source for continuous-wave (CW) terahertz (THz) generation. The CW THz system is also demonstrated with low-temperature-grown InGaAs photomixers.
We have developed the λ/4 phase-shifted 1.3-µm dual mode laser as an optical beat source of continuous-wave (CW) terahertz (THz) generation. The mode beat frequency is continuously tuned from 230 to 1485 GHz via integrated micro-heaters. The CW THz system is also demonstrated with low-temperature-grown InGaAs photomixers.
We have derived analytic expressions of bandwidth limitations of travelling-wave photodetectors (TWPDs) for only-output and both input/output impedance matching cases, without any approximations. Results are effective for design of TWPD for broadband terahertz photomixer.
A high-speed travelling-wave photodetector (TWPD) with an InGaAs absorber was designed and realized. The bandwidth of the TWPD was measured as 210GHz using electro-optic sampling techniques. This kind of device can be used for THz photomixer
We demonstrate a portable terahertz (THz) spectrometer and imaging system. Absorption lines of water vapor in the free space are clearly observed by using the THz system. A THz imaging of a medical knife behind a poly-ethylene is finely measured by the same THz system as well.
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