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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...
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.
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.
We demonstrate a frequency swept optical beat source for high speed continuous wave THz generation. The range of the sweeping bandwidth is about 2.16 THz (17.3 nm). And we observe CW THz waveforms for several static optical beat sources using a fiber coupled CW THz measurement system in order to confirm the feasibility of our frequency swept optical beat source as a CW THz radiation source.
We demonstrated a fiber-coupled THz time-domain spectroscopy (TDS) system. A THz output power of 132 nW of the THz emitter in the system was measured by a Golay-cell. Water vapor dips in the free space were clearly observed by the THz detector in the system.
We demonstrate continuous wave (CW) THz generation with a compact dual-mode laser diode (DML) and InGaAs-based photomixers (PMs). By tuning the output wavelengths of the DML, we achieved THz tuning more than 1 THz. We detected THz output from PM emitter using coherent detection scheme.
The phase shifted dual-mode laser diode (DML) is demonstrated for the optical beat source of continuous wave THz system. Optical beat frequency can be continuously tuned from 0.22 THz to 1.15 THz. High side mode suppression ratio of 40 dB is obtained through whole tuning range.
We propose a high-speed frequency-scanning optical beat source using a wavelength swept laser and a tunable laser for continuous THz wave generation. The beat frequency is scanned at 1 kHz over a range with a 2.16 THz width.
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