Abstract-Terahertz continuous wave system using phase shift interferometry for measuring the thickness of sub-100-μm-thick samples without frequency sweep

Da-Hye Choi, Il-Min Lee, Kiwon Moon, Dong Woo Park, Eui Su Lee, and Kyung Hyun Park

Fig. 1 Schematic of the experiment set-up. A beating signal generated from a tunable laser system is injected into the transmitter (Tx) for THz generation. The THz waves are divided by a beam splitter. The beams reflected from the two mirrors are focused on the receiver (Rx).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-10-14695

A terahertz continuous wave system is demonstrated for thickness measurement using Gouy phase shift interferometry without frequency sweep. One arm of the interferometer utilizes a collimated wave as a reference, and the other arm applies a focused beam for sample investigation. When the optical path difference (OPD) of the arms is zero, a destructive interference pattern is produced. Interference signal intensity changes induced by the OPD changes can be easily predicted by calculations. By minimizing the difference between the measured and the calculated signal against the OPD, the thicknesses of sub-100-μm-thick samples are determined at 625 GHz.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Semiconductor-Based Terahertz Photonics for Industrial Applications

Eui  Su Lee, Kiwon Moon, Il-Min Lee, Hyun-Soo Kim,  Dong Woo Park,  Jeong-Woo Park,Dong Hun Lee,Sang-Pil Han, Namje Kim,Kyung Hyun Park

https://ieeexplore.ieee.org/document/8234572

In developing terahertz (THz) technologies that are more suitable for industrial applications, we have focused on research on continuous-wave (CW) THz technologies to develop small, low-cost, and multifunctional THz devices and systems. In the course of this research, we have developed several key devices such as widely tunable compact beating sources in the form of dual-mode lasers, THz emitters, including nano-electrode-photomixers and unitraveling carrier photodiode photomixers, and highly sensitive THz detectors, such as Schottky barrier diodes. In this paper, along with our recently obtained results that demonstrate the enhanced performance of these devices, we also present an example of a practical industrial application of our CW THz system: a nondestructive evaluation (NDE) system. The system described can be applied in the car manufacturing factory as an NDE technique to find process errors. Although further improvements to photonics-based THz technologies are necessary, we believe that efforts in this field will begin an era of THz technologies as a widely used industrial technique.

Abstract-Compact THz time-domain spectroscopy based on pre-chirped pulses from mode-locked Yb-doped fiber laser

Ji SuKim, Hyun Moon Yang, Sang-PilHan, Kiwan Moon, Kyung Hyun Park, Min Yong Jeon

https://www.sciencedirect.com/science/article/pii/S106852001830138X

We report on a compact terahertz (THz) time-domain spectroscopy (TDS) system based on fiber-integrated log-spiral low-temperature-grown InGaAs photo-conductive antenna (PCA) modules pumped by pre-chirped pulses from a 1.03-μm mode-locked Yb-doped fiber laser. A mode-locked Yb-doped fiber laser based on a birefringent spectral filter was produced with 240 mW average output power and 2.68-ps pulse duration. The output pulse had high chirp because the mode-locked fiber laser was implemented in the normal dispersion region. Therefore, the 733-fs output pulse was pre-chirped using two parallel diffraction gratings to facilitate its use as an optical pump source with THz radiation. After propagating in the single-mode fiber, the pulse-width of the pre-chirped pulse was compressed to 331 fs and injected into fiber-integrated PCA modules to generate a THz wave. We successfully obtained a THz emission bandwidth of over 2.5 THz for 120 mm in free space using the compact THz measurement setup. THz radiation was achieved by easily aligning two fiber integrated PCA modules. Absorption lines for water vapor were observed at room temperature. We also observed absorption lines from a 30% α-lactose sample. We confirmed that the fiber-integrated PCA modules and mode-locked Yb-doped fiber laser have potential applications in compact and portable THz-TDS systems.

Abstract-Large caliber array type terahertz wave generating device having photonic crystal structure

United States Patent 9761750
Inventors:
Moon, Ki Won (Daejeon, KR) 
Park, Kyung Hyun (Daejeon, KR) 

http://www.freepatentsonline.com/9761750.html

Provided herein is a large caliber terahertz wave generating device having a photonic crystal structure. The device includes a first electrode and a second electrode. The first electrode includes a first line pattern extending in a first direction, second line patterns coupled to the first line pattern and extending in a second direction, and third line patterns which are coupled to the first line pattern, extend in the second direction, are disposed between the second line patterns, and are longer than the second line patterns. The second electrode includes a fourth line pattern which extends in the first direction, fifth line patterns coupled to the fourth line pattern and extending in the second direction, and sixth line patterns which are coupled to the fourth line pattern, extend in the second direction, are disposed between the fifth line patterns, and are longer than the fifth line patterns.

Abstract-Semiconductor-Based Terahertz Photonics for Industrial Applications

Kyung Hyun Park, Eui Su Lee, Il-MIn Lee, Kiwon Moon, Hyun-Soo Kim, Jeomg-Woo Park, Dong-Woo Park, Dong Hun Lee, and Sang-Pil Han

https://www.osapublishing.org/abstract.cfm?uri=ofc-2017-W4B.4&origin=search

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.

Abstract-Electrically controllable terahertz square-loop metamaterial based on VO2 thin film

Jun-Hwan Shin1,2, Kyung Hyun Park1,2 and Han-Cheol Ryu3

http://iopscience.iop.org/article/10.1088/0957-4484/27/19/195202/meta

An electrically controllable square-loop metamaterial based on vanadium dioxide (VO2) thin film was proposed in the terahertz frequency regime. The square-loop shaped metamaterial was adopted to perform roles not only as a resonator but also as a micro-heater for the electrical control of the VO2. A dual-resonant square-loop structure was designed to realize band-pass characteristics in the desired frequency band. The measured Q-factors of the basic and scaled-down metamaterials fabricated on VO2 thin films were 2.22 and 1.61 at the center frequencies of 0.44 and 1.14 THz in the passbands, respectively. The transmittances of the proposed metamaterial were successfully controlled by applying a bias voltage without an external heater. The measured transmittance on–off ratios of the metamaterials were over 40 at the center frequencies in the passbands. In the future, electrically controllable terahertz metamaterial based on VO2 metamaterial could be employed as high-performance active filters or sensors.

Abstract-Terahertz radiation using log-spiral-based low-temperature-grown InGaAs photoconductive antenna pumped by mode-locked Yb-doped fiber laser

Moon Sik Kong, Ji Su Kim, Sang Pil Han, Namje Kim, Kiwon Moon, Kyung Hyun Park, and Min Yong Jeon
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-7-7037

We demonstrate a terahertz (THz) radiation using log-spiral-based low-temperature-grown (LTG) InGaAs photoconductive antenna (PCA) modules and a passively mode-locked 1030 nm Yb-doped fiber laser. The passively mode-locked Yb-doped fiber laser is easily implemented with nonlinear polarization rotation in the normal dispersion using a 10-nm spectral filter. The laser generates over 250 mW of the average output power with positively chirped 1.58 ps pulses, which are dechirped to 127 fs pulses using a pulse compressor outside the laser cavity. In order to obtain THz radiation, a home-made emitter and receiver constructed from log-spiral-based LTG InGaAs PCA modules were used to generate and detect THz signals, respectively. We successfully achieved absorption lines over 1.5 THz for water vapor in free space. Therefore, we confirm that a mode-locked Yb-doped fiber laser has the potential to be used as an optical source to generate THZ waves.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstract-Bias field tailored plasmonic nano-electrode for high-power terahertz photonic devices

Kiwon Moon

, Il-Min Lee

, Jun-Hwan Shin

, Eui Su Lee

, Namje Kim

, Won-Hui Lee

, Hyunsung Ko

, Sang-Pil Han

 & Kyung Hyun Park

• • http://www.nature.com/articles/srep13817

• Scientific Reports 5, Article number: 13817 (2015)
• doi:10.1038/srep13817

Photoconductive antennas with nano-structured electrodes and which show significantly improved performances have been proposed to satisfy the demand for compact and efficient terahertz (THz) sources. Plasmonic field enhancement was previously considered the dominant mechanism accounting for the improvements in the underlying physics. However, we discovered that the role of plasmonic field enhancement is limited and near-field distribution of bias field should be considered as well. In this paper, we clearly show that the locally enhanced bias field due to the size effect is much more important than the plasmonic enhanced absorption in the nano-structured electrodes for the THz emitters. Consequently, an improved nano-electrode design is presented by tailoring bias field distribution and plasmonic enhancement. Our findings will pave the way for new perspectives in the design and analysis of plasmonic nano-structures for more efficient THz photonic devices.

Abstract-Metal-VO2 hybrid grating structure for a terahertz active switchable linear polarizer

Jun-Hwan Shin1,2, Kiwon Moon1, Eui Su Lee1, Il-Min Lee1 and Kyung Hyun Park1,2

http://iopscience.iop.org/0957-4484/26/31/315203

khp@etri.re.kr

1 THz Photonics Creative Research Center, Electronics and Telecommunications Research Institute, 218 Gajeong-ro, Yuseong-gu, Daejeon 305-700, Korea
2 School of Advanced Device Technology, University of Science & Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 305-350, Korea 

An active terahertz (THz) wave hybrid grating structure of Au/Ti metallic grating on VO2/Al2O3 (0001) was fabricated and evaluated. In our structure, it is shown that the metallic gratings on the VO2 layer strengthen the metallic characteristics to enhance the contrast of the metallic and dielectric phases of a VO2-based device. Especially, the metal grating-induced optical conductivity of the device is greatly enhanced, three times more than that of a metallic phase of bare VO2 films in the 0.1–2.0 THz spectral range. As an illustrative example, we fabricated an actively on/off switchable THz linear polarizer. The fabricated device has shown commercially comparable values in degree of polarization (DOP) and extinction ratio (ER). A high value of 0.89 in the modulation depth (MD) for the transmission field amplitude, superior to other THz wave modulators, is achieved. The experimental results show that the fabricated device can be highly useful in many applications, including active THz linear polarizers, THz wave modulators and variable THz attenuators.

Abstract & Article-Continuous-wave terahertz system based on a dual-mode laser for real-time non-contact measurement of thickness and conductivity

Kiwon Moon, Namje Kim, Jun-Hwan Shin, Young-Jong Yoon, Sang-Pil Han, and Kyung Hyun Park  »View Author Affiliations
http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-22-3-2259&id=277890

Terahertz (THz) waves have been exploited for the non-contact measurements of thickness and refractive index, which has enormous industrial applicability. In this work, we demonstrate a 1.3-μm dual-mode laser (DML)-based continuous-wave THz system for the real-time measurement of a commercial indium-tin-oxide (ITO)-coated glass. The system is compact, cost-effective, and capable of performing broadband measurement within a second at the setting resolution of 1 GHz. The thickness of the glass and the sheet conductivity of the ITO film were successfully measured, and the measurements agree well with those of broadband pulse-based time domain spectroscopy and Hall measurement results.

© 2014 Optical Society of America

Abstract-Foreign Object Detection by Sub-Terahertz Quasi-Bessel Beam Imaging

Gyeongsik Ok ¹ , Sung-Wook Choi ¹ , Kyung Hyun Park ²  and Hyang Sook Chun ^1,* 

Abstract: Food quality monitoring, particularly foreign object detection, has recently become a critical issue for the food industry. In contrast to X-ray imaging, terahertz imaging can provide a safe and ionizing-radiation-free nondestructive inspection method for foreign object sensing. In this work, a quasi-Bessel beam (QBB) known to be nondiffracting was generated by a conical dielectric lens to detect foreign objects in food samples. Using numerical evaluation via the finite-difference time-domain (FDTD) method, the beam profiles of a QBB were evaluated and compared with the results obtained via analytical calculation and experimental characterization (knife edge method, point scanning method). The FDTD method enables a more precise estimation of the beam profile. Foreign objects in food samples, namely crickets, were then detected with the QBB, which had a deep focus and a high spatial resolution at 210 GHz. Transmitted images using a Gaussian beam obtained with a conventional lens were compared in the sub-terahertz frequency experimentally with those using a QBB generated using an axicon.