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Ok G.,Korea Food Research Institute | Choi S.-W.,Korea Food Research Institute | Park K.H.,z Photonics Creative Research Center | Chun H.S.,Korea Food Research Institute
Sensors (Switzerland) | Year: 2013

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. © 2013 by the authors; licensee MDPI, Basel, Switzerland.


Kim N.,z Photonics Creative Research Center | Han S.-P.,z Photonics Creative Research Center | Ryu H.-C.,z Photonics Creative Research Center | Ko H.,z Photonics Creative Research Center | And 4 more authors.
Optics Express | Year: 2012

A widely tunable dual mode laser diode with a single cavity structure is demonstrated. This novel device consists of a distributed feedback (DFB) laser diode and distributed Bragg reflector (DBR). Microheaters are integrated on the top of each section for continuous and independent wavelength tuning of each mode. By using a single gain medium in the DFB section, an effective common optical cavity and common modes are realized. The laser diode shows a wide tunability of the optical beat frequency, from 0.48 THz to over 2.36 THz. Continuous wave THz radiation is also successfully generated with low-temperature grown InGaAs photomixers from 0.48 GHz to 1.5 THz. © 2012 Optical Society of America.


Kim N.,z Photonics Creative Research Center | Han S.-P.,z Photonics Creative Research Center | Ko H.,z Photonics Creative Research Center | Leem Y.A.,z Photonics Creative Research Center | And 6 more authors.
Optics Express | Year: 2011

We demonstrate a tunable continuous-wave (CW) terahertz (THz) homodyne system with a novel detuned dual-mode laser diode (DML) and low-temperature- grown (LTG) InGaAs photomixers. The optical beat source with the detuned DML showed a beat frequency tuning range of 0.26 to over 1.07 THz. Log-spiral antenna integrated LTG InGaAs photomixers are used as THz wave generators and detectors. The CW THz radiation frequency was continuously tuned to over 1 THz. Our results clearly show the feasibility of a compact and fast scanning CW THz spectrometer consisting of a fiber-coupled detuned DML and photomixers operating in the 1.55-μm range. © 2011 Optical Society of America.


Kim N.,z Photonics Creative Research Center | Ryu H.-C.,z Photonics Creative Research Center | Lee D.,Applied Technology Internet | Han S.-P.,z Photonics Creative Research Center | And 5 more authors.
Laser Physics Letters | Year: 2013

We have developed a 1.3 μm phase-shifted dual-mode laser diode (pDML) for a tunable continuous-wave terahertz (CW THz) emitter. The mode beat frequency of the pDML is continuously tuned from 250 to 1480 GHz by introducing monolithically integrated micro-heaters and multiple sections to an all-active structure. The pDML shows a narrow spectral linewidth and a strong four-wave mixing signal throughout the entire tuning range. By combining InGaAs based photomixers, we have successfully generated continuous-wave THz radiation, and confirmed the precise beat frequency settings and fast sweeping of this. This pDML operating at 1.3 μm shows excellent performance in terms of THz conversion efficiency, tuning range and thermal stability. © 2013 Astro Ltd.


Jeon M.Y.,Chungnam National University | Kim N.,z Photonics Creative Research Center | Han S.-P.,z Photonics Creative Research Center | Ko H.,z Photonics Creative Research Center | And 3 more authors.
Optics Express | Year: 2011

We propose a rapidly frequency-swept optical beat source for continuous wave (CW) THz generation using a wavelength swept laser and a fixed distributed feedback (DFB) laser. The range of the sweeping bandwidth is about 17.3 nm (2.16 THz), 1541.42-1558.72 nm. The achieved side mode suppression ratio for both wavelengths within the full sweeping range is more than 45 dB. We observe CW THz signals for tunable optical beat sources using a fiber coupled CW THz measurement system to confirm the feasibility of using our frequency swept optical beat source as a CW THz radiation source. The THz output signal falls to the thermal noise level of the low-temperature grown (LTG) InGaAs photomixer beyond 1.0 THz. The rapidly frequency-swept optical beat source will be useful for generating high-speed tunable CW THz radiation. © 2011 Optical Society of America.

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