• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.241-246
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• 2018

In this study, we proposed a wideband frequency tunable metamaterial absorber using a switchable ground plane (SGP). We proposed two fire retardant or flame resistant 4 (FR4) substrate structures for the SGP. An SGP is placed at the middle layer, between the top pattern and the bottom ground plane. The SGP can either be made ground or reactive, by switching the PIN diode ON/OFF. As the frequency is determined by the substrate thickness, the frequency can be switched from the SGP. The proposed absorber is demonstrated by full-wave simulations and measurements. When the SGP is turned on, an absorptivity higher than 90% is achieved from 3.5 GHz to 11 GHz. When the SGP is turned off, an absorptivity higher than 90 % is achieved from 1.7 GHz to 5.2 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.4
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• pp.399-402
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• 2016

We propose a thin electromagnetic wave absorber using varactor diodes combined with intentionally introduced multiple slits, which enables continuous sweep of an absorption frequency band throughout relatively wide frequencies. The absorption frequency range of conventional electrically tunable absorbers has been restricted by high capacitance of varactor diodes. In order to overcome the problem, we introduce parasitic capacitance and connect them with varactors in series, which reduces the total capacitance dramatically. As a result, we can raise the operating absorption frequency up to the X-band region. Moreover, we can also control the operating frequencies by modifying the number of slits with little change in an entire frequency sweep range. Good agreement between simulated and measured results show the validity of our proposal.

• Journal of the Optical Society of Korea
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• v.17 no.2
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• pp.117-129
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• 2013

We briefly review the recent progress in passively mode-locked fiber lasers (PMLFLs) based on semiconductor saturable absorber mirrors (SESAMs) and discuss the detailed characterization of a SESAM-based, passively mode-locked erbium-doped fiber (EDF) laser operating in the 1.5-${\mu}m$ spectral range for various configurations. A simple and compact design of the laser cavity enables the PMLFL to generate either femtosecond or wavelength-tunable picosecond pulses with high stability as the intra-cavity filtering method is altered. All the cavities investigated in our experiments present self-starting, continuous-wave mode-locking with no Q-switching instabilities. The excellent stability of the source eventually enables the wavelength-tunable PMLFL to be used as a master oscillator for a power-amplifier source based on a large-core EDF, generating picosecond pulses of >10-kW peak power and >100-nJ pulse energy.

• Current Optics and Photonics
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• v.6 no.3
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• pp.252-259
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• 2022

In this paper, a dual-function dynamically tunable metamaterial absorber is proposed. At frequency points of 1.545 THz and 3.21 THz, two resonance peaks with absorption amplitude of 93.8% (peak I) and 99.4% (peak II) can be achieved. By regulating the conductivity of photosensitive silicon with a pump laser, the resonance frequency of peak I switches to 1.525 THz, and that of peak II switches to 2.79 THz. By adjusting the incident polarization angle by rotating the device, absorption amplitude tuning is obtained. By introducing two degrees of regulation freedom, the absorption amplitude modulation and resonant frequency switching are simultaneously realized. More importantly, dynamic and continuous adjustment of the absorption amplitude is obtained at a fixed resonant frequency, and the modulation depth reaches 100% for both peaks. In addition, the sensing property of the proposed MMA was studied while it was used as a refractive index sensor. Compared with other results reported, our device not only has a dual-function tunable characteristic and the highest modulation depth, but also simultaneously possesses fine sensing performance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.329-334
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• 2002

Preliminary test for the design and construction of a tuned dynamic absorber is a conducted. Proposed tuned dynamic absorber is a cantilevered beam type, and is supposed to adjust its natural frequency according to the changing operation condition of the primary system. The modal mass of the dynamic absorber is the easiest to control, therefore, the position of the attached mass of the dynamic absorber is considered as the main design parameter of the absorber. The effect of the dynamic absorber is experimentally verified under various operation conditions of the primary system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.2
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• pp.123-130
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• 2016

In this paper, a novel flexible microfluidic metamaterial absorber is proposed for remote chemical sensor applications. The proposed metamaterial absorber consists of a periodic of split-ring-cross resonators(SRCRs) and a microfluidic channel. The SRCR patterns are inkjet-printed using silver nanoparticle inks on paper. The microfluidic channels are laser-etched on polydimethylsiloxane(PDMS) material. The proposed absorber can detect change of the effective permittivity at different liquids. Therefore, the absorber can be used for a remote chemical sensor by detecting change of the resonant frequencies. The performance of the proposed absorber is demonstrated with full-wave simulation and measurement results. The experimental results shows that the resonant frequency is 10.49 GHz at the empty channel. When ethanol and DI-water are injected into the channel, the resonant frequencies are 10.04 GHz and 8.9 GHz, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.5
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• pp.506-513
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• 2015

In this paper, we proposed a novel ethanol concentration sensor using microfluidic metamaterial absorber. The metamaterial absorber comprises a split-ring-cross resonator(SRCR) and a microfluidic channel. The SRCR can generate LC resonance that is very sensitive to changes in the effective dielectric constant around the capacitive gap. In addition, microfluidic channels can change the effective dielectric constant of the dielectric substrate by using an infinitesimal quantity of a liquid on the order of microliters. The proposed absorber can detect the electrical properties of different concentration of ethanol. The performance of the proposed absorber is demonstrated using the absorption measurements of a fabricated prototype sample with waveguides. In addition, the simulated results and measurement results show good agreement.

• Current Optics and Photonics
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• v.1 no.3
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• pp.203-206
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• 2017

We report a passive Q-switching of an all-fiber erbium-doped fiber laser delivering high pulse energy by using a high quality single-walled carbon nanotube saturable absorber (SWCNT-SA). A side-polished fiber coated with the SWCNT is employed as an in-line SA for evanescent wave interaction between the incident light and the SWCNT. This lateral interaction scheme enables a stable Q-switched fiber laser that generates high pulse energy. The central wavelength of the Q-switched pulse laser was measured as 1560 nm. A repetition rate frequency of the Q-switched laser is controlled from 78 kHz to 190 kHz by adjusting the applied pump power from 124 mW to 790 mW. The variation of pulse energy from 51 nJ to 270 nJ is also observed as increasing the pump power. The pulse energy of 270 nJ achieved at maximum pump power is 3 times larger than those reported in Q-switched all-fiber lasers using a SWCNT-SA. The tunable behaviors in pulse duration, pulse repetition rate, and pulse energy as a function of pump power are reported, and are well matched with theoretical expectation.

• Korean Journal of Optics and Photonics
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• v.21 no.5
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• pp.185-189
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• 2010

We demonstrate a single-frequency wavelength tunable erbium-doped fiber (EDF) ring laser. We used an unpumped-EDF as a saturable-absorber in order to obtain a stable single-frequency with a narrow-linewidth single-polarization mode in the ring cavity. The lasing wavelength was controlled by using bending-induced strain, such as tension and compression strain corresponding to the bending direction, applied to the fiber gratings. The fiber laser exhibited an output power of -1.85 dBm at a wavelength of 1540.72 nm for a pumping power of ~400 mW. An extinction ratio was measured to be more than 60 dB. The proposed tunable fiber laser maintains nearly the same output power while its lasing wavelength is controlled over in a wavelength range of 5 nm.

• Journal of the Korean Ceramic Society
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• v.55 no.4
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• pp.325-336
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• 2018

Perovskite solar cells (PSCs) are a new class of photovoltaic devices, which have attracted significant attention due to their remarkable optoelectrical properties, including high absorption coefficients, high carrier mobilities, long carrier diffusion lengths, tunable bandgaps, low cost, and facile fabrication. PSCs have reached efficiencies of 22.70% and 18.36% on rigid fluorine-doped tin oxide and poly(ethylene terephthalate) substrates, respectively; these are comparable to those of single-crystal silicon and copper-indium-gallium-selenium solar cells. Over the past eight years, the photo conversion efficiency of PSCs has been significantly improved by device-architecture adjustments, and absorber and electron/hole transport layer optimization. Each layer is important for the performance of PSCs; hence, we discuss achievements in flexible perovskite solar cells (FPSCs), covering electron/hole-transport materials, electrode materials. We give a comprehensive overview of FPSCs and put forward suggestions for their further development.