• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.3
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• pp.105-113
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• 1997

We constructed a very accurate fiber bragg grating sensor system using an unbalanced mach-zehnder interferometer which converts the measurand-induced bragg wavelength shift to phase change of th einterference signal. With a shielded reference grating, output phase drift which orginates from the thermal drift on the interferometer was compensated. Mesured accuracy of the constructed system was 0.03 .deg. C and 0.26.mu. strain for temperature and strain measuremtn, respectively. It is over 300 times better resolution compared to the conventional optical spectrum analyzer which has 0.1nm wavelength resolution capability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.11a
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• pp.187-189
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• 1994

The degree of the photodoping process in Ag(100 )/a-$Se_{75}Ge_{25}$(2000 ) films has been measured as a funcition of photon energy between 1.5eV and 2.9eV with the exposing time. The window of Ag occurs at 3400 (3.65eV) and Ag is almost transparent in this region. It was shown that transmitance is always constant (40∼50%) for the wavelength ranges of our experiment. It was found that the energy gap of a unexposed a-$Se_{75}Ge_{25}$ film is 1.81eV. Ag photodoping process result in the photodarkenting effect which the absorption edge shift to the large wavelength. Especially, we could obtain very large band shut ( ∼0.3eV) resulting in exposing He-Ne laser(6328[ ]). From the result of our experimental, we suggest that Ag photodoping process depends on the photon absorption in Ag.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.416-420
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• 2002

This Paper describes a matched-filter type strain sensor system using optical fiber Bragg grating (FBG) sensor. Matched-filter type uses another wavelength-matched FBG filter to track wavelength shift in the FBG sensor. Filter FBG is attached on a fiber stretcher and stretched by PZT actuator. To overcome the nonlinearity and hysteresis of the PZT actuator that degrades system accuracy, a string resonator which can measure an absolute strain is employed. And the effect of vibration modes on string resonator is investigated particularly regarding its sensitivity and stability.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.2
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• pp.73-80
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• 1995

We fabricated the 1.55.mu.m RWG-DFB-LD and measured its electrical and optical characteristics. Interference fringe of optical beams was used for grating formation and epi layers were grown by lower-temperature LPE. The fabricated RWG-DFB-LD operated in a single longitudinal mode with more than 30dB SMSR at 1543nm emitting wavelength and its threshold current was 40mA. The wavelength shift with operating temperature and characteristic temperature T$_{o}$ were 0.9${\AA}/^{\circ}C$ and 59K, respectively. Linewidth enhancement factor .alpha. and linewidty.optical power product were estimated as 6.15 and 60MHz$\cdot$mW respectively.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.67.2-67.2
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• 2012

Graphene is expected to have a significant impact in various fields in the foreseeable future. For example, graphene is considered to be a promising candidate to replace indium tin oxide (ITO) as transparent conductive electrodes in optoelectronics applications. We report the tunability of the wavelength of localized surface plasmon resonance by varying the distance between graphene and Au nanoparticles [1]. It is estimated that every nanometer of change in the distance between graphene and the nanoparticles corresponds to a resonance wavelength shift of ~12 nm. The nanoparticle-graphene separation changes the coupling strength of the electromagnetic field of the excited plasmons in the nanoparticles and the antiparallel image dipoles in graphene. We also show a hysteresis in the conductance and capacitance can serve as a platform for graphene memory devices. We report the hysteresis in capacitance-voltage measurements on top gated bilayer graphene which provide a direct experimental evidence of the existence of charge traps as the cause for the hysteresis [2]. By applying a back gate bias to tune the Fermi level, an opposite sequence of switching with the different charge carriers, holes and electrons, is found [3]. The charging and discharging effect is proposed to explain this ambipolar bistable hysteretic switching.

• Journal of The Korean Astronomical Society
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• v.37 no.2
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• pp.87-90
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• 2004

Spectrophotometry of the night sky over Mount Bohyun is presented for the nearly entire visible wavelengths of $3600{\~}$8600{\AA}$. The data was obtained under moonless clear sky in February 2004 with the 1.8-m telescope and the long slit spectrograph. The sky spectrum shows a number of strong emission lines originated from light pollution, especially due to high pressure sodium lamps. When compared to the night sky of Kitt Peak, our sky continuum is 1 to 2 magnitude brighter at all wavelengths, the worst being around the broad emission region near 6000${\AA}$. The night sky spectrum presented here with almost complete line identifications is a useful reference for arc-independent wavelength calibrations to check the gravity flexure of the spectrograph and the wavelength shift between FeNeArHe arc frames and science frames.

• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1593-1597
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• 2009

A biosensor has been developed based on induced wavelength shifts in the Fabry-Perot fringes in the visible reflection spectrum of appropriately derivatized thin films of porous silicon semiconductors. Porous silicon (PSi) was generated by an electrochemical etching of silicon wafer using two electrode configurations in aqueous ethanolic HF solution. Porous silicon displayed Fabry-Perot fringe patterns whose reflection maxima varied spatially across the porous silicon. The sensor system studied consisted of a mono layer of porous silicon modified with Protein A. The system was probed with various fragments of an aqueous Human Immunoglobin G (Ig G) analyte. The sensor operated by measurement of the Fabry-Perot fringes in the white light reflection spectrum from the porous silicon layer. Molecular binding was detected as a shift in wavelength of these fringes.

• ETRI Journal
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• v.31 no.2
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• pp.228-230
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• 2009

InP-based planar waveguide 48-channel concave grating demultiplexers with a channel spacing of 0.8 nm (100 GHz) are described and demonstrated. Polarization insensitivity and flattened spectral response are successfully achieved by the introduction of a polarization compensator and a two-focus grating, respectively. The fabricated device shows a polarization-dependent wavelength shift of less than 20 pm and a -3 dB spectral width of about 0.55 nm (68.75 GHz) over all channels.

• Journal of the Optical Society of Korea
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• v.16 no.3
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• pp.299-304
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• 2012

A high angular tolerance spectral filter was realized incorporating an etalon, which consists of a $TiO_2$ cavity sandwiched between a pair of Ag/Ge mirrors. The effective angle was substantially extended thanks to the cavity's high refractive index. The device was created by embedding a 313-nm thick $TiO_2$ film in 16-nm thick Ag/Ge films through sputtering, with the Ge layer alleviating the roughness and adhesion of the Ag layer. For normal incidence, the observed center wavelength and transmission were ~900 nm and ~60%, respectively; throughout the range of $50^{\circ}$, the relative wavelength shift and transmission variation amounted to only ~0.06 and ~4%, respectively.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1259-1261
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• 1993

Amorphous chalcogenide glasses are highly transparent in the near $1{\mu}m$ wavelength region, which corresponds to the wavelength region of the optical communication system. Optical properties of these materials, including the transmittance, the optical gap, and the shift associated with reversible photostruction change, were measured. Thereafter, optical waveguide was fabricated by the laser lithographic technique and then, guide modes were measured by utilizing the end-fire coupling technique. The field patterns of both the single mode and the multimode waveguide were observed.