• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.214-221
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• 2004

We theoretically and experimentally investigate the effect of apodization on the transmission characteristics of linearly chirped fiber Bragg gratings(CFBGs). Based on the UV beam scanning method along a phase mask, we fabricated several apodized CFBGs with different apodization profiles such as Gaussian, Raised-cosine, Blackman, and Hyperbolic tangent. During the UV beam scanning, the phase mask is dithered by a PZT(Piezoelectric transducer) which is precisely controlled by a computer program so that the apodization profiles can be flexibly applied to the grating. We measured the reflection spectra and group delay characteristics of CFBGs with the different apodization profiles, and compared them according to their properties such as reflectivity, sidelobes, and group delay ripple (GDR). The peak-to-peak of GDR could be suppressed to less than 20 ps.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2431-2433
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• 1999

Phase errors of arrayed waveguide degrade the performance of AWG router, especially for dense WDM system. So it is necessary to measure the phase error and to compensate. The analysis method of the interference signal from the low coherence interferometer to measure the path length difference phase error is studied. The interference signal generated assuming the intentional path length difference errors of 0.1$\sim$0.4${\mu}m$ are analyzed and the results show that the path length difference phase error of ${\Delta}L$ within ${\pm}14^{\circ}$ of sampling phase error can be accurately measured.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.52-60
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• 1999

Fabricability of phase shifted grating filters has been theoretically studied by an effective index transfer matrix method. In the optical band-pass filter with multiple ${\lambda}/4$ phase-shifts, the phase-shift error and random variation of the grating period should be suppressed such that corresponding resonance frequency lies within, the filter pass-band. The tolerance for the relative error is less than $10^3$, and is quite stringent in typical filters for WDM application. End facet reflection produces ripple in the transmission spectra and the reflectivity should be less than 1% in order to keep the ripple less than 0.25dB. Also, the effect of waveguide absorption loss is enhanced by the resonance in the filter, and the absorption should be limited to 1dB/cm for the signal loss of less than 0.2dB.

• Journal of the Optical Society of Korea
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• v.7 no.3
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• pp.135-138
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• 2003

A chirped-pulse amplification femtosecond Ti:sapphire laser operating at 1 KHz has been developed. The laser system consisted of a long-cavity femtosecond oscillator, a four-pass grating pulse stretcher, two multi-pass amplifiers and a double-pass grating pulse compressor. Thermal lensing at the amplifiers was reduced by cooling Ti:sapphire crystals using Peltier coolers. Gain narrowing and residual phase errors were compensated for by the use of an acousto-optic pulse shaper. The final laser output had an energy per pulse of 2.0 mJ and a pulse duration of 19.5 fs, reaching 0.1 TW at 1 KHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.1042-1045
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• 2002

We have carried out two-beam interference experiments to form holographic gratings on amorphous $MgF_2$/As-Ge-Se-S multi-layer. In this study, holographic gratings have been formed using He-Ne laser(632.8nm). under different polarization combinations. The diffraction efficiency was obtained by +1st order intensity. The maximum diffraction efficiency of As-Ge-Se-S single layer and $MgF_2$/As-Ge-Se-S multi-layer were 0.8% and 1.4%

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.762-765
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• 2014

We fabricated a periodically poled lithium niobate (PPLN) by direct laser-writing of a quasi-phase-matching (QPM) structure in photolithographic process. Because we do not need to prepare a photomask by electron-beam writing, the "maskless" process shortens the fabrication time and significantly reduces the cost. We evaluated the poling quality of the direct laser-written PPLN by measuring the diffraction noise from the surface relief pattern of the fabricated QPM grating and comparing the results to those from a conventional PPLN made with a photomask. The quality of the PPLN fabricated by direct laser-writing was shown to be equivalent to that fabricated by the conventional method.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.4
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• pp.460-466
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• 1988

In this paper, the theory and experiments on the one-way optical image transmission through optical fiber by using degenerate four wave mixing in BSO single crystal are demonstrated. From the theoretical analysis, the diffraction efficiency of phase conjugate wave in BSO single crystal is greatly dependent on applied electric field intensity, diffraction grating period formed in the crystal and incident beam ratio, those are also in good agreement with the experimental results. Based on the experimental results, we have arranged the typical degenerate four wave mixing system in the optimal conditions (applied electric field, E. = 5kV/cm` diffraction grating period, 3\ulcorner` beam ratio of backward pump wave versus signal wave, 2.7) and realized one-way optical image transmission system through optical fiber using BSO single crystal.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.4
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• pp.18-23
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• 2007

This paper presents a transmissive dispersion compensator based on tilted chirped fiber Bragg grating pairs which happen mode coupling between core mode and cladding mode. And, as a result of simulation, the phase matching condition and optimum tilted angle to maximize the mode-coupling in the dispersion compensator are shown and the dispersion slope and bandwidth in the proposed dispersion compensator is respectively 3,068ps/nm and 0.45nm.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.14-17
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• 2003

Vibration control of a composite plate with a surface-bonded fiber Bragg grating (FBG) sensor and piezoceramic actuators has been performed using a neural network based adaptive predictive control algorithm. For the detection of Bragg wavelength changes, two cavity lengths in Fabry-Perot read-out interferometers are used in order to produce two quadrature phase shifted signals. The FBG sensor system and real-time neuro-adaptive control algorithm could be applicable to diverse dynamic systems.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.154.1-154.1
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• 2011

IGRINS (Immersion Grating Infrared Spectrometer) is a cross-dispersed high resolution near-infrared spectrograph whose primary disperser is a silicon immersion grating (SIG) and cross-dispersers are two volume phase holographic gratings (VPHG). IGRINS covers the full ranges of H and K astronomical wavelength bands at a single exposure with the spectral resolution of 40,000. The overall layout of the IGRINS Cryostat is a $960{\times}600{\times}380$ cubic millimeter rectangular box and the whole optical train is sitting on an $880{\times}520{\times}50\;mm^3$ rectangular Optical Bench. The total volume of the instrument has been revolutionarily reduced and remained compact for the spectral coverage and sensitivity of a high resolution spectrograph in infrared. We, in this presentation, introduce the design models, the structural and thermal analysis results of the mechanics and cryogenics of IGRINS.