• Korean Journal of Optics and Photonics
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• v.20 no.4
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• pp.207-210
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• 2009

A confocal technique was demonstrated for measuring the absolute value of an air gap between substrates. Since the two surfaces were in Rayleigh range of the laser focus for air gaps less than 200 nm, complete interference patterns were observed. And since interference patterns were obtained only from the area of focus, it was an advantage of this method that air gaps between multiple thin films could be measured. Stability is less than 1 nm except in the range where the interference pattern changes slowly.

• Current Optics and Photonics
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• v.4 no.3
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• pp.221-228
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• 2020

We developed an all-fiber RGB laser light source module for application in an automobile head-up display. It is based on laser diodes and an optical fiber combiner that substantially enhances the flexibility of configuration and stability against harsh working conditions for automobiles. We coupled 13 laser diodes with optical fibers and merged them into a single output with a beam combiner device. Red (R), green (G), and blue (B) laser sources were employed to produce primary colors that were mixed into a white light output. An optical output power of approximately 1.5 W was achieved, and the color balance of the output lights was assessed based on the CIE 1931 color space. The optical output power was shown to be stable for over 160 h within an optical fluctuation of less than 0.27%.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.4_2
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• pp.693-699
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• 2020

355nm UV pulse laser is irradiated on the surface of polyimide (PI) by LDW (Laser Direct Writing) method to produce a high sensitivity flexible humidity sensor using a simple one-step process. The LDW method continuously investigates 2-D CAD data using a galvano scanner and an F-lens. This method is non-contact, so it minimizes physical strain on the PI. Laser-induced graphene (LIG) produced by lasers has a high surface area due to its high flexibility and numerous pores and oxidizers compared to conductors. For this reason, it is highly useful as a flexible humidity sensor. The humidity sensor produced in this study was attached to the inside of a mask filter, which has become a hot topic recently, and its applicability was confirmed.The measurement of humidity measured the sensitivity, reactivity, stability and recovery behavior of the sensor by measuring changes in capacitance and resistance.

• Current Optics and Photonics
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• v.6 no.3
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• pp.282-287
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• 2022

Narrowing the spectral linewidth and improving the wavelength stability of high-power laser diodes (HPLDs) are both in high demand for rapidly maturing industrial laser applications. In this study, we investigate the spectral behavior of a commercial HPLD bar module composed of 19 laser diodes (LDs) in a single-layered bar with a built-in volume Bragg grating (VBG) and an additional cascaded VBG. Optical loss due to the extra cascaded VBG is kept below 5% when the optical output is 5 W or more. The full width at half maximum of the Fabry-Perot peak from the cascaded VBG is reduced to about 12.4% and 29.1% at the edge (1^st LD) and center (10^th LD) of the HPLD bar module respectively, compared to using only a built-in VBG at an optical power of 10 W or more. In addition, fine wavelength tuning is achieved by temperature control of the extra VBG, and the obtained wavelength-tuning range amounts to about 10.6 pm/K.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.30.4-31
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• 2011

The Korea Astronomy and Space Science Institute (KASI) and the Department of Astronomy at the University of Texas at Austin (UT) are developing a near infrared wide-band high resolution spectrograph, IGRINS (Immersion Grating Infrared Spectrograph). The white-pupil design of the instrument optics uses 7 cryogenic mirrors including 3 aspherical off-axis collimators and 4 flat fold mirrors. Two of the 3 collimators are H- and K-band pupil transfer mirrors and they are designed as compensators for the system alignment in each channel. Therefore, their mount design will be one of the most sensitive parts in the IGRINS optomechanical system. The design work will include the computer-aided 3D modeling and finite element analysis (FEA) to optimize the structural stability of the mount models. The mount body will also include a tip-tilt and translation adjustment mechanism to be used as the alignment compensators.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.91.2-91.2
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• 2014

A near infrared wide-band high resolution spectrograph, immersion grating infrared spectrometer (IGRINS) has been jointly developed by the Korea Astronomy and Space Science Institute and the University of Texas at Austin. The compact white-pupil design of the instrument optics includes five cryogenic flat mirrors including a slit mirror, an input fold mirror, a dichroic mirror, and H&K camera fold mirrors. In this study, we introduce the optomechanical mount designs of the five cryogenic mirrors. In order to meet the structural stability and thermal requirements of the mount models, we conducted the design work with the aid of 3-dimensional computer modeling and the finite element analysis (FEA) method. We also present the actual fabricated parts and assemblies of the mounts and mirrors as well as their CAD models.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.215-220
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• 1998

We proposed an in situ measurement set-up and technique to measure the various electro-optic(E-O) properties of the E-O polymer. Using the proposed measurement set-up, the electro-optic effect and birefringence of unpoled side-chain E-O polymer induced by the strong dc and ac electric field were observed. The dependence of the E-O coefficients on the various poling conditions were measured with real time. To evaluate the thermal stability of the poled polymer the relaxation of the E-O effect was measured and the result was compared with well known polymer materials. The proposed measurement reduces the number of experimental steps and saves measurement time.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.460-465
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• 2003

Characteristics of 0.98 $\mu$m-pumped erbium-doped fiber (EDF) sources with double-pass forward (DPF) configuration are analyzed by numerical calculation. Various source characteristics such as output power, spectral width and mean-wavelength stability are investigated with the variation of EDF length, pump power and pump wavelength. Some of the numerical results are compared with experimental ones for verification. The results show that the characteristics of sources with DPF configuration can change considerably with the EDF length. It is also found that an optimum design can exist for stable mean-wavelength against fluctuations of pump power and pump wavelength.

• Korean Journal of Optics and Photonics
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• v.23 no.2
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• pp.71-76
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• 2012

A Sagnac-type Mach-Zehnder interferometer(SMZI) is a very stable instrument with respect to phase drift because all optical paths can share common optical components. We have observed very stable interference fringes in single photon interference experiments with an extremely attenuated laser beam, and with heralded single photons prepared from polarization correlated photon pairs in type-II spontaneous parametric down-conversion. The phase stability is measured to be about ${\pm}0.18$ rad for the SMZI, in contrast, conventional MZI showed the phase fluctuation of around ${\pm}1.02$ rad.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.337-342
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• 2004

Laser optical power stabilization of a radio frequency excited $CO_2$ slab laser using the opto-Hertzian effect generated from the laser itself is achieved on the peak of the Doppler broadened gain curve. The opto-Hertzian signal was generated by a modulation of the optical flux circulating inside the laser cavity from a variation in the cavity length caused by the vibrations of the PZT. The opto-Hertzian signal is directly coupled from a RE discharge chamber via a loop antenna into a detector and applied to a lock-in stabilizer as an reference signal. The power stability of an RF excited slab laser is estimated to be better then 0.2%.