• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.102-103
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• 2000

화학레이저는 화학연료의 반응에서 생성되는 막대한 화학에너지를 이용하여 레이저를 발생시키며, 반응하는 화학연료의 양에 따라 수천 kW의 고출력을 낼 수 있는 가장 강력한 레이저이다. 화학레이저인 Chemical Oxygen-Iodine Laser(COIL)는 염소기체(Cl$_2$)를 염기성 과산화수소수 용액과 반응시켜 고에너지의 여기산소(O$_2$($^1$$\Delta$))를 생성시키고 여기산소가 다시 요오드 원자와 반응하면서 1.3 $mu extrm{m}$ 파장의 레이저를 발생시킨다.(1)-(2) 이와같은 COIL 레이저는 발진효율이 높고 포화 강도가 높아 수십 kW 급의 고출력이 용이하게 이루어 질 수 있으며 광섬유 전송시 광손실이 가장 적어 레이저 빔의 원격 전송에 의한 재료가공에 적합한 레이저이다. 가공용레이저로 많이 사용하는 $CO_2$ 레이저에 비해 발진 파장이 짧으므로 재료의 광흡수율이 높아 일반 산업분야의 용접/절단에서 기존의 $CO_2$ 레이저를 대체할 것으로 기대되는 상용성이 큰 레이저이다.(3)-(4) 또한 COIL은 우수한 집속 특성을 유지하면서도 고출력의 개발이 가능하다. 이미 외국에서는 비록 단시간 동안 동작하지만 수백 kW급이 실현되었으며 수천 kW 급 고출력 항공기탑재형 COIL 이 수백 km의 거리에서 미사일을 요격하기위해 지금 개발중에 있다.(5) 일반 산업용 광섬유에 의해 쉽게 전송되는 파장인 1.315 $\mu\textrm{m}$ 인 수십 kW 급 COIL 은 조선 등의 중공업산업용 및 원자력 제염/해체분야에서 다용도 기술로서 광범위하게 사용될 것이다. COIL은 다양한 재료와 다양한 두께의 구조물 절단, 표면처리 그리고 용접에도 이용될 수 있다. COIL의 산업화는 빠르게 발전하고 있으며 산업용으로써 장시간 연속사용이 가능한 20-30 kW급 시설이 곧 개발될 것으로 기대된다. 따라서 개발될 고출력 화학레이저가 앞으로 원자력시설의 해체시 작업자의 안전성 향상에 크게 기여할 수 있게 되었다.(6) 여기서는 화학레이저인 COIL 장치와 기본적인 원리, 그리고 염소유량에 따른 출력특성등을 살펴보기로 하겠다. (중략)

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.594-599
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• 2003

By using the spectroscopic ellipsometry, we have measured and analyzed the optical characteristics of P $r^3$$^{+}$-doped selenide glasses of Ge-Sb-Se system, a strong candidate material for U band fiber amplifiers. The ellipsometric spectra measured in the transparent wavelengths range of the material were all fitted to a model consisting of ambient/roughness/thin fil $m_strate structures to obtain simultaneously the optical properties such as refractive index, in terms of Sellmeier parameters and film structure of P $r^3$$^{+}$-doped selenide glasses. Repeated measurements on different positions in both polished faces rendered to verify positional dependence of measured spectre-ellipsometric data. Hence, the model made possible the analysis of the optical characteristics of the glasses. Even though surface roughness was mainly responsible for the position dependencies, the averaged refractive indexes were as precise as to reflect the minute compositional change tantamount to 1 mol%. The measured refractive indexes are useful for design of core and clad compositions of single-mode selenide optical fibers.

• Korean Journal of Optics and Photonics
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• v.25 no.2
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• pp.72-77
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• 2014

We have demonstrated a terahertz (THz) time-domain spectroscopy and imaging system using compact fiber-coupled THz modules. Using this THz spectroscopy system we have measured the absorption spectrum of water vapor in free space over 3 THz, as well as the refractive indices of various substrates such as Si, $Al_2O_3$, and GaAs using the transfer-function method. Through the THz imaging system we have observed a high-quality THz image of a medical knife and metal clip sample, with a resolution of $192{\times}89$ pixels using a step size of 250 ${\mu}m$.

• Korean Journal of Optics and Photonics
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• v.29 no.1
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• pp.1-6
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• 2018

In this study, ray-tracing software was used to calculate the optical path length of an optical system. Using the optical path length, the optical phase, group delay (GD), group delay dispersion (GDD), and third-order dispersion (TOD) of the optical system were obtained. Pulse compressors using a prism pair or grating pair were designed to compensate the GDD of a real optical system for a femtosecond fiber laser. Also, a pulse stretcher using a grating pair with lenses or mirrors was designed. The results of this study can be used to calculate the dispersion of an optical system and optimize the performance of an ultrashort pulse laser optical system.

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.414-418
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• 1996

An electro-optic polymer digital optical switch was fabricated by using a photobleached waveguide and a self-aligned electrode. It features wavelength insensitive operation, fabrication tolerance and flexible design. And its possible advantages include low coupling losses to the fibers and wide bandwidths. For improving its switching performance, the guided mode profiles of the photobleached waveguides were controlled by photobleaching times to achieve optimized coupling in the branch. And the self-aligned electrode was employed to achieve both efficient overlap of the optical and electric fields and easy introduction of the adiabatically tapered electrodes. The measured crosstalks were better than -21dB at 1.32 ${\mu}{\textrm}{m}$ and 1.55 ${\mu}{\textrm}{m}$, and the extinction ratios of each output port were also more than 20 dB.

• Korean Journal of Optics and Photonics
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• v.22 no.1
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• pp.40-45
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• 2011

Design and fabrication of a TCRR (Triple-coupler Ring Resonator) filter which can provide a doubled FSR (Free Spectral Range) compared with a conventional DCRR (Double-coupler Ring Resonator) filter, are discussed. Through the use of a polymer material with a good thermo-optic property and with high contrast between core and cladding polymer, a compact TCRR filter composed of straight and curved buried waveguides of small radius is designed and fabricated. The transmission characteristics from the through and drop ports are measured using a tunable laser and a fiber array block, and the FSR is observed to be 4.4 nm, about twice that of DCRR filter, and almost the same as that obtained from the analysis using a transfer matrix method.

• Korean Journal of Optics and Photonics
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• v.19 no.4
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• pp.320-326
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• 2008

The output characteristics of a laser-diode pumped electrooptic Q-switched Nd:YAG ceramic laser were investigated. The output energy of a Q-switched Nd:YAG ceramic laser was optimized under an output coupler reflectivity of 77%, a laser-diode pulse width of $1,000\;{\mu}s$, and a delay time of $985\;{\mu}s$. The output energy of the Q-switched pulse was measured to be 0.35 mJ with a pulse width of 4 ns under a pump energy of 17.9 mJ. The output efficiency and the peak power were 1.9% and 87.5 kW, respectively.

• Korean Journal of Optics and Photonics
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• v.30 no.3
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• pp.94-100
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• 2019

The near-field subwavelength squint-less focusing system of a phased array antenna is designed and demonstrated by numerical simulation. The Huygens-Fresnel principle is applied to numerical simulation for calculation of the phased array antenna at microwave frequency. It was shown that beam squinting can be eliminated, utilizing true-time optical delay lines based on a chirped fiber grating in the proposed system. Furthermore, subwavelength focusing with high numerical aperture can be achieved by considering the fact that the array elements of the phased-array antenna can be treated as diffractive elements in an optical lens system. Also, side lobes can be suppressed by decreasing the distance between element antennas to less than half of the wavelength.

• Korean Journal of Optics and Photonics
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• v.5 no.1
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• pp.166-172
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• 1994

The fiber optic receiver, ETRI APD-FET 1.0, is developed for the application of optical communication. This fiber optic receiver includes PD sub-module and pre-amplifier case. A single lens system is introduced for the PD sub-module. The sub-module consists of the avalenche photodiode(APD), GRIN rod lens, and a single mode fiber. The above components are enclosed into the stainless steel 304L housings. By bevelling the fiber end, the single mode fiber provides less than ~ 28 dB of optical return loss. The area of image focus is controlled by adjusting the length of spacer located in-between the fiber and the GRIN rod lens. The laser welding technique is applied to achieve the maximum coupling efficiency for the joining of each housing. In the pre-amplifier case, GaAs FET pre-amplifier workes for photocurrent amplification and the thermister is mounted to control the APD bias. The performance of ETRI APD-FET1.0 shows the sensitivity of - 30.3 dBm at $10^{-10}$ BER(bit error rate) and 2.5 Gbps optical random signal of $2^{23}-1$ word length. The fiber optic receiver is one of the essensial parts of the transmission module for B-ISDN. Also, the above optical packaging technology will be adapted for the developement of 10 Gbps transmission application 2.5 Gbps 5 Gbps

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.225-228
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• 2007

The objective of this study is to characterize design parameters of rocket igniters for composite, double base and nitramine propellant. Arc image furnace and fiber optics surface reflectometer were used to measure ignition delay time and reflected optical energy of several compositions of composite, double base and nitramine base rocket propellant at different pressure levels each other. The order of ignitability was double base > composite > Nitramine propellants at initial pressure of over 75 psia. The highest ignition energy was needed to ignite nitramine propellant, however, as the pressure increased up to the range of $75{\sim}400$ psia as the ignition delay time decreased abruptly. The absorbtion of radiation energy could be increased by the addition of small amount of opacifiers as carbon black, ZrC, WC and burning catalyst.