• Journal of the Optical Society of Korea
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• v.5 no.1
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• pp.5-8
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• 2001

In this work, we studied the effect of chirped grating on optical bistability in λ/4-shifted semiconductor distributed-feedback(DFB) devices, such as an etalon with nonlinear mirrors, a λ/4-shifted DFB waveguide and aλ/4-shifted DFB laser amplifier. We found that chirped DFB devices exhibit bistable switching at a lower input power.OCIS code : 050.2770, 190.1450, 190.5970, 230.0230.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.351-354
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• 2002

The new enhanced method of temperature control need not any reference temperature, the system itself can find the melting temperature of gallium as a reference point by dithering input heat flux. If gallium is in melting state, the latent heat of fusion works, so gallium temperature does not change on dithering input heat flux. Also, the control method can determine the state of gallium; solid, liquid, or melting state by investigating the temperature in gallium. We apply this new temperature stabilization method to stabilize a Fabry-Perot cavity, which serves as a ultimate length measurement technique. We achieved 1 mK-temperature stability and 1.5426 nm/ 95 mm-length stability over 10 hours.

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.387-391
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• 1987

We have observed the optical bistabilities at $5145{\AA}$ in nonlinear etalons filled with NOA8l optical adhesive which is cured with UV light under the temperature gradient of $7^{\circ}C/mm$ on the NOA81 layer surface. The critical switch-on irradiance and switch-on time are $17\;KW/cm^2$ and $350{\mu}sec$. respectively. The switching contrast of up to 8 observed in NOA81 etalons is higher than that of ZnS or ZnSe interference filter, and the thermo-optic coefficient (dn/ndT) of NOA81 is measured to be at least $-3.8{\times}10^{-4}/^{\circ}C$ which is larger in magnitude than that of ZnS or ZnSe.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.74-77
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• 2006

A scanned Fabry-Perot(F-P) filter and a Multi-Channel Wavelength Locker(MCWL) were used to interrogate fiber Bragg grating sensor array. When the F-P filter scans over the MCWL which works as a multi-reference the temporal peaks profiles correspond to the locking wavelengths. To solve the linearity, stability, and accuracy problems caused by the nonlinear response of F-P filter, a polynomial fitting algerian was used to calculate the relationship between the peak locations and the wavelengths in all the scanning range. Then from the reflected peaks locations and the best fitting line, the Bragg wavelengths can be obtained. The measurement linearity was greatly enhanced with wavelength resolution of about 4 pm in 10Hz scanning frequency.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.218-219
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• 2000

공동광자감쇠 분광학(Cavity Ringdown Spectroscopy, CRDS)은 고감도의 흡수분광법으로 미량기체의 농도나 흡수분광선의 연구에 사용되어 왔으며 화염이나 플라스마에도 응용되고 있다. 이 분광법은 시간에 따라 지수함수로 감쇠하는 공동광자감쇠신호의 감쇠상수를 측정하는 기술인데, 레이저의 밴드폭이 흡수선폭보다 넓으면 감쇠신호가 지수함수에서 벗어나 오차를 발생하게 된다. 그러므로 오차를 줄이려면 좁은선폭의 레이저를 사용하거나 공동광자감쇠신호의 주파수를 분리하여야 한다. 분광선폭보다 매우 넓은 선폭의 레이저를 사용하고 분광기를 이용하여 공동광자감쇠신호를 분리하는 방법들이 제안되었다. (중략)

• 한국연소학회:학술대회논문집
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• 2000.12a
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• pp.168-174
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• 2000

A diode laser sensor system based on absorption spectroscopy techniques has been developed to measure $CO_2$ concentration and temperature non-intrusively in high temperature combustion environments using a 2.0 ${\mu}m$ DFB(Distributed Feedback) laser. Two optics was fabricated in pig-tail fashion and all optical components were implemented in a single box. The evolution of measurement sensitivity was done using test cell by changing sweep frequency and $CO_2$ concentration. Gas temperature was determined from the ratio of integrated line strengths. Species concentration was determined from the integrated line intensity and the measured temperature. The result show that the system has 2% error in wide operation frequency range and accuracy of $CO_2$ concentration was about 3%. The system was applied to measure temperature and concentration in the combustion region of a premixed $CH_4$ +air triangular flame. The measurement results of gas temperature agreed well with thermocouple results. Many considerations were taken into account to reduce optical noise, etalon effect, beam steering and base line matching problem. The evaluations results and actual combustion measurement demonstrate the practical and applicability for in-situ and real time combustion monitoring in a practical system.

• Journal of the Optical Society of Korea
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• v.14 no.3
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• pp.199-203
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• 2010

A mobile direct detection Doppler LIDAR based on molecular backscattering for measurement of wind in the stratosphere has been developed in Hefei, China. First, the principle of wind measurement with direct detection Doppler LIDAR is presented. Then the configuration of the LIDAR system is described. Finally, the primary experimental results are provided and analyzed. The results indicate that the detection range of the designed Doppler LIDAR reached 50 km altitude, and there is good consistency between the molecular Doppler wind LIDAR(DWL) and the wind profile radar(WPR) in the low troposphere.

• Current Optics and Photonics
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• v.4 no.1
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• pp.69-80
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• 2020

A Rayleigh Lidar used for wind detection works by transmitting laser pulses to the atmosphere and receiving backscattering signals from molecules. Because of the weak backscattering signals, a lidar usually uses a high sensitivity photomultiplier as detector and photon counting technology for signal collection. The capturing of returned extremely weak backscattering signals requires the lidar to work on dark background with a long time accumulation to get high signal-to-noise ratio (SNR). Because of the strong solar background during the day, the SNR of lidar during daytime is much lower than that during nighttime, the altitude and accuracy of detection are also restricted greatly. Therefore this article describes an ultra-narrow bandwidth filter (UNBF) that has been developed on 354.7 nm wavelength of laser. The UNBF is used for suppressing the strong solar background that degrades the performance of Rayleigh wind lidar during daytime. The optical structure of UNBF consists of an interference filter (IF), a low resolution Fabry-Perot interferometer (FPI) and a high resolution FPI. The parameters of each optical component of the UNBF are presented in this article. The transmission curve of the aligned UNBF is measured with a tunable laser. Contrasting the result of with-UNBF and with-IF shows that the solar background received by a Licel transient recorder decreases by 50~100 times and that the SNR with-UNBF was improved by 3 times in the altitude range (35 km to 40 km) compared to with-IF at 10:26 to 10:38 on August 29, 2018. By the SNR comparison at four different times of one day, the ratio-values are larger than 1 over the altitude range (25~50 km) in general, the results illustrate that the SNR with-UNBF is better than that with-IF for Rayleigh Lidar during daytime and they demonstrate the effective improvements of solar background restriction of UNBF.