• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.425-430
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• 2013

Robust and high speed underwater communication is severely limited when compared to communications in terrestial. In free space, RF communication operates over long distances at high data rates. However, the obstacle in seawater is the severe attenuation due to the conducting nature. Acoustic modems are capable of long range communication up to several tens of kilometers, but it has low data-rate, high power consumption and low propagation speed. An alternative means of underwater communication is based on optics, wherein high data rates are possible. In this paper, the characteristics of underwater channel in the range of visible wavelength is investigated. And the possibility of optical wireless communication in underwater is also described. The LED-based transceiver and CMOS sensor module are integrated in the system, and the performance of image transmission was demonstrated.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.5
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• pp.39-48
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• 2000

We newly proposed a polymer based vertical asymmetric optical coupler, which was characterized by simple fabricating procedure and short coupling length. And we fabricated a thermo-optic modulator using the polymeric optical coupler. We optimized the proposed device by coupling characteristic analysis. In a TE polarized 1.33${\mu}{\textrm}{m}$ wavelength, we obtained very short coupling length(L=277.6${\mu}{\textrm}{m}$) with 0.4${\mu}{\textrm}{m}$ thickness of middle layer, high coupling efficiency(94%), and asymmetric vertical waveguides with n$_{u}$ = 1.522, n$_{l}$ = 1.51. We implemented vortical asymmetric thermo-optic modulator with lower inverted rib waveguide and upper slab waveguide. In the 600Hz bandwidth and 4.5㎽ input power, the extinction ratio of the mode was 17㏈ with an insertion loss of 4.5㏈.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.335-339
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• 2000

A $1.31/1.55\mu\textrm{m}$ coarse WDM opncal dIrectional coupler that conslsls of two idenlical straight channel waveguides in BK7 glass has been fabricated. The separatIOn between two channel waveguides is $8\mu\textrm{m}$ and the wavegu.ide width is $4\mu\textrm{m}$ . Especlally, we assumed that the index profile is Gaussian function and complementary error function in the width direction and depth direction, respectrvely. This directional coupler operating at $1.31/1.55\mu\textrm{m}$ with crosstalk of 18dB is demonstrated and has the 16 mm long length with 12.6 mm coupling region.region.

• Particle and aerosol research
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• v.11 no.4
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• pp.93-98
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• 2015

Particles which generated from plasma enhanced chemical vapor deposition (PECVD) during thin film deposition process can affect to the process yield. By using light extinction method, ISPM can measure particles in the large-diameter pipe (${\leq}300mm$). In our research, in-situ particle monitor (ISPM) sensor was installed at the 300 mm diameter exhaust-line to count the particles in each size. In-house flange for mounting the transmitting and receiving parts of ISPM was carefully designed and installed at a certain point of exhaust line where no plasma light affect to the light extinction measurement. Measurement results of trend changes on particle count in each size can confirm that ISPM is suitable for real-time monitoring of vacuum process.

• Journal of Biomedical Engineering Research
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• v.18 no.4
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• pp.499-505
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• 1997

A non-invasive technique to measure absorption and scattering coefficients was investigated The reflected backscattered light from the surface of phantom and biological tissue was obtained by using a time-correlated single photon counting system in pico-second time domain. The absorption and scattering coefficients were acquired by the time of peak and asymptotic behavior of the time-resolved reflectance curve and agreed well the ones that is obtained with deconvolution method It was found that the approximation method was good for biological medium to calculate optical properties due to its convenience and accuracy.

• Korean Journal of Environmental Agriculture
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• v.21 no.2
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• pp.83-89
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• 2002

The effect of low dose $\gamma$ radiation on photosynthesis and the reduction of photoinhibition in red pepper plant was investigated. The seedling height leaf width and leaf length of pepper were stimulated in plants grown from seeds irradiated with the low dose of 4 Gy. The $O_2$ evolution in the 4 Gy irradiation group was 1.5 times greater than in the control. To investigate the effect of low dose $\gamma$ radiation on response to high light stress, photoinhibition was induced in leaves of pepper by illumination of high light (900 $\mu mol/m^2/s$). Pmax was decreased with increasing illumination time by 20% in the control, while hardly decreased in the 4 Gy irradiation group. The photochemical yield of PSII, estimated as Fv/Fm, was decreased with increasing illumination time by 50% after 4 hours while Fo did not change. However, Fv/Fm in the 4 Gy irradiation group was decreased by 37% of inhibition, indicating that the photoinhibition was decreased by the low dose $\gamma$ radiation. Changes in the effective quantum yield of PSII, $\Phi_{PSII}$, and 1/Fo-1/Fm, a measure of the rate constant of excitation trapping by the PSII reaction center, showed similar pattern to Fv/Fm. And NPQ was decreased after photoinhibitory treatment showing no difference between the control and the 4 Gy irradiation group. These results showed the positive effect of low dose $\gamma$ radiation on the seedling growth and the reduction of photoinhibition.

• Journal of the Korean Society of Radiology
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• v.15 no.5
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• pp.749-754
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• 2021

In order to maximize the matching ratio between the scintillation pixel and the photosensor of the PET detector using a small number of photosensor, various arrays of scintillation pixels and four photosensors were used. The array of scintillation pixels consisted of six cases from 6 × 6 to 11 × 11. The distance between the photosensors was applied equally to all scintillation pixels, and the arrangement was expanded by reducing the size of scintillation pixel. DETECT2000 capable of light simulation was used to acquire flood images of the designed PET detectors. At the center of each scintillation pixel array, light generated through the interaction between extinction radiation and scintillation pixels was generated, and the light was detected through for four photosensors, and then a flood image was reconstructed. Through the reconstructed flood image, we found the largest arrangement in which all the scintillation pixels can be distinguished. As a result, it was possible to distinguish all the scintillation pixels in the flood image of 8 × 8 scintillation pixel array, and from the 9 × 9 scintillation pixel flood image, the two edge scintillation pixels overlapped and appeared in the image. At this time, the matching ratio between the scintillation pixel and the photosensor was 16:1. When a PET system is constructed using this detector, the number of photosensors used is reduced and the cost of the oveall system is expected to be reduced through the simplification of the signal processing circuit.

• Proceedings of the Optical Society of Korea Conference
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• 2002.07a
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• pp.44-45
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• 2002

1.3$mu extrm{m}$ 대역에서 증폭특성을 갖는 광섬유 증폭기인 Praseodymium-doped fiber amplifier(PDFA)는 Ohishi 등에 의해서 처음으로 제안되었다. 수십 nm의 이득 대역폭을 갖고, 30dB 이상의 높은 신호 이득을 갖는 PDFA는 1.3～l.6$\mu\textrm{m}$에 이르는 광대역 WDM을 위한 중요한 증폭기로 사용되고 있다. 최근에는 1.3~1.6$\mu\textrm{m}$에 이르는 광대역 WDM을 위해 광섬유 증폭기의 이득을 shift시키고, 이득 평탄화를 위한 많은 연구가 진해되어 지고 있으나, 광섬유 내에서 초고속의 광 신호를 증폭 시 발생할 수 있는 상호채널 간섭, 상호변조 왜곡, bit rate 높은 펄스열의 증폭 시 발생할 수 있는 이득소멸(gain depletion)과 이득회복(gain recovery) 등과 같은 과도응답 현상에 관한 연구는 충분히 보고되어있지 않다. (중략)

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04b
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• pp.97-100
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• 2002

We analyzed the excitation coefficients and the extinction ratio as a function of waveguide width, center to center distance, and angle of input waveguide for a directional coupler. The variation of thc difference between excitation coefficients is similar to that of the extinction ratio. Also, the smaller the difference between those is, the better the extinction ratio is. This concept will have application to devices using optical coupling.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.11a
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• pp.37-39
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• 2000

오존에 대한 예보 모델을 연구하는 데는 오존의 생성과 소멸에 관한 광 화학 반응에 대한 이해가 중요한 데 대류권에서 일어나는 알짜 오존 생성(net ozone production)반응은 다음과 같다. (R1) $HO_2$.+NO$\longrightarrow$$NO_2$+OH. (R2) $RO_2$.+NO$\longrightarrow$$NO_2$+RO. (R3) $NO_2$+hu(424< nm) $\longrightarrow$NO+O($^{3}P$) (R4) O($^{3}P$)+$O_2$+M$\longrightarrow$$O_3$+M이때 (R1)과 (R2) 반응에 참여하는 $HO_2$.라디칼 / $RO_2$.라디칼은 주로 대기 중에 존재하는 탄화수소(RH)와 OH.의 반응에 의하여 직접 생성되기도 하고, 이때 생성된 알데하이드(RCHO) 화합물이 OH.과의 반응과 광분해 반응을 통해서 형성된다. 한편, 대도시 지역의 경우 자동차의 배기가스가 알데하이드 화합물의 주요 인위적인 배출원으로 알려져 있다(Viskari et al., 2000, Granby et al., 1997). (중략)