• Journal of the Optical Society of Korea
• /
• 제19권3호
• /
• pp.255-259
• /
• 2015

We have proposed and experimentally verified a pulse-width modulation (PWM) generator which directly generated a PWM signal in the optical domain. Output waveforms were clear at the repetition rate of 16 MHz; the duty cycle (DC) was from 14.7% to 72.1%; and the DC-control resolution was about 4.399%/dB. The PWM generator' operation principle is based on the injection-locking property of a single-mode Fabry-$P{\acute{e}}rot$ laser diode (SMFP-LD). The SMFP-LD, which has a self-locked mode wavelength at ${\lambda}_{PWM}$, was used to detect the power of the injection-locking signal (optical analog input). If the analog input power is high, the SMFP-LD is locked to the wavelength of the input signal ${\lambda}_a$ and there is no output after an optical bandpass filter (OBF). If the analog input power is low, the SMFP-LD is unlocked and there is output signal at ${\lambda}_{PWM}$ after the OBF. Thus, the SMFP-LD plus the OBF provide digital output for an analog input. The DC of the output PWM signal can be controlled by tuning the power of the analog input.

• ETRI Journal
• /
• 제21권3호
• /
• pp.41-48
• /
• 1999

We have calculated differential reflection coefficient for isolated well structure of micro-scale, etched on dielectric surface. The differential reflection coefficient is computed using Green's second integral theorem. The purpose of our computation is to find a class of well profiles which give maximal diffusive scattering. To have such a maximal effect, we have concluded that the waist radius of Gaussian beam and its wavelength should be comparable to the well width and that well depth has to be larger than a wavelength. Exact calculation of differential reflection coefficients of dielectric surface with isolated structure on it may be used for the examination of dielectric surfaces and also in making simple but efficient diffuser.

• Journal of applied mathematics & informatics
• /
• 제41권1호
• /
• pp.51-70
• /
• 2023

The flow of an incompressible Ellis fluid in an inclined asymmetric channel, driven by peristaltic waves was studied under low Reynolds number and long wavelength assumptions. The wave on each side of the channel are assumed to be an infinite train of sinusoidal waves, both having the same constant wave speed and wavelength however, they vary in wave amplitude, channel half width and phase angle. We derived expressions for the axial and transverse velocities, volume flow rate, pressure rise per unit wavelength and streamlines. The effects of varying the wave amplitudes, the phase angle, the channel width, the angle of inclination of the channel as well as the fluid parameters on the flow were analyzed. Trapping conditions were determined and the presence of reflux highlighted using the streamlines for the necessary channel and fluid conditions. By varying the fluid parameters, changes in the fluid that deviated from the Newtonian case resulted in a reduction in the axial velocity in the neighborhood of the center of the channel and a simultaneous increase in the velocity at the periphery of the channel. A nonlinear relation was observed with the pressure rise and the volume flow rate. This nonlinear relation is more pronounced with an increase in the absolute value of the volume flow rate. For Newtonian fluids a linear relation exists between these two variables. The fluid parameters had little effects on the streamlines. However, variations of the wave amplitudes, volume flow, channel width and phase angle had greater effects on the streamlines and hence the trapped region.

• 한국수산과학회지
• /
• 제44권4호
• /
• pp.413-422
• /
• 2011

An improved split-beam transducer for a 50 kHz fish-sizing echo sounder was developed. The main objective of this study was to minimize the side lobe level in the beam pattern and the distance between acoustic centers for adjacent transducer quadrants in the geometrical arrangement of array elements while maintaining a given number of transducer elements and beam width. To achieve these goals, a 32-element planar array transducer ($6{\times}6$ array with one element in each corner missing) was designed using the Dolph-Chebyshev shading function to suppress side lobes in the array beam pattern and fabricated by arranging the inter-element spacing to be substantially equal to half the wavelength using the transducer element of 0.4 times the wavelength in diameter. The performance characteristics of this split-beam transducer were evaluated in the experimental water tank of $5m{\times}5m{\times}6m$ (length${\times}$height${\times}$width). In this study, the design goal of the beam width and side lobe level for transmitting a beam pattern was initially set at $21^{\circ}$ and -30 dB, respectively. However, the measured beam width at 3 dB was $21^{\circ}$ in both directions with side lobe levels of -24.7 dB in the horizontal plane and -25.6 dB in the vertical plane. The averaged beam width at -3 dB of the receiving beam patterns for four receiving quadrants was $31.4^{\circ}$. The transmitting voltage response was 161.5 dB (re $1{\mu}Pa$/V at 1 m) at 50.23 kHz with a bandwidth of 2.16 kHz, and the averaged receiving sensitivity for four receiving quadrants was -178.13 dB (re 1 V/${\mu}Pa$) at 49.8 kHz with a bandwidth of 2.64 kHz.

• Journal of the Optical Society of Korea
• /
• 제13권3호
• /
• pp.330-334
• /
• 2009

A simple and compact frequency swept laser is demonstrated at $1.3{\mu}m$ using a wavelength scanning filter based on a rotating slit disk. The laser is comprised of a pigtailed semiconductor optical amplifier, a circulator, and a wavelength scanning filter in an extended cavity configuration. The wavelength scanning filter is composed of a collimator, a diffraction grating, a rotating slit disk, and a mirror. The instantaneous laser output power is more than 5 mW. The scanning range of the laser is extended to 80 nm at the maximum level, and 55 nm in the full width at half maximum at a scanning rate of 2 kHz.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마연구회
• /
• pp.100-103
• /
• 2003

고휘도 LED(light emitting diode) 빨강(R), 녹색(G), 파랑(B), 호박색(A), 백색(W) 등의 중요한 광학특성인 광속(luminous flux), 효율(luminous efficacy), 피크 파장(peak wavelength), 가중치 평균 파장(weighted average wavelength), 반치폭 (full width at ha1f maximum), 색도좌표(chromaticity coordinate), 주 파장(dominant wavelength), 자극순도 (excitation purity) 와 휘도순도(colorimetric purity)에 대해서 비교검토하였다. 시험결과로 제시된 LED의 기본적인 특성 데이터는 추후, 새로운 조명용 LED 램프나 등기구(luminaire)를 개발 및 특성연구에 많은 도움을 줄 것으로 사료된다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1998년도 추계학술대회 논문집 학회본부 C
• /
• pp.987-989
• /
• 1998

We demonstrate and characterize a volume holographic filter operating at $1.55{\mu}m$ region, which corresponds to the wavelength region of optical communication system. By changing recording times or the angle between writing beams. the reflectivity, the filtered wavelength, and the bandwidth of this filter can be controlled. A center wavelength of 1532.8 nm, reflectivity of 10.7% and a bandwidth with full width at half-maximum of 4.0nm are measured in our experiment.

• 한국통신학회논문지
• /
• 제25권10B호
• /
• pp.1707-1713
• /
• 2000

We have proposed a tunable optical ADM using a fiber-optic transversal filter which is composed of fiber couplers and metal-film coated fiber-optic tapped delay-lines with a flat spectral response in abroad range of wavelength. Simulation results show that the optical loss at the DROP and PASS wavelengths of the OADM is negligible and the wavelength tunability is 0.78${\mu}{\textrm}{m}$/ps for the unit time delay of 2 ps. In order to investigate the effects of wavelength drift of the imput optical signal on the OADM the loss at the DROP port and the crosstalks to the other ports have been calculated. The maximum bit rates have been calculated at 46.26 Gb/s for the input Gaussian pulse width of 10 ps.

• 한국광학회지
• /
• 제14권4호
• /
• pp.460-465
• /
• 2003

Double-pass forward(DPF) 방식으로 구성되고 0.98 $\mu$m 파장 대역으로 펌핑된 자이로스코프용 erbium 첨가 광섬유(EDF) 광원의 출력광 특성을 수치계산을 이용하여 분석하였다. EDF길이, 펌프 power, 그리고 펌프 파장 등의 변화에 따른 출력광 power, 파장선폭, 중심파장 안정성 둥을 분석하였으며 일부 특성에 대하여 실험결과와 비교ㆍ검증하였다. 그 결과, DPF 방식의 EDF 광원에서 광원의 특성이 EDF 길이에 크게 의존함을 알 수 있었으며 펌프 power와 펌프 파장의 변화에 대해서 안정된 중심파장을 얻을 수 있는 최적 동작조건도 존재함을 알 수 있었다.

• 대한전자공학회논문지SD
• /
• 제39권1호
• /
• pp.58-66
• /
• 2002

Tapered 방향성 가중 결합 음향파 도파로를 이용하여 음향광학형 파장가변 광 필터를 LiNbO₃와 Ti 이중 확산 공정 기술을 이용하여 제작하였다. 1551.1㎚ 파장의 TE, TM 입사 편광모드와 173.58㎒ 35㎽ RF구동 신호에 대해서 각각 -14.29㏈, -14.99㏈ 부 모드 억압과 61%, 86% 변환효율이 측정되었다. 파장변화율과 통과 대역폭은 8.6㎚/㎒ 1.8㎚로 측정되었으며, 스위칭 속도는 2.82㎲로 측정되었다. 2.5㎚ 채널 간격에 대해서 약 -l4㏈누화 레벨이 측정되었으며, 부 모드와 채널 간격이 누화에 매우 큰 영향을 미치고있음을 확인하였다.