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Lock-in 증폭기를 이용한 학부 열잡음 측정실험: 볼츠만 상수의 측정
정해양,장유민 한국물리학회 2013 새물리 Vol.63 No.3
An undergraduate experiment on the thermal noise of resistors, which can be used to measure Boltzmann’s constant, is described. A lock-in amplifier is employed to amplify, filter and detect the thermal noise so that a commercial pre-amplifier and a band-pass filter are unnecessary. Therefore, the method does not require calibration of the frequency-dependent gain. The thermal noise of a resistor is measured as functions of the resistance and the bandwidth, giving values of the Boltzmann constant of kB = (1.362 ± 0.020) × 10−23 J/K and kB = (1.373 ± 0.025) × 10−23 J/K, respectively. The experiment, thus, permits reasonably precise measurement of the Boltzmann constant with uncertainties of less than 2% while allowing the undergraduate students to gain a hands-on understanding of both a fundamental source of noise in electronic circuits and the operation of the lock-in detection technique. 열잡음 측정을 통해 볼츠만 상수를 결정하는 학부과정 실험을소개하였다. 이 실험에서는 기존의 방법에서 흔히 사용되는 저잡음증폭기와 주파수 대역 통과 필터 등 여러 측정 장비 대신 lock-in 증폭기만을 사용하여 증폭, 필터, 감지를 수행한다. 이에 따라 번거로운주파수에 따른 증폭도 눈금메기기 (gain calibration) 과정을 생략할 수있다. 상온에서 저항 값과 주파수 대역폭에 따른 열잡음을 측정하여볼츠만 상수 kB = (1.362 ± 0.020) × 10−23 J/K and kB = (1.373 ± 0.025) × 10−23 J/K값을 각각얻었다. 이 결과는 알려진 값과 오차 2% 이내로 아주 근접한 값이다. 학부생들이 이러한 실험을 통하여 전자회로의 열잡음에 대한 물리적이해를 높이고, 아울러 lock-in 증폭기 작동 원리를 학습하는데 좋은기회가 될 수 있을 것이다.
서원섭,정해양 慶熙大學校 레이저 工學硏究所 1995 레이저공학 Vol.6 No.-
Special optical fibers with high Ge contents for fiber Btragg gratings(FBR) have been fabricated by the modified chemical vapor deposition(MCVD) technique. Ge contents of 18 mol% has been confirmed by surface analysis of a fabricated fiber preform. NA of fabricated optical fibers have adjusted to 0.12 for minimizing coupling loss to communication fibers. Propagation loss of 40 dB/Km for fabricated fibers were measured by OTDR.
권요한,정해양 慶熙大學校 레이저 工學硏究所 1997 레이저공학 Vol.8 No.-
In this paper, we analyzed d. c. and microwave characteristics of GaAs-MESFET under laser illumination. We obtained the analytical expression of I-V characteristics of GaAs-MESFET for linear, knee and saturation regions by solving 2-dimensional Poisson's equation and compared calculated I-V curves with experimental data. The resulting I-V curves are in good agreement with experimental data. We also obtained the analytical expressions for the current gain cut-off frequency f?? and time constant for the linear and the knee region, respectively. It was predicted that the reduction of the current gain cut-off frequency and the increase time constant due to the photovoltaic effect under laser illumination.
김명원,이동욱,이완식,정해양 慶熙大學校 레이저 工學硏究所 1999 레이저공학 Vol.10 No.-
A simple, flexible fabrication method of long-period fiber gratings is presented. This method is based on tapering the outer fiber diameter by electrical arc discharge. Fabricated gratings have ~20dB band rejection and ~0.5dB insertion loss and show extremely good thermal endurance.
Chung,Haeyang 慶熙大學校 레이저 工學硏究所 1993 레이저공학 Vol.4 No.-
The experimental demonstration of microwave modulation and evaluation of the linear dynamic range for the 1.3㎛ wavelength crossing channel Ti:LiNbO₃waveguide modulators are presented. The feasibility of obtaining 54 dB overall dynamic range have established experimentally provided the detected optical carrier power can be increased to 12.6㎼. This can be realized by more efficient coupling and using modulators with smaller optical insertion loss. The available microwave drive power at the electrode does not limit the dynamic range.
김명원,정해양 경희대학교 레이저공학연구소 2000 레이저공학 Vol.11 No.-
A new reproducible fabrication method of long-period fiber gratings is presented. This method is based on tapering the outer fiber diameter by 20KHz AC electrical arc discharge. Fabricated gratings show good reproducible absorption wavelengths and have ∼20dB band rejection and ∼0.5dB insertion loss. Mode conversion between core and cladding mode directly observed by IR vidicon and compared with coupled mode theory.
김종관,정해양 경희대학교 자연과학종합연구원 2000 자연과학논문집 Vol.6 No.-
편광유지 광섬유의 광탄성 효과를 실험적으로 조사하였다. 편광유지 광섬유 격자의 광축과 수직 방향으로 스트레스가 가해지면 격자에 의한 반사 파장이 이동하고 반사 스펙트럼은 2개의 봉우리로 갈라지는 것을 관측하였다. 이동한 파장은 가해진 스트레스의 크기와 비례하며 입사광선이 편광유지 광섬유의 복굴절 축중 slow 방향으로 편광되어 있고 fast 방향으로 스트레스가 가해지는 경우 그 효과가 가장 큰 것을 발견하였다. We report on strong effects of uniaxial compressive stress applied on Bragg gratings written in polarization maintaining optical fibers. The splitting of reflection peaks due to non-uniform distribution of stress in gratings is observed. Under the stress reflection peaks shift in wavelength. The amount of the shift is proportional to the stress. The effect of the stress on the reflection spectrum is the greatest when input polarization of light is in the slow axis while the stress is applied in the fast axis.
실시간 홀로그래픽 간섭법을 이용한 삼차원적 미소변형의 측정
나상훈,정해양 경희대학교 자연과학종합연구원 1995 자연과학논문집 Vol.1 No.-
Three dimensional deformation of a cantilever steel plate under the bending stress is measured quantitatively by a real time holographic interferometric system using liquid gate. Quantitative data were taken by the interference fringe order counting in conjunction with the computer image processing. The experimental data show good agreement in comparison with theoretical analysis.
비틀림 방법을 통한 단일모드 광섬유의 미세 복굴절도의 측정
최태일,정해양 경희대학교 레이저공학연구소 2001 레이저공학 Vol.12 No.-
We describe a twist method for measuring ultralow birefingence(i.e. Δn□10-6~10-8) in single mode optical fibers. In twisted single-mode optical fibers the output state of polarization of light is affected by an elastooptically induced optical activity and by modification of any linear birefringence. The measuring procedure involves measurement of the light intensity only and does not require an analysis of the light-polarization state. Experimental results for commercial single mode fibers with Δn□2×10-6 are presented.