• Journal of the Optical Society of Korea
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• v.5 no.3
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• pp.67-69
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• 2001

An alternative way to determine the birefringence for uniaxial crystals with Brillouin scattering experiments equipped with a Fabry-Perot interferometer is presented. The value of the minimum cavity spacing of the interferometer to observe the birefringence was found, and it is shown that the experimental error of the birefringence could be reduced by increasing the cavity spacing. For a single crystal of $\alpha$-LiIO$_3$, the birefringence was found to be 0.14814$\pm$0.0007 at 514.5 nm.

• Ocean and Polar Research
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• v.24 no.3
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• pp.237-247
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• 2002

We report all sky camera and Fabry-Perot interferometer (FPI) observations of mesospheric gravity waves and a 12-hour wave at Resolute $(75^{\circ}N)$ and a joint observation of 10-hour wave with Eureka $(80^{\circ}N)$. All sky camera observations showed a low occurrence of mesosphere gravity waves during equinoxes, which is similar to the mid-latitude region. A slightly higher occurrence near solstice appears to indicate that gravity waves are not filtered out by the neutral wind in the winter. The FPI observation of a 12-hour wave showed amplitude variations from day to day. The phase of the wave is mostly stable and consistent with the GSWM prediction in the winter. The phase shifts with season as predicted by the GSWM. Four events of the 12-hour wave were found in spring with amplitudes larger than the GSW predictions. The FPls at Resolute and Eureka also observed a wave with period close to 10 hours. The 10-hour wave maybe the result of the non-linear interaction between the semi-diurnal tide and the quasi-two day wave. Further studies are under way. Overall, the combined Resolute and Eureka observation have revealed some new fractures about the mesospheric gravity wave, tidal wave, and other oscillations.

• International Journal of Aeronautical and Space Sciences
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• v.6 no.1
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• pp.17-26
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• 2005

An optical phase tracking technique for an extrinsic Fabry-Perot interferometer (EFPI) is proposed in order to overcome interferometric non-linearity. Basic idea is utilizing strain-rate information, which cannot be easily obtained from an EFPI sensor itself. The proposed phase tracking system consists of a patch-type EFPI sensor and a simple on-line phase tracking logic. The patch-type EFPI sensor comprises an EFPI and a piezoelectric patch. An EFPI sensor itself has non-linear behavior due to the interferometric characteristics, and a piezoelectric material has hysteresis. However, the composed patch-type EFPI sensor system overcomes the problems that can arise when they are used individually. The dynamic characteristics of the proposed phase tracking system were investigated, and then the patch-type EFPI sensor system was applied to the active suppression of flutter, dynamic aeroelastic instability, of a swept-back composite plate structure. The proposed system has effectively reduced the amplitude of the flutter mode, and increased flutter speed.

• Journal of the Optical Society of Korea
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• v.2 no.2
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• pp.74-79
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• 1998

The use of a fiber Fabry-Perot interferometer (FFPI) as an optical current transducer is demonstrated. A conventional inductive pickup coil converts the time-varying current I(t) being measured to a voltage waveform V(t) applied across a piezeolectric strip to which the FFPI is bonded. The strip experiences a longitudinal expansion and contraction, resulting in an optical phase shift ${\phi}(t)$ in the fiber proportional to V(t). This phase shift is measured using a frequency-modulated semiconductor light source, photodiodes to monitor the reflected light from the FFPI and the laser power, and a digital signal processor. Calibration routines compute V(t) and I(t) from the measured phase shift at a l KHz rate. Response to 60 Hz ac over the design range 0-1300A rms is characterized Transient response of the FFPI transducer is also measured.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.22-26
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• 2003

EFPI (extrinsic Fabry-Perot interferometer) 센서를 이용해 복합재료의 파손 신호를 취득하기 위해서는 파손 신호에 비해 상대적으로 낮은 주파수의 열적, 기계적 정적 변형에 의해 발생하는 위상 변화를 보상해 주는 기술이 필요하다. 또한 센서의 민감도를 최적화하기 위해 출력 신호의 위상을 Quadrature 지점에 유지시켜야 한다. 본 논문에서는 EFPI 센서 시스템의 출력 신호위상을 일정하게 유지시킬 수 있는 안정화 제어 시스템을 개발하였다. 안정화 제어 시스템은 광대역 파장 레이저 광원, 가변 F-P (Fabry-Perot) 필터 그리고 필터를 제어한 수 있는 전자 회로시스템으로 구성하였다. 개발된 시스템의 위상 제어 성능을 평가하기 위해 복합재료 시편의 인장 실험을 수행하여 인장 변형에 의해 발생하는 위상 변화를 개발된 시스템을 이용해 Quadrature 지점에 일정하게 유지할 수 있음을 보였다. 또한 연필심 파손 실험을 통해 개발된 시스템이 파손 신호를 잘 취득할 수 있음을 확인하였다.

• Journal of Sensor Science and Technology
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• v.16 no.5
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• pp.342-348
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• 2007

A high-speed signal processor for Fabry-Perot interferometric sensors using modified ramp modulation is implemented. The main idea for the signal processing is to find a modulation waveform that could induce a linear frequency change in a laser diode to linearize the relationship between the optical phase shift and measurand. It is found that the waveform could be modeled as the addition of a linear term and an exponential term. A signal processor adopting modified ramp modulation technique is implemented and evaluated to find linearity, drift and random walk of $<{\pm}1.5%$, $0.4^{\circ}C$, $5.28{\times}10^{-4}^{\circ}C/{\sqrt{Hz}}$.

• 대한공업교육학회지
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• v.32 no.2
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• pp.171-187
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• 2007

The purpose of this study is to measure the lathe tool vibration and verify its usefulness using the fiber optic interferometeric sensor instead of using common accelerometer. To compare two vibration signals a Fabry-Perot fiber optic sensor(FOS) is directly attached to the left-side surface of the lathe tool and an accelerometer is attached near to the fiber optic sensor. Measurement signals from the FOS and theoretical results of receptance simulation are compared. When the amplitude of tool vibration increased the frequency shift phenomena was occurred. This means that mass effect occurred and vibration spectrum moved to the low frequency region. Generally this results is agreement to the regenerative chatter. The chatter frequency is not same as the natural frequency of the tool itself. The FOS can also applied to laboratory experiments for students. This experimental technique is perhaps the first attempts because of directly attachment technique. Therefore, suggested Fabry-Perot fiber optic sensor can be used to monitoring the tool wear and vibration.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.409-413
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• 1999

A two-beam polarization (TBP) interfermeter with a reflection configuration for measuring the linear electroptic coefficient is described and investigated experimentally and theoretically. It is shown that a TBP interferometer can be used for measuring the Pockels coefficient of thin film with a strong Fabry-Perot effect. The TBP interferometer technique is used to measure the effective differential linear electro-optic coefficient $re=r_{33}-(n_0/n_0)^3r_{13}$of lead zirconate titanate (PZT) thin film. The results are in agreement with known data.

• Journal of Korean Ophthalmic Optics Society
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• v.9 no.2
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• pp.463-471
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• 2004

The Fabry-Perot interferometer filters for UV meter were designed using the design program of optical thin films. From the data obtained, two filters were fabricated. The transmittance of two filter were measured by spectrophotometer in order to analysis their optical property. The transmittance was controlled by the thickness of Ag reflector and the wavelength of the transmission was controlled by the thickness of $SiO_2$ spacer. The two UV filters were fabricated by the RF magnetron sputtering which are the multilayers of [air/$SiO_2$(174.6 nm)|Ag(78 nm)|$SiO_2$(68 nm)|Ag(78 nm)|Cr(5 nm)|glass] and [air/$SiO_2$(174.6 nm)|Ag(S8 nm)|$SiO_2$(56 nm)|Ag(58 nm)|Cr(S nm)|glass]. One filter has the maximum transmittance of 6% at the about 370nm and it has the transmittance of below 0.2% at 400nm. The other filter can be found that the transmittance is increased as the thickness of Ag is decreased and the wavelength of the transmission is controlled by the thickness of $SiO_2$ spacer layer.

• Publications of The Korean Astronomical Society
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• v.15 no.spc2
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• pp.27-35
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• 2000

The investigation of the space environment requires the use of experimental and theoretical tools and resources in order to perform the research task. Understanding of these research tools is imperative for proper interpretation of the results. In this paper, we discuss on research tools that are widely used in the field of aeronomy; Fabry-Perot interferometer and Michelson interferometer. These instruments have been used extensively as passive optical devices, spectrally monitoring the natural atmospheric emissions (airglow). This function has made both instruments valuable tools in upper atmospheric studies since they provide the ability to determine the dynamic and thermodynamic properties of the upper atmosphere by monitoring naturally-occuring emission.