• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.8
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• pp.27-33
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• 2001

The performance of the ordinary Fiber Bragg Grating(FBG) sensor strain measurement system, which uses Fabry-Perot filter for scanning wavelength, has limitation for application because of hysteresis characteristics of PZT element in the filter, slow scan rate of the filter and the high cost of system. We proposed and experimented a multiple FBG sensor system using light emitting diode(LED) as a light source and adapting Code Division Multiplexing(CDM) method to separating out individual sensor signal. Output signals for a applied static and dynamic strain and crosstalk levels between sensor signals were measured. The price of the system is very loss and the response speed is very fast. Crosstalk levels between sensor signals below - 30 dB were demonstrated.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.34-38
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• 2004

A fiber laser of which wavelength was scanned by an intra-cavity FP (Fabry-Perot) filter was used to interrogate a fiber Bragg grating strain sensor array. We calculated the wavelength variation of the fiber laser using quadrature signal processing with an unbalanced M/Z (Mach-Zehnder) interferometer and time-delayed sampling technique. The calculated wavelengths are mapped to corresponding temporal reflection peaks from the sensor array, which enables more accurate and stable interrogation without the problems caused by the FP filter's nonlinear characteristics. Wavelength resolution of ∼20 pm was obtained in our experimental setup, which could have been greatly enhanced with faster phase modulation.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.1
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• pp.43-48
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• 2009

We constructed a simple wavelength readout system for a tunable fiber laser which was used for a fiber Bragg grating sensor array system. A quadrature sampling method was used to demodulate wavelength variations of the tunable laser which consisted of a SOA(semi-conductor optical amplifier) and a fiber-optic Fabry-Perot filter. Internal triggers, which have a 90 degree phase period, have been generated by using a double-pass Mach-Zehnder interferometer. From Lissajous plots with quadrature sampled data, a mean phase error of ${\sim}2.51$ mrad was obtained. From the wavelength readout experiments, an accurate and fast linear wavelength demodulation has been confirmed.

• Korean Journal of Optics and Photonics
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• v.17 no.3
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• pp.216-222
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• 2006

We propose the use of the Gaussian-curve fitting algorithm for the improvement of measurement accuracy in wavelengthscanned Fabry-Perot filter based demodulation systems. The peak locations of FBG sensors were calculated from the fitted curves rather than from distorted PD profiles, resulting in much better measurement accuracy than that of the highest-peak search algorithm. Also, the algorithm was proved to minimize measurement uncertainty of spectrally-distorted grating sensors. From our experimental results, a temperature resolution as small as ${\sim}0.3^{\circ}C$ was readily achieved by use of the Gaussian-curve fitting algorithm whereas the highest-peak search algorithm gave a temperature resolution larger than ${\sim}4^{\circ}C$.

• Korean Journal of Optics and Photonics
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• v.10 no.5
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• pp.413-418
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• 1999

We report on the frequency response of microwave signal processing networks using optical fiber circuits. Microwave frequency rejection filters using Mach-Zehnder interferometer and Fabry-Perot interferometer are modelled theoretically and tested experimentally. Graphical representation method provides a simple tool for computating single mode fiber delay-line microwave filters. The calculated results are in good agreement with experimental results. A 36dB microwave frequency rejection filter is also demonstrated.

• Journal of the Optical Society of Korea
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• v.9 no.3
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• pp.103-106
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• 2005

Recently, polymethyl methacrylate based plastic optical fibers (POFs) have attracted considerable attention as a potential medium for local area network (LAN) and home network applications. Since the POFs have very low optical loss at around 650mm, in particular, it becomes quite important to develop GHz transmitters operating at this wavelength for high bit rate optical transmission applications of the POFs. In this paper, we present generation of ${\geq}1.5 Gbps$ pseudo-random binary sequence optical signals by using a gain switched InGaA1P Fabry-Perot semiconductor laser with a high frequency filter, operating at 650mm, and the application of these signals to bandwidth measurement of POFs.

• Korean Journal of Optics and Photonics
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• v.9 no.3
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• pp.151-155
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• 1998

A new Fabry-Perot tunable filter has been built with simple construction, which does not require any additional aligning and/or beam-confining components for the reduction of the diffraction loss. For this feature, one of the two fibers for the filter is processed to have a concave mirror whose curvature is the same as that of the wavefront of the Gaussian beam from the first fiber. After high reflection coatings, the two fibers are aligned to result in an FP filter whose bandwidth, free spectral range, and insertion loss is 1.47nm, 52nm, 5.6dB respectively.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.306-307
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• 2003

기존의 WDM용 실리콘 파브리-페로 파장 가변 필터의 경우는 E-beam 박막 증착이나 CVD 박막 증착법을 사용하여 두께 제어가 잘 이루어지지 않았고, 제작된 실리콘 파브리-페로 필터의 굴절율을 변화시키기 위한 패턴이 고가의 백금(Pt)으로 이루어졌다. 이에 수 nm로 박막 두께를 제어해보고, 고가의 백금이 아닌 저가의 물질을 이용하여 온도제어를 이루어 보고자 하였다. (중략)

• Journal of IKEEE
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• v.12 no.3
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• pp.131-137
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• 2008

A silicon Fabry-Perot tunable thermo-optic filter for WDM using the thin film silicon coating is proposed and experimented. The filter is implemented by using the CMP process and polishing both sides of the commercial silicon wafer with normal thickness of 100${\mu}m{\pm}$1%. The filter also has 2-layer or 3-layer dielectrics thin film coating mirror which are alternated ${\lambda}$/4 layers of $SiO_2$($n_{low}$=1.44) and a-Si($n_{high}$=3.48) for the central wavelength of 1550nm by RF sputtering. The experiment shows that FSR is 3.61nm and FWHM is 0.56nm and the finesse is 6.4 for 2-layer mirror with the reflection of 61%, and that FSR is 3.36nm and FWHM is 0.13nm and the finesse is 25.5 for 3-layer mirror with the reflection of 89%. According to thermo-optic effect, the transmitted central wavelength of 1549.73nm at $23^{\circ}C$ is shifted to 1550.91nm at $30^{\circ}C$ and 1553.46nm at $60^{\circ}C$ for 2-layer mirror, and the transmitted central wavelength of 1549.83nm at $23^{\circ}C$ is shifted to 1550.92nm at $30^{\circ}C$ and 1553.07nm at $60^{\circ}C$ for 3-layer mirror.

• 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.