• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.33-36
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• 2009

Laser ablation with femtosecond lasers is highly promising for microfabrication of materials. Also, the high peak power of femtosecond lasers could induce a multiphoton absorption to ablate transparent materials. Similar results have also been were obtained in the case of optical fibers. In this paper, we present our experimental results of femtosecond laser microstructuring of optical fiber and its applications to microelectronic components and fiber optic devices. Finally, we directly produced micro holes with femtosecond laser pulses in a single step by moving an optical fiber in a preprogrammed structure. When water was introduced into a hole drilled from the bottom surface of the optical fiber, the effects of blocking and redeposition of ablated material were greatly reduced and the aspect ratio of the depth of the hole was increased. We have presented circular and rectangular-shaped holes in optical fiber.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.485-489
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• 2005

I have investigated a scheme for suppressing stimulated Brillouin scattering in optical fibers. The scheme makes use of a sampled Bragg grating fabricated within the fiber used for transmitting intense Q-switched pulses. The grating is designed such that the spectrum of the Stokes pulse generated through stimulated Brillouin scattering falls entirely within its stop band. I show numerically that the number of sampled fiber Bragg gratings in 1 m is applied directly to suppressing stimulated Brillouin scattering rather than the coupling coefficient. This prevents the build up of the backward-propagating Stokes wave and mitigates the deleterious effects of stimulated Brillouin scattering. The simulation shows that 15 ns pulses with 1 kW peak power can be transmitted though a 1 m-long fiber with little energy loss using this scheme.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.485-489
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• 2004

We demonstrated numerically that both the chromatic dispersion and the dispersion slope could be compensated by using purely phase-sampled superstructure fiber Bragg gratings provided with chirp of coupling coefficient along the wavelength axis. Also, we propose a purely phase-sampled Bragg grating for dispersion and dispersion slope compensation by introducing a chirp in coupling coefficient and sampling function. The bandwidth of all reflected channels can be equalized.

• Journal of the Optical Society of Korea
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• v.1 no.2
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• pp.110-115
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• 1997

We report effcient cascaded Raman generation and signal amplification at 1.3.mu.m achieved in a ring resonator constructed solely from fiber components, i.e. fusion WDM couplers. Low-loss single-mode fiber with moderate $GeO_2$ content (18 mole %) is used as an active medium and pumped by a Nd:YAG laser at 1.064.mu.m. In a resonant cascaded geometry, this generates the third Stokes line at 1.24.mu.m, which acts as a pump for signal wavelength around 1.3.mu.m. A DFB laser operating at 1.315.mu.m is used to provide an input signal. An output signal powers up to 20 dBm (100 mW) with a 28 dB Raman gain are attained, where the Nd:YAG pump power is 3.4 W. It is also shown experimentally that it is important to use optical filters to suppress feedback from the resonator, permitting high Raman gain and good signal quality.

• Korean Journal of Optics and Photonics
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• v.5 no.2
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• pp.304-310
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• 1994

The use of thermally expanded core (TEe) fibers fabricated by thermal diffusion of dopants such as $GeO_{2}$ in hybrid fiber components has an advantage of eliminating lenses for collimation and focusing. An electric furnace is fabricated to heat the fibers locally for the core expansion. We observed an expansion of the mode size at $1.3\mu\textrm{m}$ wavelength by 27% after treating a section of single mode optical fiber at $1250^{\circ}C$ for 10 hours. hours.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.11
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• pp.3-8
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• 2016

In this paper, we design to generate 12.5 GHz spaced 256 number of multi-carrier generation module using 32 laser diodes. We modulate the generated multi-carrier generation module by 12.4 Gbps, and confirm the performance of optical channels passing through recirculating loop up to 1000km distance. An experimental result shows that the carrier away from the laser diode is significantly influence by noise effect.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.4112-4112
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• 2001

The feasibility of NIR spectroscopy as a quick and nondestructive method for quality control of uniformity of coating thickness of pharmaceutical tablets was investigated. Near infrared spectra of a set of pharmaceutical tablets with varying coating thickness were measured with a diffuse reflectance fiber optic probe connected to a Broker IFS 28/N FT-NIR spectrometer. The challenging issues encountered in this study included: 1. The similarity of the formulation of the core and coating materials, 2. The lack of sufficient calibration samples and 3. The non-linear relationship between the NIR spectral intensity and coating: thickness. A peak at 7184 $cm^{-1}$ was identified that differed for the coating material and the core material when M spectra were collected at 2 $cm^{-1}$ resolution (0.4 nm at 7184 $cm^{-1}$). The study showed that the coating thickness can be analyzed by polynomial fitting of the peak area of the selected peak, while least squares calibration of the same data failed due to the lack of availability of sufficient calibration samples. Samples of coal powder and solid pieces of coal were analyzed by FT-NIR diffuse reflectance spectroscopy with the goal of predicting their ash content, percentage of volatile components, and energy content. The measurements were performed on a Broker Vector 22N spectrometer with a fiber optic probe. A partial least squares model was constructed for each of the parameters of interest for solid and powdered sample forms separately. Calibration models varied in size from 4 to 10 PLS ranks. Correlation coefficients for these models ranged from 86.6 to 95.0%, with root-mean-square errors of cross validation comparable to the corresponding reference measurement methods. The use of FT-NIR diffuse reflectance measurement techniques was found to be a significant improvement over existing measurement methodologies in terms of speed and ease of use, while maintaining the desired accuracy for all parameters and sample forms.(Figure Omitted).

• Korean Journal of Optics and Photonics
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• v.1 no.2
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• pp.125-129
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• 1990

One method for time-division multiplexing (TDM) of Michelson type fiber-optic interferometric sensor arrays is proposed and demonstrated experimentally. This method has some advantages; fewer fiber-optic components. low cost. and high reliability.bility.

• Journal of Sensor Science and Technology
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• v.15 no.1
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• pp.40-46
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• 2006

This paper presents a novel fiber optic accelerometer system for monitoring vibration of large-size structures. The system is composed of one (or multiple) sensor head, a light control unit and a signal processing unit. The sensing mechanism of the sensor head is based on a novel integration of the moire fringe phenomenon with fiber optics to achieve a robust performance in addition to its immunity to EM interference, easy cabling, and low cost. In this paper, a prototype of the fiber optic accelerometer system has been developed successfully. A low-cost light control unit has been developed to drive the system's optic and electronic components. A unique algorithm has also been developed to derive the sensor's acceleration from the raw signals of the light control unit; it is implemented via a separate signal processing unit. Finally, the shaking table tests successfully demonstrate the performance and the potential of the moire fringe fiber optic sensor system to monitor the health of civil infrastructures.

• 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.