• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.650-656
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• 2014

We propose a novel active fiber design for selectively generating cylindrical vector beams (CVBs) or cylindrical vector modes (CVMs) which can be applied to conventional fiber lasers. A fiber is designed to have a ring-shaped core refractive index profile which can lead to the best overlap between the active dopant distribution profile and the lowest-order CVM (LCVM) field profile. Therefore, the overlap factor (OVF) of the LCVM becomes even higher than that of the fundamental mode. We emphasize that this condition cannot be satisfied by a conventional step-index core fiber (SICF) but by the ring-doped core fiber (RDCF). Because the lasing threshold is inversely proportional to the OVF, the LCVM can predominantly be stimulated even without going through special procedures to impose extra loss mechanisms to the fundamental mode. We numerically verify that the OVF of the LCVM with the doped ions can significantly exceed that of the fundamental mode if the proposed fiber design is applied. In addition, an RDCF of the proposed fiber design can also operate in a regime containing no higher-order modes besides the LCVM, so that it can selectively and efficiently generate the LCVM without being disrupted by the parasitic lasing of the higher-order modes. We highlight that an optimized RDCF can lead to a >30 % higher OVF ratio than a SICF having the same doped area. The proposed model is expected to be useful for enhancing the efficiency of generating CVBs in an all-fiber format.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.109-113
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• 2004

In this paper, we took the basic experiment in order to explore the optical CT(optical current transformer) for measuring high current in a superhigh voltage condition. It is based on the faraday effect that changes the polarization characteristic of optical signals by the magnetic field. We used 1310[nm] laser diode for a light source and comprised a sensing part with the optional fiber of 5[m], 10[m], 20[m] length each. The range of current was from 400[A] to 1300[A]. We observed the characteristic of output that changes according to the length of the optical fiber composing the sensing part. The optical fiber of 5[m] length used for the sensing part had -11.1% of the maximum ratio of error and 10[m] and 20[m] length had -3.5% and 1.7% each. This means that the power and linearity of output increase in proportion to the length of optical fiber and applied current in the same experimental condition.

• Journal of the Optical Society of Korea
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• v.19 no.2
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• pp.130-135
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• 2015

Based on the extended nonlinear Schr$\ddot{o}$dinger equation, the influences of the filter effect on pulse splitting in a passively mode-locked erbium-doped fiber laser with positive dispersion cavity are investigated theoretically. Numerical results show that, as the bandwidth of the spectral filter decreases, the nonlinear chirp appended to the pulse increases under the combined action of the filter effect of the super-Gaussian spectral filter and the self-phase modulation effect. On further decreasing the bandwidth, the wave breaking of the pulse takes place. In addition, by varying the pump power of the laser or the profile of the spectral filter, the influences of the filter effect on pulse splitting also change accordingly.

• Proceedings of the Optical Society of Korea Conference
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• 2008.07a
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• pp.409-410
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• 2008

We have demonstrated a tunable Raman fiber laser using the combination of broadband CFBG and tunable fiber Bragg grating with the center wavelength 1415nm, which is tuned by adjusting longitudinal strain in the wavelength range from 1410 to 1420nm. A total output power of the tunable laser was about 0.9W with 13.8% of laser slope efficiency.

• Korean Journal of Optics and Photonics
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• v.20 no.3
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• pp.189-194
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• 2009

We demonstrate a ring type wavelength swept laser incorporating a fiber Fabry-Perot tunable filter in a laser cavity using 1300 nm semiconductor optical amplifier as a gain medium. The output characteristics of the wavelength swept laser according to the applied scanning frequencies are analyzed in the temporal and spectral domain. The output of the wavelength swept laser decreases dramatically as the scanning frequency increases. And there is a significant peak power imbalance between the forward scan and the backward scan as the scanning frequency increases. Its use in practical applications might be limited.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.6
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• pp.231-236
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• 2007

In this paper, we studied the possibility of non-contact bill counting method using optical fiber sensor instead of traditionally used friction counting method. To implement non-contact counting, we designed and made optical fiber sensor and related parts. optical fiber sensor is made of optical fiber of 1mm diameter, photo diode and laser diode. Based on the conclusion which derived from preliminary experiment, instrument part is designed to make unevenness on the surface of bill paper and to stay parallel with optical fiber section. By analyzing the signal of optical sensor, we made counting program. Experimental instrument is composed of sensor part, instrument part, signal handling part. We checked the possibility of non-contact counting method after implementing experiment by using optical fiber sensor and instrument part.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.159-164
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• 2006

We demonstrate a compact optical coherence tomography(OCT) system based on the optical fiber delay line controlled by a cylindrical piezo-electric transducer(PZT). An 18-m length of single mode fiber is wrapped under constant tension around a PZT. Approximately 134 windings are used. Wraps of the long length of fiber allow the small expansion of the PZT to be magnified to an optical path length delay of 0.78 m. The OCT system shows characteristics for 2-dimensional imaging, exhibiting 96.9dB of signal-to-noise ratio(SNR), $18.6{\pm}0.5\;{\mu}m$ of axial resolution, and $5\;{\mu}m$ of lateral resolution with samples.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2002.11a
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• pp.27-30
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• 2002

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.353-359
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• 2000

A harmonically mode-locked fiber ring laser cavlty was theoretically analyzed. The measured charactenstlcs of a 10 GHz erbium-doped fiber ring laser were used as a basis of the theoretical analysis. From the nonlinear Schroedinger equation of an actively mode-locked erblUm-doped fiber laser. the effects of the components inside the laser cavity have been analyzed includmg nonlinear effects from group-velocity dispersion (GVD) and self-phase modulation (SPM). Usmg the analysls. we have designed a laser cavity with minimum pulsewidth and chirp by changing the intracavity optical intensity and the bandwidth of the filter. In the new design, the chirp i, reduced by 2 times and the pulsewidth by 2A times. compared to the laser used in the experiment. iment.

• Journal of Industrial Technology
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• v.28 no.B
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• pp.235-238
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• 2008

In this paper, we have developed wavelength swept laser system for the swept source optical coherence tomography(SS-OCT). A laser is constructed by using the two SOAs parallel configuration, fiber Fabry-Perot tunable filter(FFP-TF). The wavelength sweeps are repetitively generated with the repetition period of 50Hz. The wavelength tuning range of the laser is more than FWHM of 80nm centered at the wavelength of 1310nm and the line-width of the source is 0.12 nm.