• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1220-1225
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• 2009

In this paper, a tunable fiber feedback laser based on the use of Sagnac loop filter and fiber Bragg grating (FBG) is proposed. The Sagnac loop filter using a high birefringence fiber provides precise 0.33-nm channel spacing as a multi-wavelength grid filter. Ni-Cr wire wound on the FBG is useful to induce the thermo-optic effect of the fiber. Two types of FBG structures, which have a different length of wire, are demonstrated to show the wavelength shift and separation. To tune FBG by resistant heat, some current is supplied into the wire. When the wavelength matched with one of the cavity modes of Sagnac loop filter, the mode-locked lasing is occurred. The electrical power sensitivity of the resonant wavelength is measured to 1.75pm/mW. This laser configuration can be applied the electrical power system for monitoring the power fluctuation.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.46-47
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• 2000

고출력, 고효율, 그리고 고품질의 빔특성을 갖는 DPSSL을 개발하기 위해서는 출력빔을 저하시키는 원인인 비균일한 여기빔 분포에 의한 레이저 결정내의 열렌즈, stress 복굴절 등의 효과를 최소화하여야 한다. 지금까지 열효과를 줄여, 고출력이나 TE $M_{00}$ 모드의 레이저 빔을 얻기위한 방법으로 zigzag 슬랩 디자인$^{1)}$ , VPS 여기 시스템$^{2)}$ , Cusp 형 반사체$^{(3)}$ , 광섬유 결합$^{(4)}$ 등의 방법이 연구되어 왔다. 본 연구에서는 고출력, 고효율, 그리고 고품질의 레이저 빔특성을 동시에 만족하는 레이저를 개발할 목적으로 산란된 여기빔을 이용하는 여기구조를 고안하고 열효과가 감소된 Nd:YAG 레이저 시스템을 최적설계하였다. (중략)략)

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1970-1972
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• 2003

In this paper, a fiber optic current sensor(FOCS) is implemented by low birefringence fiber, and the characteristics of FOCS is investigated. Using the Faraday rotation, the electric current is measured. The measured error is calculated within 1.5% ranging from 1000 to 7500A.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.4
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• pp.53-59
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• 2000

Based on the polarization selectivity of fiber-to-planar waveguide coupler, a novel fiber optic polarizer has been designed and fabricated. The large structural birefringence of a metal-clad planar waveguide enables the polarizer to have wide operating wavelength range. The polymer and gold were used for the guiding layer and cladding layer of the planar waveguide, respectively. The experimental results showed that either TE or TM polarized lightwave could be created by adjusting the thickness of planar waveguide. Operating wavelegth range satisfying more than 16㏈ polarization extinction ratio was 130nm. The average insertion loss of fabricated devices was order of 0.5㏈.

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.419-427
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• 1996

Thermally-stabilized fiber-optic current sensors are proposed and demonstrated. The sensor head is made of two coil formers combined perpendicularly. In this sensor head, bending-induced birefringences can be reduced to the level much smaller than those of the single former type because the eigen-axes of the two perpendicular coil formers are made orthogonal to each other. Moreover, thermal variation of the birefringence is also expected to be minimized by the orthogonality of the two polarization eigen-axes. We changed the temperature slowly in the range of 20~45$^{\circ}C$ during 100 minutes. The overall linearity of the sensor is better than 1.2% in the range of 0~1000A. The long-term fluctuation of the sensor is less than 1% when measured for 3 hours at 500A and room temperature. Two orthogonally-polarized laser diodes are combined together to make the incident beam unpolarized. In the signal processing, the signals are separated by two parts and normalized respectively, which minimize the efects of optical fluctuations coming from sources, connectors, etc.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.6
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• pp.8-15
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• 2012

In this paper, we investigated possible optical parameters causing deviation of experimentally observed output spectra from theoretically predicted results in a high-order fiber comb filter based on a polarization-diversity loop configuration. They include wavelength dependency of half-wave plates (HWPs) inserted in the filter for wavelength switching and the modal birefringence of single-mode fibers (SMFs) with which optical components comprising the filter are connected. In order to consider the effect of the modal birefringence of the SMF on a filter performance, it is modeled as a low birefringence fiber with an arbitrary orientation angle and birefringence. It is found from the simulation results that the modal birefringence of SMFs strongly affects the spectral characteristics of the filter and decreases the extinction ratio of the filter, compared with the wavelength dependency of HWPs. In particular, it is also confirmed that the spectral deviation and asymmetric distortions of side-lobes in narrow band transmission spectra result mainly from the modal birefringence of SMFs.

• Korean Journal of Optics and Photonics
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• v.12 no.1
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• pp.5-9
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• 2001

A wavemeter was realized using the phenomena that the phase lag between principal polarization states in an optical retarder is a function of wavelength. The change in the polarization state of the optical beam as it passes through the optical retarder is dependent on wavelength. The wavelength of the optical beam is determined by comparing the power difference between principal polarization states. A prototype wavemeter was successfully implemented using a polarization maintaining fiber with birefringence $3\times10^{-4}$ and length 100 mm as the optical retarder. The measurement resolution was 0.08 nm over a wavelength region of 1554.38 nm-1557.l9 nm, which agreed well with theoretically calculated results. In addition, the dependence of operating characteristics on temperature was analyzed theoretically and experimentally.mentally.

• Korean Journal of Optics and Photonics
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• v.21 no.4
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• pp.168-174
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• 2010

Fiber optic current sensors based on polarization-rotated reflection interferometry are demonstrated by incorporating them into polymeric optical waveguide components, including polarization-maintaining 3-dB couplers, TE-pass waveguide polarizers, and thermooptic phase modulators. To remove the bending induced birefringence, optical fiber coil is annealed at $850^{\circ}C$ for 24 hours. The reflection interferometry comprising polymer waveguide devices exhibit a highly stable output signal corresponding to the flowing current.

• Korean Journal of Optics and Photonics
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• v.11 no.1
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• pp.33-36
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• 2000

KrF excimer laser, which is useful for fabrication of fiber gratings, was irradiated on the PLC-type WDM directional coupler and the transmission wavelength shift was observed as a function of UV exposure time. The effective refractive index change of rectangular silica waveguide was calculated from the wavelength shift measurement and the coupled mode theory. heory.

• Korean Journal of Optics and Photonics
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• v.13 no.3
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• pp.245-250
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• 2002

We study numerically the temporal evolutions of two orthogonally polarized pulses with width less than 100fsec in all-optical phase-shift switches. We analyze the complicated interplay between a soliton pulse and a higher-order soliton pulse, including the self-and the cross-Raman scattering and the walk-off effect. We also investigate the influence of these interactions on switching performance, including pulse-shape, phase-shift distribution, and contrast ratio. In particular we show that an optical fiber with a typical birefringence (Δn : 2.4$\times$10$^{-5}$ ) can be used with good switching performance in such all-optical switches.