1994 Fiscal Year Final Research Report Summary
Study on nonlinear absorption and photorefractive effect in optical fibers using a tunable dye laser
| Project/Area Number |
05452205
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
情報通信工学
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| Research Institution | Kyushu Institute of Technology |
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Principal Investigator |
MIZUNAMI Toru Kyushu Inst.Tech.Fac.Eng.Associate Professor, 工学部, 助教授 (00174029)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAGI Keiji Kyushu Inst.Tech.Fac.Eng.Professor, 工学部, 教授 (90005281)
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| Project Period (FY) |
1993 – 1994
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| Keywords | Nonlinear optics / Photorefractive effect / Silica glass fiber / Two-photon absorption / Dye laser / Fiber grating |
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| Research Abstract |
The purpose of this research is to make clear the nonlinear absorption (two-photon absorption) and UV- or blue-induced photorefractivity in optical fibers and to fabricate fiber gratings as an application of photorefractivity. In 1993, we performed a preliminary measurement on two-photon absorption (TPA) in an optical fiber using a tunable dye laser, and we also measured the TPA spectrum in the ultraviolet region. In 1994, we carried out a detailed measurement on TPA spectrum in the blue region and a direct measurement on the photorefractive index change, and we fabricated fiber Bragg gratings.
The measurement on TPA spectrum in the blue region was preformed in the range of 440-560 nm using a germanosilicate fiber. The measured TPA coefficient showed a maximum value of 1x10^<-4> cm/MW at 480 nm. This indicates that the TPA is due to Ge-Si and Ge^<2+> defects having absorption spectra around 240 nm. In the ultraviolet region of 219-260 nm, the TPA coefficient in pure silica fibers increa
… More
sed rapidly with the decrease in the wavelength.
To investigate the photorefractive index change, we made a measurement system using an interference in a fiber coupler and irradiate the fibers with a KrF excimer laser. We showed that two different mechanisms contribute to the index change, and identified them as absorption by Ge-Si and Ge^<2+> defects.
For studies on fiber gratings, we made an apparatus of holographic exposure on fibers with an injection-locked KrF excimer laser as a light source. Using multishot exposure of laser pulses, gratings with excellent reflectivity of 99% was obtained with a short exposure time of 2 minutes. Using single shot exposure, a reflectivity of 90% was obtained. Contribution of Ge^<2+> has been dominant in multishot exposure. We also performed a numerical analysis of solitons, as compression of solitons are expected using fiber gratings.
Presently we have been performing the experiment on tuning of Er-doped fiber lasers using the fiber gratings we fabricated. Less
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