Study on nonlinear absorption and photorefractive effect in optical fibers using a tunable dye laser

本研究的目的是弄清光纤中的非线性吸收（双光子吸收）和紫外光或蓝光诱导的光致发光活性，并制作光纤光栅作为光致发光活性的应用。1993年，我们用可调谐染料激光器对光纤中的双光子吸收（TPA）进行了初步的测量，并测量了紫外区的TPA光谱。1994年，我们进行了蓝区TPA光谱的详细测量和光折变变化的直接测量，并制作了光纤布拉格光栅，用锗硅酸盐光纤在440-560 nm范围内进行了蓝区TPA光谱的测量。测得的TPA系数在480 nm处显示最大值为1 × 10 - <-4>6cm/MW。这表明TPA是由于具有240 nm附近的吸收光谱的Ge-Si和Ge^2+缺陷引起的。在219-260 nm紫外区，纯石英光纤的TPA系数增大 关于我们 为了研究光折变的变化，我们制作了一个光纤耦合器干涉测量系统，并用KrF准分子激光照射光纤。研究表明，引起折射率变化的两种机制是Ge-Si和Ge^&lt;2+&gt;缺陷的吸收。为了研究光纤光栅，我们用注入锁定KrF准分子激光器作为光源，制作了光纤全息曝光装置。采用激光脉冲的多次曝光，在2分钟的短曝光时间内获得了反射率高达99%的光栅。使用单次曝光，获得90%的反射率。Ge^&lt;2+&gt;的贡献在多次曝光中占主导地位。我们还对孤子进行了数值分析，因为光纤光栅可以对孤子进行压缩。目前，我们已经在利用我们制作的光纤光栅进行掺铒光纤激光器的调谐实验。少

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