OPTICAL GENERATION OF BRAGG GRATINGS IN CERIUM-DOPED FLUORIDE GLASSES

作为组装光纤和光波导的关键技术，玻璃基质中的布拉格光栅的光生成为人们关注的焦点。为了扩大这项技术的有效性，在各种玻璃材料中寻找光写系统是很重要的。这一点在氟化物玻璃中尤其需要，因为它们作为光学增益介质具有优越性。我们用Ce离子敏化了氟化铝玻璃(AFG)，并评价了它们在Bragg光栅介质中的适用性。所考察的样品是多组分AFG板，其组成为34.5AlF3，13.5YF3，52(Mg+Ca+Sr+BaF2)F2(摩尔%)。CeF_3的浓度范围为0.05~4.0mol%。三价Ce离子(Ce^&lt；3+&gt；)在偶极允许的4f-5d跃迁中产生了4.5-6.5 eV的强吸收带。当KrF激光(46mJ/cm~2)照射到5.00 eV时，Ce^&lt；3+&gt；带的部分漂白，两个新带的生长分别在3.8和6.2 eV处达到峰值，这两个带都与Ce^&lt；3+&gt；离子的光致价态变化成正比，这表明Ce^&lt；3+&gt；离子的光致价态变化是导致吸收变化的原因。从Kramers-Kronig关系式可知，6.2 eV波段随激光曝光累积至20000次单调增加，3.2 eV波段达到饱和，最大折射率变化量为2.7×10~(-5)。等时退火测量表明，3.8 eV波段在1000℃以下基本稳定，6.2 eV波段在3000ﾟC以下基本稳定。这些结果表明掺Ce的原子力显微镜具有作为布拉格光栅介质的潜力。

Photo-generation of Bragg grating in glass matrixes has received much attention as a key technology to assemble optical fibers and waveguides. To extend the validity of this technique, it is important to search for photo-writable system in a variety of glass materials. This is required especially in fluoride glasses because of their superiority as optical gain media. We have sensitized aluminum fluoride glasses (AFG) with cerium ions and evaluated their applicability to Bragg grating media. Samples examined were multicomponent AFG plates with the composition of 34.5A1F_3, 13.5YF_3, 52 (Mg+Ca+Sr+Ba) F_2 in mol%. The concentration of CeF_3 ranged 0.05 to 4.Omol%. The dipole-allowed 4f-5d transitions of the trivalent cerium ions (Ce^<3+>) yielded intense absorption bands at 4.5 to 6.5eV.Exposure to 5.00eV light from a KrF laser (46mJ/cm^2shot) caused a fractional bleach of the Ce^<3+> bands and growths of two new bands peaking at 3.8 and 6.2eV, The both bands increased in proportion to the Ce^3 concentration and the exposure dose, which suggests that the photo-induced valence change of the Ce^<3+> ions attributes the absorption changes. The 6.2eV band increased monotonously with the accumulation of the laser exposure up to 20000 shots, while the 3.2eV band saturated at the exposure of 200 shots, From the Kramers-Kronig relation, the maximum refractive index change was estimated to be 2.7X10^<-5>. Isochronal annealing measurements showed the 3.8eV band is almost stable up to 1000C, while the 6.2eV band up to 3000ﾟC.These results suggest that the cerium-doped AFG have a potential for Bragg grating media.