Two-Dimensional Bragg Reflectors Fabricated in IOG1 Phosphate Glass using Multi-beam UV-laser Interference

摘要

The two-dimensional periodic patterning of a high performance, rare-earth doped phosphate glass is presented here. A two step patterning method is adopted, wherein high damage is induced into the glass volume by exposure to intense ultraviolet pulsed, laser radiation and subsequently, a chemical development in a strong alkali, selectively etches the exposed areas. A four beam interferometric setup is used for defining the two-dimensional periodic pattern on the sample surface. The method presented here produces relief structures of high smoothness, free of debris or defects, and without extensive optical damage, compared to other approaches. The Bragg gratings imprinted here, are tuned for reflection operation in the 1.5 μm band, having periodicities of the order of 500nm. The glass patterned is the phosphate glass IOG1, fabricated by Schott USA and codoped with Er and Yb. The exposures were performed by using the output of a high coherence 213nm, 150ps Nd:YAG laser; while the chemical developing was carried out in aqueous KOH solution. The inscribed periodic structures are characterized by means of diffraction efficiency, and surface topology by employing SEM and AFM scans. Issues related with the interferometric and wet etching processes are also presented and discussed.