Scanning near-field transmission and confocal micro-spectroscopy characterization of direct laser written rare-earth doped lithium niobate three-dimensional photonic crystals

Abstract

Reports on the optical micro-characterization of direct laser written rare-earth doped lithium niobate threedimensional photonic crystals. The femtosecond laser microstructural changes inside lithium niobate are first studied by a combination of confocal micro-Raman, rare-earth micro-luminescence and scanning near-field back-scattering microscopy, revealing a complex three-dimensional topology consisting of amorpohus (low index), unmodified (matrix index), and compressed (high index) lithium niobate. Further scanning near-field transmission images reveal specific features such as optical channeling which are not observed in far-field optical microscopy, and are theoretically interpreted in terms of the previous observed three-dimensional topologies