Laser Induced Defects for 3D Fluorescence Imaging of Optical Structures

Post-fabrication characterisation of optical device structure and geometry is essential for prototyping or verification of devices. We demonstrate a method to 3D-image optical structures in optical fibre or bulk/chip devices, by using femtosecond laser pulses to induce material defects functioning as fluorophores for confocal fluorescence imaging. The method is also useful for alignment, where complex geometries might complicate microscope imaging. The induced defects, density, and photoluminescence properties density depend on the glass and local dopant concentrations. Certain defects fluoresce when suitably pumped - here, we exploit silica nonbridging oxygen hole centre defects, which emit $\sim 600-750\ \text{nm}$ photoluminescence [1]. Mapping the fluorescence power $P_{f}(x,y,z)$ thus allows spatial resolution of different material regions. Cross section slices can be imaged quickly and transversely, without needing to cut the sample.