Femtosecond laser written embedded diffractive optical elements and their applications

Femtosecond laser direct writing (FLDW) has been widely employed to create volumetric structures in transparent materials that are applicable as various photonic devices such as active and passive waveguides, couplers, gratings, and diffractive optical elements (DOEs). The advantages of fabrication of volumetric DOEs using FLDW include not only the ability to produce embedded 3D structures but also a simple fabrication scheme, ease of customization, and a clean process. DOE fabrication techniques using FLDW are presented as well as the characterization of laserwritten DOEs by various methods such as diffraction efficiency measurement. Fresnel zone plates were fabricated in oxide glasses using various femtosecond laser systems in high and low repetition rate regimes. The diffraction efficiency as functions of fabrication parameters was measured to investigate the dependence on the different fabrication parameters such as repetition rate and laser dose. Furthermore, several integration schemes of DOE with other photonic structures are demonstrated for compact photonic device fabrication.