Design, laser direct writing prototyping, and characterization of fan-out diffractive optical elements for optical interconnect applications

We present the design, fabrication, and characterization cycle of a diffractive optical element based layout, used for 1-to-7 power splitting of a Gaussian beam emitted by a single-mode fiber. First, a modified version of our earlier demonstrated mode conversion up-taper structure is designed, fabricated, and characterized, increasing the mode-field diameter of the fundamental mode by a factor of 2. Then, a newly designed diffractive optical element is optimized to convert the expanded field distribution to a seven Gaussian-spot hexagonal array with 45 mu m spacing, at an optimal propagation distance of only 61 mu m, achieving splitting in a non-paraxial diffraction regime. The two components are combined into a monolithic design encompassing both adiabatic field expansion and efficient phase modulation in a single, highly miniaturized component. The power splitter is fabricated directly on the cleaved facet of a single-mode fiber, in a single step, using direct laser writing based on two-photon polymerization. The small spatial extent of the power splitter allows for a highly compact, integrated solution for wide-angle, fan-out power splitting of a Gaussian beam in single-mode interconnect and sensing applications.