Multiple beam splitter using volumetric multiplexed Fresnel zone plates fabricated by ultrafast laser-writing.

A simple approach to producing a 1×N beam splitter is demonstrated by fabricating a volumetric multiplex phase Fresnel zone plate in bulk transparent material. This comprised four layers of zone plates created in borosilicate glass by femtosecond laser direct-writing, each shifted laterally relative to the illumination axis, creating four separate beamlets. Since the power transmitted in each beamlet is proportional to the diffraction efficiency of the corresponding zone plate, the power ratios can be customized by adjusting the fabrication parameters of each layer. This approach demonstrates the potential of femtosecond laser direct-writing for the fabrication of complex optical elements in transparent media as components of integrated monolithic photonic devices.