Wide band UV/Vis/NIR blazed-binary reflective gratings for spectro-imagers: two lithographic technologies investigation
We report on subwavelength reflective gratings for hyperspectral applications operating in a very large spectral band (340-1040 nm). Our study concerns a blazed-binary grating having a period of 30 μm and composed of 2D subwavelength structures with size from 120 nm to 350 nm. We demonstrate the manufacturing of the gratings on 3" wafers by two lithography technologies (e-beam and nanoimprint) followed by classical dry etching process. Optical measurements show that the subwavelength grating approach enables a broadband efficiency, polarization behaviour and wavefront quality improvement with respect to the requirements for the next generation of spectro-imagers for Earth observation missions. An outlook towards spherical substrate based on nanoimprint lithography is also reported with the results of mixed features replication (holes and pillars in the range of 160-330 nm) on a 540 mm concave substrate which demonstrate uniformity and accuracy capabilities over 3" surface.