Search

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.

We report on subwavelength reflective gratings for hyperspectral applications operating in the 340 nm-1040 nm spectral range. The blazed grating period is 30 μm and is composed of 2D subwavelength binary structures with sizes in-between 120 nm and 350 nm. We demonstrate the manufacturing of gratings on 3” wafers by two lithography technologies (e-beam or nanoimprint) followed by dry etching process. These subwavelength gratings enable broadband efficiency which is in average 15%-20% above the efficiency requirement for next generation of spectro-imagers for Earth observation missions and a wavefront error that is much smaller than the 100 nm requirement for space application.

We present a study of volume index gratings operating in the form-birefringence regime and what we call the intermediate regime, defined as the regime between form birefringence and the onset of diffraction. The operating regime is characterized by the ratio between the measurement wavelength and the grating period: form birefringence regime below 10, diffraction around 3, and intermediate regime between 10 and 3. The behavior of the gratings in a given regime is studied by plotting the induced retardation as a function of the incidence angle. The shape of the curve fully characterizes the regime. We report on theoretical calculations of retardation by use of a rigorous theory and its experimental validation by measuring retardation of recorded gratings in photopolymers. OCIS codes: 050.7330, 090.7330, 160.1190, 160.3710, 230.3720.