Fig. 1. Process flow for the realization of the blazed-binary gratings.

Fig. 2. Silicon master (4″) (a) and manufactured PDMS mold (b) fixed on a thin glass plate (c) used for the NIL grating manufacturing.

Fig. 3. Manufactured gratings on 4″ wafer by e-beam lithography (a) and on 3″ wafer by NIL (b). (c) SEM top view of few subwavelength structures of the NIL grating.

Fig. 4. Spatial mapping of the diffraction efficiency in −1st order of the prototype flat grating for three different wavelengths, i.e. 376 nm (a), 600 nm (b) and 1000 nm (c).

Fig. 5. Measured −1st order diffraction efficiency of blazed-binary subwavelength gratings.

Fig. 6. Polarization sensitivity of the blazed-binary subwavelength gratings.

Fig. 7. Angular scanning of the efficiency in the diffractive plane at 633 nm for the NIL blazed-binary grating.

Fig. 8. Reflected wavefront introduced by the grating fabrication process (excluding substrate deformation) for e-beam grating (a) and for NIL grating (b).

Fig. 9. Two identified routes for blazed-binary subwavelength grating fabrication on spherical substrate. (a) Thinning and bonding of a flat grating on a spherical substrate. (b) NIL on spherical substrate.

Fig. 10. Preliminary NIL replication tests on concave (R = 540 mm) substrate. (a) Picture of the 3″ resist patterned area. (b) Scanning electron microscope photograph of the grating pattern (in resist layer).

Fig. 11. Location of the measurements zones, within the substrate.

Fig. 12. Measured width dispersion of the replicated patterns on different zones of the 3″ concave substrate. Horizontal axis corresponds to the number of the patterns. Each series of points corresponds to the zones of Figure 11.