A large-size and polarization-independent two dimensional grating fabricated by scanned reactive-ion-beam etching

Scanned reactive-ion-beam etching method was proposed to transfer two-dimensional mask patterns into quartz substrate, which would produce a larger-size and polarization-independent two-dimensional grating. This method was realized by moving grating substrate in a unidimensional scanning manner and adjusting ion beam density in the vertical scanning direction. Graphite plates between the ion beam source and the substrate were used to correct the beam density. The original Gaussian ion beam density was changed to a uniform distribution to establish a knife-edge shape around the vertical scanning direction. Therefore, a large-area pattern with consistent depth and duty cycle would be engraved into a quartz substrate. A two-dimensional, 1200 groves/mm grating with an 85-mm × 85-mm area was fabricated under scanned reactive-ion-beam etching method and exhibited a 0.197λ (λ = 632.8 nm) diffraction wave front. At 780 nm, the efficiency nonuniformity was less than 9%, and the average diffraction efficiencies of transverse-magnetic and transverse-electric polarized light were 57.2 and 58.0%, respectively. The large-size two-dimensional grating with uniform diffraction efficiency and polarization independence enabled grating displacement measurement with high resolution, long measurement range, multiple degrees of freedom, and potential miniaturization.