Analysis on Design and Fabrication of High-diffraction-efficiencyMultilayer Dielectric Gratings
2018
We report an in-depth analysis of the design and fabrication of
multilayer dielectric (MLD) diffraction gratings for spectral beam
combining at a wavelength of 1055 nm. The design involves a near-Littrow
grating and a modal analysis for high diffraction efficiency. A range of
wavelengths, grating periods, and angles of incidence were examined for
the near-Littrow grating, for the 0th and –1st
diffraction orders only. A modal method was then used to investigate the
effect of the duty cycle on the effective indices of the grating modes,
and the depth of the grating was determined for only the
–1st-order diffraction. The design parameters of the grating
and the matching layer thickness between grating and MLD reflector were
refined for high diffraction efficiency, using the finite-difference
time-domain (FDTD) method. A high reflector was deposited by electron-beam
evaporation, and a grating structure was fabricated by photolithography
and reactive-ion etching. The diffraction efficiency and laser-induced
damage threshold of the fabricated MLD diffraction gratings were measured,
and the diffraction efficiency was compared with the design’s
value.
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