  A metamaterial structure consisting of a one-dimensional metal/air-gap
subwavelength grating is investigated for optical antireflection coating on
germanium substrate in the infrared regime. For incident light polarized
perpendicularly to the grating lines, the metamaterial exhibits effective
dielectric property and Fabry-Perot like plasmon-coupled optical resonance
results in complete elimination of reflection and enhancement of transmission.
It is found that the subwavelength grating metamaterial antireflection
structure does not require a deep subwavelength grating period, which is
advantageous for device fabrication. Maximal transmittance of 93.4% with
complete elimination of reflection is seen in the mid-wave infrared range.
