Flat silicon gradient index lens with 3-layer anti-reflection structures for millimeter and submillimeter wavelengths

Kavli Affiliate: Sunil Golwala

| First 5 Authors: Fabien Defrance, Cecile Jung-Kubiak, John Gill, Sofia Rahiminejad, Ted Macioce

| Summary:

We present the design, fabrication, and test of a 100 mm diameter flat
gradient-index (GRIN) lens fabricated with high-resistivity silicon and
combined with three-layer anti-reflection (AR) structures optimized for 160 –
355 GHz. The anti-reflection layers and gradient index are created by cutting
sub-wavelength structures inside silicon wafers using multi-depth deep
reactive-ion etching (DRIE). The subwavelength structures, post or holes,
locally change the effective refractive index of silicon. The gradient index is
obtained with hexagonal holes whose size vary along the lens radius, creating a
parabolic index profile with an index of 3.15 in the middle of the lens, and
1.87 at the edge. We have fabricated a lens composed of five 525 um thick
stacked GRIN wafers with one AR wafer on each side, and characterized it at 275
GHz.

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