Optical Alignment Grating
The optical alignment gratings were designed mainly for testing purposes,
but can used to passively align optical components, substrate, or packaging
to a MEMS chip such as this one. The one on HC2 includes a flat metal
surface 1mm in diameter to match our expected laser beam size. And on
each side of this surface is a grating of unique frequency, to aid us in
both beam size and alignment. On HC1 it can be seen only as a long
rectangular area in the center of the chip.
This reconfigurable diffraction array is composed of piston-like elements
that are vertically actuated via electrostatic forces. Each piston has
two possible states: up (natural), and down (activated). Together, this
array of 6400 67um by 67um elements approximates a binary reflective-mode
holographic optical element (HOE). Because of the limited number of
layers in this process, there are a few shortcomings in the design:
Other diffraction arrays that we have designed contain elements that also float freely or rock back and forth. A couple of the arrays contain some bistability, and element sizes ranging from 20um to 80um.
This re-alignable mirror array consists of 315 72um by 90um reflective
elements that can be pushed vertically, out of the chip surface plane.
These elements are pushed out via electrostatically actuated
attached to columns of these elements. Consequently, a fine pitch adjustment
should be available at high reflection angles to the chip surface normal.