ERL MEMS Optical Interconnect Elements

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.

Reconfigurable Grating

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:
  1. The size of the individual elements is larger than desired, to accommodate addressing lines
  2. The piston addressing capability is limited to strictly horizontal and vertical addressing lines; to address a piston, actuating voltage must be applied to both a horizontal and a vertical addressing line corresponding to its position in the array.
  3. Since we will not be creating complex HOE's with this test structure, there was no need to fully connect the array. Consequently, we have arranged the pads to actuate patterns of 8 by 8 pistons.

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.

Rotating Grating

These movable diffraction gratings on this chip are mounted to on horizontally rotating micromachines. These MEMS devices rotate the surface in 7deg, 11deg, or 30deg increments, as well as sub-degree increments (on a wobble-motor), to do one of the following:
  1. Rotate the orders of a diffraction pattern about the chip surface normal
  2. Horizontally move the focal point of a Fresnel approximation

Realignable Mirrors

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 comb-motors attached to columns of these elements. Consequently, a fine pitch adjustment should be available at high reflection angles to the chip surface normal.

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David Winick, Emmanuel Maitre, Mouna Nakkar, and Paul Franzon