Electrostatic deflection in conformable mirrors

-October 11, 2017

Recently, Apex Microtechnology introduced a power amplifier IC with a high voltage operation of 220V and a continuous output current capability of 1A. The PA164 device has a monolithic MOS technology for the amplifier core and a separate output power stage.

One key thought came to mind for neat applications for such a component: conformable mirrors for such systems as NASA’s CubeSat/small satellite program, telescopes, confocal microscopes, and other adaptive optics conformable membrane mirrors. I will touch upon all of these applications in this article and then discuss adaptive optics using feedforward control of the deformable membrane mirror.

Deflecting a deformable/conformable mirror

Apex has a nice circuit for electrostatic deflection for their power amp (Figure 1).

Figure 1
An electrostatic deflection circuit (Image courtesy of Apex Microsystems)

The CubeSat deformable mirror1

A coronagraphic space telescope needs wavefront control systems to get high-contrast imaging for such applications as direct imaging of exoplanets. These kinds of adaptive optics are necessary for future mission plans in space observation and communication, as the mirrors improve distortions and reduce bit error rates for low-power space-based laser communications. High actuator count, microelectromechanical systems (MEMS) deformable mirrors (DM) will be the crucial components in such an adaptive system.

The CubeSat deformable mirror (DeMi) demonstration is to characterize the performance of a small deformable mirror over a year in low-Earth orbit. The satellite testbed platform is a 3U CubeSat bus, 150×95×25 mm allocated for the mirror driver electronics and 150×95×70 mm for the optical system (Figure 2).

Figure 2
MIT’s 3U DeMi CubeSat frame and optical payload architecture (Image courtesy of Reference 1)

The system architecture accommodates two sources of light: an internal fiber-coupled laser and an external source (bright star or extended object). A beamsplitter will transmit 92% of the incident light to the focal plane sensor and then reflect 8% back to be sent on to the Shack-Hartmann sensor.

Boston Micromachines Mini-DM deformable mirror

The Boston Micromachines Mini-DM deformable mirror surface is controlled by up to 32 electrostatic actuators, individually commanded, to give a desired shape (Figure 3).

Figure 3
The deformable mirror by Boston Micromachines (Image courtesy of Boston Micromachines)

The Shack-Hartmann sensor

The Shack-Hartmann sensor architecture is composed of a lenslet array and a camera. Wavefronts enter the lenslet array, and a spotfield is created on the camera; each spot is analyzed for intensity and location. Using this method, these sensors dynamically measure the wavefronts of laser sources or characterize the wavefront distortion caused by optical components (Figure 4).

Figure 4
A microlens array shown focusing a distorted wavefront in a Shack-Hartmann sensor (Image courtesy of ThorLabs)

The APEX PA164 greatly reduces weight, size, and cost for the control system power driver portion of this architecture.

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