WARF: P07304US
Silicon Membrane-Based Deformable Mirror for Optical Imaging Applications

INVENTORS

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Max Lagally, Kevin Turner

To study biological tissue, it is often necessary to view various layers of the tissue at different depths. Microscopes have numerous deformable mirror configurations that enable them to manipulate and reflect the light source so that the tissue is illuminated and focused properly at the desired tissue depth. The mirrors focus on the tissue layer by compensating for distortions that occur when light penetrates through the overlaying tissue. The sharpness developed from the focusing ultimately determines the image resolution of a microscope.

The focusing mechanism of current microscope technology uses piezoelectric actuators to alter the mirror shape. However, these actuators have limited uses since they are large, not scalable, difficult to manufacture and expensive. In addition, image quality suffers when attempting to image thick tissue. because current focusing mechanisms are unable to encompass many distinct points of distortion.

In comparison to other actuation phenomena, electrostatic actuation is a developing technology that offers lower power consumption, a smaller size, higher switching speed, and ease of integration with control electronics. This more cost-effective alternative offers a higher level of deformation control for the reflective surface, while still maintaining high image resolutions at various tissue depths. UW-Madison researchers have developed an adaptive-optics system that uses a controllable, electrostatically-actuated silicon membrane for manipulating the shape of the focusing mechanism. The device is composed of a thin silicon membrane, 10 nm to 10 μm thick, positioned above an array of electrodes.

This new device overcomes the problems associated with traditional approaches in that it is continuous, scalable and, most importantly, can be readily manufactured using known methods.

An electrostatic force between the electrode and membrane is generated by applying different voltage levels to each electrode in the array. This electrostatic warping force precisely deforms the back of the membrane and makes the single silicon membrane layer act as both the reflective surface and the actuator.

The membrane is a single part of the device that results in an inherent attraction to the individual electrodes in the array. An advanced control algorithm makes it possible to control the speed and range of conformational shapes. The current device geometry allows capacitive sensing of the surface profile to be integrated, thus enabling a feedback loop in this control algorithm.

The electrode size and spacing, in conjunction with the membrane thickness and support structure, determine the degree of shape control over the deformable membrane. Depending on the specific application and performance requirements, the electrode array and the membrane support structure can be easily modified when higher resolutions are needed.

• The world market for optoelectronics had revenues of $350M in 2006 and is forecast to grow rapidly and hit over $1B by 2010. 
• More specifically this technology could be used in confocal microscopes. 
• In 2005 total revenues were $93M worldwide and forecast to reach $157M by 2010. 
• The United States is the largest market, followed by Europe and then Japan.

• Multi-Photon Laser Scanning Microscopy (MPLSM) and other microscope imaging applications.

• Simple structure of a single-crystal silicon layer offers low power, fast response, high compliance, low distortion and good reflectivity.
• May have a thickness less than two µm
• Compatible with integrated circuit processing techniques
• Membrane and frame have matched coefficient of thermal expansion, so the device works over a range of operating temperatures.
• Improves resolution in adaptive optics systems
• Easily manufactured with existing methods, including common photolithography techniques
• Stress-free membrane helps achieve better flatness.
• Controlled by an advanced algorithm
• Also may also used in astronomical optics to compensate for atmospheric distortion

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