A novel MEMS actuation technique has been developed for scanned beam display and imaging applications that allows driving a two-axes scanning mirror to wide angles at high frequency. This actuation technique delivers sufficient torque to allow non-resonant operation as low as DC in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies great enough to support SXGA resolutions. Several display and imaging products have been developed employing this new MEMS actuation technique.Exceptionally good displays can be made by scanning laser beams much the same way a CRT scans electron beams. The display applications can be as diverse as an automotive head up display, where the laser beams are scanned onto the inside of the car's windshield to be reflected into the driver's eyes, and a head-worn display where the light beams are scanned directly over the viewer's vision.For high performance displays the design challenges for a MEMS scanner are great. The scanner represents the system's limiting aperture so it must be of sufficient size; it must remain flat to fractions of a wavelength so as to not distort the beam's wave front; it must scan fast enough to handle the many millions of pixels written every second; and it must scan in two axes over significant angles in order to "paint" a wide angle, two-dimensional image. Using the new actuation method described, several MEMS scanner designs have been fabricated which meet the requirements of a variety of display and imaging applications.
This paper describes the design, fabrication, and characterization of the first MEMS scanning mirror with performance matching the polygon mirrors currently used for high-speed consumer laser printing. It has reflector dimensions of 8mm X 0.75mm, and achieves 80º total optical scan angle at an oscillation frequency of 5kHz. This performance enables the placement of approximately 14,000 individually resolvable dots per line at a rate of 10,000 lines per second, a recordsetting speed and resolution combination for a MEMS scanner. The scanning mirror is formed in a simple microfabrication process by gold reflector deposition and patterning, and through-wafer deep reactive-ion etching. The scanner is actuated by off-the-shelf piezo-ceramic stacks mounted to the silicon structure in a steel package. Device characteristics predicted by a mathematical model are compared to measurements.
An electromagnetically actuated optical scanner made using standard printed circuit board technology with integrated dynamic focusing feature is presented. Dynamic focus is achieved with an independently controlled plunger machined on the flame retardant-4 (FR4) platform. Integration of a laser diode and lens, torsional scanner, and the plunger for dynamic focus adjustment on FR4 platform greatly improves the form factor of the device for imaging applications. A peak-to-peak mechanical scan angle of 50 is achieved. The dynamic focus control allows for shifting the beam waist location from 80 mm up to 650 mm.
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