Randy Sprague

Two-axis electromagnetic microscanner for high resolution displays

A novel microelectromechanical systems (MEMS) actuation technique is developed for retinal scanning display and imaging applications allowing effective drive of a two-axes scanning mirror to wide angles at high frequency. Modeling of the device in mechanical and electrical domains, as well as the experimental characterization is described. Full optical scan angles of 65deg and 53deg are achieved for slow (60 Hz sawtooth) and fast (21.3 kHz sinusoid) scan directions, respectively. In combination with a mirror size of 1.5 mm, a resulting thetasopt D product of 79.5 degmiddotmm for fast axis is obtained. This two-dimensional (2-D) magnetic 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 large enough to support SXGA (1280 times 1024) resolution scanned beam displays

High-performance silicon scanning mirror for laser printing

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 record-setting 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.

Bi-axial magnetic drive for scanned beam display mirrors

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.

FR4 Laser Scanner With Dynamic Focus

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 50deg is achieved. The dynamic focus control allows for shifting the beam waist location from 80 mm up to 650 mm.

Two-axis MEMS scanner for display and imaging applications

Two-axis gimbaled scanner used in an SVGA display product with 58deg optical scan angle, 1.5 mm mirror size, and 21 KHz resonant frequency is reported. Scanner is actuated electromagnetically using a single coil on the outer frame and by mechanical coupling of outer frame motion into the inner mirror frame

Biaxial MEMS raster scanner with linear ramp drive

A biaxial MEMS raster scanner is developed for laser scanning displays. We discuss microfabrication, packaging, and design aspects, and how to minimize power consumption and linearity error by optimizing the vertical scanner resonant frequency and drive waveform.

Advanced imaging with dynamic focus and extended depth using integrated FR4 platform

A two-degrees-of-freedom scanned beam imaging system with large dynamic range and dynamic focusing is demonstrated. The laser diode, photo-detector and the optical components are integrated on a moving platform that is made of FR4 (Flame-Retardant 4), a common polymeric substrate used in printed circuit boards. A scan angle of 52 degrees is demonstrated at 60 Hz resonant frequency while the laser is moved 250 um in the out-of-plane direction to achieve dynamic focusing. The laser is scanned by physically rotating the laser diode and the collection optics to achieve high signal-to-noise ratio and good ambient light rejection. The collection optics is engineered such that the collection efficiency decreases when collecting light from close distances to avoid detector saturation. The detection range is extended from contact distance up to 600 mm while the collected power level varies only by a factor of 30 within this long range. Slight modifications will allow increasing the detection range up to one meter. This is the first demonstration of a laser scan engine with such a high degree of integration of electronics, optoelectronics, optics and micromechanics on the same platform.

Self-oscillating FR4 laser scanner with integrated dynamic focus and extended imaging range

A self-oscillating scanned beam imaging device is presented, with variable focusing mechanism and extended imaging range. The focusing and imaging optics, as well as the die level laser diode and photodiode are integrated on the same platform, and scanned synchronously to extend the imaging range of the system. More than 600mm imaging range is achieved with 52° total optical scan angle. An integrated back-emf coil both enables the self-starting of the oscillations of the scanner, and also provides the velocity feedback for running the system in closed-loop. A special circuit is implemented to decrease the time to reach 80% of the full amplitude self-oscillations from 970ms down to 60ms.