Microscanner

Abstract: We present a novel resonantly excited 2D-micro-scanning-mirror which makes use of an electrostatic driving principle. To achieve large deflection angles, the driving electrodes are located in the chip plane. With that, small electrode gaps can be used without restricting the deflection angle geometrically. The mirror plate, with an area up to 1.5 mm×1.5 mm, is suspended by a gimbal mounting and can, therefore, be deflected along two axes. The base material for the fabrication of the device is a SOI-wafer with a top layer thickness of 30 μm. A special isolation technique which is based on open and filled isolation trenches is suitable to seperate the electrical potentials on the fixed and movable parts. In particular, the filled trenches allow to excite the two oscillations independently. The influence of the surrounding gas on the coupling of the oscillations is examined. No significant influence is observed. The investigations of the mechanical performance show that the devices have a shock resistivity of about 3.4×10 3 × g . Results of long run tests with a duration of 7×10 9 periods at a torsional angel of ±10° show that the change of the eigenfrequency is smaller than 0.01%. The performance of the novel 2D-micro-scanning-mirror is demonstrated by the generation of various Lissajous patterns by the reflected laser beam. Frequency ratios of 1:1 up to 13:1 are obtained with the presented devices.

Abstract: The dynamics of the out-of-plane comb-drive actuator used in a torsional resonant mode microscanner is discussed. The microscanner is fabricated using the standard SOI technology by Fraunhofer, IPMS and utilized in various display, barcode scanning, spectroscopy and other imaging applications. The device is a parametrically excited system and exhibits hysteretic frequency response, nonlinear transient response, subharmonic oscillations, multiple parametric resonances, and alternating-oscillation-frequency behavior. Analytical and numerical models are developed to predict the parametric system dynamics. The analytical model is based on the solution of the linear Mathieu equation and valid for small angular displacements. The numerical model is valid for both small and large deflection angles. The analytical and numerical models are validated with the experimental results under various ambient pressures and excitation schemes and successfully predict the dynamics of the parametric nature of the microscanner. As many as four parametric resonances are observed at 30 mTorr. The models developed in this paper can be used to optimize the structure and the actuator.

Abstract: A comb-actuated torsional microscanner is developed for high-resolution laser-scanning display systems. Typical torsional comb-drive scanners have fingers placed around the perimeter of the scanning mirror. In contrast, the structure in this paper uses cascaded frames, where the comb fingers are placed on an outer drive frame, and the motion is transferred to the inner mirror frame with a mechanical gain. The structure works only in resonant mode without requiring any offset in the comb fingers, keeping the silicon-on-insulator-based process quite simple. The design intent is to improve actuator efficiency by removing the high-drag fingers from the high-velocity scanning mirror. Placing them on the lower velocity drive frame reduces their contribution to the damping torque. Furthermore, placement on the drive frame allows an increase of the number of fingers and their capacity to impart torque. The microscanner exhibits a parametric response, and as such, the maximum deflection is found when actuated at twice its natural frequency. Analytical formulas are given for the coupled-mode equations and frame deflections. A simple formula is derived for the mechanical-gain factor. For a 1-mm × 1.5-mm oblong scanning mirror, a 76° total optical scan angle is achieved at 21.8 kHz with 196-V peak-to-peak excitation voltages.

Abstract: Minimally invasive medical procedures will benefit from flexible endoscopes that are extremely thin yet produce high quality images Current devices use fiber bundles or silicon image sensors placed in the distal tip where each pixel in the image is derived from an element in the distal tip, such that improving resolution requires increasing distal tip diameter The University of Washington has developed the scanning fiber endoscope (SFE) to provide full color, high resolution images from a flexible endoscope with a small distal tip diameter The SFE uses a single mode fiber vibrating in resonance to scan a focused laser spot over the tissue and a detector to record the time-multiplexed backscatter signal The SFE contains a 400 micron diameter piezoelectric tube through which a length of singlemode optical fiber is placed The tube drives the fiber tip at its resonant frequency (currently 5 KHz) in an expanding pattern of 250 spirals (500 pixel diameter image) at a frame rate of 15 Hertz Imaging parameters are determined by the lens system placed in the 106 mm diameter distal tip Prototype systems with 70 degree field-of-view and 10 micron resolution have been developed Color images are created with red, green, and blue laser sources coupled into the single scanning fiber Backscattered light is collected with twelve 250 micron multimode fibers placed around the periphery of the microscanner resulting in a total distal tip diameter of 16 mm Frame sequential color, fluorescence, and continuous color imaging modes have been demonstrated in the non-confocal geometry