Fast structured light engine for 3D image capture based on high-frequency MEMS scanning mirror

We report a compact structured light projector based on a single-axis MEMS torsion mirror with a nominal resonant frequency of 25 kHz and a mechanical scanning range of up to +/-7.5 degrees. The 2.1 mm x 1.0 mm mirror is fabricated using a silicon-on-ceramic process where structures are defined in a 250 micron-thick silicon layer and then bonded to a ceramic substrate with a thermally cured epoxy. Links that held the structure together during fabrication are then lasercut to release the moving element. The mirror is operated under vacuum to ensure high mechanical quality factor and avoid issues with breakdown at high drive voltages. A prototype has been demonstrated that can illuminate a squarebase-pyramidal field subtending angles of up to 21 degrees in X and Y. A Powell lens placed before the mirror is used to fan out the collimated beam from a 637 nm-wavelength, fiber-pigtailed laser diode. FPGA-based control electronics have been developed that can modulate the laser diode at up to 51.2 MHz so as to generate binary fringe patterns with up to 326 fringes. The hardware compensates for the sinusoidal nature of the MEMS mirror trajectory as well as the tangent distortion so as to generate uniformly spaced fringes on a plane. It is expected that the system will find applications in 3D image capture requiring high frame rate, for example production line inspection systems.