Miniaturized vectorial beam steering mirrors are required in numerous applications like (i) LIDAR, (ii) diagnostic imaging or (iii) miniaturized therapeutic laser systems. In this article we present a new type of electrostatically driven vectorial (2D quasi-static) MEMS scanning mirror with monolithic integrated position sensors. The vectorial MEMS scanner was specially optimized for the requirements of a compact therapeutic photocoagulation laser system for the treatment of retinal eye diseases. This requires a highly miniaturized MEMS scanning system for fast and precise vectorial beam positioning of the treatment laser with a positioning time of ≤ 5 ms. The quasi-static 2D drive of the presented 2D MEMS scanning mirror is based on electrostatic vertical comb actuators in combination with a noncardanic suspension of the 2.2 mm circular mirror plate. To measure and control the actual beam position piezoresistive position sensors are monolithically integrated into the MEMS design. The MEMS scanner was designed for a quasistatic (mechanical) 2D tilt angle of ± 2 ° for both scan axes each in two frequency variants with 714 Hz and 1 kHz at 70 V and 130 V drive voltage, respectively. For high laser powers of > 1.5 W (average power) at 519 nm wavelength, highly reflective optical coatings based on a symmetric HRC design of enhanced (hybrid) Al with R ≥ 98 % are used.
Miniaturized vectorial beam steering mirrors are required in numerous applications like (i) LIDAR, (ii) diagnostic imaging or (iii) miniaturized therapeutic laser systems. To increase simultaneously static tilt angle (≥ ±5°) and mirror aperture (≥ 3mm) electro-dynamic driven MEMS vector scanners, actuated by moving magnet drives, were developed. Here, Fraunhofer IPMS uses a hybrid MEMS concept combining its experience in the fabrication of monolithic silicon 2D MEMS scanning mirrors with existing know-how in MEMS micro-assembly technologies. Two designs of electro-magnetic driven vectorial 2D MEMS scanners are presented, (i) a non-gimbaled 2D vector scanner with 8 mm mirror aperture and ≥ ±2° quasi-static tilt angle and (ii) a 2D vector scanner with gimble suspended moving magnet drive. The gimbaled electro-magnetic MEMS scanner has a 5 mm large aperture and enables large quasi-static tilt angles of ±13° on both scan axis. Eigenfrequencies are 142 Hz (X) and 124 Hz (Y) allowing non-resonant vectorial scanning with speeds up to 100…400°/s. A step response time < 10 ms is achieved in closed loop control for both axes. This hybrid electro-magnetic MEMS approach significantly expands the parameter space of the previous monolithic electro-static scanners.
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