Possible applications include those that require not only a large mirror size but also maintenance-free, extremely repeatable optical beam-steering capabilities. These include many long-range uses, e.g. free-space optical communications where MEMS devices can be used for fine-tuning the optical link between transmitter and receiver systems. The company’s bonded MEMS mirrors are micro-assemblies of a monolithically fabricated actuator ‘engine’ that is combined with a separately manufactured mirror available in various sizes. The A5L2.1 is a MEMS actuator with a 7.25 x 7.25 mm footprint and is designed not to achieve a large angular reach but to maximize torque to allow high speed beam-steering when combined with larger mirror sizes.
Offering high optical mirror quality
To assess the optical quality of the MEMS mirror products, the company’s engineers utilized a 3D optical surface metrology system and confirmed excellent surface roughness and mirror flatness. Traditionally, the company’s mirrors come with a guaranteed flatness that exceeds 5 meters radius of curvature (ROC), for any mirror size. This guarantees a high optical quality – an important feature for many applications in which beams need to be directed to predictable and repeatable angles while maintaining beam wave front quality. Based on polished, pure single-crystal silicon wafers, MEMS mirrors are fabricated by deposition of a low-stress metal coating with outstanding optical characteristics, including high purity and smoothness. These mirrors flatness deviation terms better than λ /20 for most applications.
High resolution beam steering with a high bandwidth
The first 6.4 mm and 7.5 mm diameter MEMS mirrors were recently assembled onto A5L2.1 actuators, and offered a true mechanical tip/tilt capability of ± 1° in both axes, so a total mechanical sweep of 2.0° on each axis which translates into an optical field of view (FoV) of ~4° x 4°. Frequency responses are very flat from DC (for quasistatic or point-to-point actuation) to near resonant frequency. Resonant frequency for 6.4 mm diameter design is in the 700–800 Hz range and for the 7.5 mm design is in the 500–550 Hz range, in both axes. These mirrors offer a 14-bit repeatability (precision) when driven with designated MEMS drivers, so 16384 discrete angular positions are repeatably addressable in point-to-point (P2P) mode between the negative and positive maximum angles in both axes.
“We are excited to offer these large mirrors tailored to customers who need to accommodate large beam sizes,” commented Dr. Milanovic, Founder and CEO. “These devices were designed to match specific customers’ application needs and we believe that they will meet the demand in FSO communications, LIDAR, and other application spaces that require both large mirrors as well as reliable, high-resolution optical beam-steering.”
