Micro-deformable mirrors for adaptive optics applications

Adaptive optics systems are comprised of many optical elements.{09}The most critical is the deformable or "adaptive" element that will be used to correct the distorted wavefront. The requirements for this deformable element vary depending on the type of aberrations present in the optical system. The objective for this research is to create a large-stroke deformable micromirror array that can be used as the wavefront corrector in a vision science adaptive optics system.; To achieve the goal of creating a large-stroke deformable element, a number of fabrication technologies were developed and implemented on arrays of micro-deformable elements. The first array that was designed, fabricated and tested was for the DARPA funded Coherent Communications, Imaging and Targeting (CCIT) program. A flip-chip bonding technology was created to fulfill the requirements for this mirror array. The final array was fabricated using a parallel-plate electrostatic actuator and single-crystal silicon as the mirror material. To create a large-stroke device, a new actuator technology needed to be developed, as the forces produced with acceptable voltages with parallel-plate actuators were not great enough to deform our elements the required 10mum. So, a proven fabrication technology for large-force actuators was modified so that the required vertical displacement could be achieved. Self-aligned vertical comb drives were used to create a 4x4 array of actuators that displaced 1.4mum when 200V was applied. These actuators had been modeled both analytically and using commercially available multi-physics modeling software to move 10mum with 100V applied. The discrepancy in results was caused by fabrication variations that led to an increased stiffness in the springs and therefore led to the reduced displacement that was observed. Another set of large-stroke actuators was fabricated, taking into account the fabrication variations in the first iteration, and a layer of silicon was bonded to these actuators as the mirror layer. Two different bonding technologies were developed to bond these mirrors: (1) fusion bonding, and (2) photoresist bonding. The fabricated large-stroke actuators displaced 0.18mum with 200V applied, which was considerably less than the modeled 10mum displacement with 200V. Again, fabrication discrepancies led to the reduced displacement that was observed.