Large-stroke deformable MEMS mirror for focus control

Abstract

We developed a novel large-stroke deformable mirror for focus control and spherical aberration correction. The mirrors fabricated using MEMS technology provide full range (150-200 microns in tissue) of focus scanning at high numerical aperture (N.A.=0.5-0.7) for confocal microscopy and optical coherence tomography (OCT). In addition to large stroke, low power consumption and high speed operation are other key factors of the developed devices. The impact of this project is broad since the miniaturized deformable mirrors have a wide range of applications. In addition to focus scanning in microscopes they can also be used in small form factor systems such as cell phone cameras and robot vision. Furthermore, laser based microscopes equipped with the focus control mirror may be useful for skin cancer diagnosis and treatment. This thesis consists of seven chapters. The first chapter introduces optical focus control and focus control elements. The second chapter describes different schemes for optical focus control in imaging systems including transmissive variable lenses. The principle of operation, fabrication, and characterization of electrostatic deformable mirrors are reviewed in Chapter 3. High-speed focus control mirrors with controlled air damping are discussed in Chapter 4. In this chapter a model adopted from the analysis of MEMS microphone is used to design the backplate of a MEMS deformable mirror. Moreover, electrostatic-pneumatic MEMS deformable mirrors are introduced in Chapter 5. Analytical model is developed for electrostatic-pneumatic actuation in order to design a MEMS mirror with two membranes. Applications of MEMS deformable mirrors are demonstrated in optical systems in Chapter 6. Finally, a summary and future work are discussed in Chapter 7. The fabrication process details are given in Appendix A.