Development of Tunable Optical MEMS for Advanced Laser Beam Shaping, Homogenizing and Speckle Reduction

In this thesis, the development, design, fabrication and characterization of three innovative laser beam shaping, homogenizing and speckle reduction devices are reported. Typical beam shaping devices are static and not easily adaptable to a large variety of optical setups. Furthermore, the main issues when shaping coherent light are diffraction effects, speckle patterns, interferences and wavelength dependency. The devices presented in this work solve these issues. The main subjects discussed are beam shaping of coherent light and speckle reduction. Beam shaping and speckle reduction are important in many applications like laser machining, illumination, laser displays and photolithography. The first device presented is a dynamic diffuser and homogenizer for line generation. The 1D linear diffuser consists of a large single crystal silicon membrane of 5x5, 10x10 or 15x15 mm2 areas and having a thickness of 5 μm to 10 μm. This optical surface has a 100 % fill factor. The goal is to deform the membrane in one dimension only so that the light is also diffused in one dimension. The free standing continuous silicon membrane has a bridge type configuration. The actuation of the device is made electromagnetically at resonance by the use of the Lorentz force. Stiffening beams are fabricated below the membrane to decouple the 1D and 2D modes and to prevents 2D dynamic deformations. The device is fabricated on SOI wafer using standard microfabrication technologies. The devices are characterized using a laser doppler vibrometer (LDV) and a goniometer. The LDV measurements have shown that 1D and 2D modes can be excited separately. The diffusion angle is tunable between 0 to 22 mrad. The device is used to smooth out the interference effects created by a static 1D beam shaping optical element. The relative optical power efficiency of is 99.8 %. The device is capable to sustain high optical load of at least 140 W/cm2. It is now being tested in an industrial environment with high power CO2 laser for sealing glass capillaries. The second device presented is a 2D dynamic diffuser. It has to fulfill several characteristics, namely to diffuse light with small and tunable angle with high efficiency, reduce the speckle contrast and interference patterns, have a simple driving and packaging scheme and handle high optical power. A device with a 5x5 mm2 optical surface is designed, fabricated and characterized. The mirror is made of a thin and large deformable a-Si membrane which is supported by an array of posts. The disposition of the posts determines how the membrane is deformed in smaller sub-reflecting elements. A periodic and a pseudo random arrangements of the post arrays are designed. Electrostatic actuation is used to deform the membrane. The whole v deformable mirror is fabricated over a scanning stage. Out of plane resonant comb drive actuators are used to actuate the scanning stage. The diffusion of the light is performed by the deformation of the membrane whi