Principle, design and fabrication of a passive binary micro-mirror array (BMMA) for speckle reduction in grating light valve (GLV) based laser projection displays

摘要

A binary micro-mirror array (BMMA) is proposed for speckle reduction in grating light valve based laser projectors. The mirrors are driven by the electrostatic force, and have two states, i.e., '1' state (or 'static/off'state) corresponding to motionless mirrors or mirrors that are released to their zero-bias voltage position and '-1' state (or 'on' state) in accordance to the fully deflected mirrors. The phase modulation depth between the two working states of the mirror is π radian. The control electronics of the BMMA is designed by a passive driving scheme derived from a hadamard matrix or a two-level orthogonal array, thus we can avoid using the memory transistors, and number of the control electrodes could be significantly reduced. Performances of the mirrors are analyzed by the analytical model. A proof-of-concept 32 μm pitch BMMA fabricated using aluminum as the mechanical layer is presented, and the proper function of the BMMA is demonstrated with speckle reduction. About 5% speckle contrast ratio can be achieved after compounding the BMMA and a laser diode array.