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MEMS Lens Scanners for Free-Space Optical Interconnects


Optical interconnects are the next evolutionary step for computer server systems, replacing traditional copper interconnects to increase communication bandwidth and reduce overall power consumption. A variety of implementation techniques to bring optics to the rack-to-rack, board-to-board, and chip-to-chip scale are heavily pursued in the research space. In this dissertation we present a micro-electro mechanical systems (MEMS) based free-space optical link for board-to-board interconnects.

As with any free-space optical system, alignment is critical for the correction of undesired vibrations or offsets. Thus our optical system implements a variety of MEMS based lens scanners and opto-electronic feedback loops to maintain constant alignment despite both high frequency and low frequency misalignments. The full implementation of all of the MEMS devices is discussed, including the design, simulation, fabrication, characterization, and the demonstration of the full optical link.

The first device discussed is an electrostatic lens scanner with an optoelectronic feedback loop capable of tracking high frequency mechanical vibrations expected in computer server systems. The second system discussed is an electrothermal lens scanner with mechanical brakes for long term, large displacement, and zero power off-state tracking. Both linear and rotational actuators are presented to correct for the major causes of misalignment measured in board-to-board systems. A finite state machine based controller is demonstrated to act as the feedback loop required to maintain alignment. A fully integrated packaging system is proposed for the correction of all misalignment degrees of freedom. Finally, an alternative application of MEMS lens scanners for light detection and ranging (LIDAR) for 3D imaging is explored, tested, and simulated.

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