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Chapter 7:
Optical Scanning
An optical scanner directs a beam of light in different directions and senses the reflected beam to communicate what the beam is “seeing.” The scanning system consists of a light source, articulated mirror, beamsplitter, and detector. The mirror redirects the light beam, and the beamsplitter and detector interrogate the returned signal. In most scanning systems, the light source is a commercial laser diode packaged with a circular polarizer and a collimator lens. Optical scanning systems, which generate a scanning beam of light and detect the beam’s reflection off of a target, are important components in many advanced optical systems. Present optical scanners are generally based on oscillatory or galvanometric systems. These mechanisms are usually designed using bulk optical components, and as a result they are heavy, expensive, and unreliable. The need for low-cost, highly reliable, miniaturized, lightweight optical scanners for both commercial and military applications has been growing during the past decade. Recent advances in development of micro-opto-electro-mechanical (MOEM) systems have led to the growth of a new family of miniaturized devices, including the MOEM scanner, with enormous potential. The MOEM scanner has many applications, including such diverse fields as laser imaging, factory automation, information handling, printing, graphic arts, image digitizing, quality inspection, barcode reading, data storage, precision pattern generation, display, surveillance, and medical imaging. The issues to be considered are scanning angle, driving voltage, optical and electrical signal processing, structural stability, process compatibility, device size, and mirror flatness. Most of these issues are already optimized, and the overall system performance is acceptable for manufacture. Major issues remaining to be solved are packaging and process compatibility with standard CMOS. In the case that the scanner device is manufactured separately and is hybridized to CMOS electronics, the issue of process compatibility still exists, but it is not so critical. This chapter covers various aspects of micromachined optical scanners; operation principles, structural design, microactuators, testing issues, and application examples.
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