Unified Optical Scanning Technology

Chapter 6 - Summary - Major Scanner Characteristics

This work offers a consolidated presentation of the expanding technology of optical scanning. It expresses relationships between disciplines that are normally considered independently, for pedagogic and operational value. The reader may gain thereby insight to the foundations of the concepts, so that they may be interpreted and used more effectively.

The Introduction of Chapter 1 provides a combined view of active scanning (as by laser) and passive scanning (as for remote sensing). Very similar scanning devices are often used in the reciprocal ray paths of conjugate imaging. This is illustrated by two figures, and two additional figures show operation in both directions. This topic is followed by an introduction to the Lagrange invariant, its relationship to scanned resolution, and the formation of the resolution invariant. This important subject is expanded with a comprehensive coverage in Chapter 3. Chapter 1 closes with an orientation in system architecture, placing the discussion of components and systems into operational perspective. These architectural concepts are extended in several sections of Chapter 4.

The second chapter casts the foundation of the technology with a selection of the fundamentals of scanning theory. It presents some unifying analogies between optical and electrical processes that often bear different nomenclature. Factors are highlighted that govern the achievement of the desired image quality when recording or extracting its integrity when scanning. The range of subjects in these two chapters is supported with many original illustrations, rendered to solidify the concepts for later discussion and practical application.

Chapter 3, Scanned Resolution, address the remaining building block for successful component and system development, integrating several key items discussed earlier. The basic resolution equation is developed and rendered as a useful nomograph. It is then augmented to provide a more general relationship to account, for example, for a holographic disk scanner that is illuminated with a converging or diverging beam. Additional topics include the aperture shape factor with values identified, the propagation of noise and error components, and the scanned resolution of passive, incoherent, and remote sensing systems.

The first three chapters form the basis for the extensive exposition in Chapter 4, Scanner Devices and Techniques. Attention is devoted to its organization with a family tree chart and with discussion oriented to scanner function. Each device is identified within a high or a low inertia category, in performance rather than in sheer physical proper-ties. For example, the galvanometer-type resonant scanner performs as a high-inertia device, although it is of low-inertia structure, and is offered inadvertently as a low-inertia scanner. Included in this chapter, along with the more familiar resource of scanner devices, is the group now emerging from research in the field of agile beam steering, represented by the phased array and the decentered microlens array. A brief review of the devices and techniques covered in this chapter follows.

Initial regard is accorded the (high inertia) rotating polygon for its unique capability for extremely high data transfer rate (bandwidth) and for extremely high resolution at high uniformity and at high efficiency. Special attention is devoted to its design as related to its imaging optics. Polygon use as a device and with optics, some of which were introduced earlier, are developed further. Of similar qualities is the holographic scanner, which may also provide useful correction for cross-scan error. (Chapter 5 addresses the topic of error correction.) Although not providing the high speed of the polygon in its current form, the holographic scanner with matching optics serves most requirements with parallel performance. It requires, however, very astute attention to its design and fabrication.

 

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