Unified Optical Scanning Technology

Chapter 1 - Introduction: Technology Overview and Unifying Principles

1.1 OPTICAL SCANNING CHARACTERISTICS AND DISCIPLINES

Optical scanning serves as an information converter. It transforms a spatial function (such as an image) into a time domain (a signal) to adapt it to electronic processing. Or, in reciprocal form, scanning decodes a series of signal impulses to assemble its image or spatial function. Familiar examples are the systems of television or facsimile. Optical scanning may also be confined to the (nonimaging) data domain, analog or digital, as in the field of data storage and retrieval. Here, it interprets the elemental optical changes in a storage medium as an electrical signal. Or it renders the reverse process of transforming an electrical data stream into detectable changes in a storage medium. Familiar examples are bar code or compact disk (CD) recording and reading. In these ways, optical scanning serves as an information encoder or decoder, truly a key to advanced information transfer.

We can express this conversion process in terms of transformations between spatial orientations (which may be a function of time) and the time. In "moving images," for example, the spatial orientations s are themselves a function of the time. Letting sc,trepresent the three spatial coordinates (c = 1, 2, 3) and t the time, one may write,

to symbolize the reciprocal transformations by means of optical scanning of the spatial function f to or from the time function g.

Portions of these operations are performed by familiar static components. For example, in a bar code reader, in addition to the optical scanner that directs illumination to the bar code elements in rapid succession, there appear intervening optics that shape the scanned output beam, optics that collect some of the scattered flux from the bar code and concentrate it upon a detector that transduces this varying flux into a corresponding elemental signal for subsequent processing. It is the combination of such fundamental components (e.g., light source, scanner, optics, modulator, and detector) that forms a Subsystem called a digitizer, printer, or recorder. The arrangement of these components is discussed in Sections 1.3 and 1.5.

Optical scanning applies as well to the important complementary field of image detection, which is sometimes performed unobtrusively. In remote sensing, the flux radiating from a remote object is sampled and directed to a detector for conversion to a corresponding electrical signal. Because the scanning and optical components deployed in both fields (active and passive) are often very similar fundamentally, significant attention is devoted here to their unification. The reciprocal properties of these systems are introduced in Section 1.2 and are then exemplified. Other unifying principles, such as the resolution invariant, are represented in this work.

In an information handling system, optical scanning appears most often in the peripheral equipment, in the output or input devices that either enter data or interpret data for electronic manipulation. In this manner, optical scanning is analogous to the microphone and earphone of an audio system, operating in the optical domain on spatial information, rather than on acoustic waves. One can see how the characteristics and disciplines of optical scanning escalate in complexity to affirm that 'a picture is worth a thousand words.'

A pattern of unifying principles, pedagogic analogies, and rarely posed topics represented in this work may be listed usefully, in approximate sequence of introduction, to include—

  • The reciprocal space-time concept
  • Complementary active-passive scanning
  • Conjugate processes in remote sensing
  • The resolution invariant and its significance
  • Electrical-Optical signal-image theory
  • Analogous low-pass filter and scanned resolution loss
  • Analogous oversampling criteria in different fields
  • Analogous Fourier transform and spectrum analysis
  • Analogous conventional and holographic scanners
  • Analogous Bragg diffraction and prism refraction
  • Analogous radar and optical phased arrays
  • Rarely posed image rotation and derotation
  • The fast steering mirror—newly developed
  • The resonant scanner classified as 'high inertia'
  • Scanner-lens architecture options
  • Rarely posed, aperture relaying
  • The Scophony process—rarely posed
  • Rarely posed traveling lens and chirp deflectors
  • Propagation of noise and error components
  • Agile beam steering—new and comprehensive
  • Cross-scan error control—its own chapter
  • Ghost image elimination, newly rendered

The main thrust of this volume is to facilitate judgment for selecting, from a broad range of optical scanning techniques and architectures, the most effective methods for design and further development of information transfer systems. Insight for creative advancement is fostered with the unification of some diverse and arcane concepts. This work ends with Chapter 6, which summarizes the content and charts the characteristics of the principal operational scanner prototypes, judgment seldom rendered with independent consideration.