We first provide an overview of 3-D shape measurement us- ing various optical methods. Then we focus on structured light tech- niques where various optical configurations, image acquisition tech- niques, data postprocessing and analysis methods and advantages and limitations are presented. Several industrial application examples are presented. Important areas requiring further R&D are discussed. Finally, a comprehensive bibliography on 3-D shape measurement is included, although it is not intended to be exhaustive. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00101-X)

Overview of three-dimensional shape measurement using optical methods

Anti-reflective coatings (ARCs) have evolved into highly effective reflectance and glare reducing components for various optical and opto-electrical equipments. Extensive research in optical and biological reflectance minimization as well as the emergence of nanotechnology over the years has contributed to the enhancement of ARCs in a major way. In this study the prime objective is to give a comprehensive idea of the ARCs right from their inception, as they were originally conceptualized by the pioneers and lay down the basic concepts and strategies adopted to minimize reflectance. The different types of ARCs are also described in greater detail and the state-of-the-art fabrication techniques have been fully illustrated. The inspiration that ARCs derive from nature (‘biomimetics’) has been an area of major research and is discussed at length. The various materials that have been reportedly used in fabricating the ARCs have also been brought into sharp focus. An account of application of ARCs on solar cells and modules, contemporary research and associated challenges are presented in the end to facilitate a universal understanding of the ARCs and encourage future research.

Anti-reflective coatings: A critical, in-depth review

We review 20 years of development in the field of 3-D laser imaging. An overview of 3-D digitizing techniques is presented with an emphasis on commercial techniques and systems currently available. It covers some of the most important methods that have been developed, both at the National Research Council of Canada (NRC) and elsewhere, with a focus on commercial systems that are considered good representations of the key technologies that have survived the test of years. © 2004 SPIE and IS&T.

Review of 20 years of range sensor development

Diffraction characteristics of general dielectric planar (slab) gratings and surface-relief (corrugated) gratings are reviewed. Applications to laser-beam deflection, guidance, modulation, coupling, filtering, wavefront reconstruction, and distributed feedback in the fields of acoustooptics, integrated optics, holography, and spectral analysis are discussed. An exact formulation of the grating diffraction problem without approximations (rigorous coupled-wave theory developed by the authors) is presented. The method of solution is in terms of state variables and this is presented in detail. Then, using a series of fundamental assumptions, this rigorous theory is shown to reduce to the various existing approximate theories in the appropriate limits. The effects of these fundamental assumptions in the approximate theories are quantified and discussed.

Analysis and applications of optical diffraction by gratings

The linear transform kernel for fractional Fourier transforms is derived. The spatial resolution and the space–bandwidth product for propagation in graded-index media are discussed in direct relation to fractional Fourier transforms, and numerical examples are presented. It is shown how fractional Fourier transforms can be made the basis of generalized spatial filtering systems: Several filters are interleaved between several fractional transform stages, thereby increasing the number of degrees of freedom available in filter synthesis.

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Fractional Fourier transforms and their optical implementation. II

In this paper we discuss the properties of optical elements fabricated by holographically recording an ultrahigh spatial-frequency pattern in a photoresist mask followed by reactive ion etching to transfer this pattern into the surface of a quartz substrate. Such optical elements are environmentally durable, potentially easy to replicate, and exhibit diffraction efficiencies in excess of 85%. In addition, two other properties are reported for the first time. Such elements at normal (0°) incidence are antireflective, with broadband reflection coefficients as low as 0.035%. Also, the elements exhibit artificially produced birefringence making them useful as wave plates. These results may be particularly significant in the UV and IR, where damage-resistant antireflection coatings and transparent birefringent materials may not exist.

Optical elements with ultrahigh spatial-frequency surface corrugations.

Structured light vision systems offer a practical solution to many 3-D inspection problems. This paper examines the trade-offs involved in the design of 3-D inspection systems that use triangulation. General equations describing the behavior of such systems are derived. The implementation of a multistripe system is discussed. Problems common among structured light systems are explored, and alternative solutions are suggested. Experimental results from a prototype system are presented.

Three dimensional inspection using multistripe structured light

A high speed high precision laser based alignment sensor system for use on surface mount component placement machines. A laser system is utilized to correctly align and position component parts which range between 0.02 inches and 2.0 inches in size. The laser sensor system consists of a laser light source which is passed through a collimating lens and then through an aperture to create a stripe of collimated laser light which is focused past the component being aligned to strike a multi-element CCD sensor array. The sensor system is mounted directly on the carrying mechanism for the surface mount component placement machine. During transit of the component between the bin of components is to be placed, the component is rotated and the shadow which falls on the detector array is monitored. When the minimum width of shadow is detected, the correct angular orientation is determined, the average of the edges of the shadow when compared with the center of the quill determines the coordinate (X,Y) location of the component on the quill. Two alignments normally occur displayed by 90°. Thereafter, the sensor sends correcting signals to the component placement machine to assure the correct angular orientation and the correct X,Y position for the component to be placed on the circuit board by the component placement machine.

High precision component alignment sensor system

A new type of holographic optical element combines some of the flexibility of computer-generated holograms with the high light efficiency of volume phase holograms to produce optical elements capable of arbitrary illumination transformations with nearly 100% light efficiency. The optical element is recorded by subdividing a volume hologram film surface into numerous small areas (facets), each of which is individually exposed. A final optical system consisting of two dichromated gelatin holograms in series is demonstrated. The first hologram spatially redistributes the incident light, and the second hologram produces a desired phase front on the redistributed light.

Multifacet holographic optical elements for wave front transformations.

The method utilizes a multi-faceted holographic optical element, the various individual diffraction gratings of each facet collectively functioning to effect a desired wavefront transformation. In this way, a laser beam can be transformed into a specific pattern, permitting unusually shaped objects to be efficiently illuminated with laser light.

Steven K. Case

Papers

Optical elements with ultrahigh spatial-frequency surface corrugations.

Three dimensional inspection using multistripe structured light

High precision component alignment sensor system

Multifacet holographic optical elements for wave front transformations.

Holographic method for producing desired wavefront transformations