Optical EngineeringAutomated three-dimensional surface profilometry using dual-frequency optic fiber phase-shifting method
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A novel automatic profilometry technique using the dual frequency of an optical fiber projection grating is introduced. 3-D shape can be measured automatically with this technique even with the problems of true discontinuities and phase noise. This method combines a singlemode optical fiber phase-shifting interferometer as the illumination part of the configuration. The design of the optical fiber interferometer has the following features: (1) easily adjustable fringe space and rotation and (2) automatic phase shifting. In addition, it has a number of important advantages over the more conventional methods for producing projection fringes, such as extremely small size and weight, high visible fringes with little noise and absolute sinusoidal intensity distribution, etc. These are very important and necessary to dual-frequency automatic measurement of 3-D shapes. Fringes generated by the interferometer are analyzed, and the relationship between the fringe phase and height distribution of an illuminated diffused surface is derived. The dual-frequency automatic phase unwrapping method is described. An example of the profilometry in operation is given.