Microshape and rough-surface analysis by fringe projection

Abstract

A fringe-projection system for microscopic applications, fringe-projecting microscopy, is developed and analyzed. Projection of the grating and imaging of the fringe system, modulated by the surface, are accomplished by the same high-aperture objective. The spectrum of the grating is spatially filtered and projected into the aperture with a lateral shift, which leads to a telecentric projection under oblique incidence and telecentric imaging. Topographies of specularly as well as diffusely reflecting surfaces can be obtained. The measurement of highly rough surfaces is described together with preprocessing steps. The resulting intensity distribution of the fringes is analyzed. Formulas for vertical and lateral resolution, measuring range, and dynamic range, based on noise considerations, are presented and verified by topographies of technical surfaces.

Metrology, Inspection, and Process Control in Micro‐Scales

“…Typical resolutions are on the order of a 100 nm, though the technique has been used to reach resolutions of 20 nm [11]. Fringe projection is viable for semirough surfaces (>300 nm RMS) because of its speed, but not as good as confocal microscopy or white light interferometry for out-of-plane resolution [12].…”

Ray-based calibration for the micro optical metrology system

“…Typical methods include interferometry, speckle metrology, fringe projection, image correlation etc 1 . Due to the advanced performance and flexible setup, microscopic 3D shape measurement based on fringe projection attracted continuous attention in the past two decades [2][3][4][5][6][7][8][9] . In general, fringe projection 3D microscopy (FP-3DM) achieves 3D imaging in microscopic field with the assistant of structured illumination, but the specific implementation may be realized with quite different arrangements and principles.…”

“…For instance, the system configurations may be single-aperture 2 or binocular stereo 3,5,6,9 , telecentric 2, 3, 6-8 or perspective 9 , grating projection 2, 3, 8 or digital projection [3][4][5][6][7]9 . Meanwhile, the 3D reconstruction may be analytical-expression-based [2][3][4][5][6][7][8] or stereovision-based 9 , and the error compensation may rely on a reference topography 1, 5 or distortion model 9 . Different researchers would like to propose distinctive system models for their individual system configurations, which make people confused to select an appropriate one for their specific application.…”

One-grating projection for absolute three-dimensional profiling

“…Fringe projection is a commonly used method for various 3-D surface profiling techniques, e.g., moiré techniques and Fourier transform profilometry [1][2][3][4][5][6][7][8] resulting in the projection of a grating onto the surface of a specimen. The deformation of the image of the grating is used as a signal for the determination of the height map.…”

“…In the simplest way, only a grating with one single grating period is imaged onto the specimen for the illumination. 2,3,6,7 From previous work it is known that the signal can be interpreted as an interferometric signal. 8 Therefore, the same signal evaluation algorithms ͑phase shifting͒ can be used, which are known in the field of interferometry.…”