Improving holographic reconstruction by automatic Butterworth filtering for microelectromechanical systems characterization

Abstract

Digital holographic microscopy is an important interferometric tool in optical metrology allowing the investigation of engineered surfaces with microscale lateral resolution and nanoscale axial precision. In particular, microelectromechanical systems (MEMS) surface analysis, conducted by holographic characterization, requires high accuracy for functional testing. The main issues related to MEMS inspection are the superficial roughness and the complex geometry resulting from the several fabrication steps. Here, an automatic procedure, particularly suited in the case of high-roughness surfaces, is presented to selectively filter the spectrum, providing very low-noise reconstructed images. The numerical procedure is based on Butterworth filtering, and the obtained results demonstrate a significant increase in the images' quality and in the accuracy of the measurements, making our technique highly applicable for quantitative phase imaging in MEMS analysis. Furthermore, our method is fully tunable to the spectrum under investigation and automatic. This makes it highly suitable for real-time applications. Several experimental tests show the suitability of the proposed approach.

Sources and propagation of errors in quantitative phase imaging techniques using optical interferometry

“…Other methods to reduce noise include phase error compensation, spatial light modulation (SLM), and multiple frequency overlapping [9] [10][11][12][13], which improve the contrast of phase measurements. Noise reduction is also accomplished by filtering certain frequencies, both in the spatial and Fourier planes, with Butterworth filters and masks, respectively [14,15] [6]. In addition, efficient encoding methods and correlation based de-noising algorithms have been developed to significantly reduce speckle noise [16,17].…”

Holographic microscopy for 3D tracking of bacteria

“…Other methods to reduce noise include phase error compensation, spatial light modulation (SLM), and multiple frequency overlapping [13][14][15][16], which improve the reconstructed phase image of holograms. Noise reduction is also accomplished by filtering certain frequencies, both in the spatial and Fourier planes, with Butterworth filters and masks, respectively [17][18][19]. In addition, efficient encoding methods and correlation based de-noising algorithms have been developed to significantly reduce speckle noise [20,21].…”

Phase based method for location of the centers of side bands in spatial frequency domain in off-axis digital holographic microcopy

“…Due to the requirement of the micro-object measurement, the DH in microscope configuration is allowed to insert a microscope objective (MO) behind the specimen to realize the three-dimensional (3D) information measurement of specimen in micron, even submicron order. The DH imaging in microscope configuration has been paid increasing attention to the 3D morphology measurement applications such as biology [2][3][4][5][6][7], micro-electromechanical systems (MEMS) and micro-optical mechanic electronic system (MOEMS) [8][9][10]. The off-axis geometry of DH setup, proposed by Leith and Upatniecks [11], may spatially separate the different diffraction orders only by a single hologram.…”