Optical inspection of liquid crystal variable retarder inhomogeneities

Abstract

Liquid crystal variable retarders (LCVRs) are starting to be widely used in optical systems because of their capacity to provide a controlled variable optical retardance between two orthogonal components of incident polarized light or to introduce a known phase shifting (PS) between coherent waves, both by means of an applied voltage. Typically, the retardance or PS introduced by an LCVR is not homogeneous across the aperture. On the one hand, the LCVR glass substrates present a global bend that causes an overall variation of the retardance or PS. On the other hand, in the manufacturing process of an LCVR, there sometimes appears a set of micro-air bubbles that causes local retardance or PS inhomogeneities. In this work, we present an interferometric technique based on a Mach-Zehnder interferometer that is insensitive to vibrations and capable of inspecting and characterizing the LCVR's retardance or PS inhomogeneities. The feasibility of the proposed method is demonstrated in the experimental results, where the LCVR retardance is measured with an error of about 0:2 rad. The thickness of possible micro-air bubbles is obtained with a resolution of about 50 nm.

Defect detection using windowed Fourier spectrum analysis in diffraction phase microscopy

“…In these techniques, we obtain a fringe pattern or interferogram which encodes information about the quantity of interest. The main objective for defect detection algorithms is to identify defects such as the presence of cracks, fracture and debonds from a fringe pattern [4,5]. The fringe pattern serves as a good marker for defect identification because of the rapid fringe density variations in the vicinity of defect region.…”

Fast Method for Liquid Crystal Cell Spatial Variations Estimation Based on Modeling the Spectral Transmission

“…These include systems for multidimensional imaging [3], remote sensing from space [4], biomedical imaging [5], spectral imaging of paintings [6], and ellipso-polarimetric imaging [7,8]. Achieving a spatially uniform liquid crystal cell (LCC) remains a fabrication challenge [9], and gap variations appear throughout the cell [10]. As the LCC’s retardance and spectral transmission (ST) depend on the cell gap, they suffer from spatial variations as well, affecting the performance of the systems utilizing the LCC.…”

Dynamic microparticle manipulation through light structures generated by a self-calibrated Liquid Crystal on Silicon display

“…In the abovementioned microparticle manipulation cases, as the light bottle structures are mainly controlled by addressing DOEs, the LCoS display introduced is operated in the phase-only regime. However, the disproportion of the phase-voltage relation and the spatial phase inhomogeneity [27,28] of the LCoS screen related with fabrication inaccuracy distort the DOE patterns generated, which influence the obtained light bottle structures for particle manipulation. Therefore, the precalibration and the optimization of the imperfect phase distribution of the LCoS are mandatory.…”