An interferometer with off-axis and phase-shifting methods is developed to quantitatively measure complex amplitude distributions of fabricated metasurfaces. The developed interferometer switches between the off-axis and phase-shifting methods depending on the maximum spatial frequency components of a specimen metasurface. The off-axis method allows complex amplitude measurements from a single interference pattern and is robust to environmental vibrations, whereas the phase-shifting method can achieve high spatial resolutions via sequential recording of multiple interference patterns. We measured the complex amplitude distribution of fabricated metasurfaces using the developed interferometer. This interferometer would be useful for reducing design and fabrication errors and optimizing metasurface structures.
We previously proposed a grating-assisted phase-shifting method for incoherent digital holography (IDH). This method leverages the diffraction of a binary phase grating, making it possible to create four self-interference holograms with different phase shifts in parallel. By simultaneously capturing the holograms with four image sensors, implementing a four-step phase-shifting algorithm and detecting complex amplitude distribution at a single exposure are possible. In this study, we investigated the effect of the axial misalignment of image sensors on the reconstructed images in the grating-assisted phase-shifting method via numerical simulations. The numerical simulations are based on the scalar diffraction theory and allows us to emulate IDH systems. The numerical results provide basic insight and a guideline to design an optical setup for the method within an acceptable tolerance.
We configured a coded aperture-based real-time super-resolution imaging system using digital micromirror device (DMD). We encoded an object with 128 random patterns using a DMD that can spatially modulate at high speed. ADMM (Alternating Direction Method of Multiplier) was used as an algorithm to solve the inverse problem with a small number of iterations and low computational cost. It took 0.52 seconds to acquire the low-resolution coded images and 0.07 seconds to reconstruct a super-resolution image from them. As a result, we confirmed 1.7 fps imaging capable of acquiring 16x super-resolved 128x128 pixel images in the horizontal and vertical directions.
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