Abstract
We report on unwanted effects of pixel cross-talk and its mitigation on the experimental realization of the double-phase method with phase-only spatial light modulators. We experimentally demonstrate that a generalized sampling scheme can reduce nonuniform phase modulation due to the pixel cross-talk phenomenon and, consequently, improve the quality of amplitude and phase images obtained with this encoding method. To corroborate our proposal, several experiments to reconstruct amplitude-only as well as fully independent amplitude and phase patterns under different spatial sampling schemes were carried out. We also show how a convenient implementation of the well-known polarization-based phase-shifting technique can be employed to measure the encoded complex field using only a conventional CMOS camera.
Highlights
Those based on the use of parallel-aligned liquid crystal on silicon (PA-LCoS) SLMs have gained special attention because of their relative high efficiency and due to their proven ability to accurately modify the physical behavior of laser beams using just a single-phase element encoded into a phase-only SLM.[3,4,7,8,9,10,11,12,13,14]
Among many other applications and/or signal-displaying methods, computer-generated holograms have been synthetized by means of conventional iterative Fourier transform algorithms,[15] employing a search, iterative, algorithm capable of generating binary holograms;[16] using a complex amplitude modulation method for three-dimensional dynamic holographic display;[17] by the application of the one-step phase-retrieval approach, which allows a rapid computation of phase-only holograms;[18] by downsampling the intensity image with uniform grid-cross lattices;[19] or more recently by adding a periodic phase pattern to the source image.[20]
Our experiments show that nonuniform phase modulation due to pixel cross-talk may deteriorate the quality of reconstructed images, which basically have less sharpness and contrast than expected
Summary
There is a wide variety of reported optical methods to optically manipulate the complex field of laser beams using spatial light modulators (SLMs).[1,2,3,4,5,6,7,8,9,10,11,12,13,14] Among them, those based on the use of parallel-aligned liquid crystal on silicon (PA-LCoS) SLMs have gained special attention because of their relative high efficiency and due to their proven ability to accurately modify the physical behavior of laser beams using just a single-phase element encoded into a phase-only SLM.[3,4,7,8,9,10,11,12,13,14] In this context, among many other applications and/or signal-displaying methods, computer-generated holograms have been synthetized by means of conventional iterative Fourier transform algorithms,[15] employing a search, iterative, algorithm capable of generating binary holograms;[16] using a complex amplitude modulation method for three-dimensional dynamic holographic display;[17] by the application of the one-step phase-retrieval approach, which allows a rapid computation of phase-only holograms;[18] by downsampling the intensity image with uniform grid-cross lattices;[19] or more recently by adding a periodic phase pattern to the source image.[20]. Temporal fluctuations of the LC molecular orientation as a function of time causes depolarization effects, deteriorating the diffraction efficiency of SLM.[28] Another harmful effect is related to the Fabry–Perot multiple beam interference generated by the intrinsic layer structure of the LC device[29] that may originate nonlinear phase modulation or even some coupling of amplitude modulation In this context, there is a particular unwanted effect that becomes critical for applications that require encoded patterns with abrupt phase discontinuities, e.g., diffraction gratings with few phase levels or phase distributions associated with high scattering media. From the SLM on the measurements done throughout this work, a fixed blazed grating was added to each phase element sent to the SLM, in the same manner as proposed in Ref. 23
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