Diffractive performance of square Fresnel zone plates

Author(s): Javier Alda, José María Rico-García, Francisco Javier Salgado-Remacha, Luis Miguel Sanchez-Brea

Abstract:

“We analyze the optical behavior of square Fresnel zones plates. A theoretical analysis and numerical simulations based on the Rayleigh–Sommerfeld approach have been developed analyzing properties such as the depth of focus and the intensity of the focus in terms of the number of zones. In addition, an experimental verification has been performed using a Spatial Light Modulator to implement the designed square Fresnel zones plates.”

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Publication: Optics Communications
Issue/Year: Optics Communications, Volume 282, Issue 17, 1 September 2009, Pages 3402-3407
DOI: 10.1016/j.optcom.2009.05.053

Complementary Filtering Approach to Enhance the Optical Reconstruction of Holograms from a Spatial Light Modulator

Author(s): Mostafa Agour, Claas Falldorf, Christoph von Kopylow

Abstract:

“Electrically-addressed spatial light modulators (SLMs) are programmable diffractive optical elements (DOE), which are capable to modulate the amplitude and/or the phase of the incident light through a matrix structure. They are organized in a two-dimensional array of discrete pixels, which is geometrically specified by pixel pitch and pixel gap. Pixel pitch is the distance between the centres of neighboring pixels and pixel gap is the non-active area between them. The ratio of the SLM active area to its total area is referred to as its fill factor. SLMs can be used to optically reconstruct the complex amplitude of a wavefield. However, the reconstructed wavefield in the far field is corrupted by effects arising from the discrete nature, the finite pixel size and the limited fill factor of nowadays light modulators. One of the principal drawbacks is the appearance of unwanted laterally shifted replicas which are called higher diffraction orders. Another is the modulation of the wavefield in the reconstruction domain by an envelope function that affects the quality of the recovered signal. In this report, a complementary two-step filtering process is described to enhance the quality of the signal in the reconstruction plane. Firstly, the high diffraction orders are filtered by means of a limiting aperture in the Fourier domain of a classical 4f-arrangement. The second filter is digitally applied by changing the signal to be encoded into the SLM in order to compensate the effect of the envelop function.”

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Publication: Fringe 09 – Proceedings of the 6th International Workshop on Advanced Optical Metrology
Issue/Year: Fringe 2009 – Proceedings, pp. 205 – 210 (2009)
DOI: 10.1007/978-3-642-03051-2_34

Comparison and unification of speckle-based phase retrieval and holography with applications in phasefront alignment and recognition

Author(s): P. F. Almoro, G. Pedrini, F. Zhang, A. M. S. Maallo, A. Anand, P. N. Gundu, W. Wang, A. Asundi, W. Osten and S. G. Hanson

Abstract:

“Comparisons between various wavefront reconstruction methods such as wavefront curvature sensing and phase diversity have been reported in the literature. These comparative studies highlight the differences,
similarities, relative advantages, operating regimes and main applications of the various reconstruction methods. For coherent light metrological applications, especially on rough objects, Digital Holography (DH) is
considered one of the established interferometric methods because of its sub-wavelength accuracy. For investigations of smooth surfaces, Phase Retrieval (PR) or the non-interferometric approach offers a simple setup since no reference beam (RB) is required. In PR, recent trends favour the use of multiple intensity images, rather than a few images, due to its robustness against quantization error. Recently, a multiple speckle-pattern PR method was utilized in the interferometric analysis of object rotation and deformation and in the numerical correction of aberrations, indicating a point of convergence between the two, traditionally parallel, reconstruction methods. To the best of our knowledge, no comparative study has been done between PR and DH. Recognition of test objects has been carried out by correlation with a reference object wavefront obtained through DH. Since no RB is used, PR may offer a more robust recognition method. The objectives of this study are: 1) compare off-axis DH and PR in terms of setup and reconstruction algorithm; 2) present a new model for the PR method interpreting it as a special case of holography called “phase-shifting broadband DH”; 3) describe a novel method for phasefront alignment of uncorrelated laser beams using PR; and, 4) describe a novel method for object recognition using PR.”

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Publication: Fringe 09 – Proceedings of the 6th International Workshop on Advanced Optical Metrology
Issue/Year: Fringe 2009 – Proceedings, pp. 57 – 62 (2009)
DOI: 10.1007/978-3-642-03051-2_8