Near field focusing by edge diffraction

Spherical microparticles have the ability for nonresonant focusing of light in the near field zone, forming nanojet (NJ) beams. Arbitrary-shaped microstructures, with wave-length-scale dimensions, may offer similar functionality with lower fabrication complexity. The focusing properties are ruled by the edge diffraction phenomenon. The diffraction of light on the edge of a dielectric microstructure forms a tilted focused beam whose deviation angle depends on the index ratio between the structure material and host medium. The beam geometry and field intensity enhancement can be tuned by varying the curvature of the edge line. Interference of edge diffracted waves from different segments of the edge line creates a condensed beam in the nearfield zone, the photonic nanojet.

Near field focusing by edge diffraction“, A. Boriskin, V. Drazic, R. Keating, M. Damghanian, O. Shramkova, L. Blondé. Optics Letters, vol. 43, Issue 16, pp. 4053-4056 (2018)

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An Image Rendering Pipeline for Focused Plenoptic Cameras

 In this paper, we present a complete processing pipeline for focused plenoptic cameras. In particular, we propose (i) a new algorithm for microlens center calibration fully in the
Fourier domain, (ii) a novel algorithm for depth map computation using a stereo focal stack and (iii) a depth-based rendering algorithm that is able to refocus at a particular depth or to create all-in-focus images. The proposed algorithms are fast, accurate and do not need to generate Subaperture Images (SAIs) or Epipolar Plane Images (EPIs) which is capital for focused plenoptic cameras. Also, the resolution of the resulting depth map is the same as the rendered image. We show results of our
pipeline on the Georgiev’s dataset and real images captured with different Raytrix cameras. 

An Image Rendering Pipeline for Focused Plenoptic Cameras“, M. Hog, N. Sabater, B. Vandame, V. Drazic, IEEE Transactions on Computational Imaging, Vol. 14, No 8, August 2015.

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Optimal design and critical analysis of a high-resolution video plenoptic demonstrator, Invited whitepaper

 A plenoptic camera is a natural multiview acquisition device also capable of measuring distances by correlating a set of images acquired under different parallaxes. Its single lens and single
sensor architecture have two downsides: limited resolution and limited depth sensitivity. As a first step and in order to circumvent those shortcomings, we investigated how the basic design parameters of a plenoptic camera optimize both the resolution of each view and its depth-measuring capability. In a second step, we built a prototype based on a very high resolution Red One® movie camera with an
external plenoptic adapter and a relay lens. The prototype delivered five video views of 820 × 410. The main limitation in our prototype is view crosstalk due to optical aberrations that reduce the depth accuracy performance. We simulated some limiting optical aberrations and predicted their impact on the performance of the camera. In addition, we developed adjustment protocols based on a simple pattern and analysis of programs that investigated the view mapping and amount of parallax crosstalk on the sensor on a pixel basis. The results of these developments enabled us to adjust the lenslet array with a submicrometer precision and to mark the pixels of the sensor where the views do not register properly. 

Optimal design and critical analysis of a high-resolution video plenoptic demonstrator“, V. Drazic, JJ Sacré, A. Schubert, J. Bertrand, E. Blondé.  Journal of Electronic Imaging 21(1), 011007 (JanMar 2012) .

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Three-dimensional transfer function of coherent confocal microscopes with extended source and detector

We consider the effect of the finite size of the source and of the detector on the three-dimensional transfer function of an incident light coherent confocal scanning microscope. Up to now the source has always been modeled as being punctiform. We will show that a finite source alters the 3D resolution and hence the imaging properties of such a microscope much more than a finite detector of the same size. It is also the aim of this paper to determine the greatest size of the source and the detector which still preserves the 3D resolution attained with a confocal microscope.

Three-dimensional transfer function of coherent confocal microscopes with extended source and detector“, Valter DRAZIC, Journal of Modern Optics, 1992, vol. 39, No. 8, 1777-1790.

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Dependence of two- and three-dimensional optical transfer functions on pinhole radius in a coherent confocal microscope

Previous papers about coherent scanning optical microscopes took into account two types of microscope: those with a point detector called type-II or confocal microscopes and those with an infinitely large area detector called type-I or conventional microscopes. Here the pinhole size of a type-II microscope was permitted to vary, and it is shown how the size could affect the imaging properties of a real microscope. The three-dimensional optical transfer function is established, and we discuss in particular the resolution capabilities, lateral as well as longitudinal, of a scanning microscope with a given pinhole size or detector area. Finally, a rigorous confocality criterion, which will answer the question of how small the pinhole should be made to give confocal imaging properties to a scanning microscope, is given.

Dependence of two- and three-dimensional optical transfer functions on pinhole radius in a coherent confocal microscope“, Valter DRAZIC, Journal of the Optical Society of America A, Vol. 9, No 5, May 1992, 725-731

Dependence of two- and three-dimensional optical transfer functions on pinhole radius in a coherent confocal microscope – comments“, C. J. R. Sheppard, Min Gu, Journal of the Optical Society of America A, Vol. 10, No 3, March 1993, 533-534

Dependence of two- and three-dimensional optical transfer functions on pinhole radius in a coherent confocal microscope – reply to comments“, Valter DRAZIC, Journal of the Optical Society of America A, Vol. 10, No 3, March 1993, 535-537

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