Search results for "Fourier optics"

Common-path phase-shifting digital holographic microscopy: A way to quantitative phase imaging and superresolution

2008

We present an experimental setup useful for complex amplitude evaluation and phase image quantification of three-dimensional (3-D) samples in digital holographic microscopy (DHM). It is based on a common-path interferometric configuration performed by dividing the input plane in two contiguous regions and by placing a translation grating near to the Fourier plane. Then, complex amplitude distribution of the sample under test is recovered with phase-shifting standard method obtained by moving the grating using a linear motion stage. Some experimental results of an USAF resolution test are presented for different numerical aperture (NA) microscope lenses. In a second part, the proposed setup …

Optical phase retrieval using four rotated versions of a single binary mask – simulation results

2018

In signal processing one often faces the phase problem, i.e., when an image is formed information about the phase is lost so that only information about intensity is available. This is often an issue in astronomy, biology, crystallography, speckle imaging, diffractive imaging where the phase of the object must be known. While there have been many approaches how to find a solution to the phase problem, numerical algorithms recovering the phase from intensity measurements become more and more popular. One of such algorithms called PhaseLift has been recently proposed. In this study, we show that even 4 masks may be sufficient for reasonable recovery of the phase. The original wavefront and th…

A microscope configuration for nanometer 3-D movement monitoring accuracy.

2011

In this paper we present a new microscopy configuration based upon temporal tracking of a secondary reflected speckle by imaging the speckle through properly defocused optics. The configuration is used to monitor three-dimensional (3-D) spontaneous contraction of rat cardiac muscle cells while achieving nanometer tracking accuracy at a rate of 30 frames per second (fps) without using interferometric recording. Estimation of the change in the optical path of accuracy of 50 nm in the transverse direction and of 200 nm in the axial direction was achieved.

Ray matrix analysis of anamorphic fractional Fourier systems

2006

In this work we extend the application of the ray matrix approach to analyse anamorphic fractional Fourier systems, i.e., fractional Fourier optical systems where the fractional power is different for two orthogonal directions. The application of the ray matrix approach allows for easily obtaining the properties of the optical system, and it is therefore a powerful tool to design and simplify complicated systems. For simplicity we consider fractional Fourier systems with real orders and systems without apertures. We start by presenting the analysis of some previously reported anamorphic Fourier and fractional Fourier systems, and we end by proposing a simple optical system with tunable anam…

Quasi-wavelength-independent broadband optical Fourier transformer

1999

The chromatic behaviour associated with diffractive optical elements is exploited herein to design a hybrid (diffractive-refractive) lens triplet showing very great wavelength-compensation capabilities for the Fraunhofer diffraction pattern of any diffracting screen under broadband point-source illumination. Within the paraxial Fresnel diffraction theory, we show that perfect compensation for the axial position of the Fourier transform of the input can be accomplished if we neglect the secondary spectrum of the refractive objective. Simultaneously, an achromatic correction for the scale of the Fraunhofer pattern is achieved. In this way, even for white light, only a low residual transversal…

Time-multiplexed chromatic-controlled axial diffractive optical elements

2010

Programmable diffractive optical elements DOEs with axial response have many interesting applications, including diffractive lenses, axicons, and optical tweezers. In all these cases, it is essential to properly select the modulation configuration of the spatial light modulator SLM where the DOE is displayed, in order to avoid the undiffracted zero order component that appears on axis and overlaps the desired axial response. However, in general, the chromatic dispersion in liquid crystal SLMs prevents the cancellation of the zero order for a broadband light source, thus limiting the possibilities for polychromatic program- mable axial DOEs. We operate a ferroelectric liquid crystal on silic…

Space-Time Analogies in Optics

2011

Abstract The so-called space-time analogy constitutes a source of inspiration to understand, engineer, and implement new systems for ultrafast optical signal processing based on concepts borrowed from the well-established field of Fourier Optics. In this review, we start by describing in a comprehensive manner the most basic notions of this analogy and discuss some recent developments with state-of-the-art technology, including the silicon-chip-based time lens and ultra-dispersive Raman devices, among others. Apart from the applications in optical communications, special emphasis is paid on the collateral benefits that the “ultra” appellative brings in fields as diverse as optical frequency…

Light Propagation in Clouds: From Digital Holography to Non-Exponential Extinction

2019

Optical propagation is strongly influenced b y t he n umber concentration, size distribution, thermodynamic phase, and spatial distribution of particles in atmospheric clouds. These properties have been investigated in the field using an airborne digital holographic instrument. A laboratory facility has also been developed, in which optical propagation is being investigated in steady-state turbulent-cloud conditions.

Fractional Fourier Transforms and Geometrical Optics

2010

Fabrication of long period fiber gratings of subnanometric bandwidth.

2017

This paper reports on the fabrication of long period fiber gratings having subnanometric bandwidth in the 1500 nm spectral region. Large gratings have been photo-inscribed in a high NA fiber, the grating pitch and the order of the HE cladding mode are optimized to produce gratings with a large number of periods and preventing the coupling to TE, TM or EH modes. Resonances with a FWHM of 0.83 nm and 0.68 nm have been achieved for gratings 15 and 20 cm long respectively, the free spectral range between transmission notches is 125 nm. The polarization effects and the sensitivity of the gratings to temperature and to strain variations are presented as well. © 2015 Optical Society of America Thi…