Search results for "Modulator"
showing 10 items of 210 documents
Wavelength-multiplexed computational temporal ghost imaging
2017
Ghost imaging is a novel imaging technique based on correlation measurements between a structured illumination pattern (the reference) and the total intensity transmitted or reflected by an object [1]. The reference illumination patterns may be either randomly generated by a spatially incoherent light source, or pre-programmed e.g. with a spatial light modulator. Light transmitted (or reflected) by the object is measured by a single-pixel “bucket” detector with null spatial resolution. A unique feature associated with ghost imaging is that (i) neither the bucket detector nor the reference measurement caries enough information to retrieve the object shape and (ii) it is insensitive to distor…
Second order diffractive optical elements in a spatial light modulator with large phase dynamic range
2013
International audience; A study of the diffraction efficiency of a spatial light modulator with a large dynamic phase range is reported. We use a phase-only device that reaches 4π phase modulation depth for the wavelength of 454 nm. This allows operating phase-only diffractive optical elements in the second harmonic diffraction order, instead of in the usual first diffraction order. This type of implementation shows advantages in terms of resolution and diffraction efficiency. Experimental results are reported for blazed diffractive gratings and diffractive lenses.
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…
Adaptive Kerr-Assisted Transverse Mode Selection in Multimode Fibers
2019
Multimode optical fibers (MMFs) have recently regained interest because of the degrees of freedom associated with their different eigenmodes. In the nonlinear propagation regime in particular, new phenomena have been unveiled in graded-index (GRIN) MMFs such as geometric parametric instabilities and Kerr beam self-cleaning [1, 2]. The speckled pattern observed at the output of the MMF at low powers, is transformed at high powers into a bell-shaped beam close to the fundamental mode. Recent work has also demonstrated that Kerr beam self-cleaning can lead to a low-order spatial mode, different from a bell-shape, by adjusting the laser beam in-coupling conditions [3]. An attractive way to syst…
Common-path phase-shifting lensless holographic microscopy
2010
We present an approach capable of high-NA imaging in a lensless digital in-line holographic microscopy layout even outside the Gabor's regime. The method is based on spatial multiplexing at the sample plane, allowing a common-path interferometric architecture, where two interferometric beams are generated by a spatial light modulator (SLM) prior to illuminating the sample. The SLM allows phase-shifting interferometry by phase modulation of the SLM diffracted beam. After proper digital processing, the complex amplitude distribution of the diffracted object wavefront is recovered and numerically propagated to image the sample. Experimental results are reported that validate the proposed metho…
Poincaré sphere analysis of a ferroelectric liquid crystal optical modulator: application to optimize the contrast ratio
2008
The Poincare sphere representation is used to analyze the polarization transformation achieved with a ferroelectric liquid crystal (FLC) optical modulator. This device acts as a switchable wave-plate, in which the orientation of the principal axes rotates under the action of an applied bipolar voltage. In the standard operational mode for intensity switching, the rotation angle of the principal axes is �θ = π/4 and the phase shift is φ = π (half-wave-plate). However, for wavelengths different from the design one, the FLC deviates from the half-wave-plate performance and the optical contrast is diminished. We use the Poincare sphere representation to perform a theoretical analysis of the int…
Synchronized photonic modulators driven by surface acoustic waves
2013
Photonic modulators are one of the most important elements of integrated photonics. We have designed, fabricated, and characterized a tunable photonic modulator consisting of two 180 degrees-dephased output waveguide channels, driven by a surface acoustic wave in the GHz frequency range built on (Al,Ga)As. Odd multiples of the fundamental driven frequency are enabled by adjusting the applied acoustic power. A good agreement between theory and experimental results is achieved. The device can be used as a building block for more complex integrated functionalities and can be implemented in several material platforms. (C) 2013 Optical Society of America
Through-focus response of multifocal intraocular lenses evaluated with a spatial light modulator
2012
A new testing technique based on the use of a liquid crystal spatial light modulator (SLM) is proposed to analyze the optical quality of multifocal intraocular lenses (MIOLs). Different vergences and decentrations of the incident beam can be programmed onto the SLM in order to record the point spread function (PSF) for different object positions. From these axial PSFs, the through-focus modulation transfer function is computed. Because there are no moving parts in the experimental setup, this method is fast and versatile to assess MIOLs. Experimental results confirm the potential of the proposed method.
Infrared linear dichroism spectroscopy by a double modulation technique
1990
A linear IR dichroism experiment has been devised using a FTIR instrument in combination with a photoelastic modulator. Based on the Mueller-Stokes calculus, a method to directly obtain the absorbance spectra Av parallel and Av perpendicular from the modulated interferogram is developped, which allows the sensitive evaluation of the dichroic ratio. The photoelastic modulator, in combination with a FTIR instrument, offers high sensitivity, high speed, excellent signal to noise ratio and a broad spectral range from 3300 to 850 cm-1. First experimental results obstained from SBS block copolymer are reported.
Linear infrared dichroism by a double modulation technique
1991
In the first part of this paper an experimental setup using Fourier-transform infrared spectroscopy (FTIR) in combination with a photoelastic modulator (PEM) for linear dichroism measurements is described. The second part shows the influence of PEM-amplitude and scan-velocity on the sensitivity of the instrument. The third part deals with the fringe-problem in the baselines of absorbance spectra and its influence on the determination of the linear dichroic ratio.