Blazed photon sieve for the correction of presbyopia.

What we believe to be a new type of transparent photon sieve is presented with application for presbyopia correction. Inspired by blazed gratings, we propose to design an intracorneal implant with slanted holes. The slopes introduce a new degree of freedom, breaking the symmetry of energy distribution along the optical axis and allowing to balance the energy between near and far vision. This new implant design is presented together with the simulation, manufacturing and validation methods. The first experimental results obtained with an implant manufactured in a biocompatible material are presented confirming the potential of the approach.

Impact of virtual reality headset use on eye blinking and lipid layer thickness.

PURPOSE: Blinking plays an important role in protecting the eyes, and the use of computers has been associated with a reduction in the blink rate. The goal of this study was to evaluate the effect of a virtual reality headset on blinking and lipid layer thickness and to compare these data to those associated with a conventional desktop monitor. METHODS: Two experiments were performed to compare the effect of 20minutes of use of a virtual reality headset (FOVE) and 20minutes of use of a desktop monitor on the frequency and length of blinks (experiment 1, 15 participants) and on the thickness of the lipid layer as measured by Lipiview (experiment 2, 12 participants). RESULTS: In the first experiment, the blink rate [F(1.83)=4.3, P=0.04, ß=0.36] and duration [F(1.83)=13, P=0.001, ß=0.35] increased with time under both conditions, but no statistical difference was found between the two conditions (headset vs. desktop monitor) either for blink rate [rmANOVA F(1.11)=0.01, P=0.92; headset: 15.1 blinks, 95% CI: 12.6 to 17.6 blinks; desktop: 14.6 blinks, 95% CI: 13.6 to 15.7 blinks] or for blink duration [rmANOVA F(1.11)=4.534, P=0.06; headset: 205.75ms, 95% CI: 200.9 to 210.6ms; desktop: 202.82ms, 95% CI: 198.2 to 207.5ms]. However, strong individual variations were observed. Evaluation of simulator sickness and visual fatigue by questionnaire showed no significant differences between the two conditions (SSQ simulator sickness questionnaire: V=46, P=0.62; VFQ visual fatigue questionnaire: V=15.5, P=0.13). In the second experiment, the lipid layer thickness increased significantly after use of the VR headset [F(1.18)=11.03, P=0.004, headset: 76.2nm, desktop: 58.8nm]. CONCLUSION: In terms of recommendations, the effect of virtual reality headsets on blink duration and frequency during a moderate exposure (20minutes) is comparable to that of a conventional desktop monitor. However, the strong individual variations observed, the lack of reliable tests to evaluate this individual sensitivity, and the significant increase in lipid layer thickness in experiment 2 suggest the value of a more detailed investigation, in particular with consideration of a longer exposure time and other tear film parameters.

A laser emitting contact lens for eye tracking.

In this paper, we present the first realisation and experimentation of a new eye tracking system using an infrared (iR) laser pointer embedded into a wireless smart contact lens. We denote this contact lens prototype as the cyclops lens, in reference to the famous hero of the X-Men comics. The full eye tracker device combines the smart contact lens and its eyewear, which provides a primary source of energy and the beam detection system. We detail the assembling and encapsulation process of the main functionalities into the contact lens and present how a gaze tracking system is achieved, compared to existing conventional eye-tracking ones. Finally, we discuss future technical improvements.

Object kinetics perception in auto-stereoscopic vision.

In this paper, we study the conditions for the perception of object kinetics, produced by a multiview auto-stereoscopic system and a set of still images. We assess the capabilities and performances of such an optical system to encode complex trajectories and kinetics of objects moving in depth. In particular, we set up rules to create motions with nonuniform velocities, when obtained by motion parallax induced by the observer. We establish a link with plenoptic systems from where we derive applicable scaling rules to ensure stereoscopic vision and to provide fluid motion perception with satisfying visual comfort. Finally, we scale the optical system, thanks to obtained parameters, to emulate the perception of object motions in depth with fluid kinetics and to create impressive motion effects.

[Assessment of a 3D digital orthoptic test platform]. / Évaluation d'une plateforme d'orthoptie numérique 3D.

PURPOSE: To compare standard orthoptic tests with a novel digital 3D orthoptic platform, 3DeltaEasy(©) from Orthoptica(®). MATERIALS AND METHODS: This study tests the 3D digital orthoptics platform, 3DeltaEasy(©) from Orthoptica(®) and compares it to the corresponding standard orthoptic tests. This platform consists of a computer equipped with dedicated software, a video projector and 3D liquid crystal glasses. Three tests were compared: Wirt test, measurement of horizontal and vertical phorias, and the horizontal fusional amplitude in convergence and divergence. A total of 102 subjects, 53 males (52 %) and 49 females (48 %), aged between 9 years and 72 years (mean age 33±16.4 years) were examined at the ophthalmologic department of the Brest Hospital (France) and included in this observational cross-sectional study. Subjects recruited in this study were patients requiring orthoptic screening or therapy. Patients without their optimal visual corrections were excluded. All patients underwent both ophthalmological and orthoptic examination including Wirt fly stereotest with polarizing spectacles, cover tests to evaluate and measure the horizontal and vertical deviation of the lines of sight, horizontal vergence ranges using prism bar and their equivalent tests implemented in the digital 3D orthoptic tests 3DeltaEasy(©) from Orthoptica(®). RESULTS: All data were processed using MedCalc Statistical Software version 14.12.0 (MedCalc Software bvba, Ostend, Belgium). The main result of this study is that 3DeltaEasy(©) and the classical Wirt test are correlated (Spearman's coefficient of rank correlation: ρ=0.74; P<0.0001), cover tests are equivalent for intermediate and far vision (paired t-test; P=0.46 and P=0.51), and horizontal and vertical vergence range are comparable for distance vision (paired t-test; P=0.34 and P=0.94). CONCLUSION: New digital 3D tools could easily substitute for some orthoptic tests with better ergonomics. Eventually, by increasing the number of tests performed, it could substitute for nearly all tests.

Nano-polymer-dispersed liquid crystal as phase modulator for a tunable vertical-cavity surface-emitting laser at 1.55 mum.

We demonstrate what we believe is the first nonmechanical tunable vertical-cavity surface-emitting laser operating in the C band. This was achieved as a result of the combination of an InGaAs quantum well structure with a 6lambda thickness tunable index nano-polymer-dispersed liquid-crystal material. Experimental results exhibited a potential tunable range close to 10 nm, in the preliminary version, and excellent single mode locking due to the side-mode suppression ratio (more than 20 dB) over the whole spectral range. Another decisive advantage, compared to mechanical solutions, was the tuning response time of a few tens of microseconds (>30 micros) to scan the full spectral range (10 nm), making this device appropriate for some access network functions, as well as being robust and low cost. The voltage values are the main limitation to wavelength range extension. We present a first version of the device optically pumped. The next version will be electrically pumped as required for the access network applications targeted here.

Normal-law quantile phase filters for mode conversion in single-mode fibers applied to wavelength blockers.

We propose the definition of a new family of complex-amplitude filters. These filters are optimal for mode conversion in single-mode fibers and give rise to a large variety of spatial designs. Among them, we focus on a few that are easy to manufacture and implement, in particular, in an array shape, and present some technical advantages such as tolerance to positioning. In the second part, we discuss their implementations by using various technologies and the effect of some technical constraints on filter shape and phase distribution. Finally, we illustrate their uses in the case of a dynamic wavelength blocker within the frame of wavelength-division-multiplexing network systems.

Self-imaging properties of polychromatic Gaussian beams: application to wavelength demultiplexing and space routing.

We propose an analytical model of the self-imaging of Gaussian beams and discuss the impact of the finite aperture and the beam truncation on the quality of the self-image reconstruction. Extension to polychromatic operation is then presented in the context of wavelength division multiplexing systems. From the first point we derive conditions for good self-imaging, compatible with the requirements of the telecommunication environment. A basic optical setup is then proposed to implement both wavelength demultiplexing and routing in a lensless configuration.

Principle of pattern-signature synthesis and analysis based on double optical correlations.

Pattern-recognition problems for which patterns cannot be recognized directly but by their attitudes and/or behaviors is addressed. To analyze these attitudes, pattern signatures are generated from picture sequences. Two complementary signature synthesis algorithms are presented. The architecture is made up of two cascaded correlators. The first is used to create the signatures and the second to classify them. We focus our analysis on the case of optical implementations. Illustrations are given in the case of face recognition by attitudes (multisensor in the optronic imaging range) and moving-target recognition by behavior (in the radar imaging range).

Optical implementation of segmented composite filtering.

We investigate possible performance improvements of coherent optical correlators by using an appropriate filter design. Multidecision strategies are often required in high-level image-processing tasks. For an optical system characterized by a given space-bandwidth product we show that the filter design plays a crucial role in satisfying both system and processing requirements, with respect to the optimization of the encoding capacity. This leads us to the definition of segmented composite filtering, which is discussed in terms of processing performance. This filtering is assessed experimentally in the case of a face-recognition problem.

Reconfigurable two-dimensional diffractive phase element with the fractional talbot effect.

We investigate the technical feasibility of the optical implementation of a four-phase-level diffractive element with two {0, pi}-phase spatial light modulators in a fractional Talbot configuration. The space-bandwidth product of the spatial light modulators is seen as the main theoretical limitation of the proposed approach. We investigate the robustness of technological and geometrical parameters on the diffraction efficiency of the whole system. Ferroelectric liquid-crystal silicon backplane spatial light modulators are chosen because of their high reconfiguration rates and good electro-optics interface. Similarly, we assess the influence of liquid-crystal technical parameters on system performance.

Design and characterization of a liquid-crystal spatial light modulator for a polarization-insensitive optical space switch.

We report preliminary results concerning a free-space optical switch between single-mode fibers with a ferroelectric liquid-crystal (FLC) spatial light modulator (SLM). In particular, we show experimentally that such a device can operate in a polarization-insensitive manner. The influence of the geometrical and physical features of the FLC SLM on the overall performance of the optical fiber switch are also discussed.

Single-mode fiber optical crossbar routing switch with ferroelectric liquid-crystal-VLSI technology and free-space optics.

We investigate a possible extension of the optically connected parallel machine crossbar system to telecommunication routing-switching systems. The critical issue concerns the realization of a free-space interconnection system between two single-mode fiber arrays in the case of a fully interconnected architecture, such as a crossbar system. In particular, we assess the throughput capability of such a system. This evaluation is based on both theoretical analysis and experimental results. We demonstrate that the number of channels is severely constrained by the limited numerical aperture of a single-mode fiber. Finally, we discuss some architectural alternatives and propose some technical recommendations for interconnecting single-mode fiber arrays in free space.

Performance comparison of ferroelectric liquid-crystal-technology-based coherent optical multichannel correlators.

Our purpose is to compare two architectures when implemented with ferroelectric liquid-crystal technology: the conventional VanderLugt and joint transform correlators. The architectures are compared in the single-correlation and multichannel cases. The analysis covers both theoretical aspects and practical considerations regarding implementation. Specifications for a multichannel correlator design, including considerations of both spatial light modulators and architecture configurations, are discussed. Experimental results are presented for both architectures. Finally, the benefit resulting from extension to multichannel operation is discussed in terms of both multiplexing and algorithmic capabilities.

Complex amplitude modulation by use of liquid-crystal spatial light modulators.

We propose to study the conditions for implementation of complex amplitude modulation on standard liquid-crystal spatial light modulators when illuminated by polarized light. The spatial light modulators are used in a conventional configuration, i.e., the voltage is applied parallel to the wave-front propagation direction. The most commonly used liquid-crystal materials are compared and their usefulness in some general applications discussed. Their specificities with respect to different modulation types and application requirements are briefly described. Typical characteristics such as response time, modulation range, and wavelength insensitivity are also discussed. Finally, as an illustration, a first attempt at nomenclature is proposed for the case of a linearly polarized light.

Composite versus multichannel binary phase-only filtering.

Multichannel filtering and its inherent capacity for the implementation of data-fusion algorithms for high-level image processing, as well as composite filtering and its capacity for distortion-invariant pattern-recognition tasks, are discussed and compared. Both approaches are assessed by use of binary phase-only filters to simplify implementation issues. We discuss similarities and differences of these two solutions and demonstrate that they can be merged efficiently, giving rise to a new category of filters that we call composite-multichannel filters. We illustrate this comparison and the new filter design for the case of rotation-invariant fingerprint recognition. In particular, we show that the gain in terms of encoding capacity in the case of the composite-multichannel approach can be used efficiently to introduce multichannel-filter reconfigurability.

Scale-invariant optical correlators using ferroelectric liquid-crystal spatial light modulators.

New experimental results for scale-invariant implementations of the binary phase-only matched filter and the nonlinear joint transform correlator using ferroelectric liquid-crystal spatial light modulators are presented. We provide a comparative study of both architectures for real-time road-sign recognition. Signal-to-peak-noise ratios in excess of 5 dB over a scale range of 1.0 to 2.0 are achieved under realistic conditions of clutter.

Binary logic based purely on Fresnel diffraction.

Binary logic operations on two-dimensional data arrays are achieved by use of the self-imaging properties of Fresnel diffraction. The fields diffracted by periodic objects can be considered as the superimposition of weighted and shifted replicas of original objects. We show that a particular spatial organization of the input data can result in logical operations being performed on these data in the considered diffraction planes. Among various advantages, this approach is shown to allow the implementation of dual-track, nondissipative logical operators. Image algebra is presented as an experimental illustration of this principle.

120 x 100 pixel antiblooming array based on optically addressed ferroelectric liquid-crystal cells.

We describe the principle and the operation of a 120 x 100 pixel antiblooming array. Each cell in the array is made up of a hydrogenated amorphous silicon photoconductor layer driving a ferroelectric liquid-crystal shutter. The device is designed to be coupled with a CCD camera to prevent high-blooming overload and image lag.

Fractional Talbot four-level phase-only holograms using ferroelectric liquid-crystal spatial light modulators.

We propose a new technique for generating a four-level reconfigurable phase-only hologram, using two binary phase {0,pi} ferroelectric liquid-crystal spatial light modulators. The principle is based on the self-imaging properties of periodic structures operating in a Fresnel field double-diffraction system. Fractional Talbot planes are shown to be of particular interest. The problem of hologram bandwidth reduction that results from the holographic pattern replication is addressed. A trade-off between diffraction efficiency and hologram coding capacity is considered.