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LEDs will replace in a near future the current worldwide lighting mainly due to their low production-cost and energy-saving assets. Visible light communications (VLC) will turn gradually the existing lighting network into a communication network. Nowadays VLC transceivers can be found in some commercial centres in Europe; some of them broadcast continuously an identification tag that contains its coordinate position. In such a case, the transceiver acts as a geolocation beacon. Nevertheless, mobile transceivers represent a challenge in the VLC communication chain, as smartphones have not integrated yet a VLC customized detection stage. In order to make current smartphones capable to detect VLC broadcasted signals, their Ambient Light Sensor (ALS) is adapted as a VLC detector. For this to be achieved, lighting transceivers need to adapt their modulation scheme. For instance, frequencies representing start bit, 1, and 0 logic values can be set to avoid flicker from illumination and to permit detecting the under-sampled signal. Decoding the signal requires a multiple steps real-time signal processing as shown here.

L’arrivee de diodes electroluminescentes (LED) plus puissantes et plus rapides a permis de penser a leur utilisation comme des transmetteurs d’information. La lumiere emise par les LED devient un canal de communication sans fil permettant des applications dans des espaces interieurs et dans certains cas dans des espaces ouverts. Nous connaissons ce type de communications sous le nom de « Li-Fi ».

The information networks of the future will consist of an all-optical core, with wireless access technologies wherever possible. The fibre networks are extending their reach rapidly, and will further extend to individual spaces within homes and office buildings. The data traffic on networks and the demand for wireless services are also growing exponentially and the nature of services is also evolving with rapid increase in the number of devices. A new generation of 3D displays, with the ability to create Virtual Reality (VR) environments, is being launched. VR technology places significant demands on bandwidth, latency, positioning and mobility. One challenge addressed by our European collaborative project WORTECS is the development of an optical wireless system able to deliver ultra-high throughput (up to Tbps). The first demonstrator focuses on a high density network that can provide > 1 Gbps per user with multi user, but has the potential to provide Tbps per indoor environment. The second demonstrator focuses on ultra-high data rate links with a novel fibre-optical wireless-fibre approach to create Tbps capable links. VR is targeted as a demanding application, however, other applications include wireless data centers and aircraft cabins. In this paper, after introduction on the demand for wireless Terabit/s communication, we will focus on VR use case and the need for multi-Gigabit/s data rates. Then we will present the challenges for the project and propose new optical wireless system architecture and system engineering associated to new approach in space and frequency diversity with OFDM and adaptive bit rate for VR.

Visible Light Communications (VLC) use LEDbase lighting as transmitters. This is a typical use case in current VLC lighting systems. The lighting becomes a beacon to transmit its coordinates and other kind of information at low-transmission rates, typically 1 kbps. This can easily permit the smartphone's camera to get and decode the message. Transmitting information by light can decrease the luminous emittance because of off-state used to transmit logic zeros. Here, we have modified the transmission code to increase lighting efficiency while continue to use light in transmissions.

Visible Light Communications (VLC) receivers adapted to be used in high transmission rates will eventually use either, high aperture lenses or non-linear optical elements capable of converting light arriving to the receiver into an electric signal. The high aperture lens case, reveals a challenge from an optical designers point-of-view. As a matter of fact, the lens must collect a wide aperture intensity flux using a limited aperture as its use is intended to portable devices. This last also limits both, lens thickness and its focal length. Here, we show a first design to be adapted to a VLC receiver that take these constraints into account. This paper describes a method to design catadioptric and monolithic lenses to be used as an optical collector of light entering from a near point light source as a spherical fan L with a wide acceptance angle α◦ and high efficiency. These lenses can be mass produced and therefore one can find many practical applications in VLC equipped devices. We show a first design for a near light source without magnification, and second one with a detector’s magnification in a meridional section. We utilize rigorous geometric optics, vector analysis and ordinary differential equations.

The ability of red blood cells (RBC) to deform under vascular conditions is essential for circulation. RBC deformability, measured at different shear rates and osmolalities, provides a useful way to evaluate RBC function and is used to diagnose several hereditary blood disorders. In clinical practice, ektacytometry has been used as a routine automated technique for measuring RBC deformability under shear stress at known osmolalities. RBC suspension is exposed to laser light and the resulting diffraction pattern is recorded. The mean deformability of the cells is characterized by the diffraction pattern. Our study is the first to compare the correspondence between two methods that measure diffraction simultaneously, on the same apparatus. Additionally, while others conducted studies under varying shear we used varying osmolalities. A laser beam splitter produced two identical diffraction patterns, evaluated by synchronous data acquisition and analysis: One pattern was acquired by a digital camera and analyzed by image processing software. The other was analyzed using photodiode measurement at four fixed points and a microcontroller interface. Data analysis resulted in two deformability vs. osmolality curves. Comparing these curves shows excellent overlap in shape with a clear difference in amplitude. Since routine Manuscript received Jan 15, 2013; revised March 1, 2013. patient curves are always compared to a normal control curve, the amplitue difference is not significant. Our results indicate that either method may be used for clinically-usable interpretation of RBC deformability, but also that additional studies are required in order to compare repeatability for both methods, and to demonstrate that the two curves overlap for a variety of pathologies.

For over a century and Mr. Guglielmo Marconi invention, systems using radio waves have controlled over wireless telecommunication solutions; from Amplitude Modulation (AM) radio products to satellite communications for instance. But beyond an increasingly negative opinion face to radio waves and radio spectrum availability more and more reduced; there is an unprecedented opportunity with LED installation in displays and lighting to provide optical wireless communication solutions. As a result, technologically mature solutions are already commercially available for services such as Location Based Services (LBS), broadcast diffusion or Intelligent Transport Services (ITS). Pending finalization of the standard review process IEEE 802.15.7 r1, our paper presents the results of the European collaborative project named "ACEMIND". It offers an indoor bilateral optical wireless communication prototype having the following characteristics: use of the existing electrical infrastructure, through judicious combination with Light Fidelity (LiFi), Power Line Communication (PLC) and Ethernet to reduce the implementation cost. We propose a bilateral optical wireless communication even when the light is switched off by using Visible Light Communication (VLC) and Infra-Red Communication (IRC) combined to a remote optical switch. Dimensionally optimized LiFi module is presented in order to offer the possibility for integration inside a laptop. Finally, there is operational mechanism implementation such as OFDM/DMT to increase throughput. After the introduction, we will present the results of a market study from Orange Labs customers about their opinion on LiFi components. Then we will detail the LiFi prototype, from the physical layer aspect to MAC layer before concluding on commercial development prospects.

We describe an efficient continuous-wave diode-pumped Nd:YLiF4 laser oscillating on the σ-polarized 4F3/2-4I13/2 transition at λω = 1312 nm. With a simple linear cavity laser, we reached an intracavity power of 310 W at λ = 1312 nm for 16 W of absorbed pump power (λp ~ 806 nm). A 0.25 W of tunable radiation (λ2ω = 656−658 nm) was obtained by intracavity second-harmonic generation (SHG) with a 5 × 5 × 7 mm3β-BaB2O4 crystal. Up to 10 mW of tunable single-frequency operation was observed using a 200 μm thin fused silica intracavity solid etalon. The optimal waist for a maximum conversion efficiency has been calculated theoretically using Boyd and Kleiman model. For the 1312–656 nm SHG, we found a walk-off parameter B = 8.99 and an optimal waist of 25 μm. Comparing to the experimental measurement of the optimal waist, we found a relative discrepancy of 2.84 × 10-2. This laser is dedicated to the spectroscopic study of silver atoms trapped in a buffer-gas-free paraffin coated Pyrex cell that will be used in a compact atomic optical clock.

In the last years, two main ICT enablers have been massively explored to enforce vehicular safety: GNSS-based positioning and wireless communications. In fact, by exchanging information on their respective positions, vehicles are expected to be timely aware of the hazards around them and, consequently, to be able to promptly react, hopefully decreasing the rate of accidents. Both wireless communications and positioning are unfortunately far from being ideal, especially on board: however, as recently proposed, they may both significantly benefit from the integration of the emerging Light-Fidelity (Li-Fi) technology. The paper discusses the Li-Fi perspective, shedding light on its potential benefits and issues, also with practical consideration.

This paper presents a model to design bi-aspherical catadioptric lenses with limited image diffraction. A first refractive Cartesian oval surface that does not introduce any spherical aberration is used. When total internal reflection occurs, this surface can also be simultaneously used as a mirror. The reflective characteristics of Cartesian ovals are also well described in this paper. The theoretical work described here can considerably reduce computing time in optical system design. This model is applied to examples of antennae design for visible light communications (VLC).

International audience; In this paper, we present the second versionof our system which is dedicated to Visible LightCommunication (VLC) for automotive applications. Itexhibits improved performances compared to the firstversion regarding the distance for which data aretransmitted. It also includes real time variable gainadjustment in order to increase robustness againstenvironmental conditions. The system is detailed andexperimental results are provided.

International audience; — This paper presents a visible light communication system, focusing mostly on the aspects related with the hardware design and implementation. The designed system is aimed to ensure a highly-reliable communication between a commercial LED-based traffic light and a receiver mounted on a vehicle. Enabling wireless data transfer between the road infrastructure and vehicles has the potential to significantly increase the safety and efficiency of the transportation system. The paper presents the advantages of the proposed system and explains same of the choices made in the implementation process. Keywords — intelligent transportation system, light emitting diode, traffic light, vehicle safety, visible light communications. I. INTRODUCTION Light Emitting Diodes (LEDs) are highly reliable, energy efficient and have a lifetime that exceeds by far the classical light sources. These unique features made the car manufacturers thinking of replacing the halogen lamps by LED lighting systems. At this moment, car lights based on LEDs are common. The efficiency of the LEDs made them being used also for LED-based traffic lights. This new generation of traffic lights is becoming more and more popular and begins to be used on extended scale. The main advantages of these traffic lights are: low maintenance cost, long life, low energy consumption and better visibility. These advantages had already convinced some of the cities authorities to replace the classical traffic lights with new generation LED-based traffic lights [1, 2] whereas, other cities are progressively do this replacement. Besides the advantages mentioned above, LEDs are capable of rapid switching, which enables them to be used for Visible Light Communications (VLC). VLC uses the visible light spectrum as a communication medium and since there are no regulations that limit the use of the light spectrum, VLC has the potential to reach extremely high data rates [3].

International audience; This paper presents the experimental results fora cooperative system that uses Infrastructure-to-Vehicle (I2V)and Vehicle-to-Vehicle (V2V) communication to increases thetraffic safety, efficiency and adaptability. The wirelesscommunication technique chosen to enable the data transmissionis Visible Light Communication (VLC) due to its numerousadvantages. The system consists of a commercial LED-basedtraffic light as a Road-Side-Unit (RSU) emitter, a transceiver thatreceives the message from the traffic light and retransmits it tothe vehicle behind by using the tail lights, and also a secondreceiver that receives the message from the transceiver.Measurements exhibit a Bit Error Ratio of 10-7, both for the I2Vand V2V, without using any complex error correction codes,which is considered good, even for traffic safety applications. Thetests results show that the proposed cooperative system allows theRSU to communicate with vehicles outside the service area byusing multi-hop communication.

International audience; Since a few years, the vehicle industry tends to increase the performances of the lights based on led technologies. Nowadays, led systems are used as a standard by motor vehicles manufacturers. Led lights present higher reliability and are more flexible regarding the design or power adjustments. Furthermore, led systems are also very convenient for intensity modulation like in telecommunication fields. We developed a very simple data transmission system based on led that aims to be highly robust at short or medium distances - a few meters up to 15 meters. This visible light communication is dedicated to the cooperation between vehicles and road infrastructures to enhance the security of the traffic. This paper explains the choices and first results on the data transmission performances. In this paper, we present a first prototype of the system we made and experimental results.

In order to assure hygiene safety for patients, optimal use of drugs is necessary for controlling the number of clinically observed tumor cells. Based on a mathematical model of drug therapy for cancer, and on an objective function, the optimal solution is reached. The model therapy is considered for an individual patient over a fixed time horizon. The disease dynamics are given by an ordinary differential equation that describes the evolution of cancer cells in time. An optimization theory is applied in order to minimize the number of cancer cells at the end of treatment. A comparative study is performed on different treatments profiles applied to different types of cancer. This study shows the usefulness of the suggested mathematical deterministic or hybrid model. It considers the treatment in terms of duration and drug dosage, the initial number of detected cancer cells and the objective function.

Common laser wavemeters are based on a scanning Michelson interferometer. Displacements of the moving mirror as long as tens of centimeters are needed to reach a relative accuracy of 1 × 10(-6) (1σ) on the unknown laser wavelengths. Such a long displacement range makes the system very sensitive to mechanical vibrations and to misalignments of the laser beams. The purpose of this paper is to demonstrate a new concept of laser wavemeter based on the measurements of the ellipsometric parameters ψ and Δ of the laser beams. Experimental results show that a 10(-6) (1σ) accuracy level could be reach with a displacement range of only 4 μm. Implementations of the device are described. Comparisons between our polarimetric wavemeter and a calibrated wavemeter are presented for two lasers, an extended cavity laser diode at 656 nm and a 532 nm green line Nd:YAG laser.

We developed a home-made sample-holder unit used for 2D nano-positioning with millimeter travelling ranges. For each displacement axis, the system includes a long range travelling stage and a piezoelectric actuator for accurate positioning. Specific electronics is integrated according to metrological considerations, enhancing the repeatability performances. The aim of this work is to demonstrate that near-field microscopy at the scale of a chip is possible. We chose here to characterize highly integrated optical structures. For this purpose, the sample-holder is integrated into an Atomic Force Microscope in order to perform optical imaging. To demonstrate the overall performances, a millimeter scale optical images have been realized.

We show how a Fabry Perot interferometer could be used to determine the gravitational axis of the earth g with an high sensitivity. Our method lie g axis to an optical beat frequency value between two lasers. The principle is described and a budget error is presented. The sensitivity of the sensor is estimated to be below of 85 nrad/MHz. This method could be used as a high sensitivity and absolute tilt sensor or even as a seismometer. This sensor is dedicated to the french watt balance project as described in this paper.

We propose an alternative design to the wavemeters based on scanning Michelson interferometers. Using realistic experimental parameters, we show that a relative accuracy of one part in 6x10 -8 can be reached with a displacement of the target mirror of only 360 mm. This improvment becomes possible thanks to the significant advances in polarimetry that permit measurement of the ellipsometric parameters p and D with an accuracy of 0.07° with readily-available commercial equipment. This leads to an interpolation rate of l/10000. The proposed method has been setup and the chief parameters limiting its accuracy are determined.

Since few years ago, visible light communications (VLC) have experience an accelerated interest from a research point of view. The beginning of this decade has seen many improvements in VLC at an electronic level. High rates of transmission at low bit error ratios (BER) have been reported. A few numbers of start-ups have initiated activities to offer a variety of applications ranging from indoor geo-localization to internet, but in spite of these advancements, some other problems arise. Long-range transmissions mean a high BER which reduce the number of applications. In this sense, new redesigned optical collectors or in some cases, optical reflectors must be considered to ensure a low BER at higher distance transmissions. Here we also expose a preliminary design of a catadioptric and monolithical lens for a LI-FI receiver with two rotationally symmetrical main piecewise surfaces za and zb. These surfaces are represented in a system of cylindrical coordinates with an anterior surface za with a central and refractive sector surrounded by a peripheral reflective sector and a back piecewise surface zb with a central refractive sector and a reflective sector, both characterized as ideal for capturing light within large acceptance angles.