Yasser Alayli

Visible light communications: Application to cooperation between vehicles and road infrastructures

The last couple of years, the vehicle industry tends to increase the performance of 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 design or power adjustments. Furthermore, led systems are also very convenient for intensity modulation used in telecommunication fields. We developed a very simple data transmission system based on led lights which is highly robust for short or medium distances ± from a few meters up to 15 meters. This visible light communication is dedicated to the cooperation between vehicles and road infrastructures to enhance traffic security. This paper explains the choices and first results on the data transmission performances. In this paper, we present a first prototype of our system and experimental results.

Enlarged atomic force microscopy scanning scope: Novel sample-holder device with millimeter range

We propose a homemade sample-holder unit used for nanopositionning in two dimensions with a millimeter traveling range. For each displacement axis, the system includes a long range traveling 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. For this we chose to characterize highly integrated optical structures. For this purpose, the sample holder was integrated into an atomic force microscope. A millimeter scale topographical image demonstrates the overall performances of the combined system.

Heterodyne interferometric technique for displacement control at the nanometric scale

We propose a method of displacement control that addresses the measurement requirements of the nanotechnology community and provide a traceability to the definition of the meter at the nanometric scale. The method is based on the use of both a heterodyne Michelson’s interferometer and a homemade high frequency electronic circuit. The system so established allows us to control the displacement of a translation stage with a known step of 4.945 nm. Intrinsic relative uncertainty on the step value is 1.6×10−9. Controls of the period of repetition of these steps with a high-stability quartz oscillator permits to impose an uniform speed to the translation stage with the same accuracy. This property will be used for the watt balance project of the Bureau National de Metrologie of France.

A 2D nano-positioning system with sub-nanometric repeatability over the millimetre displacement range

We propose a 2D displacement control system with sub-nanometric repeatability on position over the millimetre travel range on both axes. It could be useful for nanofabrication processes or other applications related to the nanotechnology community. In our case, the apparatus is planned to be used in atomic force microscopes and lithography systems as a sample-holding device. The method is based on a heterodyne interferometric sensor and a home-made high frequency phase-shifting electronic board. This paper presents the complete mechanical system and gives experimental results showing a repeatability of 0.5 nm over a moving range of 5 mm.

Highly accurate positioning control method for piezoelectric actuators based on phase-shifting optoelectronics

We propose a sub-nanometric positioning control method for piezoelectric actuators based on a home-made high frequency phase shifting electronic circuit and a heterodyne interferometer. The method has been set up. Using a readily available piezoelectric actuator, we demonstrate that our method allows back and forth displacement without nonlinearities. Repeatability of 0.053 nm has been obtained over 1 µm displacement range. Displacement steps as low as 260 pm are presented. Such a method could be very useful for the nanotechnology and nanometrology communities for nano-scale manipulations or nano-assembly applications.

Visible light communications cooperative architecture for the intelligent transportation system

This paper presents the experimental results for a cooperative system that uses Infrastructure-to-Vehicle (I2V) and Vehicle-to-Vehicle (V2V) communication to increases the traffic safety, efficiency and adaptability. The wireless communication technique chosen to enable the data transmission is Visible Light Communication (VLC) due to its numerous advantages. The system consists of a commercial LED-based traffic light as a Road-Side-Unit (RSU) emitter, a transceiver that receives the message from the traffic light and retransmits it to the vehicle behind by using the tail lights, and also a second receiver that receives the message from the transceiver. Measurements exhibit a Bit Error Ratio of 10-7, both for the I2V and V2V, without using any complex error correction codes, which is considered good, even for traffic safety applications. The tests results show that the proposed cooperative system allows the RSU to communicate with vehicles outside the service area by using multi-hop communication.

A robust system for visible light communication

In this paper, we present the second version of our system which is dedicated to Visible Light Communication (VLC) for automotive applications. It exhibits improved performances compared to the first version regarding the distance for which data are transmitted. It also includes real time variable gain adjustment in order to increase robustness against environmental conditions. The system is detailed and experimental results are provided.

A new type of fiber-optic-based interferometric ellipsometer for in situ and real-time measurements

It is shown that it is possible to improve interferometric ellipsometers by using a Pockels cell or a Bragg cell hence avoiding the use of any moving components. Furthermore, these methods allow one to increase the beat frequency signal permitting a better insensitiveness to mechanical disturbances. It is also shown how to incorporate an optical fiber between the neutral beam splitter and the sample without losing any information concerning the ellipsometric angles of the sample. Several configurations are described and theoretically analyzed. The last ones do not contain any active component around the sample. They offer a new measurement technique for real-time and in situ measurements.

Note: Multiscale scanning probe microscopy

Combining the nanoscopic and macroscopic worlds is a serious challenge common to numerous scientific fields, from physics to biology. In this paper, we demonstrate nanometric resolution over a millimeter range by means of atomic-force microscopy using metrological stage. Nanometric repeatability and millimeter range open up the possibility of probing components and materials combining multiscale properties i.e., engineered nanomaterials. Multiscale probing is not limited to atomic-force microscopy and can be extended to any type of scanning probe technique in nanotechnology, including piezoforce microscopy, electrostatic-force microscopy, and scanning near-field optical microscopy.

High accuracy velocity control method for the french moving-coil watt balance

We describe a novel method of velocity control dedicated to the French moving-coil watt balance. In this project, a coil has to move in a magnetic field at a velocity of 2 mm s−1 with a relative uncertainty of 10−9 over 60 mm. Our method is based on the use of both a heterodyne Michelson’s interferometer, a two-level translation stage, and a homemade high frequency phase-shifting electronic circuit. To quantify the stability of the velocity, the output of the interferometer is sent into a frequency counter and the Doppler frequency shift is recorded. The Allan standard deviation has been used to calculate the stability and a σy(τ) of about 2.2×10−9 over 400 s has been obtained.