Georgia Tech Lorraine

About: Georgia Tech Lorraine is a education organization based out in Metz, France. It is known for research contribution in the topics: Terahertz radiation & Semiconductor laser theory. The organization has 201 authors who have published 291 publications receiving 4761 citations.

Optical Cryptosystem Based on Synchronization of Hyperchaos Generated by a Delayed Feedback Tunable Laser Diode

Abstract: We propose a method for encrypting a signal within the high dimensional chaotic fluctuations of the wavelength from a delayed feedback tunable laser diode. Decoding is performed remotely by using a slave laser diode fully synchronized with the master one. No additional synchronization channel is required.

Experimental observation of locally-resonant and Bragg band gaps for surface guided waves in a phononic crystal of pillars

Abstract: We report on the experimental study of the propagation of surface guided waves in a periodic arrangement of pillars on a semi-infinite medium. Samples composed of nickel pillars grown on a lithium niobate substrate were prepared and wide bandwidth transducers were used for the electrical generation of surface elastic waves. We identify a complete band gap for surface guided waves appearing at frequencies markedly lower than the Bragg band gap. Using optical measurements of the surface vibrations and by comparison with a finite element model, we argue that the low frequency band gap arises because of local resonances in the pillars. When resonance is reached, the acoustic energy is confined inside the pillars and transmission through the array is strongly reduced. At higher frequencies and inside the Bragg band gap, the incident surface elastic waves are almost completely reflected and the observed exponential decay of the transmission is similar to the case of phononic crystals made of holes in a substrate.

Coding for Secrecy: An Overview of Error-Control Coding Techniques for Physical-Layer Security

Abstract: While secrecy in communication systems has historically been obtained through cryptographic means in the upper layers, recent research efforts have focused on the physical layer and have unveiled ample opportunities for security design. In particular, the combination of signal processing techniques with channel coding for secrecy has been central to the development of physical-layer security efforts. Although implicit coding techniques for secrecy have been known since the 1970s, explicit code constructions have only been discovered within the last decade. The purpose of this article is to provide a synopsis of the state of the art in coding for secrecy. We discuss the general principles of coding, and we illustrate them with several examples. In particular, we discuss the importance of a nested code structure and stochastic encoding, which allow for both data reliability and security.

Nondestructive evaluation of forced delamination in glass fiber-reinforced composites by terahertz and ultrasonic waves

Abstract: Glass fiber-reinforced composite laminates in polyetherimide resin have been studied via terahertz imaging and ultrasonic C-scans. The forced delamination is created by inserting Teflon film between various layers inside the samples prior to consolidating the laminates. Using reflective pulsed terahertz imaging, we find high-resolution, low-artifact terahertz C-scan and B-scan images locating and sizing the delamination in three dimensions. Furthermore, terahertz imaging enables us to determine the thicknesses of the delamination and of the layers constituting the laminate. Ultrasonic C-scan images are also successfully obtained; however, in our samples with small thickness-to-wavelength ratio, detailed ultrasonic B-scan images providing quantitative information in depth cannot be obtained by 5 MHz or 10 MHz focused transducers. Comparative analysis between terahertz imaging and ultrasonic C-scans with regard to spatial resolution is carried out demonstrating that terahertz imaging provides higher spatial resolution for imaging, and can be regarded as an alternative or complementary modality to ultrasonic C-scans for this class of glass fiber-reinforced composites.