3D displacement field measurement with correlation based on the micro-geometrical surface texture

Image correlation methods are widely used in experimental mechanics to obtain displacement field measurements. Currently, these methods are applied using digital images of the initial and deformed surfaces sprayed with black or white paint. Speckle patterns are then captured and the correlation is performed with a high degree of accuracy to an order of 0.01 pixels. In 3D, however, stereo-correlation leads to a lower degree of accuracy. Correlation techniques are based on the search for a sub-image (or pattern) displacement field. The work presented in this paper introduces a new correlation-based approach for 3D displacement field measurement that uses an additional 3D laser scanner and a CMM (Coordinate Measurement Machine). Unlike most existing methods that require the presence of markers on the observed object (such as black speckle, grids or random patterns), this approach relies solely on micro-geometrical surface textures such as waviness, roughness and aperiodic random defects. The latter are assumed to remain sufficiently small thus providing an adequate estimate of the particle displacement. The proposed approach can be used in a wide range of applications such as sheet metal forming with large strains. The method proceeds by first obtaining cloud points using the 3D laser scanner mounted on a CMM. These points are used to create 2D maps that are then correlated. In this respect, various criteria have been investigated for creating maps consisting of patterns, which facilitate the correlation procedure. Once the maps are created, the correlation between both configurations (initial and moved) is carried out using traditional methods developed for field measurements. Measurement validation was conducted using experiments in 2D and 3D with good results for rigid displacements in 2D, 3D and 2D rotations.     

Fourier-transform, integrated-optic spatial heterodyne spectrometer on a silica-based planar waveguide with 1 GHz resolution

Spatial heterodyne spectrometers (SHS) can achieve high resolution with excellent optical throughput. We demonstrate a planar waveguide SHS incorporating 64 asymmetric Mach-Zehnder interferometers and show measurements that verify 1 GHz resolution across a 64 GHz measurement range.     

Nonlinear friction dynamics on fibrous materials, application to the characterization of surface quality. Part?II: local characterization of phase space by recurrence plots

As has been shown in the first part of this series of papers, the global analysis of phase spaces does not allow one to access topographies of attractors, generated by the singular dynamic contacts between MODALSENS and our evaluated fibrous surfaces. By using the same time series from MODALSENS, this second paper presents a local exploration of the recurrences of the phase spaces. As a complement of the results from Part I, we propose, in this part of the work, a finer analysis of the vibrations of MODALSENS. Therefore, this part of the work aims at tracing friction dynamics cartographies of fibrous surfaces with the help of Recurrence Plots. This tool allows one to obtain images of recurrences in the space portraits. Hence, by regarding passages between strong and low magnitudes of vibrations, it is possible to take into account strong heterogeneities of relief and also the various mechanical and frictional behaviors of the asperities encountered during friction. Finally, Recurrence Quantification Analysis is performed in order to discuss the relationship between expected performances of the tested surfaces and their friction dynamics behaviors.     

Management of the electrical injection uniformity in broad-area top-emitting VCSELs

The electrical properties of broad-area 850 nm top emitting VCSELs have been investigated in order to improve carrier injection uniformity in their active zone. First, we have demonstrated using an electrical simulation tool that a multi-point localized injection design associated with a spreading layer at the top of the device (ITO) can lead to a significant improvement of carrier injection and on its spatial distribution. Secondly, the electrical contrast achievable by applying this method with localized etchings has been experimentally measured. Finally, stripe-shaped devices with output power up to 50 mW in a continuous-wave operation at room temperature have been demonstrated.