Polarization conversion by dielectric subwavelength gratings in conical mounting

Subwavelength dielectric gratings are examined in total-internal-reflection configuration. It is demonstrated experimentally that such elements, fabricated in TiO2, can perform full polarization conversion from incident TE to TM with nearly 100% efficiency. The dependence of the polarization conversion on the angle of incidence is analyzed. Rigorous diffraction theory is used to cross check the experimental results

Matrixes of unconventional micro-optical components molded with etched silicon

This paper reports on a process to create microlenses characterized by unconventional footprints, spherical profiles and a wide range of sizes. Fabricated shapes such as squares, rectangles, ellipses, triangles and hexagons are tested alone as well as in matrix with high fulfill factors. The technique is based on molds from which microlenses are fabricated by UV-molding replication. The molds are produced by silicon wet isotropic etching in an acid solution. The process is mainly steered by temperature and etching concentration. The use of the proposed technology opens a wide range of geometries allowing the fabrication of microlenses matrices with high fulfill factors as well as microlenses for beam-shaping

Reduction of helium permeation in microfabricated cells using aluminosilicate glass substrates and Al2_2O3_3 coatings

The stability and accuracy of atomic devices can be degraded by the evolution of their cell inner atmosphere. Hence, the undesired entrance or leakage of background or buffer gas, respectively, that can permeate through the cell walls, should be slowed down. In this work, we investigate helium permeation in microfabricated alkali vapor cells filled with He and whose windows are made of borosilicate glass (BSG) or aluminosilicate glass (ASG). The permeation is then derived from routine measurements of the pressure-shifted hyperfine transition frequency of an atomic clock. We first confirm that ASG reduces He permeation rate by more than two orders of magnitude, in comparison with BSG. In addition, we demonstrate that Al$_2$O$_3$ thin-film coatings, known to avoid alkali consumption in vapor cells, can also significantly reduce He permeation. The permeation through BSG is thereby reduced by a factor 110 whereas the one through ASG is decreased by a factor up to 5.8 compared to uncoated substrates. These results may contribute to the development of miniaturized atomic clocks and sensors with improved long-term stability or sensitivity.Comment: 7 pages, 5 figure

Beam-shaping longitudinal range of a binary diffractive optical element

International audienc

Multi-wafer bonding technology for the integration of a micromachined Mirau interferometer

The paper presents the multi-wafer bonding technology as well as the integration of electrical connection to the z-scanner wafer of the micromachined array-type Mirau interferometer. A Mirau interferometer, which is a key-component of optical coherence tomography (OCT) microsystem, consists of a microlens doublet, a MOEMS Z-scanner, a focus-adjustment spacer and a beam splitter plate. For the integration of this MOEMS device heterogeneous bonding of Si, glass and SOI wafers is necessary. Previously, most of the existing methods for multilayer wafer bonding require annealing at high temperature, i.e., 1100 degrees C. To be compatible with MEMS devices, bonding of different material stacks at temperatures lower than 400 degrees C has also been investigated. However, if more components are involved, it becomes less effective due to the alignment accuracy or degradation of surface quality of the not-bonded side after each bonding operation. The proposed technology focuses on 3D integration of heterogeneous building blocks, where the assembly process is compatible with the materials of each wafer stack and with position accuracy which fits optical requirement. A demonstrator with up to 5 wafers bonded lower than 400 degrees C is presented and bond interfaces are evaluated. To avoid the complexity of through wafer vias, a design which creates electrical connections along vertical direction by mounting a wafer stack on a flip chip PCB is proposed. The approach, which adopts vertically-stacked wafers along with electrical connection functionality, provides not only a space-effective integration of MOEMS device but also a design where the Mirau stack can be further integrated with other components of the OCT microsystem easily

Technological platform for vertical multi-wafer integration of miniature imaging instruments

We describe a technological platform developed for miniaturization of optical imaging instruments, such as laser scanning confocal microscopes or Optical Coherence Tomography devices. The platform employs multi-wafer vertical integration approach, combined with integrated glass-based micro-optics and heterogeneous bonding and interconnecting technologies. In this paper we focus on the unconventional fabrication methods of monolithic micro-optical structures and components in borosilicate glass (e. g. micro beamsplitters, refractive microlenses) for optical beam shaping and routing. In addition, we present hybrid laser-assisted integration of glass ball microlenses on the silicon MEMS actuators for transmissive beam scanning as well as methods of electrical signals distribution through thick glass substrates, based on HF etched via holes