Norbert Fabre

Micro-deformable mirror for next-generation adaptive optical systems

Next generation giant telescopes as well as next generation instrumentation for 10m-class telescopes relies on the availability of highly performing adaptive optical systems. Different types of AO systems are currently under study, including Multi-Conjugate AO (MCAO), high dynamic range AO, and low-order AO for distributed partial correction AO. These systems require a large variety of deformable mirrors with very challenging parameters. The development of new technologies based on micro-opto-electro-mechanical systems (MOEMS) is promising for future deformable mirrors. The major advantages of the micro-deformable mirrors (MDM) are their compactness, scalability, and specific task customization using elementary building blocks. We are currently developing a MDM based on an array of electrostatic actuators with attachments to a continuous mirror on top. A high optical quality mirror is the most challenging building block for this device. The originality of our approach lies in the elaboration of a sacrificial layer and of a structural layer made of polymer materials. With this structure, very efficient planarization has been obtained: the long-distance flatness is below 0.2 μm, the print-through of localized 9μm steps is reduced to below 0.5μm and a rms roughness of 15 nm has been measured over the surface. The integration of this mirror surface on top of an actuator array is under investigation.

Tunability of Carbon NanoTubes Resistance Deposited by Inkjet Printing at Low Temperature

A deposition method based on inkjet printing technology and conductive double-wall carbon nanotubes (DWNT) suspension is, hereby, presented. The approach exploits the selective transfer capabilities offered by the inkjet printing process and the excellent conductive characteristics of the available DWNTs, in order to realize microelectronic interconnects of arbitrary patter and given electrical properties. The DWNTs are prepared by CCVD process, oxidized and dispersed in ethylene-glycol (EG) and in water solution. The DWNTs lines are fabricated on tests structures and then characterized through impedance and current-voltage measurements. 400 μm long and 90 μm wide transmission lines have been printed by varying the number of overwrites for given DWNT density. The results confirm that the DC resistance of DWNTs lines can be changed according to the number of overwrites and that the lines preserve ohmic characteristics up to 100 MHz.

Manufacturability of gas sensor with ZnO nanoparticles suspension deposited by ink jet printing

Zinc oxide is used in many applications thanks to its various characteristics as well as photoresistivity, piezoelectricity, wide band gap for power components but also its capability for gas detection. In this article, we first present new process based on ZnO nanoparticles from Sigma Aldrich manufacturer; a stable ink obtained by mixing 10% weight of commercial powder with ethylene glycol, has been deposited by ink-jet printing on a silicon oxide substrate covered by platinum interdigitated electrodes. To obtain homogeneous deposits of nanoparticles, the working area of the sensor was bounded by functionalisation by the n-Octadecyltrichlorosilane. These deposits were optimized at 65°C. Then, the study was focused on the correlation between parameters of deposit and global resistance and gas sensitivity: conductivity for different operating temperatures under methane and isopropyl alcohol vapours. The best results have been obtained for thicknesses in the range of 0.5 and 2.5 μm. The ZnO resistance is stable under gas from 200°C and the relative sensitivity to methane and isopropyl alcohol are maximum and opposite at 225°C and 300°C respectively. This work shows that ink-jet is a promising technique to manufacture a new generation of low cost gas sensors at lower temperature deposition.

Design, fabrication, and thrust prediction of solid propellant microthrusters for space application

With the development of microspacecraft technology micropropulsion concepts are introduce for course correction, orbit insertion as well as attitude control of the microspacecraft. In this context, we have introduced a new concept of MEMS based technology microthruster responding to the spatial constraints and MEMS characteristics. The originality and advantages of these new thrusters is the use of only one solid propellant stored in a small tank micromachined in a ceramic or silicon substrate and the possibility of fabricating arrays of N addressable independently microthrusters in the same chip. The thrust force generated can be set from a few (mu) N to a few 150mN by geometrical and dimensional considerations. Fabrication and assembly of array of 16 microthrusters proved the technological feasibility and the functioning performances of this new concept of small scale thrusters.

MOEMs devices for future astronomical instrumentation in space

Based on the micro-electronics fabrication process, Micro-Opto-Electro-Mechanical Systems (MOEMS) are under study in order to be integrated in next-generation astronomical instruments for ground-based and space telescopes. Their main advantages are their compactness, scalability, specific task customization using elementary building blocks, and remote control. At Laboratoire d’Astrophysique de Marseille, we are engaged since several years in the design, realization and characterization of programmable slit masks for multi-object spectroscopy and micro-deformable mirrors for wavefront correction. First prototypes have been developed and show results matching with the requirements.

MOEMs devices designed and tested for future astronomical instrumentation in space

Next generation of astronomical instrumentation for space telescopes requires Micro-Opto-Electro- Mechanical Systems (MOEMS) with remote control capability and cryogenic operation. MOEMS devices have the capability to tailor the incoming light in terms of intensity and object selection with programmable slit masks, in terms of phase and wavefront control with micro-deformable mirrors, and finally in terms of spectrum with programmable diffraction gratings. Applications are multi-object spectroscopy (MOS), wavefront correction and programmable spectrographs. We are engaged since several years in the design, realization and characterization of MOEMS devices suited for astronomical instrumentation.

Study of two-dimensional photonic crystals cavity using organic gain materials

In this paper, we report the investigation of two-dimensional organic photonic crystal microcavity laser (2D OPCM). The gain medium consists of an Alq3:DCJTB layer deposited on a planar Si3N4 photonic crystal microcavity. Both H2 and L3 photonic crystal cavities are studied in terms of quality factor and the resonance wavelength by 3D FDTD simulations. The structures are characterized under optical pumping by using a Nd:YAG frequency-tripled laser emitting at 355 nm with a repetition frequency of 10 Hz and a pulse duration of 6 ns. A laser peak at 652 nm is observed for both cavities with lasing thresholds of 0.014 nJ and 0.017 nJ for the H2 and the L3 cavities, respectively.

Polymer-based micro-deformable mirror for adaptive optics applications

Next generation giant telescopes as well as next generation instrumentation for 10m-class telescopes relies on the availability of highly performing adaptive optical systems, for studying new fields like circumstellar disks and extrasolar planets. These systems require deformable mirrors with very challenging parameters, including number of actuators up to 250 000 and inter-actuator spacing around 500μm. MOEMS-based devices are promising for future deformable mirrors. However, only limited strokes for large driving voltages have been demonstrated. In order to overcome these limitations, we are currently developing a micro-deformable mirror based on an array of electrostatic actuators with attachment posts to a continuous mirror on top. The originality of our approach lies in the elaboration of a sacrificial layer and of a structural layer made of polymer materials, using low-temperature process. This process allows the realization of high optical quality mirrors on top of an actuator array made with various techniques. We have developed the first polymer piston-motion actuator in order to reach high strokes for low driving voltages: a 10μm thick mobile plate with four springs attached to the substrate, and with an air gap of 10μm exhibits a piston motion of 2μm for 30V. Preliminary comparison with FEM models show very good agreement and design of a complete polymer-based MDM looks possible.