Christophe Gorecki

French National Centre for Scientific Research, Lutetia Parisorum, Île-de-France, France

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Publications (147)67.62 Total impact

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    ABSTRACT: Scientific articles focusing on fabrication of micro-components often evaluate their optical performances by techniques such as scanning electron microscopy or surface topography only. However, deriving the optical characteristics from the shape of the optical element requires using propagation algorithms. In this paper, we present a simple and intuitive method, based on the measurement of the intensity point spread function generated by the micro-component. The setup is less expensive than common systems and does not require heavy equipments, since it requires only a microscope objective, a CMOS camera and a displacement stage. This direct characterization method consists in scanning axially and recording sequentially the focal volume. Our system, in transmissive configuration, consists in the investigation of the focus generated by the microlens, allowing measuring the axial and lateral resolutions, estimating the Strehl ratio and calculating the numerical aperture of the microlens. The optical system can also be used in reflective configuration in order to characterize micro-reflective components such as molds. The fixed imaging configuration allows rapid estimation of quality and repeatability of fabricated micro-optical elements.
    SPIE Optical Engineering + Applications; 08/2014
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    ABSTRACT: This paper presents a simple method based on the measurement of the 3D intensity point spread function for the quality evaluation of high numerical aperture micro-optical components. The different slices of the focal volume are imaged thanks to a microscope objective and a standard camera. Depending on the optical architecture, it allows characterizing both transmissive and reflective components, for which either the imaging part or the component itself are moved along the optical axis, respectively. This method can be used to measure focal length, Strehl ratio, resolution and overall wavefront RMS and to estimate optical aberrations. The measurement setup and its implementation are detailed and its advantages are demonstrated with micro-ball lenses and micro-mirrors. This intuitive method is adapted for optimization of micro-optical components fabrication processes, especially because heavy equipments and/or data analysis are not required.
    Optics Express 06/2014; 22(11):13202-13212. · 3.55 Impact Factor
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    ABSTRACT: This paper reviews the progress made in the miniaturization of an isotropic space-qualified optically pumped magnetometer. Sensor isotropy is provided by a liquid crystal polarization rotator that sets the linear pumping beam polarization at 90◦ with respect to the ambient magnetic field. It allows a continuous polarization rotation from 0 to more than 300◦ with response times compatible with mobile or space applications. This rotator is nonmagnetic and can be easily integrated close to the gas cell. The miniature helium-4 sensor reaches a sensitivity of 10 pT/√Hz in a bandwidth from DC to 100 Hz. http://authors.elsevier.com/a/1PNBe3IC9cin~9
    Sensors and Actuators A Physical 05/2014; 216:386-393. · 1.84 Impact Factor
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    ABSTRACT: In this paper, we adapt a technique employed for glass microlenses fabrication in order to obtain matrices of millimeter size lenses for inspection applications. The use of microfabrication processes and Micro-Electro-Mechanical Systems (MEMS) compatible materials allow the integration of lenses larger than usual in microsystems. Since the presented lenses can have 2 mm in diameter or more, some aspects apparently irrelevant when diameters are lower than 500 μm must be reviewed and taken into account. Indeed, when the lenses are in the millimeter range, problems such as size nonuniformities within a matrix and asymmetric shapes of each lens are dependent on parameters as mask design, depth of the silicon cavities and enclosed vacuum control after anodic bonding, glass reflow temperature and even the position of the lenses on the substrate. Issues related to the fabrication flow-chart are addressed in this paper and solutions are proposed. First results are shown to prove the pertinence of this technique to fabricate MEMS-compatible millimetersized lenses to be integrated in miniature inspection systems. We also discuss some of the paths to follow that could help improving the performances.
    SPIE Photonics Europe; 05/2014
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    ABSTRACT: High-resolution miniature imaging systems require high quality micro-optical elements. Therefore, it is essential to characterize their optical performances in order to optimize their fabrication. Usually, basic evaluation of micro-optical elements quality is based on the measurement of their topography since their optical properties are largely defined by their shape. However, optical characteristics have to be derived from the measured geometry. An alternative method is the direct measurement of their optical properties. Unlike topography measurement, it allows characterization of high numerical aperture components. Moreover, it can be applied to single elements but also to optical systems composed of several micro-optical components. In this work, we propose a simple method based on the measurement of the 3D intensity point spread function (IPSF). IPSF is defined by the 3D shape of the focal spot generated by the micro-element. The direct characterization of focusing response through the measurement of IPSF allows very precise estimation of micro-structures quality. The considered method consists in imaging different slices of the focal volume generated by the focusing component. It allows, depending on the configuration, characterizing both transmissive and reflective micro-optical components.
    Optical Micro- and Nanometrology V, Brussels; 04/2014
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    ABSTRACT: The presented paper shows the concept and optical design of an array-type Mirau-based OCT system for early diagnosis of skin cancer. The basic concept of the sensor is a full-field, full-range optical coherence tomography (OCT) sensor. The micro-optical interferometer array in Mirau configuration is a key element of the system allowing parallel imaging of multiple field of views (FOV). The optical design focuses on the imaging performance of a single channel of the interferometer array and the illumination design of the array. In addition a straylight analysis of this array sensor is given. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
    SPIE Optical Micro- and Nanometrology V, Brussels; 04/2014
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    ABSTRACT: A process based on deep reactive ion etching (DRIE) has been developed and optimized for the fabrication of millimeter deep silicon cavities with smooth sidewalls. The process combines two approaches which involve an optimized etching process based on the classical Bosch process (Alcatel A601E equipment) followed by the use of an aqueous etchant solution of potassium hydroxide (KOH) to smooth the surface and remove the fluorocarbon contaminants remaining after the DRIE process. As DRIE highly depends on the opening size of the patterned etch mask, different opening sizes have been tested to completely etch through a 1.4 mm thick silicon wafer. Additionally, the effect of different etch-stop materials onto the sidewalls quality has also been characterized. Sidewall quality of etched-through cavities was characterized by scanning electron microscopy (SEM) and contact surface profilometry. This single-step DRIE etching followed by short exposure to KOH solution permits to smooth sidewalls and achieve a surface roughness as low as 50 nm, which is the roughness typically obtained with the Bosch process on standard depths.
    Sensors and Actuators A Physical 02/2014; · 1.84 Impact Factor
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    ABSTRACT: This letter reports on the development of an integrated micro-optical beam splitter that can be array-arranged. The proposed wafer-level fabrication, based on 45$^{circ}$ saw-dicing of glass substrates, allows rapid and low-cost processing. In particular, it leads to high compactness and possibility of wafer-level alignment/assembly, suitable for vertically integrated imaging micro-instruments. The device, including additional out-of plane reflection for extraction of sensing beam, can be as small as 1 ${rm mm}^{3}$.
    IEEE Photonics Technology Letters 01/2014; 26(1):100-103. · 2.04 Impact Factor
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    ABSTRACT: VIAMOS benefits from advanced MOEMS technologies, enabling a new generation of miniature instruments. The challenge is to provide hand-held, low-cost, fully parallel spectral domain miniature OCT devices adapted for early diagnosis of cutaneous pathologies. VIAMOS will lean on the experience and results fostered from a previous European collaborative project, diffusing the technology to medical diagnostic applications. The consequence will be a significant upgrade by adding new features such as heterodyne detection and integrated swept source.
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    ABSTRACT: The wafer-level integration technique of PageWafer® (SAES Getters' solution for getter film integration into wafer to wafer bonded devices) has been tested in hermetically sealed miniature glass-Si-glass cells filled with Cs and Ne, e.g. for microelectromechanical systems (MEMS) atomic clock applications. Getter effects on the cell atmosphere are analyzed by quadruple mass spectroscopy and coherent population trapping (CPT) spectroscopy. The quadruple mass spectroscopy revealed that the residual gases (H2, O2, N2 and CO2) that are attributed to anodic bonding process are drastically reduced by the getter films while desirable gases such as Ne seem to remain unaffected. The impurity pressure in the getter-integrated cells was measured to be less than 4 × 10−2 mbar, i.e. pressure 50 times lower than the one measured in the cells without getter (2 mbar). Consequently, the atmosphere of the getter-integrated cells is much more pure than that of the getter-free cells. CPT signals obtained from the getter-integrated cells are stable and are, in addition, similar to each other within a cell batch, suggesting the strong potential of applications of this getter film and especially for its wafer-level integration to MEMS atomic clocks and magnetometers.
    Journal of Micromechanics and Microengineering 04/2013; 23(5):055022. · 1.79 Impact Factor
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    ABSTRACT: We present the preliminary design, construction and technology of a microoptical, millimeter-size 3-D microlens scanner, which is a key-component for a number of optical on-chip microscopes with emphasis on the architecture of confocal microscope. The construction of the device relies on the vertical integration of micromachined building blocks: top glass lid, silicon electrostatic comb-drive X-Y and Z microactuators with integrated scanning microlenses, ceramic LTCC spacer, and bottom lid with focusing microlens. All components are connected on the wafer level only by sequential anodic bonding. The technology of through wafer vias is applied to create electrical connections through a stack of wafers. More generally, the presented bonding/connection technologies are also of a great importance for the development of various silicon-based devices based on vertical integration scheme. This approach offers a space-effective integration of complex MOEMS devices and an effective integration of various heterogeneous technologies.
    Proc SPIE 03/2013;
  • Physical Review A 02/2013; 87(2). · 3.04 Impact Factor
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    ABSTRACT: We report on a theoretical study and experimental characterization of coherent population trapping (CPT) resonances in buffer gas-filled vapor cells with push-pull optical pumping (PPOP) on Cs D1 line. We point out that the push-pull interaction scheme is identical to the so-called lin per lin polarization scheme. Expressions of the relevant dark states, as well as of absorption, are reported. The experimental setup is based on the combination of a distributed feedback (DFB) diode laser, a pigtailed intensity Mach-Zehnder electro-optic modulator (MZ EOM) for optical sidebands generation and a Michelson-like interferometer. A microwave technique to stabilize the transfer function operating point of the MZ EOM is implemented for proper operation. A CPT resonance contrast as high as 78% is reported in a cm-scale cell for the magnetic-field insensitive clock transition. The impact of the laser intensity on the CPT clock signal key parameters (linewidth - contrast - linewidth/contrast ratio) is reported for three different cells with various dimensions and buffer gas contents. The potential of the PPOP technique for the development of high-performance atomic vapor cell clocks is discussed.
    Physical Review A 02/2013; 87(1). · 3.04 Impact Factor
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    ABSTRACT: This work presents the development of an integrated micro-optical beam splitter that can be arranged in array, and based on saw-dicing of glass substrates. The latter allows a rapid and rather low-cost processing, and in addition leads to high compactness and possibility of wafer level alignments, suitable for vertically integrated imaging microinstruments. The device allowing additional out-of plane reflection for extraction of sensing beam can be as small as 1mm3.
    Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII), 2013 Transducers & Eurosensors XXVII: The 17th International Conference on; 01/2013
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    ABSTRACT: In this paper, we investigate the influence of different masking parameters onto the surface quality of the ${111}$ sidewalls in order to generate specifically deep cavities by wet-anisotropic-etching of bulk silicon, for optical sensors using cavity sidewalls as reflectors. Mask alignment with crystal planes prior to wet-etching is found to be essential in order to avoid the appearance of additional planes during long etching. Mask deposition processes have been also evaluated. Among the different employed mask materials, Cr/Au gives the best results. It is then shown that cavities as deep as 1 mm with low roughness sidewalls can be simply produced with potassium hydroxide solution with periodic piranha cleaning.
    Journal of Microelectromechanical Systems 01/2013; 23(3):585 - 591. · 2.13 Impact Factor
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    ABSTRACT: This paper reports on a compact table-top Cs clock based on coherent population trapping (CPT) with advanced frequency stability performance. The heart of the clock is a single buffer gas Cs-Ne microfabricated cell. Using a distributed feedback (DFB) laser resonant with the Cs D1 line, the contrast of the CPT signal is found to be maximized around 80°C, a value for which the temperature dependence of the Cs clock frequency is canceled. Advanced techniques are implemented to actively stabilize the clock operation on a zero-light-shift point. The clock frequency stability is measured to be 3.8 × 10¿(11) at 1 s and well below 10¿(11) until 50 000 s. These results demonstrate the possibility to develop highperformance chip-scale atomic clocks using vapor cells containing a single buffer gas.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 11/2012; 59(11):2584-7. · 1.80 Impact Factor
  • Christophe Gorecki, Anand K. Asundi, Wolfgang Osten
    Proc SPIE 05/2012;
  • Christophe Gorecki, Katarzyna Krupa, Michał Józwik
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    ABSTRACT: Micro-electro-mechanical systems are exposed to a variety of environmental stimuli, making a prediction of operational reliability difficult. Here, we investigate environmental effects on properties of piezoelectrically actuated microcantilevers, where AlN is used as actuation material. The environmental effects to be considered include thermal and humid cycling, as well as harsh electrical loading performed under normal conditions. Investigated properties are defined for the static and dynamic behavior of microcantilevers. A Twyman-Green interferometer, operating in both stroboscopic regime and time-average interferometry mode, is used as a metrology tool. The initial deflection and frequency changes of the first resonance mode of the microcantilevers are monitored during accelerated thermal aging tests, humidity tests, as well as harsh electrical loading and fatigue tests. Finally, the resonant fatigue tests accelerated by application of a high voltage are accomplished to evaluate a lifetime of microcantilevers. Monitoring the micromechanical behaviors of devices driven by AlN during the lifetime tests assists monitoring of their long-term stability. FEM calculation is used to identify critical areas of stress concentration in the cantilever structure and to further explain various failure mechanisms.
    Proc SPIE 05/2012;
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    ABSTRACT: This paper reports a batch-fabrication technique based on micromachining of silicon molds to create, after replication, arrays of microlenses characterized by high fill factors. The technique for single microlens generation (compatible with various types of replication or integration so that microlenses made of plastics or glass can be generated) was reported previously and showed its potential in terms of range of shapes and cost. However, subtleties of chemical etching makes more difficult the generation of high fill factor matrices when microlenses size overcomes several tenth of microns. Thus, in this paper, we describe the analysis of the chemical etching process and the corresponding adaptation of the mask design to achieve 100% fill factors arrays of microlenses. The process to fabricate arrays of microlens, with hexagonal footprints and element sizing from 30 to 270 microns and having NA from 0.2 to 0.4, is described. The hexagonal footprint shape of the elements in the arrays leads to 100% geometrical fill factor of fabricated structures. Isotropic etching used for the molds fabrication preserves the spherical profile of the resulting microlenses.
    Proc SPIE 05/2012;
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    ABSTRACT: This paper describes a study of the thermal behaviour of fully packaged Caesium vapour cell developed in the framework of the European collaborative research project called “MEMS atomic clocks for timing, frequency control and communications (MAC-TFC)”. This cell, along with various electronic and optical components, is embedded in a Low Temperature Co-fired Ceramics (LTCC) structure, in order to build a compact MEMS-based atomic clock. Functioning of such atomic clock depends on inner and outer environment of the Cs vapour cell, including parameters such as pressure and temperature of buffer gas. This paper is then devoted to study the thermal behaviour of a fully LTCC-packaged Cs vapour cell according to the ambient temperature change when it is locally temperature controlled. Simulations have been carried out by using analytical modelling and finite element based softwares. Different solutions concerning the LTCC structure such as bridges/suspensions, vacuum environment, metallic coating, as well as the optimal positions of the temperature-control elements have been investigated. Finally, preliminary experiments based on a prototype resulting from this study are presented and an additional solution based on the dynamic adjustment of the set temperature as a function of the ambient temperature is proposed.
    Sensors and Actuators A Physical 02/2012; 174:58–68. · 1.84 Impact Factor

Publication Stats

194 Citations
67.62 Total Impact Points

Institutions

  • 2013
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2000–2012
    • University of Franche-Comté
      • Institut FEMTO-ST
      Becoinson, Franche-Comté, France
  • 2011
    • Institut Franche-Comté Electronique Mécanique Thermique et Optique Sciences et Technologies
      Becoinson, Franche-Comté, France
  • 2008
    • Nanyang Technological University
      • School of Mechanical and Aerospace Engineering (MAE)
      Tumasik, Singapore
  • 1998
    • The University of Tokyo
      • Laboratory for Integrated Micro Mechatronic Systems
      Edo, Tōkyō, Japan