Capteur photographique CCD | EPFL Graph Search

vignette|Capteur photographique CCD pour l'imagerie astronomique. Un capteur photographique CCD est un capteur photographique basé sur un dispositif à transfert de charges (charge coupled device, CCD). Dans les scanners de documents et beaucoup d'autres applications similaires, les dispositifs sont linéaires ; ils passent transversalement sur l'objet à explorer. Dans les appareils photographiques et les caméras vidéo numériques, les capteurs sont regroupés sur une surface rectangulaire, où chaque CCD forme une ligne, souvent dans la plus petite dimension de l'image. Chaque élément photosensible charge un des éléments du CCD proportionnellement à son illumination. L'insolation est ensuite suspendue pendant qu'un signal d'horloge provoque le transfert de la charge à l'élément voisin, effectuant en bout de ligne une sérialisation des informations. Principe vignette|Le capteur CCD d'une webcam. Les capteurs d'image CCD consistent en une matrice de photodiodes qui peuvent être

Quantum optomechanics at room temperature

Hendrik Schütz

Why are classical theories often sufficient to describe the physics of our world even though everything around us is entirely composed of microscopic quantum systems? The boundary between these two fundamentally dissimilar theories remains an unsolved problem in modern physics. Position measurements of small objects allow us to probe the area where the classical approximation breaks down. In quantum mechanics, Heisenbergâs uncertainty principle dictates that any measurement of the position must be accompanied by measurement induced back-action---in this case manifested as an uncertainty in the momentum. In recent years, cavity optomechanics has become a powerful tool to perform precise position measurements and investigate their fundamental limitations. The utilization of optical micro-cavities greatly enhances the interaction between light and state-of-the-art nanomechanical oscillators. Therefore, quantum mechanical phenomena have been successfully observed in systems far beyond the microscopic world. In such a cavity optomechanical system, the fluctuations in the position of the oscillator are transduced onto the phase of the light, while fluctuations in the amplitude of the light disturb the momentum of the oscillator during the measurement. As a consequence, correlations are established between the amplitude and phase quadrature of the probe light. However, so far, observation of quantum effects has been limited exclusively to cryogenic experiments, and access to the quantum regime at room temperature has remained an elusive goal because the overwhelming amount of thermal motion masks the weak quantum effects. This thesis describes the engineering of a high-performance cavity optomechanical device and presents experimental results showing, for the first time, the broadband effects of quantum back-action at room temperature. The device strongly couples mechanical and optical modes of exceptionally high quality factors to provide a measurement sensitivity

\sim\!10^4

times below the requirement to resolve the zero-point fluctuations of the mechanical oscillator. The quantum back-action is then observed through the correlations created between the probe light and the motion of the nanomechanical oscillator. A so-called âvariational measurementâ, which detects the transmitted light in a homodyne detector tuned close to the amplitude quadrature, resolves the quantum noise due to these correlations at the level of 10% of the thermal noise over more than an octave of Fourier frequencies around mechanical resonance. Moreover, building on this result, an additional experiment demonstrates the ability to achieve quantum enhanced metrology. In this case, the generated quantum correlations are used to cancel quantum noise in the measurement record, which then leads to an improved relative signal-to-noise ratio in measurements of an external force. In conclusion, the successful observation of broadband quantum behavior on a macroscopic object at room temperature is an important milestone in the field of cavity optomechanics. Specifically, this result heralds the rise of optomechanical systems as a platform for quantum physics at room temperature and shows promise for generation of ponderomotive squeezing in room-temperature interferometers.

EPFL2017

Fabrication and Characterization of MEMS Piezoelectric Accelerometers

Myriam Yvonne Käppeli

In this master thesis, the use of MEMS technology to miniaturize existing accelerometers used for vibration sensing is demonstrated. An updated process flow was established and carried out in the cleanrooms. MEMS piezoelectric accelerometers were fabricated and known fabrication issues were successfully avoided. A first characterization of the fabricated devices was done, and results show a strong agreement with the FEM simulations done during and before this project. FEM simulations were done for alternative designs and showed a possibility to almost double the charge generation of the accelerometers.

2020

Analysis of photosensor frontends for biomedical applications: a focus on noise

Paul Stanislas Gosselin

Photosensing has proven to be highly useful in biomedical research and medical care. Being able to detect and quantify the light emitted by fluorescent or bioluminescent reporters has significantly participated in the development of new cancer treatments and made possible the development of cost-effective diagnosis techniques. While these advances relied on the large CCD devices or on laboratory-on-chips, the design of a bioluminescence-based implant for the continuous monitoring of biological data can be considered and would allow for the acquisition of insightful information in both research and care. To exist, such an implant requires a suited photosensing circuit, the design of which can be challenging due to the weakness of the target bioluminescent signal. This thesis addresses the design and evaluation of an appropriate analog-to-digital converter (ADC), with a focus on its expected accuracy. In particular, three integration-base current-to-frequency converters are considered: the current-controlled oscillator, the first-order Sigma-Delta converter with instantaneous feedback, the first-order Sigma-Delta converter with continuous feedback. Theoretical formulas are established to assess how the input-referred noise would impact the results from such ADCs, depending on the integration time as well as the time passed since last calibration. In addition to the general case, specific formulas are provided for white noise, flicker noise, and Lorentzian-shaped noise. Moreover, in practical cases that are conceivable with target application, these formulas cannot be used as they are due to the finite resolution of computing softwares. Consequently, the related implementation issues are addressed and solved. To guide the design of the current-to-frequency converters, how each of their imperfections affects their accuracy is analyzed in depth. This analysis and the obtained formulas serve a top-level-focused design strategy that is argued for in this thesis. It relies on maintaining a detailed top-level description of the system under study to help focus the designing efforts on the most impactful areas as well as guide the design choices at the transistor level. Applying such a strategy is made possible by the development of a MATLAB tool providing a flexible graphic user interface to explore the impact of each parameter of the design. In addition, to further assist the design of the ADC and/or of the photodetector, a Python tool is presented to explore configurations for successive simulations and data analyses, even when using multiple softwares. As an opening chapter, emphasizing the importance of considering the top-level in design, the case of heart rate monitoring through photoplethysmography is addressed. In this case, the highest level of the system includes the data processing, and only the latter can actually allow for drastic improvements of the power consumption by alleviating the requirements on the data acquisition. In fact, it is demonstrated that in many situations, the sampling frequency for the acquisition of the plethysmograph could be brought down to 10 to 25 Hz, while still ensuring a satisfying accuracy for the heart rate and heart rate variation monitoring.

EPFL2019