The emergence of curved detectors, first proposed by Ko et al in their Nature paper [1], certainly represents the major disruptive technology for imaging systems that will come up in a near future.
As pixels shrink in CMOS detectors, scaling effects could lead to potential issues with existing colored filters because of
their thickness (approx. 1μm).
In this paper, we propose to investigate a new generation of filters that are potentially thinner by approximately a decade.
Several years ago [1], nanometric metallic gratings have been found to have very unusual transmission properties.
Especially, unexpected high transmission has been measured at specific wavelengths. Since these first experiments,
studies have shown that very different optical processes can be responsible for these resonant transmissions, depending
on the geometry of the grating. This has led to the demonstration of first applications in imaging[2]. With our designs,
we show that such components are suitable for RGB color filters.
We first discuss the theoretical performances and the integration of these components through modeling with rigorous
electromagnetical techniques (RCWA and FDTD) in 2D and in 3D. As an example we evaluate the impact of the
pixelization, the technological errors and the illumination conditions on the filter performances. Thanks to an algorithm
that can optimize color correction matrix, we show that we have a satisfactory color rendering (dE=4.3).
In a second part we realize these samples. We sputter Al layers on glass substrates and structure them with Focused Ion
Beam technology that enables approximately 30 nm resolution. These structures are compatible in size with pixel
dimensions (1.5 μm X 1.5 μm) and are tested with a dedicated micro-spectrometer.
Kawata and Tani's [4] experiments showed that the evanescent field created on the surface of an ion exchanged
waveguide could trap and move microparticles. This opened up the possibility of combining conventional optical
trapping with integrated optics in order to create new microsystems for the manipulation of particles or biological
objects. Recently, the use of strip silicon nitride waveguides increased the performances of these systems enabling
higher particles speeds and reduced guided power [12].
Our experiments demonstrate that polarization affects drastically the way particles are propelled along the waveguide
surface. For example in TM polarization, 0,6 &mgr;m diameter gold particles are moving along the center of the waveguide
whereas in TE, they are propelled along its sides. Moreover, it appears that gradient forces involved in this phenomenon
depend on the particle size.
To understand this behavior, a numerical approach of the problem based on the finite element method has been
developed. This method enables the calculation of the 3D distribution of the electric fields. The resulting optical forces
are calculated thanks to the Maxwell stress tensor formalism.
This first experimental and theoretical illustration of repulsive gradient forces on metallic particles opens up perspectives
for polarization based sorting systems.
Over the past years, DNA-chip technology has exploded. Yet
scientists using such devices have to face many problems. One of
them, due to the very low concentration of biological species to
be detected, is the weakness of fluorescence signal collected
through the reading system (microscope or scanner). To solve this
problem, we proposed to use optical thin films technology. We
studied the potentialities of this method step by step. The first
step was to be able to understand, explain and forecast the
fluorescence emitted by a DNA-chip in terms of fluorescence
angular patterns. A theoretical and experimental study enabled us
to master this issue even in the case of multi-layers substrates.
Using this knowledge we were then able to explain, through
simulations, the potentialities of this new type of substrates in
terms of fluorescence enhancement. Thus we showed that a
theoretical enhancement of twenty-fold (compare to a glass
substrate) was achievable.
Photothermal deflection technique is a very sensitive mean to measure optical absorbance. This study is aimed at evaluating its potentiality in order to detect hybridation and to monitor quality control. The principle of the technique relies on the fact that nucleic acids present the property to absorb light between 220 nm to 280 nm.
A first theoretical approach based on solving light and thermal equations demonstrates the ability of photothermal deflection to detect hybridisation. This point is checked through several experimentations with oligonucleotid with 32 mers targets lengths. An important point to stres is the specificity of the signals obtained and the ability of automation of the reading with image processing algorithms.
At last we focus our attention on the ability of this technique to in-situ synthesis process. Our experimental study shows the ability of this characterisation with a detection sensitivity of one base.
Quantifying hybridization and therefore fluorescence signals has become a key-issue in DNA-chip technology. Thus a better understanding of fluorescence near a surface has become a necessity. To study this issue, we modeled the fluorophore after an electromagnetic dipole radiating over the substrate; we then developed a simulation code which enabled us to calculate the observation-angle-dependent-intensity radiated by a population and altitude. In the mean time we developed a polarized-gonio-fluoimeter which permits angular fluorescence patterns and fluorescence polarization measurements. We studied DNA-chips obtained by covalent grafting of labeled oligonucleotides. Simulation curves perfectly matched experimental ones, enabling an accurate determination of fluorophore localization on the substrate. Once achieved a better understanding of the fluorophore emission, we designed and realized a thin-film-coated microscope slide dedicated to the enhancement of DNA-chip fluorescence. This substrate was used in a c-DNA gene analysis. Fluorescence enhancement was clearly observed enabling the detection of Cart1 and P2A which are undetectable when using non-coated microscope slides.
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