The understanding and analyzing of solid particle behavior in a liquid is a challenge in numerous fields and engineering industry as the petroleum or the cosmetic one. It is indeed essential to know the behavior of soft matter process to avoid problems and ensure the product quality. This study presents the viscometer development working on a resonant optical signal principle by measuring the Free Spectral Range (FSR) parameter of a resonant optical mode during nanoparticles (NPs) sedimentation in a liquid which consists of a water/glycerol mixture. The photonic structure is composed of racetracks micro-resonators made of a UV210 polymer fabricated by deep-UV photolithography developed on an oxidated silicon layer to get a Si/SiO2 bi-layer. The chip is then integrated in an optical bench to track the evolution of the FSR during the complete sedimentation process. The resonant signal analysis established by an adapted signal processing of silica nanoparticles sedimentation in different water/glycerol concentrations allows us to determine stages and velocity rate of the sedimentation process to finally access to their viscosity. At the same time, measures are performed on a commercial mechanical rheometer so as to compare the dynamic evolution of their viscosity and their associated FSR. The plot of those data versus the glycerol concentration in water obviously shows a possible mathematical transformation between viscosity and FSR slope. There is therefore a good agreement between mechanical and resonant optical measures if we consider the dynamic evolution of both curves; so, this work proves the feasibility of an optical viscometer based on resonant signal.
In this study we are interested in the implementation of mixed processes for the realization of symmetrical structures shaped in thin layers for integrated photonics and based on silicon plus organic UV210. We used the so called UV210 polymer for shaping the core waveguide. The UV210 polymer made up of poly (p-hydroxystyrene) and poly (t-butyl acrylate) is a chemically amplified resin; a photo-acid generator is added to the matrix of the copolymer in order to increase the sensitivity of the resin and create a chain reaction during developments so as to develop sub-wavelength patterns. Several families of multilayers structures have been produced by specific sub-wavelength lithography plus PECVD, and then properly characterized by including stoichiometry analyses plus imaging by Raman. The advantage of achieving Si/SiO2/UV210/Si/SiO2 symmetry relates first of all to the equations of electromagnetism and guidance which no longer impose a cut-off thickness (or frequency) during extreme miniaturization, but also for an adequate protection of the components by an upper layer of silicon covering the surface of the chip for sensor applications and specific detection of aggressive substances / agents. All structures, including the addition of silicon directly onto the organic, exhibit excellent mechanical strength and optical stability; the last silicon/silica bilayer also acts as a thin protective shell. Various families of resonant photonic structures could be cleanly characterized on platform. Furthermore, by statistical measurements of resonance parameters, we conclude that the processes and properties of the materials obtained have good reproducibility. This opens the way to the realization of sensors dedicated to aggressive substances directly in contact with the resonant elements probing it.
In integrated photonics, the calculation of the solutions regarding the propagation equations modes may be summed up as a problem with eigenvalues and eigenvectors to be solved. Based on such global principle, we have investigated the ability to monitor the impact of a lack of material (or void) on the evolution of eigenvalues of waveguides. To this end, specific families of resonators have been designed with several slits nano-inscribed upon them. The signal resonant light is then characterized while considering the whole geometry taking account of the void: thus, it contains the information regarding the pre-defined recessed volume. The UV 210 polymer is processed (deep UV 248 nm) so as to shape specific slots within a set of waveguides. Then, such waveguides have been re-looped as micro-resonators circuits with a view to measuring experimentally relevant variations of the eigenvalue considering the Free Spectral Range (FSR) associated with resonances. Experiments allowed us to highlight such changes in effective indices clearly correlated to the amount of void. As the lack of material reaches 10% (imprinted within space), a noticeable variation can be observed. It made possible to measure the impact of a given lack of material (defined grooved volume) within the cyclic resonators, on the measured and normalized FSR optical quantity showing then a dynamic evolution close to 1.5%. Moreover, simulations have been carried out so as to confirm the experimental measurements: accordingly, the relevant results allow us to validate a quantified description regarding the hollowed out volume (or mass recessed). Then, by way of the COMSOL software, apt simulations allowed us to confirm the measured evolution in agreement with experiments. This study provides a way to evaluate the global dynamic ranging effect due to a given mass hollowed out from such looped structures as regards the entailed spectral signature linked to the eigenvalues.
The sedimentation of solid particles in a liquid is a physical phenomenon that necessitate to be well understood and measured in several cases. In medical diagnosis, a knowledge of the sedimentation speed of red blood cells for example, allows the early diagnosis of various inflammations. In study, optical Micro-Resonators (MRs) are used as sensors to track the dynamical phenomenon of sedimentation of a cloud of nano-particles in water, and the associated consequences on the spectral characteristics of the guided mode are analyzed. A MR is characterized by its eigenvalue, namely the effective index of an optical mode propagating inside. A progressive modification of the environment thus induces a temporal variation of the effective index. Such a variation can be measured by the tracking of the Free Spectral Range (FSR) of the transduced spectra against time. The transduced optical signal is then directed towards an Optical Spectrum Analyzer (OSA) from which spectra are acquired against time. A millimeter tank filled with water is judiciously deposited on the surface of the chip, before the adding of the solution of nano-particles. The spectra are acquired during the whole duration of the process of sedimentation. The data collected this way are then compared to a simple theoretical model describing the sedimentation of a spherical particle in water. Moreover, the sedimentation theory and the derivation of the speed of sedimentation of a spherical particle is presented, plus the presentation of the experimental setup, from the fabrication of the photonic structure by photolithography, to the inclusion of this circuit in an optical characterization platform and the presentation of the data acquisition and treatment program. The experimental results are analyzed and discussed. The differences are around 10% over the theoretical Stokes velocities relating to such sedimentation process. An overall generic curve or spectral response is clearly demonstrated on these sedimentation processes.
In this study, we are interested in giant tapers operating in a totally Multi-Mode Interference (MMI) regime capable of producing still an adequate single-mode field at the output. The idea is therefore to provide an answer on a possible giant acceptable limit of such MMI tapers still causing a single-mode output and then determining which opto-geometric parameters on this simple mathematical object and geometry act on the behavior. To this end, we have defined energy criteria per volume at the output. We consider families of tapers with a constant height corresponding to the output rib waveguide and a triangle shape. Each taper is defined by its input size, its length and its output size. The objective is to determine the minimum length of the taper to get enough energy or the desired guided mode(s) in the output waveguide. Two various approaches have been investigated and compared: numerical simulations by a finite element method (COMSOL) and a pure mathematical and geometrical study in conditions of total reflection on the walls of the taper plus a specific plane transformation. When the length of the taper increases, the energy increases in the core up to a limit value and decreases in the cladding. The size of the output guide is fixed to ws = 2 microns and the input size of the taper varies from typically 6 microns to `giant' 400 microns. Four kinds of behavior were identified. For small lengths all the energy is reflected by the walls of the taper. For first intermediate lengths a part of the light is difused in the cladding and the other part is guided to the output guide. For following intermediate lengths the major part of the light is guided to the output guide with multi-modes propagation. Lastly for greater lengths only the fundamental guided mode appears in the output guide.
We have investigated the ability to monitor the dynamics transition phase of various substances by resonant probe light. Such a specific Micro-Total Analysis Systems (μTAS) can be used in food, cosmetic and biology applications. Such labon- chip sensors present the possibility of data treatment with an embedded system. The serial of transduced spectra are then acquired with an optical spectrum analyzer linked to a computer on which Matlab software record and process the data in real time. Then specific quantities can be linked to the intrinsic physico-chemical characteristics of the substances. As an example (not exhaustive) the development and the ability of an optical integrated polymeric resonator, acting as a surface light probe, for monitoring temperature-induced supramolecular phase transitions will be presented. The homogeneous detection of the transitions between different self-assembled structures in an aqueous solution of fatty acids (12-hydroxystearic acid, in association with amino-pentanol) was studied by investigating the coupling between the solution and the integrated photonic micro-cavity. Tuning the self-organized assemblies of surfactant is very attractive for many applications, such as cosmetic products, food, drug delivery and medical, and the development of alternative tools - especially those requiring minute amount of solution - to monitor their structural changes are essential. These original studies at temperatures ranging from 17 to 24 °C, based on a statistical treatment of optical resonance spectra, have evidenced the thermoresponsive nature of the optical features, and that different regimes occur with temperature. The optical results were corroborated with the measurement of the solution viscosity as a function of temperature, confirming that we can ascribe the optically-detected regimes to a surfactant assembly shifting reversibly from a tubular shape to a micellar one. The comparison between the optical and the rheological responses showed different accuracies: while the viscosity data exhibited a rather smooth and monotonous transition, the behavior changes were sharper and non-monotonous in terms of optical properties, allowing us to unambiguously identify in intermediate regime between 18.5 and 20°C. These morphological transition experiments represent a unique opportunity to extend the numbers of available techniques studying these systems through integrated optical techniques with potential opportunities of real time detection and working on low sampling volume. Other examples will be developed as the detecting of phase transition of sphingomyelin in biology and health corroborate by differential scanning calorimetry.
We have investigated the effect of brutal steam condensation processes and the behavior of its condensed water prior evaporation, with an integrated resonant photonic structure and dynamic tracking of its transduced signal. The aim of this analysis is to develop a steam condensation lab-on-chip sensor, with the possibility of data treatment with an embedded system. Integrated photonic micro-resonators (MRs) devices have been designed and fabricated with polymer UV210 by means of Deep-UV photolithography. Thanks to this technique, we have achieved racetrack shaped micro-resonators coupled to suited access waveguides. We have assessed such MRs with different geometrical characteristics while changing respectively; the coupling length (LC), the radius of curvature (R) and the width (w) of the guides. The chosen values for the set of parameters LC-R-w (in μm) are 5-5-3 and 10-10-3. The laser source used with the injection bench is a Gaussian broadband laser (λcentral=790 nm, FWHM=40 nm) allowing us to visualize several resonances at the same time in order to multiplex the relevant measurements. The transduced spectrum is then acquired with an Optical Spectrum Analyzer (OSA) linked to a computer with Labview and Matlab software recording and processing data in real time. Then, relevant characteristics to be tracked are the Free Spectral Range (FSR) and the transmitted energy; these quantities can be linked to the physical characteristics of the structure considering both the effective refractive index and the absorption coefficient. The experimental set-up also includes various movies with a top-view imaging camera of the chip (MRs) recording the soft matter process steps, so as to correlate the changes in the transduced spectrum and the behavior of the condensed steam mechanisms (condensation, coalescence and evaporation). Then, the chip is fitted with a temperature controller, so as to carry out measurements at different temperatures: 20°C, 24°C and 28°C.
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