Nolwenn Huby

Native spider silk as a biological optical fiber

In this study, we demonstrate the use of eco-friendly native spider silk as an efficient optical fiber in air, highly bent fibers, and physiological liquid. We also integrated the silk filament in a photonic chip made of polymer microstructures fabricated by UV lithography. The molding process is non-destructive for silk and leads to an efficient micro-optical coupling between silk and synthetic optical structures. These optical performances combined with the unique biocompatibility, bioresorbability, flexibility, and tensile strength of silk filaments pave the way for new applications in biological media and for original biophotonic purposes.

Light propagation in single mode polymer nanotubes integrated on photonic circuits

We report the theoretical and experimental study of photonic propagation in organic dielectric nanotubes elaborated by a wetting template method and showing off an aspect ratio as high as 200. Single mode behaviour is theoretically demonstrated without any cut-off conditions. Efficient evanescent coupling between polymer microstructures and nanotubes dispersed on a photonic chip as well as the high confinement and propagation in a single nanotube have been demonstrated. These results show the potential of well-defined one-dimensional nanostructures as building blocks for integrated organic photonic devices. Applications such as sensing and high speed communication are envisaged.

Fabrication and optical characterization of sub-micronic waveguide structures on UV210 polymer

In this paper, we report on the interest in a new polymer, UV210, in the field of integrated optics. As 400 nm wide and 1 µm high UV210 rib waveguides have been obtained by deep ultraviolet (DUV) lithography and controlled by scanning electron micrographs (SEMs), they allow us to realize sub-wavelength structures by way of easy and cheap processes. Structural and optical investigations have been carried out on UV210 resist as a function of exposure to DUV light. On the one hand, structural properties through ellipsometric measurements have been investigated: the UV210 refractive index increases with the DUV exposure dose, yielding a large index contrast at 980 nm between areas exposed or not (Δn = 2 × 10 − 2). It is expected that we shall soon be able to photo-print nanometric patterns onto UV210 films. On the other hand, optical studies of propagation losses measured in both irradiated and unexposed single-mode UV210 waveguides have been performed by a cut-back method. Concerning as-deposited rib waveguides, optical losses for TE00 and TM00 optical modes have been evaluated to 3.4 ± 0.4 dB cm − 1 and 6.2 ± 0.5 dB cm − 1, respectively. Hence, the UV210 polymer appears to be a promising candidate for the development of low-cost nanometric structures for miniaturized optical chips, with numerous applications in telecommunication and sensor technology.

Investigation of fabrication and resonant optical coupling in various 2D micro-resonator structures in a UV210 polymer

In this paper, we report on the design and the overall realization of micro-resonators based on the development of adequate processes on a UV210 polymer. These micro-optical structures are developed by deep ultraviolet lithography allowing fabrication of nano-structured devices by means of low cost and reproducible processes. Two families of resonant micro-structures shaped on disk and stadium with various sizes are investigated. Structural and optical imaging characterizations have been carried out to ensure their ability to act as resonant integrated micro-structures. At first, scanning electron microscopy and Nomarsky microscopy studies confirm the UV-light process resolution down to 450 nm developed on a UV210 polymer. Then, optical characterizations have been performed as regards intensity and spectral properties of such micro-resonators. Field intensity measurements in visible and infrared ranges have been realized and validate light propagation by evanescent coupling between waveguides and micro-resonators. Finally, spectral analyses on TE modes demonstrate the presence of optical resonances with 1.45 nm and 2.19 nm free spectral range values for respectively disk and stadium micro-structures. The UV210 polymer appears appropriate for the realization of micro-structures requiring a few hundred nanometers gap-scale while maintaining adequate spectral properties for versatile applications in telecommunication and metrology.

Injection and waveguiding properties in SU8 nanotubes for sub-wavelength regime propagation and nanophotonics integration

We report photonic concepts related to injection and sub-wavelength propagation in nanotubes, an unusual but promising geometry for highly integrated photonic devices. Theoretical simulation by the finite domain time-dependent (FDTD) method was first used to determine the features of the direct light injection and sub-wavelength propagation regime within nanotubes. Then, the injection into nanotubes of SU8, a photoresist used for integrated photonics, was successfully achieved by using polymer microlensed fibers with a sub-micronic radius of curvature, as theoretically expected from FDTD simulations. The propagation losses in a single SU8 nanotube were determined by using a comprehensive set-up and a protocol for optical characterization. The attenuation coefficient has been evaluated at 1.25 dB mm(-1) by a cut-back method transposed to such nanostructures. The mechanisms responsible for losses in nanotubes were identified with FDTD theoretical support. Both injection and cut-back methods developed here are compatible with any sub-micronic structures. This work on SU8 nanotubes suggests broader perspectives for future nanophotonics.

Improvement of efficient coupling and optical resonances by using taper-waveguides coupled to cascade of UV210 polymer micro-resonators

In this paper, we report the overall design, fabrication and optical characterization of single and multiple resonant micro-structures patterned on the UV210 polymer and shaped by adequate deep-UV lithography procedures. Various families of ring and racetrack forms are investigated with different geometrical dimensions linked to the micro-resonators and the specific taper-waveguides and gaps allowing the optimized coupling. Well defined photonic structures families in the sub-micrometer range obtained by this deep UV-light process are clearly confirmed through scanning electron microscopy. In order to evaluate and quantify the efficiency of the sub-micrometer coupling, the recirculation of the light and the quality of the optical resonance aspects, a global study including top view intensity imaging, spectral measurements and Fast Fourier Transform analysis is performed for all these devices based on single and multiple family resonators. The experimental TE-mode resonance transmissions reveal a complete agreement with the period of the theoretically expected resonances. A maximum value of the quality factor Q = 3.5 x 10^3 at 1035 nm with a 3.2 times higher resonance contrast is assessed for cascade of triple micro-resonators respect to the photonic devices based on only one micro-resonator. In addition, these UV210 circuits made of specific tapers coupling to cascade loops act directly on the improvement of the evanescent coupling and resonances in terms of quality factor and extinction rate, by selecting successively and more precisely the optical mode resonance. All these designs and low cost technological reproducible steps, and furthermore the devices and protocol measurements are markedly suitable for mass fabrication and metrology applications.

Structural investigation of the photoinduced spin transition in the three states molecular system [Fe(2-pic)3]Cl2EtOH

We present the detailed results of the investigation by x-ray diffraction of the photoinduced phase transition in the tris(α-picolylamine)iron(II) chloride–ethanol complex. This system undergoes a two-steps spin transition between a high spin state at room temperature and a low spin state at low temperature. The intermediate phase consists of stripes of high spin and low spin molecules. The x-ray diffraction data evidence the structural rearrangement at the molecular scale accompanying the photoinduced change of electronic state between the low-spin phase and the photo-steady high-spin one, which is similar to the stable one in the high temperature phase. The dynamical mechanism of the transformation is discussed with the observation of a domain nucleation process, associated with the coexistence of the stable and photoinduced phases.

Efficient active waveguiding properties of Mo6 nano-cluster-doped polymer nanotubes

We investigate 1D nanostructures based on a Mo6@SU8 hybrid nanocomposite in which photoluminescent Mo6 clusters are embedded in the photosensitive SU8 resist. Tens of micrometers long Mo6@SU8-based tubular nanostructures were fabricated by the wetting template method, enabling the control of the inner and outer diameter to about 190 nm and 240 nm respectively, as supported by structural and optical characterizations. The image plane optical study of these nanotubes under optical pumping highlights the efficient waveguiding phenomenon of the red luminescence emitted by the clusters. Moreover, the wave vector distribution in the Fourier plane determined by leakage radiation microscopy gives additional features of the emission and waveguiding. First, the anisotropic red luminescence of the whole system can be attributed to the guided mode along the nanotube. Then, a low-loss propagation behavior is evidenced in the Mo6@SU8-based nanotubes. This result contrasts with the weaker waveguiding signature in the case of UV210-based nanotubes embedding PFO (poly(9,9-di-n-octylfluorenyl-2,7-diyl)). It is attributed to the strong reabsorption phenomenon, owing to overlapping between absorption and emission bands in the semi-conducting conjugated polymer PFO. These results make this Mo6@SU8 original class of nanocomposite a promising candidate as nanosources for submicronic photonic integration.

Transferable Integrated Optical SU8 Devices: From Micronic Waveguides to 1D-Nanostructures

We report on optical components for integrated optics applications at the micro-and nanoscale. Versatile shapes and dimensions are achievable due to the liquid phase processability of SU8 resist. On the one hand, by adjusting the UV-lithography process, waveguiding structures are patterned and released from their original substrate. They can be replaced on any other substrate and also immerged in liquid wherein they still show off efficient light confinement. On the other hand, filled and hollow 1D-nanostructures are achievable by the wetting template method. By exploiting the large range of available SU8 viscosities, nanowires of diameter ranging between 50 nm and 240 nm, as well as nanotubes of controllable wall thickness are presented. Optical injection, propagation, and coupling in such nanostructures are relevant for highly integrated devices.

A laterally coupled UV210 polymer racetrack micro-resonator for thermal tunability and glucose sensing capability

Authors report and demonstrate the feasibility of a laterally coupled racetrack microresonator based on UV210 photoresist to act as a thermal and glucose sensor. The large thermo-optic coefficient and the detection principle based on the interaction of the evanescent field with different glucose concentrations demonstrate that this sensor displays high sensitivity on detection properties. Deep-UV lithography procedures allow us to develop a laterally coupled microresonator with submicrometer patterns. The thermo-optic response of the racetrack microresonator is interrogated by using a NiCr alloy tip positioned on the top of the device. Temperatures ranging between 19 and 33°C yield a red shift of the resonant wavelength with a linear sensitivity of 220 pm °C− 1. Additionally, the thermal tunability is successively demonstrated by covering the resonator with DI water. A blue shift of the resonant wavelength is obtained with a linear sensitivity of 200 pm °C− 1. The resonance optical properties under this top cladding conditions lead a Q-factor of 4000 with a finesse of 5.7. Glucose homogeneous sensing capability is also experimentally demonstrated. Different concentrations of glucose solutions result in a red shift of the resonant wavelengths with a linear sensitivity of 280 pm mg− 1 ml− 1. Finally, these results validate the laterally coupled racetrack microresonator as an operative photonic component for integrated optical devices such as optical filters applied on telecommunication, or transducer components devoted to assess biochemical interactions. Graphical Abstract