Hervé Lhermite

Chalcogenide glass optical waveguides for infrared biosensing.

Due to the remarkable properties of chalcogenide (Chg) glasses, Chg optical waveguides should play a significant role in the development of optical biosensors. This paper describes the fabrication and properties of chalcogenide fibres and planar waveguides. Using optical fibre transparent in the mid-infrared spectral range we have developed a biosensor that can collect information on whole metabolism alterations, rapidly and in situ. Thanks to this sensor it is possible to collect infrared spectra by remote spectroscopy, by simple contact with the sample. In this way, we tried to determine spectral modifications due, on the one hand, to cerebral metabolism alterations caused by a transient focal ischemia in the rat brain and, in the other hand, starvation in the mouse liver. We also applied a microdialysis method, a well known technique for in vivo brain metabolism studies, as reference. In the field of integrated microsensors, reactive ion etching was used to pattern rib waveguides between 2 and 300 μm wide. This technique was used to fabricate Y optical junctions for optical interconnections on chalcogenide amorphous films, which can potentially increase the sensitivity and stability of an optical micro-sensor. The first tests were also carried out to functionalise the Chg planar waveguides with the aim of using them as (bio)sensors.

Chalcogenide coatings of Ge15Sb20S65 and Te20As30Se50

Chalcogenide coatings are investigated to obtain either optical components for spectral applications or optochemical sensors in the mid-infrared. The deposition of Ge(15)Sb(20)S(65) and Te(20)As(30)Se(50) chalcogenide glasses is performed by two physical techniques: electron-beam and pulsed-laser deposition. The quality of the film is analyzed by scanning electron microscopy, atomic force microscopy, and energy dispersive spectroscopy to characterize the morphology, topography, and chemical composition. The optical properties and optical constants are also determined. A CF(4) dry etching is performed on these films to obtain a channeled optical waveguide. For a passband filter made by electron-beam deposition, cryolite as a low-refractive-index material and chalcogenide glasses as high-refractive-index materials are used to favor a large refractive-index contrast. A shift of a centered wavelength of a photosensitive passband filter is controlled by illumination time.

RF sputtered amorphous chalcogenide thin films for surface enhanced infrared absorption spectroscopy

The primary objective of this study is the development of transparent thin film materials in the IR enabling strong infrared absorption of organic compounds in the vicinity of metal nanoparticles by the surface plasmon effect. For developing these optical micro-sensors, hetero-structures combining gold nanoparticles and chalcogenide planar waveguides are fabricated and adequately characterized. Single As2S3 and Ge25Sb10Se65 amorphous chalcogenide thin films are prepared by radio-frequency magnetron sputtering. For the fabrication of gold nanoparticles on a chalcogenide planar waveguide, direct current sputtering is employed. Fabricated single layers or hetero-structures are characterized using various techniques to investigate the influence of deposition parameters. The nanoparticles of gold are functionalized by a self-assembled monolayer of 4-nitrothiophenol. Finally, the surface enhanced infrared absorption spectra of 4-nitrothiophenol self-assembled on fabricated Au/Ge-Sb-Se thin films hetero-structures are measured and analyzed. This optical component presents a ~24 enhancement factor for the detection of NO2 symmetric stretching vibration band of 4-nitrothiophenol at 1336 cm−1.

Optical amplification of Pr3+ -doped ZBLA channel waveguides for visible Laser emission.

We report on the first observation of optical signal amplification in the visible range into praseodymium doped ZBLA glass channel waveguides obtained by ion exchange. Up to 30% signal amplification was obtained at 639 nm. This result shows the potential of rare earth doped fluoride glasses in the form of channel waveguides for integrated solid state visible laser sources.

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.

Chalcogenide waveguide for IR optical range

Due to remarkable properties of the chalcogenide glasses, especially sulphide glasses, amorphous chalcogenide films should play a motivating role in the development of integrated planar optical circuits and their components. This paper describes the fabrication and properties of optical waveguides of pure and rare earth doped sulphide glass films prepared by two complementary techniques: RF magnetron sputtering and pulsed laser deposition (PLD). The deposition parameters were adjusted to obtain, from sulphide glass targets with a careful control of their purity, layers with appropriate compositional, morphological, structural characteristics and optical properties. These films have been characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray measurements (EDX). Their optical properties were measured thanks to m-lines prism coupling and near field methods. Rib waveguides were produced by dry etching under CF4, CHF3 and SF6 atmosphere. The photo-luminescence of rare earth doped GeGaSbS films were clearly observed in the n-IR spectral domain and the study of their decay lifetime will be presented. First tests were carried out to functionalise the films with the aim of using them as sensor.

Infrared optical sensor for CO2 detection

Among the measures to reduce CO2 emissions, capture and geological storage holds out promise for the future in the fight against climate change. The aim of this project is to develop a remote optical sensor working in the mid-infrared range which will be able to detect and monitor carbon dioxide gas. Thus, chalcogenide glasses, transmitting light in the 1-6 μm range, are matchless materials. The first of our optical device is based on the use of two GeSe4 chalcogenide optical fibers, connected to an FTIR spectrometer and where CO2 gas can flow freely through a 4 mm-spacing between fibers. Such sensor system is fully reversible and the sensitivity threshold is about 0.5 vol.%. Fiber Evanescent Wave Spectroscopy technology was also studied using a microstructured chalcogenide fiber and first tests led at 4.2 μm have provided very promising results. Finally, in order to explore the potentiality of integrated optical structures for microsensor, sulphide or selenide Ge25Sb10S(Se)65 rib waveguide were deposited on Si/SiO2 wafer substrates, using pulsed laser deposition and RF magnetron sputtering deposition methods. The final aim of this study is to develop a rib waveguide adapted for middle-IR including an Y-splitter with a reference beam and sensor beam targeting an accurate CO2 detection.

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.

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