Raphael Kribich

Wide-range transmitting chalcogenide films and development of micro-components for infrared integrated optics applications

Development of micro-components for IR integrated optic devices requires the elaboration of IR waveguides. It is shown that amorphous chalcogenide films from the Ge-Se-Te system are well suited to such development. Thermal and optical characteristics of films elaborated by thermal co-evaporation are first measured. The Se-rich (> 60 at. %) region with a Ge content of about 25 at. % comprises films with a vitreous transition temperature, Tg, larger than 400K, a high thermal stability (ΔT > 100K) and a well-controlled refractive index, n, owing to a weak dependence of n with composition in this region. Films in this composition region are then profitably used to develop optical structures, such as straight or S-bend waveguides, spirals, Y-junction or Mach-Zehnder interferometer, by stacking and further etching of the films. The transmission region accessible to these structures lies from telecommunication wavelength up to 16-17 µm. When a higher transmission region is required, the use of pure Ge-Te films is mandatory. A modal filter allowing a light rejection efficiency of 6.10−5 to be a part of a spatial interferometer is then elaborated.

Chemical sensors based on optical sensitivity of metal oxide materials deposited on multimode interference couplers

An optical sensor based on MMI structures has been studied. We have used the optical parameters of a new hybrid material deposited by sol-gel method leading to waveguide structures after UV-photoinscription, and of ZnO, sensitive material characterised in previous studies. The variation of optical properties such as the refractive index of the covering sensitive material leads to a modification of waveguiding conditions in the MMI. A gas sensor can be developed by measuring the variation of light intensity at the output of the MMI structure under gas exposure. Simulations have been performed in order to optimise the output light intensity variations to increase sensitivity. We have shown that these structures are more sensitive than Mach-Zehnder interferometers, and that the relation between dimensions and sensitivity of the MMI is not trivial. Computations have to be performed to optimise the structure for given parameters.

Code division multiple access with MMI mineral organic circuits

The optical fiber, which offers a large bandwidth (about five TeraHertz per telecommunication window), can be fully used only if the techniques of multiple access are sufficiently effective. Our technology based on an organic-inorganic material offers a solution for the realization of the coupling and the decoupling of transmitted channels: in addition to the multiplexer with division by wavelength (WDM) based on multimode interference couplers, we present here a system of multiple access with division by code (CDMA) using multimode interference couplers as well.

First steps towards the realization of optical sensors to characterize spray deposits of pesticides on the leaves of vine plants

The reduction of inputs is a strategic stake for the wine industry, the main consumer of plant protection products. The development of research / experimentation and technical transfer on this topic over the past few years reflect this ambition shared by all actors. If efforts are mainly based on finding alternative products or developing decision support tools (DAOs) to reduce doses of applied products, optimizing the quality of spraying is also an important lever and can be directly mobilized by the winegrowers. The “spray deposit” is an indicator that reveals the dose received locally by the various organs of the plant that the treatment aims to protect. Thus, the “spray deposition” measure provides valuable information for optimizing the use of inputs. At present, the measurement of this surface quantity (surface covered, size of drops) is based on a constraining and tedious implementation based on artificial collectors. This operation requires to install and then retrieve all the collectors (more than a hundred in general) completely manually. Then, the analyzes are done in laboratory, which mobilizes time, manpower and consumables. Thus, automation of this measure would make it possible to acquire more references mobilizable by the manufacturers of sprayers to optimize their machines and the farmers themselves with a view to defining more precisely the optimal dose to be used thus causing a reduction in the use of plant protection products. In this context, our objective would be to develop optical sensors to characterize the quantity and distribution of a liquid spray. These optical sensors will have waveguides as basic bricks: the idea will be to analyze the impact of a liquid spray on the surface of the guides on their light guiding properties.

Chalcogenide circuits for the realization of CO 2 micro-sensors operating at 4.23 µm

In a context where the control of gases becomes important in a wide range of applications - health care, industry, housing, transportation, environment - we have in sight the realization of infrared optical micro-sensors. In particular, we wish to develop an optical micro-sensor operating at the wavelength 4.23 μm, wavelength corresponding to an absorption band of carbon dioxide, the main greenhouse gas.

Study of light emission and collection in a transparent dielectric cantilever-based near-field optical probe

We report the design of a new type of scanning near‐field optical microscopy probes combining the advantages of both tapered optical fibres type and cantilever type commercial scanning near‐field optical microscopy probes. The material is an organomineral synthesized by the sol‐gel method. This material matches mechanical and optical performances for such a scanning near‐field optical microscopy probe fabrication. Numerical calculations were carried out using finite element method in order to study the optical transmission of the probe in emission and collection modes. The influence of the probe geometry on the intensity distribution in the vicinity of the aperture and in the extremity of the cantilever is studied in details.

First steps towards CO 2 gas micro-sensors operating at 4.26 µm

In a context where the control of gases becomes important in a wide range of applications - health care, industry, housing, transportation, environment, etc. - we have in sight the realization of infrared optical micro-sensors. In particular, we wish to develop an optical micro-sensor operating at the wavelength 4.26 µm, wavelength corresponding to an absorption band of carbon dioxide, the main greenhouse gas. The first step consists in manufacturing straight waveguides, but also circuits such as Y-junctions or interferometers, that are capable of operating at this wavelength. The straight waveguides and other guiding structures are obtained by stacking and etching of layers of the ternary system Ge-Se-Te, a chalcogenide system widely studied for its transparency properties in the infrared. Manufacturing objects are realized by: (i) depositing a first low refractive index Ge-Se-Te layer (buffer layer) on a Si substrate by thermal co-evaporation; (ii) depositing a second layer Ge-Se-Te characterized by a higher refractive index (guiding layer), again by thermal co-evaporation, and (iii) modifying the geometry of the second layer by laser lithography and ion beam etching. The waveguides opto-geometrical parameters such as refractive indices, thicknesses of the layers, etching depth and waveguide core width are set through a design process to obtain a single mode behavior at 4.26 µm. After fabrication, objects are optically characterized at λ = 4.26 µm on a bench dedicated to the study.

Integrated planar silver halide waveguides and quantum cascade lasers for liquid phase chemical sensing

The goal of this work is to create efficient infrared sensor systems that take advantage of the unique properties of quantum cascade lasers (QCLs) as a light source. The use of single mode distributed feedback (DFB) QCLs allows for the creation of wavelength-tailored waveguides matched to the laser emission frequency. This study designs and develops a novel IR sensing platform based on integrated waveguide technology.