Caroline Vigreux

Realization of single-mode telluride rib waveguides for mid-IR applications between 10 and 20 μm.

The feasibility of all-telluride integrated optics devices based on waveguides presenting a single-mode behavior in the spectral range (10-20 μm) is demonstrated. These waveguides are constituted of a several micrometer thick Te(82)Ge(18) film deposited onto a Te(75)Ge(15)Ga(10) bulk glass substrate by thermal coevaporation and further etched by reactive ion etching under the CHF(3)/O(2)/Ar atmosphere. The obtained structures were proven to behave as channel waveguides with a good single-mode transmission over the whole spectral range. These results allowed validating our technological solution for the fabrication of integrated optics modal filters for spatial interferometry.

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.

Fabrication and testing of all-telluride rib waveguides for nulling interferometry

The feasibility of two types of all-telluride integrated optics devices being able to single-mode guiding of light in the spectral ranges [6-11 µm] and [10-20 µm], respectively, has been demonstrated. The so-called “rib” waveguides show a several micron thick Te82Ge18 film deposited onto a Te75Ge15Ga10 bulk glass substrate by thermal co-evaporation and further etched by reactive ion etching in CHF3/O2/Ar atmosphere. The obtained structures were proved to behave as channel waveguides with a satisfactory confinement of light in the whole spectral ranges. These results allowed validation of our technological solution for the fabrication of micro-components for spatial interferometry.

Fabrication of far infrared rib waveguides based on Te-Ge-Ga films deposited by co-thermal evaporation

In the present paper we focus on the fabrication of rib waveguides being able to work in the large infrared window [6-20μm], compatible with the Darwin mission requirements. The rib waveguides to be realized are based on etched thick films of telluride materials deposited on telluride glass. The choice of the Te75Ge15Ga10 material as the substrate is justified by its excellent transmission in the infrared region and its thermal stability. Films of the ternary system made of Te, Ge and Ga were investigated as the core layer and the superstrate. Details are provided on the film deposition and etching technologies: (i) Te-Ge-Ga films are prepared by co-thermal evaporation from the pure elements Te, Ge and Ga; (ii) the geometry of the as-obtained films is modified by reactive ion etching under an atmosphere of CHF3 + O2 or CH4 + H2. First results concerning Te-Ge binary films are particularly interesting.

All-telluride channel waveguides for mid-infrared applications

In this paper, the different steps of the fabrication of single-mode RIB waveguides for both [6-11µm] and [10-20µm] spectral bands are described and the first results in term of light guiding and modal filtering are presented.

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.

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.

Buried channel waveguides for nulling interferometry in 6–20 μm spectral range: Fabrication and preliminary testing

One of the technological challenges of direct observation of extra-solar planets remains to develop a modal filter operating from 6 to 20 μm. In the present paper we present one of the two candidate technologies for the fabrication of such modal filters, together with Fiber Optics: Integrated Optics. The solution based on alltelluride buried channel waveguides was considered. In the so-called waveguides, the vertical confinement of the light is achieved in a higher-index core layer consisting in a 15 μm-thick Ge17Te83 film which is deposited onto a lower-index Te75Ge15Ga10 substrate, and further covered by a lower-index superstrate consisting in a 15 μm-thick Ge24Te76 film. Concerning the horizontal confinement of the light, it is obtained by etching the core layer. As this stage, the all-telluride buried channel waveguides are proved to transmit light from 2 to 5 μm and to behave as channel waveguides with a satisfactory confinement of the light. It confirms the validity of the technology and the good quality of the input and output facets. Tests between 6 and 20 μm are being performed and will allow giving a confirmation of the potential of Te-based integrated optics components for nulling interferometry.

Waveguides based on TeGe thick films for spatial interferometry

In the present paper we focus on the fabrication of waveguides which will be able to work in the large infrared window [6-20μm], compatible with the ESA requirements in the framework of the detection of Exo-solar planets by nulling interferometry. The first step in the fabrication of such components is the realization of planar waveguides being able to guide light in this spectral range. In order to do so, telluride materials were selected: Te75Ge15Ga10 bulk glasses were chosen as substrates and TeGe films as guiding layers. The Te75Ge15Ga10 bulk glasses were purified during their synthesis which ensures an optimal transmission in the whole range from 6 to 20 μm. TeGe thick films with different compositions were deposited by thermal co-evaporation. Homogeneous films with thickness up to 15 microns could be produced. The M-lines measurement of their refractive index at λ = 10.6 μm highlighted a linear behavior versus the atomic percentage in tellurium and confirmed their compatibility for the project. First planar waveguides could be optically characterized after having prepared their input and output facets by an appropriate polishing procedure. Guidance of light was demonstrated in the whole range [6-20 μm].