Integration concepts: heterogeneous integration, material physics

Vertical integration :

 Structure test du capteur de CH4 composée de guides optiques diffractifs juxtaposés (le pas des réseaux de diffraction est égal à 1,28 µm).
Schematic of vertical coupling between the mode of a micro-ring resonator (red) and that of an access waveguide (green) controled by an AlOx diaphragm.

As an integral part of our research on multifunctional integrated devices, the vertical integration scheme, where by the various functions are carried out on different levels on the wafer, is considered as very attractive. Indeed, in this case, different materials can be used for the different levels and thereby can be chosen to better suit the particular function to be carried out. Furthermore, this approach enables to fully exploit thickness control which turns out to be easier then controlling lateral features and etching profiles especially when the required patterns exhibit widely different dimensions (combining for instance nanometric and multi-micron scales).
Technically, we focus our attention to the use of the GaAs platform and its associated AlOx oxide since, like the Si/SiO2 technology, it enables the fabrication of high-index-contrast photonic structures but also because it possesses the additional advantage of offering a direct route to integrate active devices such as amplifiers and lasers based on InGaAs(N)(Sb) or GaAsBi quantum-wells or quantum-dots. In this case, the oxide, as a insulator, can also serve to control the electrical injection.
The study of integrated optical frequency combs is a prime example of the use of this approach.

Multifunctional photonic crystal with mesoscopic self-collimation :

Représentation schématique du micro-interféromètre intégrant un réseau d'amplitude et une photodiode. (Encadré : Photographie du dispositif opérationnel constitué d'une photodiode recouverte d'un réseau de période égale à 1 µm.)
Mesoscopic self-collimation mirror capable of efficient reflection and refocussing of an incident spherical wave.

One ultimate approach followed by the photonic team in order to achieve photonic integration is to design, model and fabricate photonic crystals that have simultaneously several optical functions. We focussed more specifically on mesoscopic self-collimating photonic crystals that combine various optical functions (slow light, zero chromatic dispersion, ...) with a propagation of light without any lateral spreading of the energy in a structure that does not have any waveguide.
This study started with the ANR CLAC project (collaboration with LASMEA and Université technique de Troyes), and continues now within an international collaboration with Politecnico di Bari in Italy.
We are now investigating the ability to control the reflectivity in self-collimating structures together with the design of stable cavities with high-Q factors made of planar self-collimating mesoscopic mirrors.

Publications associées :

Heterogeneous integration on glass :

Cartographie du coefficient de réflexion du filtre pour tous les états de polarisation incidente (au voisinage de la longueur d'onde de 1580 nm).
Optical checkerboard with two levels (with an empty top level) sealed and compatible with reports on curved substrates for pixellated optics

The challenges of the future seem to be more related to functional optics (3D displays, electronic paper, instrumentation or adaptive optics). The optical functions involved are related to the display capabilities, but also to the correction capabilities of the wave fronts, either in phase or amplitude, irrespective of the wavelength. They also can not treat the surface in the same way but contain a digitization through structuring (passive method) or by adaptive capacity in operation (active method). These challenges cannot be addressed and resolved by current technologies due to problems of compatibility, transparency, size and cost. It will no longer realize components of small sizes but rather associate them in large number by way of methods compatible to large area technology. On the other hand, these new devices allowing multipoint corrections will be more attractive and insertable into more complex systems if it is possible to make them transparent. These types of advances involve the development of new technological fields that silicon cannot fully achieve and for which the glass has some interest.

Related publications :