Laser diodes are a key element for a wide range of potential applications in optical telecommunications, storage and information processing, instrumentation, environment ... Despite a constant improvement of their performance, the integration in the optical systems remains the major obstacle to their development.

1) GaInAsN/GaAs laser diodes emitting at 1.3µm for optical telecommunications

The study of dilute-nitride quantum-well laser diodes has been supported by the French RNRT programs « SINTROPS » and «AHTOS » (OPTO+, LPN, LNMO/INSAT) with the objectives to design and to achieve laser diodes on low cost GaAs substrates for high rate transmission at 1.3µm.
The SINTROPS project has demonstrated the potentialities of GaInAsN/GaAs, in particular, a higher stability in temperature than for the conventional GaInAsP/InP alloy. In the following AHTOS project led with the same partners, the aim was to evaluate the industrial future of the GaInAsN/GaAs alloys with the realisation of a module allowing transmissions at 10Gb/s without thermal control and with a low spectral shift for coarse wavelength division multiplexing (C-DWDM).

We are involved in the development of tools for design and optimization of the structure by exploiting the properties of transparency, differential gain and optical confinement of this material. Different active structures have been investigated and compared: high strain or high nitrogen content, confinement with or without aluminium, barriers with or without nitrogen ...  Designing parameters for multi quantum-well structures have been extracted to achieve high frequency modulation.
Moreover, we have developed an experimental set-up to determine the intrinsic properties of these dilute-nitride alloys such as the gain and the origin of the nonradiative recombinations. Now our work concerns the design and the development of a fabrication process to realize a narrow ridge structure with an aluminium oxide aperture by means of a lateral oxidation in view of a better electrical and optical confinement control.

2) Laser sources with photonic band gap structures

Properties of photonic crystals such as confinement and spectral selectivity open the way towards novel types of photonic devices defined to the wavelength scale. The 2D nanostructuration of the epitaxial layers of a laser diode is very promising to achieve an electrically pumped laser nanosource for planar photonic integration. From the generic feature of the concept, this approach enables planar collective fabrication very interesting for the emergence of new integrated photonic functionalities.

The objectives of our research are the study of the impact of the photonic crystals on the miniaturisation and on the performance of the laser diodes, the demonstration of the electrical pumping for these laser nanosources and the exploration of their potentialities for a planar integration of the source in a photonic circuit.

They deal with
- the design and the realisation of AlGaAs/GaAs laser diodes with 1D or 2D photonic crystal mirrors. These mirrors achieve a high reflectivity of around 90% and to design new types of horizontal microcavities with a low threshold current, a low linewidth, a high bandwidth, ..



- the realisation of InGaAsP/InP laser nanosources only defined with photonic crystals and with an electrical pumping. This work is supported by the French RNRT project CRISTEL (OPTO+, Orsay Physics, IEF, GES, LPN, LAAS) to achieve such a multi wavelength laser source containing a bar with 8 lasers emitting at the different 50GHz spaced ITU wavelengths, a wavelength multiplexer and an adaptator between the two elements and at the output for the coupling in an optical fiber.


3) Microsystems, integrated photonic functions on silicon

Due to the default of generic concept and technology, the introduction of optical components in a microsystem is mainly performed by hybridation on a silicon platform.
In this context, the aims of our work are the exploitation of the potentialities of a conventional  CMOS technology to study different approaches of generic integration:
    - "smart" optical functions associating on a same chip optical and electronical functions,
    - innovating optical functions such as the association of diffractive and detection structures to achieve new functionalities for compact interferometric or phase control systems
    - new optical device generations including nanophotonics on silicon: sources based on silicon nanoclusters, advanced optical functions exploiting the properties of the  bandgap photonic structures