CArbon nanotubeS for TELecommunications applications – CASTEL

The one-dimensional excitonic features of carbon nanotubes (CNT) optical transitions confer great potential on CNT for direct telecommunications applications at 1,55m. Regeneration signal in high-bit-rate long-haul optical fibre transmission systems based on saturable absorbers (SA) need efficient optoelectronic devices with ultrafast optical response time (defined at 1/e-maximum), great contrast ratio (CR, between ON/OFF states) and low saturation threshold fluence (SF, defined as midsaturation). Saturable absorbers (SA) based on excitonic properties of multiple-quantum-wells (MQW) nanostructures inserted in microcavity have already demonstrated great potential for such signal regeneration. These MQW 2D-nanostructures are grown by molecular beam epitaxial (MBE) technique and in-situ-MQW-doping or ex-situ-MQW-irradiation techniques have been developed to reduce MQW optical response time from nanosecond to subpicosecond scales. The purpose of this project is to demonstrate that intrinsic ultrafast carrier dynamics and large 1D-excitonic nonlinearities of bundled CNT, in telecommunications wavelengths range, make potentially these interesting nanomaterials as prime candidate to replace SA based on MQW for telecommunications applications. Moreover, these 1D-systems take an original between usually studied MQW and quantum-dots (QD) semiconductor 2D and 0D-nanostructures, respectively, which are grown by MBE. At present time, ex-situ or in-situ techniques have not been developed to reduce QD-optical response time (a few hundred picoseconds intrinsically, at 1/e-maximum). And, absorption coefficient of QD-layer is six times weaker than QW-layer, requiring consequently important quantity of matter grown by MBE in order to reach equivalent MQW SA optical properties. This project aims at developing efficient ultrafast SA based on technologically inserted-in-microcavity CNT for telecommunications applications, using commercial low-cost original 1D-systems source (with respect to EJM technique). We will first deposit CNT on substrates in clean room in order to characterize basic bundled CNT optical properties by infra-red absorption spectroscopy (absorption inhomogeneous broadening, first excitonic optical transition transmittivity of semiconductors CNT, at 1,55m) and by femtosecond-pulses and picosecond-pulses pump-probe experiments (1/e-maximum response time, CR and SF measurements). Environmental effect will be studied (substrate nature, embedded-in-a-line CNT). Note that deposited CNT form naturally bundles (or 'ropes'), in which CNT are strongly linked by interactions, which are precisely at the origin of the ultrafast carrier dynamics in bundled CNT. These preliminaries characterisations will be helpful to design best technological solutions for CNT inserted in microcavity, fabricated in clean room, taking into account environmental and thermal effects. In-microcavity CNT insertion is indeed a powerful technological step to exalt matter-light interaction and to obtain efficient samples based on CNT with greater CR and lower SF than in single-pass samples (deposited CNT on substrates), which are required for optoelectronic devices SA. Such enhanced CR and reduced SF will be precisely determined by pump-probe experiments. Dichroïsm and thermal effects studies will be performed too. Finally, all-optical signal regeneration potential of technologically elaborated SA based on CNT will be demonstrated at high-bit-rate (>10GHz), for high-speed optical transmission applications. Experiences in all project steps, internationally recognized, and complementarity of young researchers team presented here will be powerful for the success of this project.