Periodic Reporting for period 3 - FORWARD (New Frontiers for Optoelectronics with Artificial Media)
Période du rapport: 2021-11-01 au 2023-04-30
To detect or generate complex light beams that are increasingly needed in biology and photonics (light with non-zero angular momentum and non-classical light), it is necessary to rely on bulky and sophisticated setups, considerably limiting their potential. The FORWARD project aims at obtaining the same functionalities with a new generation of optoelectronic components of submicron thickness in the near infrared range. This ambitious objective implies to devise radically new ways of creating and manipulating complex light at the nanoscale. In FORWARD, this tremendous challenge will be addressed by hybridizing two classes of artificial media—colloidal quantum dots (CQDs) and metamaterials—and leveraging advanced cooperative behaviours within the hybrids. In the new devices, which will be pumped electrically, the active layers will be made of a film of CQDs interwoven with the metallic inclusions of an optical metamaterial.
FORWARD has a strong multidisciplinary character as it lies at the crossroads of nanocrystal processing, nanofabrication, nanophotonics, condensed matter physics and optoelectronics. First, we will hybridize metallic metamaterials and CQDs, study the transport properties in these devices and develop metamaterial/ CQD photodetectors demonstrating the advantage of the hybridization. Second, we will induce classical cooperative effects between the different metamaterial inclusions and utilize this approach to fabricate hybrids LEDs capable of emitting optical vortices. Last, we will induce collective synchronizations among the CQDs and demonstrate hybrids LEDs that produce coherent and non-classical light.
FORWARD has a strong multidisciplinary character as it lies at the crossroads of nanocrystal processing, nanofabrication, nanophotonics, condensed matter physics and optoelectronics. First, we will hybridize metallic metamaterials and CQDs, study the transport properties in these devices and develop metamaterial/ CQD photodetectors demonstrating the advantage of the hybridization. Second, we will induce classical cooperative effects between the different metamaterial inclusions and utilize this approach to fabricate hybrids LEDs capable of emitting optical vortices. Last, we will induce collective synchronizations among the CQDs and demonstrate hybrids LEDs that produce coherent and non-classical light.
The first thrust aims at understanding the optoelectronic properties of artificial media hybridizing PbS colloidal quantum dots (CQDs) and optical metamaterials. This thrust is well under way. First, we have shown that the behaviour of the PbS CQDs alone are governed by a thermalization of their carriers (https://hal.archives-ouvertes.fr/hal-03233881/) explaining all the salient properties of this system (Stokes shift between absorption and emission, dependence of the emission spectra on the pumping power, energy distribution of the excited carriers…). Secondly, we have used this knowledge to maximize the interactions between the CQDs and optical metamaterials. It turns out that the key figure of merit that must be optimized is the absorption of the CQDs—and not the local density of photonic states as is usually admitted. This discovery allowed us to introduce a new type of metasurface that specifically enhances this absorption cross-section (paper under review). Last, as a last step of this thrust, we have begun to engineer the carriers within the hybrids to introduce novel transport properties.
The second thrust aims at developing LEDs emitting complex forms of light, and, in particular, vector vortex beams. The key challenge is that the formation of optical vortices requires coherence properties that are possessed by lasers—but not by LEDs that emit incoherent light. This thrust is also well under way. First, we have experimentally shown that this concept was valid in photoluminescence, using a local source of CQDs coupled with plasmonic holograms that imparts the necessary spatial coherence to the system (https://hal.archives-ouvertes.fr/hal-03111873). Secondly, we have demonstrated the photoluminescence of composite vector beams using extended incoherent sources. (https://hal.archives-ouvertes.fr/hal-03412641v1). Based on these results, we have engaged in the development of vortex emitting LEDs. This task is very difficult because LEDs are multilayer structures with a constrained environment for efficient carrier injection that is not compatible with the realizations in photoluminescence described previously. We have not yet been able to satisfy all the conditions for efficient carrier injection and vortex generation simultaneously.
The third thrust, chronologically started after the two others in full accordance with the work plan, has only recently begun. At this stage, we are trying to identify the most promising avenues to trigger a collective behaviour into our systems made of colloidal CQDs and optical metamaterials.
The second thrust aims at developing LEDs emitting complex forms of light, and, in particular, vector vortex beams. The key challenge is that the formation of optical vortices requires coherence properties that are possessed by lasers—but not by LEDs that emit incoherent light. This thrust is also well under way. First, we have experimentally shown that this concept was valid in photoluminescence, using a local source of CQDs coupled with plasmonic holograms that imparts the necessary spatial coherence to the system (https://hal.archives-ouvertes.fr/hal-03111873). Secondly, we have demonstrated the photoluminescence of composite vector beams using extended incoherent sources. (https://hal.archives-ouvertes.fr/hal-03412641v1). Based on these results, we have engaged in the development of vortex emitting LEDs. This task is very difficult because LEDs are multilayer structures with a constrained environment for efficient carrier injection that is not compatible with the realizations in photoluminescence described previously. We have not yet been able to satisfy all the conditions for efficient carrier injection and vortex generation simultaneously.
The third thrust, chronologically started after the two others in full accordance with the work plan, has only recently begun. At this stage, we are trying to identify the most promising avenues to trigger a collective behaviour into our systems made of colloidal CQDs and optical metamaterials.
So far, four main achievements beyond the state of the art have been made:
1) We have identified two carrier thermalization regimes within assemblies of PbS CQDs, allowing a unified understanding of their transport and luminescent properties;
2) We have introduced a new generation of optical metasurfaces that are specifically tailored to control the properties of thermalized active media (paper under review);
3) We have pushed the control of the spontaneous emission to a level usually achieved with lasers, by experimentally demonstrating the spontaneous emission of vector vortex beams;
4) We have realized extended incoherent sources emitting composite vector beams.
Among the expected results until the end of the project, we can list the realization of photodetectors based on an as-yet unexploited transport regime, the introduction of vortex emitting LEDs and the introduction of LEDs emitting coherent, but non-lasing light.
1) We have identified two carrier thermalization regimes within assemblies of PbS CQDs, allowing a unified understanding of their transport and luminescent properties;
2) We have introduced a new generation of optical metasurfaces that are specifically tailored to control the properties of thermalized active media (paper under review);
3) We have pushed the control of the spontaneous emission to a level usually achieved with lasers, by experimentally demonstrating the spontaneous emission of vector vortex beams;
4) We have realized extended incoherent sources emitting composite vector beams.
Among the expected results until the end of the project, we can list the realization of photodetectors based on an as-yet unexploited transport regime, the introduction of vortex emitting LEDs and the introduction of LEDs emitting coherent, but non-lasing light.