The lack of compact and effective light sources and optical amplifiers with high efficiency in the near-IR region is one of the main unresolved issues against the application of nanophotonic integrated circuits for future computers and information systems. Despite the great success of semiconductor optical amplifiers and lasers, several intrinsic deficiencies limit their performances. Our project aims to evaluate the possibility of realization of alternative efficient, solid-state, ultrafast-modulated emitting source at telecom wavelengths (1.5 µm). This target will be pursued combining the enhancement of Er emission rate in silica due to resonant near-field localization in plasmonic nanoantenna arrays with the fast commutation time triggered by the ultrafast switching between the metal/insulator phase of VO2 thin films coupled with the Er emitters. This provides an external dynamical control of the local optical density of states around the Er emitters. In addition, the coupling with ordered nanoantenna arrays can be used to control the far-eld scattering pattern, in terms of direction and polarization state of the emitted radiation. This control of polarization is the key to advanced imaging techniques such as stimulated emission depletion (STED) or differential interference contrast (DIC) microscopies. This Project could take these techniques to the next level as well as enabling new polarization-dependent light-emitting devices for applications in imaging, optical displays, sensing, and spectroscopy.
The significance of expected results in terms of advancement of knowledge with respect to the state of art are related to the potential development of an alternative solution to the lack of compact light sources and optical amplifiers with large bandwidths and high energy efficiencies. Despite great success of semiconductor optical amplifiers, there are several intrinsic deficiencies. For example the carrier lifetimes in semiconductors, of the order of a few hundred picoseconds, limit the modulation speed of semiconductors to tens of gigabits per second. Also, sensitive temperature dependence of the bandgap in semiconductors and other optical properties severely limit the performance of semiconductor optical amplifiers and lasers. Another issue with semiconductor-based materials is the large change of refractive index due to the large carrier-induced index¿gain coupling (through the alpha factor). Such large index change could be important in some cases, but detrimental in many other situations. The crosstalk and induced signal distortion within a wide gain bandwidth is another serious issue for wavelength-division multiplexing. Finally, silicon compatibility remains one of the biggest challenges for semiconductor-based approaches due to the inefficient light emission of silicon and the complexity and high costs of heterogeneous integration technologies. The combined effect of fast LDOS modulation provided by VO2 phase transition on the nanoantenna arrays and the enhanced efficiency due to fields¿ localization effect could make it possible to use alternative materials (mostly rare earth doped materials) by increasing the optical gain and achieving ultra-fast modulation.
The activities of the project are partially overlapping with the activities of our group in the framework of a broader PRIN 2017 project that has been submitted in collaboration with the previously mentioned partners having, as scientific goal, the development of an efficient, solid-state, ultrafast-modulated Er-based emitting source at telecom wavelengths in the near-IR. With respect to the PRIN proposal, our project is more focused on the investigation of the phenomena and mechanisms allowing efficient control of LDOS throught the phase transition of the VO2. The understanding of these effects can find several applications beyond the telecommunication area. The development of integrated light sources for a broad band of applications ranging from communication to spectroscopy, microscopy and sensing will have great impact on the second pillar of the H2020 program, ¿Industrial Leadership¿, in particular as regards the call ¿Nanotechnology, Advanced Materials, Biotechnology, Advanced Manufacturing and Processing¿. Indeed, the proposed idea strongly relies in Nanotechnology and Photonics, which are two of the six Key Enabling Technologies (KETs) of H2020 that will have in the near future a significant impact on many different areas: ¿Advances in nano-scale technologies will develop into mass markets in the coming years, with new products and services developed by the industry capable of enhancing human health, while also conserving resources and protecting the environment¿[European Commission-Research in Nanosciences & technologies, website]. One of the main point of the project is that it could lead to the development of efficient emitting devices that do not require complex fabrication strategies. The fabrication techniques chosen are advantageous in terms of easy deployment, low cost, scalability and high throughput. Moreover, their industrially scalable synthesis protocols elect them as an ideal platform for collaborations with SME or the establishment of start-ups, especially in the realm of highly technical applications as spectroscopy and sensing, up to single photon management.