The key challenge that the Project InnoSpace faces is the design, implementation and experimental demonstration of new optical fibre technologies that offer the required parallelism for compact and tuneable true-time delay operation using a single optical fibre, without resorting to bulky, heavy, power-consuming and expensive replication architectures.
The research activities of InnoSpace are structured in three work packages. The first two focus on the original design and the fabrication of the proposed fibre technologies. Here, we would like to highlight the research developed in terms of dispersion-engineered heterogeneous multicore fibres. The exploitation of heterogeneous multicore fibres as true time delay lines involves the design of totally new fibres, where the refractive index profile of each core is independently customized to match the chromatic dispersion behaviour required for true time delay line operation, while keeping a low level of intercore crosstalk and sensitivity against fibre curvatures. Beyond the evaluation of different possible sources of degradation, we focused on the design and external fabrication of novel multicore fibres which, for the first time, behave as dispersion-diversity signal processing elements. This portfolio includes among others: (1) a GeO2-doped silica 7-core fibre where each core has been drawn from a different fibre preform and, therefore, is made from a different material (i.e. different dopant concentration) and exhibits different radial dimensions, (2) a GeO2-doped silica 19-core fibre drawn from three different fibre preforms, and (3) a preliminary air-hole silica 19-core photonic crystal fibre.
Regarding few-mode fibre links, we can also implement tuneable delay line operation if we engineer the fibre so that every mode experiences the adequate chromatic dispersion, while ensuring low coupling between groups of modes. So far, we have designed and fabricated: (1) solutions based on commercially available step-index few-mode fibres with the in-house inscription of different dispersive elements at specific longitudinal positions, and (2) a dispersion-tailored double-clad step-index few-mode fibre that that features evenly spaced incremental chromatic dispersion among 5 mode groups.
The third work package embraces the experimental validation of the developed delay lines as they are applied to fibre-wireless communications. We have demonstrated with success in our laboratories the microwave signal processing functionalities proposed in the Project proposal: parallel 5G signal distribution, microwave signal filtering, optical beamforming networks for phased-array antennas, and arbitrary waveform generation. In addition, we have reported as well other applications not considered a priori: microwave frequency measurement, temporal differentiation and integration, multi-cavity optoelectronic oscillation and high-speed analog-to-digital conversion.
The results of InnoSpace have led to the publication of 17 journal peer-reviewed papers, a book chapter and 24 peer-reviewed international conference papers (including 12 invited talks), along with several seminars in recognized Universities and participation in conference workshops.
