Periodic Reporting for period 4 - InnoSpace (Revolutionizing fibre-wireless communications through space-division multiplexed photonics)
Période du rapport: 2021-09-01 au 2023-08-31
Next-generation communications paradigms with massive penetration in our society, such as Beyond 5G communications, require new technologies to address the current limitations to massive capacity, connectivity and flexibility. The key lies in a full integration and smooth interfacing between the optical fibre and the wireless network segments.
The present fibre-wireless communications landscape is characterized, in first place, by “distribution” architectures that are static and inefficient, with a replication of bundles of standard optical fibres. In second place, we find microwave signal “processing” systems that are bulky, heavy and power consuming (including antenna beam-steering or channel filtering). To overcome these limitations, the Project InnoSpace proposes the application of space-division multiplexing technologies (currently restricted to long-haul high-capacity digital communications) to fibre-wireless scenarios. Our goal is to provide, in a single optical fibre, a compact and efficient approach for both distribution and processing applications, simultaneously, leading to the novel concept of “fibre-distributed signal processing”.
Most of these applications rely on a key optical component: the tuneable delay line. We propose to exploit the inherent parallelism of space-division multiplexing in optical fibres to implement tuneable delay lines with more versatility, bringing novel 2-D operation by using both diversity in space and diversity in optical wavelength. The roadmap to achieve this goal involves different technologies that provide the required parallelism by using either the independent cores of a multicore fibre or the orthogonal modes of a few-mode fibre. After finalizing the Project, we conclude that the most promising one is dispersion-diversity heterogenous multicore fibres, where we tailor “à la carte” the chromatic dispersion of each individual core.
InnoSpace goes beyond the State of the Art as it provides unique 2-dimensional distributed, reconfigurable and broadband radiofrequency signal processing "on the fly". It brings unrivalled features, enabling in a one-step solution, considerable gains in compactness, stability and versatility, altogether with reduced weight, power consumption and cost. Following the completion of the Project, the impact in our society comes not only on the hand of microwave signal processing for upcoming pervasive communications, such as 6G systems, but also extends to additional optical signal processing functionalities in a myriad of Information Technology scenarios.
The present fibre-wireless communications landscape is characterized, in first place, by “distribution” architectures that are static and inefficient, with a replication of bundles of standard optical fibres. In second place, we find microwave signal “processing” systems that are bulky, heavy and power consuming (including antenna beam-steering or channel filtering). To overcome these limitations, the Project InnoSpace proposes the application of space-division multiplexing technologies (currently restricted to long-haul high-capacity digital communications) to fibre-wireless scenarios. Our goal is to provide, in a single optical fibre, a compact and efficient approach for both distribution and processing applications, simultaneously, leading to the novel concept of “fibre-distributed signal processing”.
Most of these applications rely on a key optical component: the tuneable delay line. We propose to exploit the inherent parallelism of space-division multiplexing in optical fibres to implement tuneable delay lines with more versatility, bringing novel 2-D operation by using both diversity in space and diversity in optical wavelength. The roadmap to achieve this goal involves different technologies that provide the required parallelism by using either the independent cores of a multicore fibre or the orthogonal modes of a few-mode fibre. After finalizing the Project, we conclude that the most promising one is dispersion-diversity heterogenous multicore fibres, where we tailor “à la carte” the chromatic dispersion of each individual core.
InnoSpace goes beyond the State of the Art as it provides unique 2-dimensional distributed, reconfigurable and broadband radiofrequency signal processing "on the fly". It brings unrivalled features, enabling in a one-step solution, considerable gains in compactness, stability and versatility, altogether with reduced weight, power consumption and cost. Following the completion of the Project, the impact in our society comes not only on the hand of microwave signal processing for upcoming pervasive communications, such as 6G systems, but also extends to additional optical signal processing functionalities in a myriad of Information Technology scenarios.
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.
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.
Our research activities have resulted in a variety of advances beyond the state of the art. The most relevant ones are:
• Original design, fabrication and experimental demonstration of novel heterogeneous multicore fibres where each core is tailored “a la cartè” to provide the required value of chromatic dispersion for a particular signal processing application. These multicore fibres combine cores drawn from different preforms that exhibit particular refractive index profiles attending to different materials and radial dimensions.
• Original design, fabrication and experimental demonstration of a double-cladding few-mode fibre where each mode is tailored “a la cartè” to provide the required value of chromatic dispersion for a particular optical or microwave signal processing application, while keeping a low level of crosstalk.
• First-ever experimental demonstration of a series of tuneable microwave signal processing functionalities that will be of prime interest in future fibre-wireless communications scenarios implemented on a multicore optical fibre or few-mode fibre: radiofrequency signal filtering, optical beamforming network for phased-array antennas, 5G signal parallel transmission, multi-cavity optoelectronic oscillation, arbitrary waveform generation, microwave frequency measurement.
• First-ever experimental demonstration of several tuneable optical signal processing functionalities implemented on a multicore optical fibre: time differentiation and integration for optical computing, as well as multigigabit-per-second analog-to-digital conversion.
• Original design, fabrication and experimental demonstration of novel heterogeneous multicore fibres where each core is tailored “a la cartè” to provide the required value of chromatic dispersion for a particular signal processing application. These multicore fibres combine cores drawn from different preforms that exhibit particular refractive index profiles attending to different materials and radial dimensions.
• Original design, fabrication and experimental demonstration of a double-cladding few-mode fibre where each mode is tailored “a la cartè” to provide the required value of chromatic dispersion for a particular optical or microwave signal processing application, while keeping a low level of crosstalk.
• First-ever experimental demonstration of a series of tuneable microwave signal processing functionalities that will be of prime interest in future fibre-wireless communications scenarios implemented on a multicore optical fibre or few-mode fibre: radiofrequency signal filtering, optical beamforming network for phased-array antennas, 5G signal parallel transmission, multi-cavity optoelectronic oscillation, arbitrary waveform generation, microwave frequency measurement.
• First-ever experimental demonstration of several tuneable optical signal processing functionalities implemented on a multicore optical fibre: time differentiation and integration for optical computing, as well as multigigabit-per-second analog-to-digital conversion.